This PDF file contains the front matter associated with SPIE Proceedings Volume 10449, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

A Diffractive Optical Element (DOE) is passive optical component containing complex micro structure patterns which can transform light in predetermined way. It can realize almost all the same optical functions as conventional refractive optics such as lenses, prisms or aspheric lenses. The microstructured surface relief profile has three dimensional features with widths and depth tolerance on the order of micrometers or less. Thus any minor error in design or fabrication will result in huge deviation from the desired optical function and performance. Therefore measurements of DOE before and after fabrication are important. The objective of this system is to measure DOE prior to and after fabrication for both design verification and fabrication quality validation. Digital Holography Microscopy (DHM) method is the methodology to be implemented. The measurement of the DOE design before the real sample being fabricated is realized by using a liquid crystal spatial light modulator (LCSLM) loaded with designed DOE pattern simulating the DOE sample. Featured with low cost, non-invasive, real-time, high-resolution and full-field measurement for entire effective area of DOE, the system is versatile in measuring different types of DOE.

Additive manufacturing (AM) is a rapidly developing technique which presents both substantial opportunities and challenges for manufacturing industry. However, the internal defects will influence the mechanical behavior of AM structures, and thus characterization of the defects of AM materials becomes an interesting issue. In this study, a non-destructive testing technique for AM structures is proposed based on the reflective coherent gradient sensing (CGS) method. Using this method, the slope of a reflective surface can be measured accurately. In the study, the measured structure is firstly prepared a reflective film using replication technique, and then is exerted an external load. The full filed slope of the structure can be measured using CGS and will show a turbulence which can be used to determine the location of the defects of structure (pores or cracks). Using this technique, the spatial resolution of defect size can reach 200μm. From the experimental results, the method shows the merits of full-field, non-contact and real-time measurement. The successful experimental results show that reflective CGS method is effective for detecting the internal defects of AM structures, and will have a good prospect of further application.

We present the development of stereoscopic shadow microscopy, which is arguably the most simple 3D microscopy because it is lens-free and it only needs a pair of coloured shadow images. Two spectrally-modulated light sources illuminate the object and cast two sets of coloured shadow images directly on an array of digital pixel sensors. The magnified 3D image of the object can be stereoscopically visualized simply by using a digital screen and a pair of spectrally-modulated glasses. Our analytical model shows that the optimal position of the object is governed by both the positions and the dimensions of the light sources.

Angle closure glaucoma accounts for majority of the bilateral blindness in Asian countries such as Singapore, China, and India. Abnormalities in the optic nerve and aqueous outflow system are the most indicative clinical hallmarks for glaucoma of this clinical subtype. Traditional photographic imaging techniques to assess the drainage angle are contact based, and may expose patients to risk of corneal abrasion and infections. In addition, these procedures require the use of viscous ophthalmic gels as coupling medium to overcome the phenomenon of total internal reflection at the tear-air interface. In this paper, we propose an integrated flexible handheld probe consisting of a micro color CCD video camera and white light LEDs. The handheld probe is able to capture images of the fundus and opposite iridocorneal angle when placed at the central cornea or limbus respectively. Here, we propose the use of hydrogel contact lens as an index matching medium and better protective barrier, as an alternative to conventional ophthalmic gels. The proposed imaging system and methodology has been successfully tested on porcine eye samples, ex vivo. With its high repeatability, reproducibility, and a good safety profile, it is believed that the proposed imaging system and methodology will complement existing imaging modalities in the diagnosis and management of glaucoma.

Phase Measuring Deflectometry (PMD) is a powerful tool to measure the three-dimensional shape for freeform specular surfaces. In this work, a model based method is applied to PMD, called as Modal Phase Measuring Deflectometry (MPMD). The surface height and slopes are represented in mathematical models and updated by optimizing the model coefficients, in order to minimize the discrepancy between the reprojection in ray tracing and the actual measurement. The pose of the screen relative to the camera is pre-calibrated and then optimized together with the surface shape coefficients. Moreover, the correspondence residuals because of the discrepancies between the modal estimation and practical acquisition are analyzed. Slope residuals are calculated from these discrepancies. Zonal integration methods which are good at dealing with local variations are used to reconstruct the height residual for compensation. Simulations and experiments are conducted to demonstrate the feasibility of the proposed approach.

Recently, Fiber Bragg Grating (FBG) sensors are being used for motion tracking applications. However, the sensitivity, linearity and stability of the systems have not been fully studied. Herein, an embroidered optical Fiber Bragg Grating (FBG) on a stretchable supportive textile for elbow movement measurement was developed. The sensing principle of this system is based on the alteration of Bragg wavelength due to strain from the elbow movements. The relationship between elbow movements and reflected Bragg wavelength was found to be linear. The dynamic range of FBG sensor on elbow support is between 0 and 120 degree. Finally, the stability of the FBG sensor on the supportive textile was tested during the exercise and the cleaning process with water. The sensitivity of FBG sensors for joint angle measurement and the effect of the movement and cleaning process to signals from FBG sensors after using in the real activity will be the basis knowledge for design and actual implementation of future optical fiber based wearable devices.

Photographic imaging methods allow the tracking of anatomical changes in the iridocorneal angle structures and the monitoring of treatment responses overtime. In this work, we aim to design an imaging probe to evaluate the iridocorneal angle structures using geometrical optics. We first perform an analytical analysis on light propagation from the anterior chamber of the eye to the exterior medium using Snell’s law. This is followed by adopting a strategy to achieve uniform near field irradiance, by simplifying the complex non-rotational symmetric irradiance distribution of LEDs tilted at an angle. The optimization is based on the geometric design considerations of an angled circular ring array of 4 LEDs (or a 2 × 2 square LED array). The design equation give insights on variable parameters such as the illumination angle of the LEDs, ring array radius, viewing angle of the LEDs, and the working distance. A micro color CCD video camera that has sufficient resolution to resolve the iridocorneal angle structures at the required working distance is then chosen. The proposed design aspects fulfil the safety requirements recommended by the International Commission on Non-ionizing Radiation Protection.

The characterization of nanoscale grating asymmetries is an indispensable prerequisite for improving the accuracy of process control in modern semiconductor lithography. Model-based scatterometry is the state-of-the-art optical waferinspection technique. We suggest to extend it by coherent phase-structured illumination. The resulting intensity and phase profiles are evaluated in the far-field image plane. By means of rigorous simulations, it has already been demonstrated that the use of phase-structured illumination increases the sensitivity towards any kind of grating asymmetry including asymmetric sidewall angles (SWAs), floor tilts, asymmetric top and bottom roundings, and even overlay errors. Furthermore, it is possible to determine both the absolute value and the sign (magnitude and direction) of an asymmetry. In this paper, we will recapitulate the evaluation strategy and summarize the most important simulation results. Subsequently, we will present first proof-of-principle measurements obtained by digital off-axis holography. A direct comparison between simulation and measurement demonstrates the validity of the suggested approach.

This paper analytically investigates the picosecond laser ablation of ABS/PVC. Laser-pulsed ablation is a wellestablished tool for polymer. However the ablation mechanism of laser processing for polymer has not been thoroughly understood yet. This study utilized a thermal transport model to analyze the relationship between the ablation rate and laser fluences. This model considered the energy balance at the decomposition interface and Arrhenius law as the ablation mechanisms. The calculated variation of the ablation rate with the logarithm of the laser fluence agrees with the measured data. It is also validated in this work that the variation of the ablation rate with the logarithm of the laser fluence obeys Beer’s law for low laser fluences. The effects of material properties and processing parameters on the ablation depth per pulse are also discussed for picosecond laser processing of ABS/PVC.

Axicon lenses are conical prisms, which are known to focus a light source to a line comprising of multiple points along the optical axis. In this study, we analyze the potential of axicon lenses to view, image and record the object behind opaque obstacles in free space. The advantage of an axicon lens over a regular lens is demonstrated experimentally. Parameters such as obstacle size, object and the obstacle position in the context of imaging behind obstacles are tested using Zemax optical simulation. This proposed concept can be easily adapted to most of the optical imaging methods and microscopy modalities.

It is well known for structured illumination microscopy (SIM) that the lateral resolution by a factor of two beyond the classical diffraction limit is achieved using spatially structured illumination in wide-field fluorescence microscope. In the state of art SIM systems, grating patterns are generally generated by physical gratings or by spatial light modulators such as digital micro mirrors (DMD), liquid crystal displays (LCD). In this study, using a combination of LCD and ground glasses, size controlled randomized speckle patterns are generated as an illumination source for the microscope. Proof of concept of using speckle illumination in SIM configuration is tested by imaging fixed BPAE cells.

Time averaged imaging is one of the widely used methods to achieve improved image quality, used in different types of microscopic methods. Time averaged imaging refers to adjusting the exposure time of the imaging system to obtain optimal images. In state of the art microscopes, the region of interest (ROI) of illumination beam for time averaged imaging can be selected to be of regular shapes such as circle or rectangle. This forces smallest possible ROI to be larger than the actual sample’s ROI which can be of a specific shape with complex contours. In this context, we present a flexible fiber bundle based illumination probe capable of illuminating samples of irregular shapes for time averaged imaging. Further, this probe is capable of multi-wavelength illumination, hence can be used for multi-fluorescence imaging. The fiber probe with features such as region selective and multi- wavelength illumination allows it to be used for optimal imaging of multi-fluorescence sample.

Spatially non-uniform illumination patterns have shown significant potential to improve the imaging. Recent developments in the patterned illumination microscopy have demonstrated that the use of an optical speckle as an illumination pattern significantly improves the imaging resolution at the same time reducing the computational overheads. We present a DMD based method for generation of digital speckle pattern. The generated digital speckle and uniform white light illumination are used as two illuminations to acquire images. The image reconstruction algorithm for blind structured illumination microscopy is used to get the high resolution image. Our approach does not require any calibration step or stringent control of the illumination, and dramatically simplifies the experimental set-up.

Based on the cross grind ing mode for large-diameter aspheric, a high-precision profile error compensation method by using an on-machine noncontact measuring sensor is presented to improve the manufacturing accuracy and efficiency of large and middle-diameter aspheric elements. Profile errors arising from machine motion errors and tool offset errors are obtained through the measured data from on-machine noncontact measurement. By measuring a standard flat ruler, the motion errors of the measurement sensor from the machine positioning errors is calibrated, the grinding tool setting error could be calculated according to the on-machine coordinate to achieve the grinding tool offset quick eccentricity calibration. By comparing the measured profile and the ideal profile, the normal residual error of each grinding program point was calculated, and the new compensation path was generated thereafter. The 300-mm-diameter K9 mirror was ground to verify the proposed compensation grinding method. Results indicate that the profile error was reduced from 35μm to 10μm through the tool setting error elimination during semi-finish grinding stage. Using the compensation grinding path according to the normal residual error, the profile accuracy was improved from 10μm to 4μm in fine grinding stage. It could be concluded that the proposed compensation grinding method is effective to improve profile accuracy and manufacturing efficiency for the large and middle-diameter aspheric elements.

In this paper, we propose a new technique for double image encryption in the Fresnel domain using wavelet transform (WT), gyrator transform (GT) and spiral phase masks (SPMs). The two input mages are first phase encoded and each of them are then multiplied with SPMs and Fresnel propagated with distances d₁ and d₂, respectively. The single-level discrete WT is applied to Fresnel propagated complex images to decompose each into sub-band matrices i.e. LL, HL, LH and HH. Further, the sub-band matrices of two complex images are interchanged after modulation with random phase masks (RPMs) and subjected to inverse discrete WT. The resulting images are then both added and subtracted to get intermediate images which are further Fresnel propagated with distances d₃ and d₄, respectively. These outputs are finally gyrator transformed with the same angle α to get the encrypted images. The proposed technique provides enhanced security in terms of a large set of security keys. The sensitivity of security keys such as SPM parameters, GT angle α, Fresnel propagation distances are investigated. The robustness of the proposed techniques against noise and occlusion attacks are also analysed. The numerical simulation results are shown in support of the validity and effectiveness of the proposed technique.

The availability of spatial light modulators as standard turnkey components and their ongoing development makes them attractive for a huge variety of optical measurement systems in industry and research. Here, we outline two examples of how optical measurements can benefit from spatial light modulators. Ultrasound testing has become an indispensable tool for industrial inspection. Contact-free measurements can be achieved by laser-induced ultrasound. One disadvantage is that due to the highly divergent sound field of the generated shear waves for a point-wise thermoelastic excitation, only a poor spatial selectivity can be achieved. This problem can be solved by creating an ultrasound focus by means of a ring-like laser intensity distribution, but standard fixed-form optical components used for their generation are always optimised to a fixed set of parameters. Here, we demonstrate, how a predefined intensity pattern as e.g. a ring can be created from an arbitrary input laser beam using a phase-retrieval algorithm to shape an ultrasound focus in the sample. By displaying different patterns on the spatial light modulator, the focus can be traversed in all three directions through the object allowing a fast and highly spatially resolving scanning of the sample. Optical measurements take often place under difficult conditions. They are affected by variations of the refractive index, caused e.g. by phase boundaries between two media of different optical density. This will result in an increased measurement uncertainty or, in the worst case, will cause the measurement to fail. To overcome these limitations, we propose the application of adaptive optics. Optical flow velocity measurements based on image correlation in water that are performed through optical distortions are discussed. We demonstrate how the measurement error induced by refractive index variations can be reduced if a spatial light modulator is used in the measurement setup to compensate for the wavefront distortions.

This paper presents a novel Phase Measuring Deflectometry (PMD) method to measure specular objects having discontinuous surfaces. A mathematical model is established to directly relate the absolute phase and depth, instead of the phase and gradient. Based on the model, a hardware measuring system has been set up, which consists of a precise translating stage, a projector, a diffuser and a camera. The stage locates the projector and the diffuser together to a known position during measurement. By using the model-based and machine vision methods, system calibration is accomplished to provide the required parameters and conditions. The verification tests are given to evaluate the effectiveness of the developed system. 3D (Three-Dimensional) shapes of a concave mirror and a monolithic multi-mirror array having multiple specular surfaces have been measured. Experimental results show that the proposed method can obtain 3D shape of specular objects having discontinuous surfaces effectively

Digital projector is a main component in Fringe projection profilometry (FPP). To acquire precise 3D profiles, it is crucial to accurately calibrate and compensate projector distortion. In this paper, we propose a new method to improve the accuracy of projector compensation. Coefficients of projector distortion are first accurately calibrated. And based on the calibration results, non-uniform fringe patterns are designed to compensate the projector distortion. With the non-uniform fringe patterns, phase errors in absolute phase map can be automatically and effectively offset. Experimental results are shown to demonstrate the validity of the proposed method.

This paper uses the dual-phase-lag model to study the ablation characteristics of femtosecond laser processing for nanometer-sized ceramic films. In ultrafast process and ultrasmall size where the two lags occur, a dual-phase-lag can be applied to analyse the ablation characteristics of femtosecond laser processing for materials. In this work, the ablation rates of nanometer-sized lead zirconate titanate (PZT) ceramics are investigated using a dual-phase-lag and the model is solved by Laplace transform method. The results obtained from this work are validated by the available experimental data. The effects of material thermal properties on the ablation characteristics of femtosecond laser processing for ceramics are also discussed.

Due to its multi properties, including excellent stiffness-to-weight and strength-to-weight ratios, closed-cell aluminum and its alloy foams become candidate materials for use in many high-technology industries, such as the automotive and aerospace industries. For the efficient use of closed-cell foams in structural applications, it is necessary and important to detailly understand their mechanical characteristics. In this paper, the nonlinear vibration responses of the cantilever beams of closed-cell aluminum foams were investigated by use of electronic speckle pattern interferometry (ESPI). The nonlinear resonant mode shapes of testing specimens under harmonic excitation were measured. It is first time to obtain from the experimental results that there exist super-harmonic responses when the cantilever beams of closed-cell aluminum foam were forced to vibrate, which was caused by its specific cellular structures.

The rapid advent of Silicon Photonics presents many challenges for test and packaging. Here we concisely review SiP device attributes that differ significantly from classical photonic configurations, with a view to the future beyond current, connectivity-oriented silicon photonics developments, looking to such endeavors as all-optical computing and quantum computing. The necessity for nano-precision alignment of optical elements in test and packaging operations quickly emerges as the unfilled need. We review the industrial test and packaging solutions developed back in the 1997-2001 photonics boom to address the needs of that era's devices, and map their gaps with the new SiP device classes. Finally we review the new state-of-the-art of recent advances in the field that address these gaps.

The advantage of 3D printing technique is flexible in design and fabrication. Using 3D printing technique, the traditional manufacturing limitations are not considered. The optical lens is the key component in an optical system. The traditional process to manufacture optical plastic lens is injection molding. However injection molding is only suitable for plastics lens, it cannot fabricate optical and mechanical components at same time. The assembly error of optical system can be reduced effectively with fabricating optical and mechanical components at same time. The process of printing optical and mechanical components simultaneously is proposed in previous papers, but the optical surface of printing components is not transparent. If we increase the transmittance of the optical surface, the printing components which fabricated by 3D printing process could be high transmission. Therefore, precise diamond turning technique has been used to turning the surface of 3D printing optical lens in this paper. The precise diamond turning techniques could process surfaces of components to meet the requirements of optical system. A 3D printing machine, Stratasys Connex 500, and a precise diamond turning machine, Precitech Freeform705XG, have been used in this paper, respectively. The dimension, roughness, transmission and printing types of 3D printing components have been discussed in this paper. After turning and polishing process, the roughness of 3D printing component is below 0.05 μm and the transmittance increase above 80 %. This optical module can be used in hand-held telescope and other system which need lens and special mechanical structure fabricated simultaneously.

The ISO standards which are related to the calibration of areal surface topography measuring instruments are the ISO 25178-6xx series which defines the relevant metrological characteristics for the calibration of different measuring principles and the ISO 25178-7xx series which defines the actual calibration procedures.

As the field of areal measurement is however not yet fully standardized, there are still open questions to be addressed which are subject to current research. Based on this, selected research results of the authors in this area are presented. This includes the design and fabrication of areal material measures. For this topic, two examples are presented with the direct laser writing of a stepless material measure for the calibration of the height axis which is based on the Abbott- Curve and the manufacturing of a Siemens star for the determination of the lateral resolution limit.

Based on these results, as well a new definition for the resolution criterion, the small scale fidelity, which is still under discussion, is presented. Additionally, a software solution for automated calibration procedures is outlined.

In manufacturing engineering the surface finish of a machined component is of fundamental importance in order to ensure its performance. A non-contact and non-destructive device based on optical technique, is a promising alternative to stylus based device for carrying out measurement of surface quality. In addition to this, in situ monitoring of surface roughness on a workpiece is an important requirement in modern machining process, since it would increase on-line machining rate and consequently productivity. Here, measurement approaches and system configuration for surface roughness measurement using laser speckle intensity and contrast are discussed. The technique would allow full-field measurement over sample of interest having both rough and shiny surface properties. Measurement data on standard calibration plates is presented with details on the measurement accuracy and reliability.

The surface roughness parameters encoded in a speckle pattern can be effectively extracted through correlation experiments. In the case of spectrally correlated speckle images, the degree of decorrelation arises from wavelength difference in the laser light irradiated on the surface. To obtain accurate results in such methodology, a proper design of experiments is important due to more than one parameter involved in the experiment. Here, experimental investigations and parametric studies of surface roughness measurements using spectral speckle correlation methodology are presented, considering the potential variables in the system. The sources of error and factors affecting the accuracy in measurement are identified and the experimental results obtained from standard calibration plate samples are presented.

Effects of coherence on imaging systems problem has been discussed previously using many criterions and methods. But they don't consider the polarimetric properties of light. Polarization imaging of an edge object with partially coherent and partially polarized light are investigated and related to the parameters of an imaging system. Theoretical results are presented to describe the imaging parameters and the coherent and polarized field effects. the Fourier transform of the generalized Stokes parameters is discussed by it modulus and phase.

A concise explanation of spectroscopic scatterometry is presented that is used for modelbased shape metrology of etched features in the production of Memory and Logic semiconductor devices. We also present an angle-resolved scatterometry technique that can measure at high throughput on very small test targets. First measured results are shown that demonstrate the capability on 5×5 μm² targets.

A touch panel is an input device for human computer interaction. It consists of a network of sensors, a sampling circuit and a micro controller for detecting and locating a touch input. Touch input can come from either finger or stylus depending upon the type of touch technology. These touch panels provide an intuitive and collaborative workspace so that people can perform various tasks with the use of their fingers instead of traditional input devices like keyboard and mouse. Touch sensing technology is not new. At the time of this writing, various technologies are available in the market and this paper reviews the most common ones. We review traditional designs and sensing algorithms for touch technology. We also observe that due to its various strengths, capacitive touch will dominate the large-scale touch panel industry in years to come. In the end, we discuss the motivation for doing academic research on large-scale panels.

A method to directly pattern nanoscale periodic features within optically transparent solid materials by means of a configurable multi-beam femtosecond laser interference is proposed. While femtosecond micromachining of optically transparent solid materials has been explored in great detail in the recent past, research in direct interference patterning on such materials has not been well established. Therefore, different design considerations such as complete void formation and flexibility of the patterned substrate are investigated as part of this study. The relationship between intensity distributions and actual void formation in optically transparent materials is also investigated to establish critical parameters for pattern formation. It is envisaged that this proposed method and data obtained may enable to explore the untapped domains of developing substrates for solid-state 3D microbattery applications.

Camera calibration is a crucial key in image-based optical measurement. Calibration methods based on different targets are popular. The camera calibration method based on traditional sphere targets can calibrate cameras that are arranged in various angles at the same time, but the calibration precision is relatively low. The camera calibration method based on checkerboard-based targets proposed by Zhang offers a simple calibration process and high accuracy, but it is not suitable for simultaneous calibration of multiple cameras at different angles. In this paper, we propose a new form of target, namely, grid sphere target, which combines the advantages of sphere target and planar target. The grid sphere target is a sphere target with circles of latitude and longitude, similar to the globe. The proposed camera calibration method can not only calibrate cameras that are arranged in many different angles at the same time, but also obtain high accuracy similar to that of Zhang’s method. In the proposed method, the initial solutions of the intrinsic and extrinsic parameters of the camera are solved according to elliptical images of the latitude and longitude circles in the target. The intersection points of longitude and latitude circles are then used as the image feature points, and the optimal solutions of the intrinsic parameters of the camera are obtained by nonlinear optimization. Experimental results validate the effectiveness of the proposed method.

In this paper, we will be initially doing review on the advancement of interference lithography (IL) which is a wellestablished technique for its facile, efficient, and economical approach to achieve large-scale patterning in a wide variety of substrates at sub-wavelength resolution. Following this, we have configured a two-beam IL patterning system to achieve patterns in a photoresist and verified against the theoretically calculated results. This work will be further extended using near-field patterning techniques to improve the resolution of the pattern as compared to the current conventional IL system. It is envisaged that the obtained initial results can be employed in a graphene substrate for further research and applications in the area of flexible electronics.

This paper proposes a multi-attribute automatic optimization method for lens system design. The method is based on the exploitation of the multi-attribute property of lens systems. Quality attribute and sensitivity attribute of lens system are our main concerns in the proposed method. The quality attribute is considered to characterize the optical performance and the physical constraints of lens system. The sensitivity attribute is perceived as the description of feasibility and practicality in lens manufacturing. Modified coordinate-wise algorithm is employed to perform the optimization of imaging performance as well as specific constraints. The sensitivity attribute is processed to incorporate manufacturing sensitivity into the metrics to evaluate the system more comprehensively by means of minimizing incident and refracted ray angles on optical surfaces. As a result, compromise solutions between quality attribute and sensitivity attribute are obtained. Experiments on two typical lens designs demonstrate the effectiveness of the proposed method.

Digital holography system can quantitatively obtain the microscopic appearance of the measured surface, with non-contact, high precision, large measuring range, etc. Among the varies of characterizing a system, Instrument Transfer Function (ITF) is the most appealing method, which can describe the system response in terms of an input signal’s frequency content. In this paper, we proposed a method to calculate the system transfer function of digital holography system for measure a high quality phase step, which contains all spatial frequencies. The ITF can be calculated across all frequencies with a single measurement by comparing the Power spectral Density (PSD) of a measured step to the theoretical PSD. The method is applied to calculate the ITF of digital holography system. Experimental result shows that the ITF of the digital holography system is above 60%.The result shows that the ITF of digital holography system could be kept at acceptable levels within the range of interest.

A high-precision test method based on infinity optical transformation system was investigated to detect the focusing performance of a small fiber lens. Consider the ultra-small gradient-index (GRIN) fiber probe as an example of the small fiber lens, its characters of focusing performances are analyzed. The infinity optical transformation system was employed to amplify and capture the exit beam from the probe in the non-contact mode. Then the curve fitting method is used to deal with the experimental data. The result shows that with the given small fiber lens the obtained working distance and waist diameter in the experiment system are 0.72 mm and 35 μm, respectively, while the calculated working distance and waist diameter based on the theory are 0.75 mm and 33 μm accordingly. The experimental results are in good agreement with the theoretical results. Therefore, the proposed test method based on infinity optical transformation system is applicable to detect the focusing performance of the small fiber lens.

Short-coherence in-line phase-shifting digital holographic microscopy based on Michelson interferometer is proposed to measure internal structure in silicon. In the configuration, a short-coherence infrared laser is used as the light source in order to avoid the interference formed by the reference wave and the reflected wave from the front surface of specimen. At the same time, in-line phase-shifting configuration is introduced to overcome the problem of poor resolution and large pixel size of the infrared camera and improve the space bandwidth product of the system. A specimen with staircase structure is measured by using the proposed configuration and the 3D shape distribution are given to verify the effectiveness and accuracy of the method.

Image steganography is one way of data hiding which provides data security in digital images. The aim is to embed and deliver secret data in digital images without any suspiciousness. However, most of the existing optical image hiding methods ignore the visual quality of the stego-image for improving the robustness of the secret image. To address this issue, in this paper, we present a Region of Non-Interest (RONI) steganographic algorithm to enhance the visual quality of the stego-image. In the proposed method, the carrier image is segmented into Region of Interest (ROI) and RONI. To enhance the visual quality, the 3D image information is embedded into the RONI of the digital images. In order to find appropriate regions for embedding, we use a visual attention model as a means of measuring the ROI of the digital images. The algorithm employs the computational integral imaging (CII) technique to hide the 3D scene in the carrier image. Comparison results show that the proposed technique performs better than some existing state of art techniques.

Fringe Projection Profilometry (FPP) is a popular optical method for 3D shape measurement because of its high accuracy, fast measurement speed and full-field inspection nature. However, due to the limited dynamic range of the digital camera, saturated and dark pixels in the captured images will lead to serious phase error and measurement error when the measured object has a drastic texture variation. To deal with such problem, a novel adaptive digital fringe projection technique for high dynamic 3D shape measurement is proposed. In this method, phase-shifting fringes are adaptively generated with the aid of a coordinates mapping process and binary-search technique. Compared with previous adaptive fringe projection techniques, the camera response function and homographic mapping between the camera and projector are not needed, making the whole measurement easier to carry out and less laborious. Experiments validate the effectiveness and superiority of the proposed method for high dynamic range 3D shape measurement

Laser ultrasonics is a technique currently studied for nondestructive inspection of aerospace composite structures based on carbon fibers. It combines a pulsed laser impacting the surface generates an ultrasound inside the material, through the nondestructive thermoelastic effect. Second a detection interferometer probes the impacted point in order to measure the displacement of the surface resulting from the emitted ultrasound wave and the echo coming back from the different interfaces of the structure. Laser ultrasonics is of interest for inspecting complex shaped composites. We have studied the possibility of using frequency doubled YAG laser for the generation and which is fiber-coupled, together with a fibercoupled interferometric probe using a YAG laser in the NIR. Our final system is a lightweight probe attached to a robot arm and which is able to scan complex shapes. The performances of the system are compared for different wavelengths of generations. Also we have studied some experimental parameters of interest such as tolerance to angle and focus distance, and different geometries of generation beams. We show some examples of inspection of reference parts with known defects. In particular C-scans of curved composites structures are presented.

The use of carbon fiber-reinforced polymer (CFRP) composite materials in the aerospace industry have far improved the load carrying properties and the design flexibility of aircraft structures. A high strength to weight ratio, low thermal conductivity, and a low thermal expansion coefficient gives it an edge for applications demanding stringent loading conditions. Specifically, this paper focuses on the behavior of CFRP composites under stringent thermal loads. The properties of composites are largely affected by external thermal loads, especially when the loads are beyond the glass temperature, Tg, of the composite. Beyond this, the composites are subject to prominent changes in mechanical and thermal properties which may further lead to material decomposition. Furthermore, thermal damage formation being chaotic, a strict dimension cannot be associated with the formed damage. In this context, this paper focuses on comparing multiple speckle image analysis algorithms to effectively characterize the formed thermal damages on the CFRP specimen. This would provide us with a fast method for quantifying the extent of heat damage in carbon composites, thus reducing the required time for inspection. The image analysis methods used for the comparison include fractal dimensional analysis of the formed speckle pattern and analysis of number and size of various connecting elements in the binary image.

Hyperspectral imaging combines imaging and spectroscopy to provide detailed spectral information for each spatial point in the image. This gives a three-dimensional spatial-spatial-spectral datacube with hundreds of spectral images. Probe-based hyperspectral imaging systems have been developed so that they can be used in regions where conventional table-top platforms would find it difficult to access. A fiber bundle, which is made up of specially-arranged optical fibers, has recently been developed and integrated with a spectrograph-based hyperspectral imager. This forms a snapshot hyperspectral imaging probe, which is able to form a datacube using the information from each scan. Compared to the other configurations, which require sequential scanning to form a datacube, the snapshot configuration is preferred in real-time applications where motion artifacts and pixel misregistration can be minimized. Principal component analysis is a dimension-reducing technique that can be applied in hyperspectral imaging to convert the spectral information into uncorrelated variables known as principal components. A confidence ellipse can be used to define the region of each class in the principal component feature space and for classification. This paper demonstrates the use of the snapshot hyperspectral imaging probe to acquire data from samples of different colors. The spectral library of each sample was acquired and then analyzed using principal component analysis. Confidence ellipse was then applied to the principal components of each sample and used as the classification criteria. The results show that the applied analysis can be used to perform classification of the spectral data acquired using the snapshot hyperspectral imaging probe.

Hyperspectral imaging was first used in remote sensing and since then, it has been used in many other applications such as cancer diagnosis, precision farming and assessment of the level of flaking in ancient murals. In order to make hyperspectral imaging available for a wide variety of applications, its imagers can be made to operate using different methods and developed into different configurations. This leads to each variant having a set of specifications suitable for certain applications. The many variants of hyperspectral imager produce a set of three-dimensional spatial-spatialspectral datacube, which is made up of hundreds of spectral images of one scene. A snapshot hyperspectral imaging probe has recently been developed by integrating a fiber bundle, which is made up of specially-arranged optical fibers, with a spectrograph-based hyperspectral imager. The snapshot method is able to produce a datacube using the information from each scan. The fiber bundle has 100 fiberlets which are arranged in a row in the one-dimensional proximal end, and are rearranged into a 10×10 hexagonal array in the two-dimensional distal end. The image captured by the two-dimensional end of the fiber bundle is reduced from two to one spatial dimension at the one-dimensional end. The raw data acquired from each scan has to be remapped into a datacube with the correct representation of the spectral and spatial features of the captured scene. This paper reports the spatial calibrations of both ends of the fiber bundle and image processing that have to be performed for such a remapping.

Surface characterization of the working components has always been a subject of interest among researchers and industry specialists. Especially in the aerospace industry where the aerodynamic capabilities are largely altered by the surface quality of the component of interest, there remains an extensive need for developing systems for effectively characterizing the surface quality. To realize an optical based non-contact and an in-line surface roughness measurement system, it is essential to understand the relationship between the quality of the surface and statistical parameter of the reflected speckles. The range of the measurement system being proportional to the wavelength of light used makes the analysis fundamentally important in order to understand the properties of speckles at a different wavelength. In this context, this paper examines the nature of the formed IR speckles from three different diffusers by analyzing their raw structure. Image processing algorithms that are developed study the different parameters of the 8-bit binary speckles, namely, the fractal property and number of connecting components. The paper also discusses the future work direction on relating the proposed analysis to derive the algorithm required for evaluating the surface finish parameters.

Computer holography has made a notably progress in recent years. The point-based method and slice-based method are chief calculation algorithms for generating holograms in holographic display. Although both two methods are validated numerically and optically, the differences of the imaging quality of these methods have not been specifically analyzed. In this paper, we analyze the imaging quality of computer-generated phase holograms generated by point-based Fresnel zone plates (PB-FZP), point-based Fresnel diffraction algorithm (PB-FDA) and slice-based Fresnel diffraction algorithm (SB-FDA). The calculation formula and hologram generation with three methods are demonstrated. In order to suppress the speckle noise, sequential phase-only holograms are generated in our work. The results of reconstructed images numerically and experimentally are also exhibited. By comparing the imaging quality, the merits and drawbacks with three methods are analyzed. Conclusions are given by us finally.

Phase-shifting profilometry using binary patterns with projector defocusing has been widely used for high-speed 3D measurement. Recently, a ternary Gray-code based phase unwrapping method has been proposed, which enables to accurately unwrap the phase but reduces the required binary patterns. This paper presents a comparison between the ternary and the traditional binary Gray code-based phase unwrapping methods.

A dual-wavelength common-path digital holographic microscopy is presented to simultaneously improve the phase measurement accuracy and stability. Two laser beams with different wavelength are reflected by the front and back surface of a parallel glass plate to form the composite hologram in the lateral shearing region, and a shorter synthetic wavelength Λ289nm is obtained by calculating the arctangent and product of the two reconstructed complex amplitudes. Thus, phase speckle noise can be reduced in the dual-wavelength numerical reconstruction process, and the phase measurement accuracy and stability can be improved. The experiment results of the peony pollens specimen show the feasibility of the proposed configuration.

In this paper we studied Photo physical properties and estimated ground and excited state dipole moments of Acridine Orange Hemi Zinc salt and Acridine Yellow G laser dyes with help of various solvatochromic methods which considers bulk solvent polarity parameters and compared with theoretically estimated values which considers microscopic polarity parameters. We calculated the angle between ground and excited state dipole moments for both molecules. This paper reports that both molecules are PH sensitive due to presence of central protonated nitrogen atom, That PH sensitivity leads to efficiency loss as compared with other dye like acriflavine.

We present a comb-based spectroscopic method that enables simultaneous detections of multiple gases by adopting an erbium-doped fiber femtosecond laser as a single broadband probing beam. The method takes multiple continuous-wave diode lasers as the frequency references, each being assigned to its distinct gas absorption line. The interference of the probing femtosecond laser with the diode lasers produces multi-heterodyne beats in the radio frequency domain, which are captured using a high-speed photodetector and electronically processed to identify the absorption lines of interest with a comb-mode spectral resolution. The experimental result of this study demonstrates that two gas absorption lines of H¹³CN and ¹²CO₂, separated by a 23 nm spectral offset, can be detected concurrently at a 10 μs update rate with a 100 kHz spectral resolution. The proposed method finds applications in not only fundamental spectral line measurements for atomic and molecular physics but also diverse practical uses for remote sensing of trace and toxic gas molecules.

Fluorescence microscopy, utilizing fluorescence labeling, has the capability to observe intercellular changes which transmitted and reflected light microscopy techniques cannot resolve. However, the parts without fluorescence labeling are not imaged. Hence, the processes simultaneously happen in these parts cannot be revealed. Meanwhile, fluorescence imaging is 2D imaging where information in the depth is missing. Therefore the information in labeling parts is also not complete.

On the other hand, quantitative phase imaging is capable to image cells in 3D in real time through phase calculation. However, its resolution is limited by the optical diffraction and cannot observe intercellular changes below 200 nanometers.

In this work, fluorescence imaging and quantitative phase imaging are combined to build a multimodal imaging system. Such system has the capability to simultaneously observe the detailed intercellular phenomenon and 3D cell morphology. In this study the proposed multimodal imaging system is used to observe the cell behavior in the cell apoptosis. The aim is to highlight the limitations of fluorescence microscopy and to point out the advantages of multimodal quantitative phase and fluorescence imaging. The proposed multimodal quantitative phase imaging could be further applied in cell related biomedical research, such as tumor.

Spectroscopic imaging ellipsometry (SIE) is a powerful technique devoted to the study of optical properties and thickness of thin films by measuring the change in polarization state of light reflected from the surface. SIE measures two quantities (Ψ and Δ ), which represent the amplitude ratio and phase angle of deflection of the p-polarized light and s-polarized light reflected from the sample surface. The SIE measurement of thin film is difficult when the substrate is uniaxial anisotropic crystal for two reasons - firstly the p-polarized and s-polarized components of reflective light are coupled which makes the data processing more complex and secondly an optical model is needed for SIE data processing with the substrate optical constants as known parameters in the model, but the substrate optical constants are not unique when the plane of the optical axis changes. Hence in the measurement of thin film on an anisotropic material using generalized ellipsometry, significant errors due to the complex calculation arise. The best approach is to measure the uniaxial substrate as an isotropic material by adjusting the optical axis in the incident plane. In this paper, the crystal optical axis is determined by rotating the sample using the SIE setup and the incident light is adjusted in the optical axis plane to eliminate the effects of uniaxial substrate. A uniaxial KDP (Potassium Dihydrogen Phosphate) crystal with thin oil film and a bare KDP substrate are prepared. A scheme to determine KDP crystal optical axis is proposed. Finally, the optical constants of the KDP substrate are determined, and the oil film thickness on KDP crystal is measured when the incident light is in crystal optical axis plane.

A single-shot color fringe projection profilometry is proposed to measure a diffuse object by using two-step phase shifting and centerline marker. One color fringe pattern encoded with two sinusoidal patterns and one rectangular pulse pattern is projected by a DLP project and recorded by a CCD camera. The approach requires two sinusoidal patterns, which is composed of the red and blue components, to establish two-step phase shifting for wrapping the primary phase, and needs a centerline marker, which is encoded in the green channel, to obtain the phase order for unwrapping the absolute phase. Simulation and experiment results demonstrate that the proposed approach is able to effectively unwrap the absolute phase and compensate the phase errors.

Stereo matching is an important and hot research topic in computer vision. In order to solve the well-known streaking effects of dynamic programming, and reduce the mismatch points on edges, discontinuous and textureless regions, we propose a cross-scale constrained dynamic programming algorithm for stereo matching. The algorithm involves both image pyramid model and Gaussian scale space to operate a coarse-to-fine dynamic programming on multi-scale cost volumes. For the purpose of improving the disparity accuracy in textureless region, a cross-scale regularized constraint is added to ensure the cost consistency, the computational burden is reduced by using the disparity estimation from lower scale operation to seed the search on the larger image. Both synthetic and real scene experimental results show our algorithm can effectively reduce the mismatch in textureless regions.

Targeting at 3D point cloud data without any foreknowledge of information, this paper presents a new algorithm of point cloud simplification. Because of usual way of shooting in daily life, there often exist more detailed information in x-y direction in the point cloud.By using this feature, the proposed algorithm firstly selects x-y axis as the direction for division and computation and obtains x-y boundary. After observation of normal vector of point cloud, it is easy to find that if the normal vector of the points in the local region changes gently, it indicates that the region is relatively flat. On the contrary, if the normal vector changes greatly, it indicates that the region fluctuates greatly. Therefore, compute the arithmetic mean of the included angle between the normal vector of one point in the point cloud and the normal vector of its k-neighborhood point. Define the feature of that point, and based on this, extract key feature points in data. Finally, the gridding method is used to divide the scattered point cloud data whose boundary and key points have been extracted and thus finish simplification. Experimental results show the effectiveness of the proposed algorithm.

Focusing light through strongly scattering media plays an important role in biomedical imaging and therapy. Here, we experimentally demonstrate light focusing through ZnO sample by controlling binary amplitude optimization using genetic algorithm. In the experiment, we use a Micro Electro-Mechanical System (MEMS)-based digital micromirror device (DMD) which is in amplitude-only modulation mode. The DMD consists of 1920×1080 square mirrors that can be independently controlled to reflect light to a desired position. We control only 160 thousand mirrors which are divided into 400 segments to modulate light focusing through the scattering media using advanced genetic algorithm. Light intensity at the target position is enhanced up to 50±5 times the average speckle intensity. The diameters of focusing spot can be changed ranging from 7 μm to 70 μm at arbitrary positions and multiple foci are obtained simultaneously. The spatial arrangement of multiple foci can be flexibly controlled. The advantage of DMDs lies in their switching speed up to 30 kHz, which has the potential to generate a focus in an ultra-short period of time. Our work provides a reference for the study of high speed wavefront shaping that is required in vivo tissues imaging.

3D printing is a high freedom fabrication technique. Any components, which designed by 3D design software or scanned from real parts, can be printed. The printing materials include metals, plastics and biocompatible materials etc. Especially for those high transmission components used in optical system or biomedical field can be printed, too. High transmission lens increases the performances of optical system. And high transmission cover or shell using in biomedical field helps observers to see the structures inside, such as brain, bone, and vessels. But the surface of printed components is not transparent, even the inside layer is transparent. If we increase the transmittance of surface, the components which fabricated by 3D printing process could have high transmission. In this paper, we using illuminating and polishing methods to improve the transmittance of printing surface. The illuminating time is the experiment parameters in illuminating method. The roughness and transmission of printing components are the evaluating targets. A 3D printing machine, Stratasys Connex 500, has been used to print high transmittance components in this paper. The surface transmittance of printing components is increasing above 80 % by polishing method.

Ultrashort pulses have been found to have important applications in many fields, such as ultrafast diagnosis, biomedical engineering, and optical imaging. Passively mode-locked fiber lasers have become a tool for generating picosecond and femtosecond pulses. In this paper, the evolution of a picosecond laser pulse in different stable passively mode-locked fiber laser is analyzed using nonlinear Schrödinger equation. Firstly, different mode-locked regimes are calculated with different net cavity dispersion (from ~-0.3 ps² to ~+0.3 ps² ). Then we calculate the maximum small-signal gain on the different net cavity dispersion conditions, and estimate the pulse width, 3 dB bandwidth and time bandwidth product (TBP) when the small-signal gain coefficient is selected as the maximum value. The results show that the small signal gain coefficient is approximately proportional to the net cavity. Moreover, when the small signal gain coefficient reaches the maximum value, the pulse width of the output pulse and their corresponding TBP show a trend of increase gradually, and 3dB bandwidth shows a trend of increase firstly and then decrease. In addition, in the case that the net dispersion is positive, because of the pulse with quite large frequency chirp, the revolution to dechirp the pulse is researched and the output of the pulse is compressed and its compression ratio reached more than 10 times. The results provide a reference for the optimization of passively mode-locked fiber lasers.

The two-dimensional wavefront reconstruction method based on double-shearing and least squares fitting is proposed in this paper. Four one-dimensional phase estimates of the measured wavefront, which correspond to the two shears and the two orthogonal directions, could be calculated from the differential phase, which solves the problem of the missing spectrum, and then by using the least squares method the two-dimensional wavefront reconstruction could be done. The numerical simulations of the proposed algorithm are carried out to verify the feasibility of this method. The influence of noise generated from different shear amount and different intensity on the accuracy of the reconstruction is studied and compared with the results from the algorithm based on single-shearing and least squares fitting. Finally, a two-grating lateral shearing interference experiment is carried out to verify the wavefront reconstruction algorithm based on doubleshearing and least squares fitting.

Camera calibration plays an important role in the field of machine vision and photogrammetry, and among the practical calibration methods, the one proposed by Zhang ZhengYou is higher accuracy and easily operated. However, this method needs to move the camera (or the planar target) to get three or more target images at different locations, and it is better to uniformly fill the calibration target in whole measurement volume to improve the calibrate precision. But manual movement and placement of the targets frequently will increase the difficulty in guaranteeing the uniform distribution of target. In view of this situation and according to the linear imaging model of the camera, a new camera calibration method based on the virtual planar targets is proposed in this paper. A liquid crystal display was used as a target plane, and the 2D target graphics were displayed on this LCD screen. Using TSai’s camera calibration method to get initial parameters, a serial of images of the virtual planar targets in different positions were captured with keeping the display position unchanged and are used to calculate the internal and external parameters of the camera by classic Zhang’s camera calibration method, and the new internal and external parameters would again guide the movement of virtual target. After several iterations, camera parameters can be obtained with high precision. The presented method is flexible and easy to operate, and it has been applied to calibrate different cameras and an actual 3D shape measurement system in our Lab. The comparison results of the transverse coordinates in plane calculated by this method and by Zhang’s camera calibration method shows that this proposed method is quite accurate and reliable.

The ripening of fruits is associated with changes, in some cases subtle, in the color of the fruit. Traditionally spectroscopy used to measure these subtle changes and infer the ripeness of fruits. Spectrometers provides high-resolution but only measure a small area of the fruit. That might not be a good indicator of the overall ripeness. In this paper, we propose a compact tunable LED based hyper spectral imaging system that scans through a set of wavelengths and images, the reflectance from the whole fruit. Based on the type of fruit, only specific wavelengths need to be scanned. Following a validation using a Rubik’s cube, an example banana going through its ripening cycles is used to demonstrate the system.

Two kinds of tunable double-wavelength erbium-doped fiber (EDF) ring lasers were developed and their application to step height measurement using two-wavelength self-mixing interferometry (SMI) was demonstrated. The fiber lasers can emit two different wavelengths without any laser mode competition. Each wavelength has its own gain medium which is a length of erbium-doped fiber. Fiber Bragg gratings are used to determine the value of the emitted wavelengths. Large step heights can be measured using multiple self-mixing interference of the two wavelengths. The maximum height that can be measured is half synthetic wavelength of the two wavelengths. A step height of 2mm constructed with two gauge blocks has been measured. The standard deviation of measurement results is 2.5nm.

Smart windows can electrically switch between clear and opaque states. Current smart windows based on polymer dispersed liquid crystal are expensive and they have moderate range of transparency tuning. Elastomeric tunable window devices are being researched as the low-cost alternates. They consist of a transparent elastomer substrate with surface electrodes that provide electrically controlled micro-wrinkling. They diffusely scatter the transmitted light and thus appear opaque when the surfaces are micro-wrinkled. On electrical activation the wrinkles are flattened, thus making the windows transparent like window blinds. However, the initial prototypes of these electrically tunable window devices showed limited transparency tuning because their transparent electrodes cannot be completely flattened. For example, the brownish e-beam evaporated indium-tin-oxide thin films (50 nm thick) remains mildly wrinkled (with 52.08% transmittance) even when subjected to 37% areal expansion, while its opaque state allows 39.14% transmittance. There is a need for more transparent thin-film electrode with better controllability of surface micro-wrinkling. This work reports a greatly improved tunable window device with enlarged range of transmittance tuning: a clear state of 71.5% transmittance and an opaque state of 2% transmittance. This new device made use of ultra-thin (6 nm) ITO thin films as the transparent compliant electrodes, which were initially wrinkled and can be flatten by 12.2% voltage-induced areal expansion. These ultra-thin ITO thin films are clearer with fewer thermally-induced wrinkles on the flat elastomer substrate (VHB 4905) as they were deposited at a lower surface growth temperature using the RF magnetron sputtering technique. In addition, they make compliant electrodes of higher electrical conductivity and can electrically unfold the mechanically induced micro-wrinkles by a small voltage-induced areal expansion (~12.2%). With the greatly enhanced performance, this electrically tunable window device is promising approach for low-cost smart windows.

In order to measure the transmittance for a large field of view (FOV), a system based on scanning LED is developed. The system mainly consists of tunable LEDs, a glass diffuser and a camera. The LED panel would display different colors in the CIE color space. An algorithm of converting the light wavelength to the RGB values is adopted. The images are captured using a monochrome camera. Depending on the number of colors displayed, the transmittance map for the entire spread of visible colors can be determined. Results are compared with those measured through a spectrometer. The spectral transmittance for the two methods exhibit good similarity. The system provides a means of measuring transmittance with no moving parts and can be extended to other hyperspectral imaging applications.

Interest in the use of laser-based sensors operating in stand-off mode is increasing due to the wide range of options offered in the evaluation of distant targets. In this work, a stand-off laser induced breakdown spectroscopy (ST-LIBS) system has been developed and demonstrated to determine the heavy elements in soil samples. Initially, different parameters of the device have been optimized in ambient atmosphere and tested for quantitative analysis of Nickel and Chromium at two different stand-off distances (1 m and 6 m). The prepared concentrations were in the range of 100 ppm to 600 ppm. The laser energy of 150 mJ was maintained through out the experiment and to obtain a real time situation the target was in static state.

Laser material processing has become an indispensable tool in modern production. With the availability of high power pico- and femtosecond laser sources, laser material processing is advancing into applications, which demand for highest accuracies such as laser micro milling or laser drilling. In order to enable narrow tolerance windows, a closedloop monitoring of the geometrical properties of the processed work piece is essential for achieving a robust manufacturing process. Low coherence interferometry (LCI) is a high-precision measuring principle well-known from surface metrology. In recent years, we demonstrated successful integrations of LCI into several different laser material processing methods. Within this paper, we give an overview about the different machine integration strategies, that always aim at a complete and ideally telecentric integration of the measurement device into the existing beam path of the processing laser. Thus, highly accurate depth measurements within machine coordinates and a subsequent process control and quality assurance are possible. First products using this principle have already found its way to the market, which underlines the potential of this technology for the monitoring of laser material processing.

With a penchant for integrated photonics and miniaturization, the fabrication of micron sized optical elements using precision laser pulse management is drawing attention due to the possibility of minimizing tolerances for collateral material damage. The work presented here deals with the design, fabrication and characterization of a range of diffractive optics - gratings, grids and Fresnel zone plates – on transparent and metallic samples. Their low volume, light weight, transmission bandwidth, high damage threshold and flexible design make them suited for replacing conventional refractive optical elements. Our one-step, mask-less, 3-D laser direct writing process is a green fabrication technique which is in stark contrast to currently popular Photo-lithography based micro-structuring. Our method provides scope for modifications on the surface as well as within the bulk of the material. The mechanism involved in the fabrication of these optics on transparent and thin metallic substrates differ from each other. Our studies show that both amplitude and phase versions of micro-structures were achieved successfully with performances bearing ~98% accuracy vis-a-vis theoretical expectations.

A speckle pattern is a direct fingerprint of surface height variation on the sample. In this paper, angular speckle correlation technique is applied to estimate surface roughness Ra of an additive manufactured sample with different surface roughness Ra values varying from 5μm to 20μm. Feasibility study is conducted to evaluate the correct incidence and the change in incidence angle for angular speckle correlation. Speckle correlation is computed from two speckle images that are recorded at two different incidence angles on the rough surface and surface roughness information is gleaned. Test results in terms of surface roughness measurement from standard calibration plate and additive layer manufactured samples are presented.

A novel Empirical mode decomposition (EMD) profilometry has been developed for dynamic measurement, which can reconstruct the 3D shape of an object by projecting only fringe pattern. The distinctive technique of the system is the newly developed Sinusoids-assisted Bidimensional EMD (SBEMD) algorithm, which can decompose an image into different pure scales. As even very detailed information can be purely extracted for analysis, EMD profilometry is able to measure the object with complex or discontinuous surface. However, the Gamma errors of the system become more obvious just due to these advantages of SBEMD, which also can be represented as high harmonics. In this paper, a simple yet effective phase filtering method is proposed also based on the SBEMD, which can filter the gamma errors but meantime avoid losing detailed phase. Experiments show the effectiveness of the method.

Since the cylinder surface is closed and periodic in the azimuthal direction, existing stitching methods cannot be used to yield the 360° form map. To address this problem, this paper presents two methods for stitching interferometry of cylinder: one requires overlap regions, and the other does not need the overlap regions. For the former, we use the first order approximation of cylindrical coordinate transformation to build the stitching model. With it, the relative parameters between the adjacent sub-apertures can be calculated by the stitching model. For the latter, a set of orthogonal polynomials, termed Legendre Fourier (LF) polynomials, was developed. With these polynomials, individual sub-aperture data can be expanded as composition of inherent form of partial cylinder surface and additional misalignment parameters. Then the 360° form map can be acquired by simultaneously fitting all sub-aperture data with LF polynomials. Finally the two proposed methods are compared under various conditions. The merits and drawbacks of each stitching method are consequently revealed to provide suggestion in acquisition of 360° form map for a precision cylinder.

Laser triangulation displacement sensor using the single point laser or linear laser as the source is widely used in industry. The sensor uses the triangulation principle among light source, tested object and receiver with high speed and non-contact advantages. However, the structure of most of traditional laser triangulation sensors is split that an external amplifier controller is necessary, causing a complicated system. An integrated structure of laser triangulation displacement sensor is put forward in this paper. All signal collection and processing systems are integrated in the probe so that the sensor can be convenient to measure. The limited volume of sensor leads to the change of layout. So the image quality of spots also changes as well. The layout and the principle of the sensor are introduced. The expression of the light spot is also analyzed. A new measurement method of spot processing is also proposed at the same time. Some experimental results are also given to show the efficiency of the new algorithm.

Fringe projection is an extensively used technique for high speed three-dimensional (3D) measurements of dynamic objects. However, the motion often leads to artifacts in reconstructions due to the sequential recording of the set of patterns. In order to reduce the adverse impact of the movement, we present a novel high speed 3D scanning technique combining the fringe projection and stereo. Firstly, promising measuring speed is achieved by modifying the traditional aperiodic sinusoidal patterns so that the fringe images can be cast at kilohertz with the widely used defocusing strategy. Next, a temporal intensity tracing algorithm is developed to further alleviate the influence of motion by accurately tracing the ideal intensity for stereo matching. Then, a combined cost measure is suggested to robustly estimate the cost for each pixel. In comparison with the traditional method where the effect of motion is not considered, experimental results show that the reconstruction accuracy for dynamic objects can be improved by an order of magnitude with the proposed method.

Digital holographic interferometry has been implemented for inspection of defect in an electronic circuit. A simulated defect using Joule’s law of heating has been used. Temperature profile on the surface of the defect has been obtained using the digital holographic interferometry. Abel inversion and Lorentz-Lorentz equation have been used for relating the temperature to the reconstructed phase. Goldstein phase unwrapping algorithm has been implemented to obtain continuous variation of the phase distribution over the defect. Experiments are conducted on the electronic circuit. This paper presents the experimental investigation of defect produced in electronic circuit using the hologram reconstruction, two dimensional Goldstein phase unwrapping method, Abel inversion and Lorentz-Lorentz equation.

Quantitative phase detection is a new methodology that provides quantitative information on cellular morphology to monitor the cell status, drug response and toxicity. In this paper the morphological changes in acute leukemia cells treated with chitosan were detected using d’Bioimager a robust imaging system. Quantitative phase image of the cells was obtained with numerical analysis. Results show that the average area and optical volume of the chitosan treated cells is significantly reduced when compared with the control cells, which reveals the effect of chitosan on the cancer cells. From the results it can be attributed that d’Bioimager can be used as a non-invasive imaging alternative to measure the morphological changes of the living cells in real time.

High precision optical components with large numerical aperture are widely used in industrial products. The stitching interferometry system was designed to measure high-numerical-aperture sphericity and extended the measurement range of interferometry. Firstly, sub-aperture stitching model and experimental system were analyzed. Adjustment mechanism with seven degrees of freedom was built to keep spherical surface in the null position. Then, optical path difference caused by adjustment errors was described by mathematical model. The misalignment aberrations in measurement result were removed after fitted by the Zernike polynomial and the accurate surface shape of single aperture is gained. Finally, a high-numerical-aperture sphericity was measured by the error homogenization algorithm. The PV and RMS are consistent with the results of full aperture testing.

Interaction of noble metal nanoparticles (NPs) with fluorophores has been an important research area in the field of material science and biomedical field. In the proximity of a metal nanoparticle, there is a quenching or enhancement in the intrinsic fluorescence of the fluorophore . The conditional quenching of the fluorescence can be used for negative sensing whereas enhancement in the fluorescence can be used to gain greater sensitivity and high signal to noise ratio in the molecular sensing/imaging. The current work deals with the systematic studies to understand the fluorescence quenching for few bio-fluorophores (NADH and FAD) when interacted with different sized silver nano-particles of (10nm, 40nm and 100nm). Home assembled Laser Induced Fluorescence (LIF) set-up was used to study the fluorescence quenching of NADH and FAD for different sized silver nanoparticles.

Locating defects in CFRP composite materials is a hot topic in nondestructive inspection (NDI). Beside classical NDI technique, such as ultrasound testing (UT), contactless techniques are actively studied. Generally manufacturers of CFRP structure incorporate artificial defects in the bulk, with different extents and depths, in order to study the performance of a specific NDI technique to detect the defect. One of the most common defects in CFRP is delamination between two layers. This is simulated by inserting teflon sheets which, like air, acts as ultrasound blocker in UT. When such reference part is used to assess NDI performance of thermography or shearography, we only observe respectively the thermal or mechanical response of teflon with respect to external loading used with these techniques. In this work, we assess other possibilities for artificial defects in CFRP matrix. For that a CFRP structure was developed and which incorporates teflon, flat-bottom holes and delamination obtained by the pull-out method. We experimentally studied the signals and we discuss the difference between the various artificial defects methods.