This PDF file contains the front matter associated with SPIE Proceedings Volume 7386, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The characterization of single biological cells in a microfluidic flow by using a 2D light scattering microfluidic cytometric technique is described. Laser light is coupled into a microfluidic cytometer via an optical fiber to illuminate a single scatterer in a fluidic flow. The 2D light scattering patterns are obtained by using a charge-coupled device (CCD) detector. The system is tested by using standard polystyrene beads of 4 μm and 9.6 μm in diameter, and the bead experimental results agree well with 1D Mie theory simulation results. Experiments on yeast cells are performed using the microfluidic cytometer. Cell results are studied by finite-difference time-domain (FDTD) method, which can simulate light scattering from non-homogeneous cells. For example, a complex biological cell model with inner mitochondrial distribution is studied by FDTD in this paper. Considering the yeast cell size variations, the yeast cell 2D scatter patterns agree well with the FDTD 2D simulation patterns. The system is capable of obtaining 2D side scatter patterns from a single biological cell which may contain rich information on the biological cell inner structures. The integration of light scattering, microfluidics and fiber optics described here may ultimately allow the development of a lab-on-chip cytometer for label-free detection of diseases at a single cell level.

Recent advancements in the integration of photonic technologies with microfluidics for Micro-Total Analysis Systems (μTAS) have paved way for the realization of a lot of potential applications in the field of biosensing and biomedical detections. Some of the prominent features of these integrated μTAS are improved performance, high sensitivity and signal-to-noise ratio, reduced consumption of samples and reagents, and portability, among others. In this work, a hybrid integrated biophotonic μTAS on silicon-polymer platform is presented. Herein, the optical fibers are directly integrated with the Silicon microfluidic chip and an Echelle grating based Spectrometer-on-Chip on Silica-on-Silicon (SOS) is integrated with the opto-microfluidic assembly. Flow actuation within the system is enabled by a mechanical Piezodriven Valveless Micropump (PVM). Finite Element Analysis (FEA) has been carried out in order to study the behavior of the fluid flow within the microfluidic channels due to the piezo actuation, and the geometry of the bio-detection chamber within the microfluidic system has been optimized accordingly in order to obtain no-stagnation flow conditions. The opto-microfluidic performance and the piezo-actuated valveless micropump were characterized in separate experiments. The integrated μTAS was tested for flow cytometry and particle detection using laser induced fluorescence. The experimental results show that the system is suitable for high throughput biodetections.

Full-Field Optical Coherence Microscopy (FF-OCM) is a microscopic imaging device based on interferometry. It can produce cross-sectional images of bio-tissue or cell samples at a resolution in the order of a micron. Because it can extract an en-face image directly from the sample, it does not need 2D scanning mechanism, which greatly increases the imaging speed compared to fibre-based OCT systems. However, a controlled translation stage is still required in the reference arm of the interferometer to perform the depth scan. Swept-Source OCT (SS-OCT) technology is the second generation of the OCT systems, which not only removes the mechanical scanning, but also increases the signal / noise ratio of the extracted OCT images. In this paper, we describe the design and implementation of a swept-wavelength source based FF-OCM with 60X magnification; 8 um depth resolution; 4 μm depth resolution; 20 mm working distance and 15 frames / second imaging speed.

Signal-Transducer-and-Activator-of-Transcription 3 (STAT3) protein plays an important role in the onset of cancers such as leukemia and lymphoma. In this study, we aim to test the effectiveness of a novel peptide drug designed to tether STAT3 to the phospholipid bilayer of the cell membrane and thus inhibit unwanted transcription. As a first step, STAT3 proteins were successfully labelled with tetramethylrhodamine (TMR), a fluorescent dye with suitable photostability for single molecule studies. The effectiveness of labelling was determined using fluorescence correlation spectroscopy in a custom built confocal microscope, from which diffusion times and hydrodynamic radii of individual proteins were determined. A newly developed fluorescein derivative label (F-NAc) has been designed to be incorporated into the structure of the peptide drug so that peptide-STAT3 interactions can be examined. This dye is spectrally characterized and is found to be well suited for its application to this project, as well as other single-molecule studies. The membrane localization via high-affinity cholesterol-bound small-molecule binding agents can be demonstrated by encapsulating TMR-labeled STAT3 and inhibitors within a vesicle model cell system. To this end, unilaminar lipid vesicles were examined for size and encapsulation ability. Preliminary results of the efficiency and stability of the STAT3 anchoring in lipid membranes obtained via quantitative confocal imaging and single-molecule spectroscopy using a custom-built multiparameter fluorescence microscope are reported here.

Using the vectorial diffraction theory established by Richards and Wolf, we demonstrate that the resolution of a two-photon microscope can be improved with a radially polarized TM₀₁ laser beam and an interface between dielectrics, instead of the linearly polarized Gaussian beam already used in laser scanning microscopy. To verify the theoretical results, we developed a mode converter producing radially polarized beams and we have integrated it in a commercial two-photon microscope.

The optical and analytical modeling of a line-scan optical coherence tomography (LS-OCT) system for high-speed three-dimensional (3D) endoscopic imaging is reported. To avoid complex lens system and image distortion error, an off-axis cylindrical mirror is used for focusing the line illumination on the sample surface and a micro mirror scanner is integrated with the proposed configuration for transverse scanning. The beams are swept on the cylindrical mirror by the micro mirror rotation and finally focused on the sample surface for transverse scanning. A 2mm by 3.2mm en-face scanning is configured with a 2mm focused line and ±3° scanning mirror rotation. The proposed configuration also has the capability of dynamic focusing by the movement of the cylindrical mirror without changing the transverse resolution. The cylindrical mirror enhances the image quality by reducing the aberration. The system is capable of real-time 3D imaging with 5μm and 10 μm axial and transverse resolutions, respectively.

Objective: Develop a representative calcium target model to evaluate penetration of calcified plaque lesions during atherectomy procedures using 308 nm Excimer laser ablation. Materials and Methods: An in-vitro model representing human calcified plaque was analyzed using Plaster-of-Paris and cement based composite materials as well as a fibrinogen model. The materials were tested for mechanical consistency. The most likely candidate(s) resulting from initial mechanical and chemical screening was submitted for ablation testing. The penetration rate of specific multi-fiber catheter designs and a single fiber probe was obtained and compared to that in human cadaver calcified plaque. The effects of lasing parameters and catheter tip design on penetration speed in a representative calcified model were verified against the results in human cadaver specimens. Results: In Plaster of Paris, the best penetration was obtained using the single fiber tip configuration operating at 100 Fluence, 120 Hz. Calcified human lesions are twice as hard, twice as elastic as and much more complex than Plaster of Paris. Penetration of human calcified specimens was highly inconsistent and varied significantly from specimen to specimen and within individual specimens. Conclusions: Although Plaster of Paris demonstrated predictable increases in penetration with higher energy density and repetition rate, it can not be considered a totally representative laser ablation model for calcified lesions. This is in part due to the more heterogeneous nature and higher density composition of cadaver intravascular human calcified occlusions. Further testing will require a more representative model of human calcified lesions.

Methods that avoid intermediate amplification steps to detect protein markers of pathological disturbances would be of wide interest in the clinical environment. This is particularly the case in cancer diagnosis, where protein fragments are released into the blood by the emerging cancer cells. These fragments generate an antigen-antibody reaction, and the concentration of the antigen is known to modulate this interaction. Here we report on the development of a novel optical tweezers-based procedure to measure minute amount of antigen in a biological fluid. The force was applied on a 3μm polystyrene bead coated with Bovine Serum Albumin (BSA) attached on a 1.5 μm diameter borosilicate rod tip coated with anti-BSA antibody. First, we verified that the binding strength was dependent on the protein concentration on the bead. We then assessed the sensitivity range by finding the minimal BSA concentration in solution that can still interfere with the bead-rod linkage. On the whole, the results demonstrated that proteinous antigen present in a biological fluid could possibly be detectable at atomolar concentration through the use of an optical tweezers.

Here we report the results of investigations of Surface Enhanced Raman Scattering (SERS) from amino acids and peptides. In order to obtain optimum signals a standard microfluidic chip has been modified with the help of laser micromachining technique to increase scattering light collection efficiency. We have studied the SERS signals from the following amino acids: tryptophan (Trp), phenylalanine (Phe) and glycine (Gly) and peptides Trp-Trp and Gly-Gly-Gly. The optimum conditions for observing the spectrum from these amino acids and peptides have determined. In our studies the highest enhancement observed is from the amino acid Trp. Large signal enhancements were observed and the lowest detectable concentration of Trp was estimated to 4·10 ^-9 M.

Doppler Optical Coherence Tomography (DOCT) is a biomedical imaging technique that allows simultaneous structural imaging and flow monitoring inside biological tissues and materials with spatial resolution in the micrometer scale. It has recently been applied to the characterization of microfluidic systems. Structural and flow imaging of novel microfluidics platforms for cytotoxicologic applications were obtained with a real-time, Near Infrared Spectral Domain DOCT system. Characteristics such as flow homogeneity in the chamber, which is one of the most important parameters for cell culture, are investigated. OCT and DOCT images were used to monitor flow inside a specific platform that is based on microchannel division for a better flow homogeneity. In particular, the evolution of flow profile at the transition between the microchannel structure and the chamber is studied.

In this paper, we report the preliminary development of a fiber coupled microfluidic flow cytometer with its potential application of sorting the very small embryonic like (VSEL) stem cells out of a mixture of platelets and VSEL stem cells. The identification of a VSEL stem cell from a platelet is based on the large difference of their abilities to scatter light. A simple cytometer prototype was built by cutting the fluidic and other channels into a polymer sheet and bonding it with epoxy between two standard glass slides. Standard photolithography was used to expose an observation window over the upper coated glass to reduce background scattered light. Liquid sample containing micro-particles (such as cells) is injected into the microfluidic channel. Light from a 532-nm CW diode laser is coupled into the optical fiber that delivers the light to the detection region in the channel to interrogate the flowing-by micro-particles. The scattering light from the interrogated micro-particle is collected by a photodiode placed over the observation window. The device sorts the micro-particle into the sort or waste outlet depending on the level of the photodiode signal. We used fluorescent latex beads to test the detection and sorting functionalities of the device. It was found that the system could only detect about half of the beads but could sort almost all the beads it detected.

Our work uses 1080 images sequence obtained from "in vitro" samples taken every 4 min from a microscope under phase contrast technique. These images are in JPEG format and are 500×700 pixels size with a compression rate of 3:1. We developed an algorithm and characterize it over several image operations against the tracking effectiveness and its robustness respect mitosis and cell shape change. Image equalization, dilation and erosion were the image processing procedures founded to provide best tracking results. Equalization procedure, for example, required a time delay of 5 sec for a size target of 60×90 pixels and 9 sec for size target of 89×100 pixels. This algorithm was implemented into a FPGA which controlled our optical correlator in order to performance all Fourier operations by optical method. Our results showed that the use of the optical correlator can reduce the time consuming in the image process until for 90% which able us to track cells in vascular structure.

High-throughput detection and identification of foodborne pathogens are in increasing demand for rapid bacteria detections in food safety and quality monitoring. As an effective method, microchip-based flow cytometry (microcytometery) has a potential to be less expensive and high throughout, and requires less bulky instrumentation than conventional methods. In this work, a low-cost and robust microcytometer with a simple optical setup was developed for demonstrating the high-throughput identification of foodborne bacterial pathogens that integrate sample flow focusing and detection into one testing procedure. High performance identification capability was achieved through simultaneously detecting the fluorescence and scatter light emitted from micro-fabricated channel, after designing and optimizing the laser shaping optical system and the micro-channel structure to improve the excitation light intensity as well as the detection sensitivity. In our configuration, the simple testing configuration with the collection angle of 42° in the orthogonal plane to micro chip presents the best SNR for both signals through simulation and systematic measurements. As a result, the maximum throughput of 83particles/s for the fluorescence-labelled bead with diameter of 1.013μm was obtained as well as the high detection efficiency (above 99%) and the correlation percentage (above 99.5%). Apart from the high detection sensitivity and identification power, this microcytometer also has the advantages of simple optical structure, compactness and ease in building.

This work implements a novel hybrid method for detection and tracking of biological cells of "in vitro" samples (Goobic,¹ 2005). The method is able to detect and track cells based on image processing, nonlinear filters and normalized cross correlation (ncc) and it is tested on a full sequence of 1080 images of cell cultures. In addition of the cell speed, Cell tracking differentiate itself from tracking other kinds of tracking because cells show: mitosis, apthosis, overlapping and migration (Liao,² 1995). Image processing provides an excellent tool to improve cell recognition and background elimination, set as a priori task on this work and conveniently implemented by a Fourier analysis. The normal cross correlation was developed in the Fourier space to reduce time processing. The problem of the target detection was formulated as a nonlinear joint detection/estimation problem on the position parameters. A bank of spatially and temporally localized nonlinear filters is used to estimate the a posteriori likelihood of the existence of the target in a given space-time resolution cell. The shapes of the targets are random and according to the sequence, the targets change of shape almost every frame. However, the cross correlation result is based on the target shape matching, not in the position; and the system is invariant to rotation. Nonlinear filter makes a robust cell tracking method by producing a sharper correlation peak and reducing the false positives in the correlation. These false positives may also be reduced by using image preprocessing. Fourier and nonlinear filtering implementation showed the best results for the proposed cell tracking method presenting the best time consumption and the best cell localization.

A new multiple lifetime fitting algorithm is presented which deconvolves a time-domain system Instrument Response Function (IRF) from a measured Fluorescence Time Point Spread Function (FTPSF) prior to lifetime fitting. Deconvolution is followed by filtering, using a special case of the optimal Wiener filter, where the signal-to-noise ratio (SNR) in the spectral domain is evaluated empirically, and thus tuned with respect to each specific FTPSF-IRF combination at hand. Comparisons between the proposed deconvolution scheme and the classical Iterative Convolution (IC) scheme over a set of simulated and experimental data reveal that the proposed scheme typically exhibits order-of-magnitude performance gains (accuracy and efficiency combined) over the IC scheme in realistic conditions.

We recently developed a time-domain technique for localizing in 3D discrete fluorescent inclusions embedded in a scattering medium. It exploits early photon arrival times (EPATs), that is the time of flight of early arriving photons at a detector determined via numerical constant fraction discrimination. Our localization technique requires the knowledge of the speed of propagation of diffuse light pulses in the turbid medium to convert measured propagation times to distances. We have developed an experimental method for measuring the speed of propagation of such pulses. We have shown that time differences between a reference detector position and other positions around the medium allow finding the position of the inclusion. Our technique allows localizing inclusions to millimeter precision in a thick 5 cm diameter turbid medium. Herein, we analyze the stability of EPAT differences introduced above and propagation speeds with respect to changes in the medium's optical properties for optical properties typical of biological tissues. As we target small animal imaging, we concentrate on optical properties of mouse organs and tissues. Our objective is to determine bounds to be expected on the precision that can be achieved when media properties can vary and determine the limits of validity of our localization technique. Our results show that EPAT differences and propagation speeds obtained by our approach can vary; these values depend on the medium. We study 5 kinds of mouse organs and tissues. Propagations speeds are between 2.97 × 10⁷ms^-1 and 5.52 × 10⁷ms^-1. Thus, it becomes important to evaluate the discrepancy between true geometrical distance differences and distances as obtained by our approach using a constant propagation speed and the measurement of EPAT differences. It is such discrepancies that ultimately determine the localization accuracy of our algorithm because if distance differences based on EPATs are far from true distances, our algorithm although it has a certain tolerance will have to consider that. The distance error and so the localization accuracy of our algorithm is between 2.5mm and 8.6mm.

In this study we compare the single-photon autofluorescence and multi-photon emission spectra obtained from the luminal surface of healthy segments of artery with segments where there are early atherosclerotic lesions. Arterial tissue was harvested from atherosclerosis-prone WHHL-MI rabbits (Watanabe heritable hyperlipidemic rabbit-myocardial infarction), an animal model which mimics spontaneous myocardial infarction in humans. Single photon fluorescence emission spectra of samples were acquired using a simple spectrofluorometer set-up with 400 nm excitation. Samples were also investigated using a home built multi-photon microscope based on a Ti:sapphire femto-second oscillator. The excitation wavelength was set at 800 nm with a ~100 femto-second pulse width. Epi-multi-photon spectroscopic signals were collected through a fibre-optics coupled spectrometer. While the single-photon fluorescence spectra of atherosclerotic lesions show minimal spectroscopic difference from those of healthy arterial tissue, the multi-photon spectra collected from atherosclerotic lesions show marked changes in the relative intensity of two-photon excited fluorescence (TPEF) and second-harmonic generation (SHG) signals when compared with those from healthy arterial tissue. The observed sharp increase of the relative SHG signal intensity in a plaque is in agreement with the known pathology of early lesions which have increased collagen content.

The optical properties and significant surface area of CdSe/ZnS QDs make such nanoparticles an interesting platform for the preparation of nucleic acid biosensors based on fluorescence resonance energy transfer (FRET). Interactions between QDs and oligonucleotides affect biosensor performance and are not fully understood. Ensemble data obtained via FRET experiments indicated that, on average, 4-5 added oligonucleotides saturated the surface of green emitting QDs. An increase in the number of oligonucleotides per QD appeared to cause the oligonucleotides to transition from collapsed to upright conformations. Since bulk averaging hides details of such processes, methods must be developed and materials identified for studying QD-oligonucleotide conjugates at the single molecule level. Single QDs have been immobilized and fluorescence intensity trajectories measured. High count rates and good photostability were achieved using carboxyl polymer-coated QDs. Modeling of FRET efficiency based on the dimensions of QDs and oligonucleotides indicated that transitions between collapsed and upright conformations can be accurately measured based on changes in QD fluorescence lifetime. The ultimate goal of this work is to elucidate QD-oligonucleotide dynamics for better design and optimization of nucleic acid biosensors based on QDs.

Effects of apodization on distributed feedback fiber laser (DFB FL) output power and threshold gain are theoretically investigated by employing the transfer matrix method. Three distinct types of profile are investigated: the gaussian, flat or nonapodize, and sigmoid profile. The gaussian and sigmoid profiles are the two extreme cases examined; the former has a strong profile around a centrally located phase shift, while the latter is with a weaker profile. Findings indicate that the tradeoff between output power and higher order mode threshold performance are resulting from the interplay between these profile shapes. The comprehensive results presented in this paper should assist the development of high performance DFB FLs.

We present a theoretical scheme for a Tm³⁺-doped radiation-balanced (athermal) continuous-wave fiber amplifier. This mode of operation allows amplification without detrimental heating of the fiber with optical pumping. Athermal amplification is realized by laser cooling in which waste heat is disposed of in the form of spontaneous fluorescence by balancing the radiated and absorbed power. The athermal fiber amplification can be realized using a specially designed distributed pumping scheme.

Self-similarity is a ubiquitous concept in the physical sciences used to explain a wide range of spatial- or temporalstructures observed in a broad range of applications and natural phenomena. Indeed, they have been predicted or observed in the context of Raman scattering, spatial soliton fractals, propagation in the normal dispersion regime with strong nonlinearity, optical amplifiers, and mode-locked lasers. These self-similar structures are typically long-time transients formed by the interplay, often nonlinear, of the underlying dominant physical effects in the system. A theoretical model shows that in the context of the universal Ginzburg-Landau equation with rapidly-varying, mean-zero dispersion, stable and attracting self-similar pulses are formed with parabolic profiles: the zero-dispersion similariton. The zero-dispersion similariton is the final solution state of the system, not a long-time, intermediate asymptotic behavior. An averaging analysis shows the self-similarity to be governed by a nonlinear diffusion equation with a rapidly-varying, mean-zero diffusion coefficient. Indeed, the leadingorder behavior is shown to be governed by the porous media (nonlinear diffusion) equation whose solution is the well-known Barenblatt similarity solution which has a parabolic, self-similar profile. The alternating sign of the diffusion coefficient, which is driven by the dispersion fluctuations, is critical to supporting the zero-dispersion similariton which is, to leading-order, of the Barenblatt form. This is the first analytic model proposing a mechanism for generating physically realizable temporal parabolic pulses in the Ginzburg-Landau model. Although the results are of restricted analytic validity, the findings are suggestive of the underlying physical mechanism responsible for parabolic (self-similar) pulse formation in lightwave transmission and observed in mode-locked laser cavities.

We present a theoretical description of the generation of ultra-short, high-energy pulses in an all-normal dispersion laser cavity with spectral filtering. A reduced variational model based upon the Haus master mode-locking equations with quintic saturation is shown to characterize the experimentally observed dynamics. Critical in driving the intra-cavity dynamics is the nontrivial phase profiles generated and their periodic modification from the spectral filter. The theory gives a simple geometrical description of the intra-cavity dynamics and possible operation modes of the laser cavity. Further, it provides a simple and efficient method for optimizing the laser cavity performance.

As data traffic increases on telecommunication networks, optical communication systems must adapt to deal with this increasing bursty traffic. Packet switched networks are considered a good solution to provide efficient bandwidth management. We recently proposed the use of spectra amplitude codes (SAC) to implement all-optical label processing for packet switching and routing. The implementation of this approach requires agile photonic components including filters and lasers. In this paper, we propose a reconfigurable source able to generate the routing codes, which are composed of two wavelengths on a 25 GHz grid. Our solution is to use a cascade of two chirped fibre Bragg gratings (CFBG) in a semiconductor fibre ring laser. The wavelength selection process comes from distributed phase shifts applied on the CFBG that is used in transmission. Those phase shifts are obtained via local thermal perturbations created by resistive chrome lines deposited on a glass plate. The filter resonances are influenced by four parameters: the chrome line positions, the temperature profile along the fibre, the neighbouring heater state (ON/OFF) and the grating itself. Through numerical modeling, these parameters are optimized to design the appropriate chrome line pattern. With this device, we demonstrate successful generation of reconfigurable SAC codes.

Photodarkening and photobleaching processes affect the level of photodegradation of Yb-doped fibers. Characterization and modeling of each process is crucial to understand how to optimize the operating conditions of fiber amplifiers and lasers to obtain acceptable output power degradation. We show that photobleaching is a key factor in the modeling and simulation of a 10-ns pulsed Yb-doped LMA fiber amplifier. Each parameter of the model was separately determined from induced excess loss measurements under selective pump and wavelength excitations. The model was used to simulate accurately the measured fiber amplifier degradation. Optimized fiber length and gain were calculated to improve the output power stability over time and increase the fiber lifetime. Furthermore, eight fibers have been fabricated with various Yb, Al, and P content using the MCVD process to optimize the core composition. The level of photodarkening in each fiber was evaluated by measuring separately rate coefficient and excess loss. It was found that all fibers followed a similar inversion-dependent rate while the maximum excess loss was dependent on the ratios [Al]/[Yb] and [P]/[Yb]. The proposed model allows for rapid evaluation and optimization of fiber parameters and operation conditions to assist Yb-doped laser system design in achieving the desired performance with low photodegradation.

The work presented in this paper had two main objectives. The first objective was to develop a very stable nanosecond infrared pulsed fiber laser oscillator platform offering a straightforward and accurate control over the pulse characteristics in the time domain. The second objective was to deliver what we call "high quality photons", which means delivering pulses with high energy and excellent beam quality and narrow spectral linewidth, all at the same time and with very good stability. Oscillators with such attributes find applications in material processing fields, for example in memory repair, photovoltaic cell processing or micro-milling, to name just a few. In order to achieve the first objective, an embedded digital platform using high-speed electronics was developed. Using this platform and a computer, pulse shapes have been programmed straightforwardly in the non-volatile memory of the instrument, with an amplitude resolution of 10 bits and a time resolution of 2.5 ns. Optical pulses having tailored temporal profiles, with rise times around 1 ns and pulse energy stability levels better than ± 3% at 3σ, have been generated at high repetition rates (> 100 kHz) at a wavelength of 1064 nm. Achieving the second objective required amplifying the low power master oscillator signal (10-100 mW) to output power levels in the range of 1 to 50 W. A multi-clad, polarization maintaining, Yb-doped large mode area fiber was specially designed to allow for the amplification of high peak power optical pulses, while keeping control over the nonlinear effects and preserving an excellent beam quality. Optical pulses with tailored shapes and pulse energy levels in excess of 140 μJ have been produced for pulse durations in the range of 10 to 80 ns, with 86% of the power emitted in a 0.5-nm bandwidth. The linearly polarized beam M² parameter was smaller than 1.1, with both the astigmatism and the asymmetry below 15%. The pulse energy stability was better than ± 3% at 3σ. We conclude with a discussion about some of the applications of the developed platform.

We demonstrate the usefulness of INO's pulse-shaping fiber laser platform to rapidly develop complex laser micromachining processes. The versatility of such laser sources allows for straightforward control of the emitting energy envelop on the nanosecond timescale to create multi-amplitude level pulses and/or multi-pulse regimes. The pulses are amplified in an amplifier chain in a MOPA configuration that delivers output energy per pulse up to 60 μJ at 1064 nm at a repetition rate of 200 kHz with excellent beam quality (M² < 1.1) and narrow line widths suitable for efficient frequency conversion. Also, their pulse-on-demand and pulse-to-pulse shape selection capability at high repetition rates makes those agile laser sources suitable for the implementation of high-throughput complex laser processing. Micro-milling experiments were carried out on two metals, aluminum and stainless steel, having very different thermal properties. For aluminum, our results show that the material removal efficiency depends strongly on the pulse shape, especially near the ablation threshold, and can be maximized to develop efficient laser micro-milling processes. But, the material removal efficiency is not always correlated with a good surface quality. However, the roughness of the milled surface can be improved by removing a few layers of material using another type of pulse shape. The agility of INO's fiber laser enables the implementation of a fast laser process including two steps employing different pulse characteristics for maximizing the material removal rate and obtaining a good surface quality at the same time. A comparison of material removal efficiency with stainless steel, well known to be difficult to mill on the micron scale, is also presented.

In this work, we examine how the linewidth of high-power Yb-doped fiber lasers changes as a function of laser power. Four-wave mixing between the various longitudinal modes of the laser cavity tends to broaden the laser linewidth, while Bragg reflectors have a narrow bandwidth that limits the extent of this broadening. An analytical model taking into account these effects predicts that the laser linewidth scales as the square root of laser power, in agreement with numerical simulations [1]. This model has been previously validated with a low-power Er-doped fiber laser [1] and with Raman fiber lasers [2]. In this paper, we compare the measurements taken with Yb-doped fiber lasers at power levels ranging from a few watts to hundreds of watts with the model. The broadening of high-power fiber lasers deviate from the model. Experimental data show that the linewidth broadens as a power function (between 0.5 to 1) of the laser power. A simple modification of the model is proposed which fits all the experimental data.

We demonstrate and optimize, for a mJ/ns release, the operation of a compact laser system designed in the form of a hybrid Q-switched Nd³⁺:YAG/Cr⁴⁺:YAG microchip laser seeding an Yb-doped specialty (GTWave-based) fiber amplifier. A gain factor as high as ~25 dB is achieved for nanosecond single-mode pulses at a 1-10-kHz repetition rate as the result of optimization

Although many practical hurdles remain to be addressed in the future, laser oil and gas well drilling has potential advantages over the conventional rotary drilling approach, such as a smaller footprint of the drilling rig, higher rates of penetration, reduction of downtime due to dull bits, reduction of waste caused by drilling mud, creation of a natural casing while drilling, and ability to drill in hard rock formations. One of the most promising applications is downhole laser perforation for well completion as an alternative to explosive technologies currently in use. In order to establish both the technical and economic feasibility of using lasers in oil and gas drilling operations, one can measure the laser energy required to remove a unit volume of rock. The resulting specific energy is a measure of the efficiency of the laser drilling process and depends on the rock type and the laser operation regime that determines the laser-rock interaction mechanism. In the present feasibility study, we compare the results of laser drilling tests conducted in two types of reservoir rocks, namely limestone and sandstone, at different laser wavelengths and for different laser operation regimes (continuous wave and pulsed regimes, different repetition rates and duty cycles) in terms of specific energy. We also discuss preliminary results on the influence of the temporal shape of the laser pulses in the nanosecond regime on the rock removal process as obtained with INO pulse-shaping fiber laser platform, with the objective to take advantage of the flexibility and the agility of such a laser source for drilling operations in different rock types.

The invited paper explains the transmission properties of a range of near-, mid-, and far-IR optical fibres for their applications in chemical and biological sensing. Methods for the fabrication of single and multiple-core mid-IR fibres are discussed in view of controlling the thermal and viscosity properties for fibre drawing. In particular, the need for removing impurity bands in the 5000 to 1000 cm^-1 range is explained. The importance of engineering multi-core fibres is also discussed for simultaneous measurements of Raman, IR and surface plasmon enhanced modes together with say, temperature using a mid-IR transmitting tellurite fibre e.g. in a chemical process. The paper explains the principles and advantages of evanescent wave coupling of light at the resonant frequency bands for chemical sensing using a fibre evanescent wave spectroscopic sensor having a GeTeSe chalcogenide fibre. Using fibre based techniques, measurements for Cr⁶⁺ ions in solution and As³⁺ and As⁵⁺ in solids have been characterized at visible and mid-IR regions, respectively. In this paper we also explain the importance of using mid-IR fibres for engineering novel laser and broadband sources for chemical sensing.

We report high power phase locked fiber amplifier array using the Self-Synchronous Locking of Optical Coherence by Single-detector Electronic-frequency Tagging technique. We report the first experimental results for a five element amplifier array with a total locked power of more than 725-W. We will report on experimental measurements of the phase fluctuations versus time when the control loop is closed. The rms phase error was measured to be λ/60. Recent results will be reported. To the best of the authors' knowledge this is the highest fiber laser power to be coherently combined.

The variable stripe length (VSL) is a convenient method for the measurement of optical gain. However, several inherent experimental constraints such as pump beam non-uniformity, diffraction from the movable cache and sample edges, and gain saturation challenge its proper implementation. A modified VSL configuration, which addresses these constraints, has been developed and implemented for gain measurements in SiO₂ structures containing silicon nanocrystals. A microprocessor based acquisition of several control parameters provides reliable and reproducible optical gain measurements.

In the last decade, the luminescent properties of silicon nanocrystals (Si-nc) have been increasingly studied, since Si-nc are considered as good candidates for optical interconnects between ever-smaller integrated circuits (ICs) components, and for the monolithic integration of all-silicon photonic and electronic devices. For these applications, an efficient coupling between optical and electrical signals within Si-nc structures is required. In this article, the interaction between simultaneous optical and electrical stimulation of Si-nc is examined. To this end, the photoluminescence (PL) spectra of Si-nc obtained by ion implantation in a thin (40 to 60 nm) oxide layer of metal-oxide-semiconductor (MOS) devices has been recorded as a function of variable applied voltage biases at room temperature. Two remarkable features have been observed: an optical memory effect, due to asymmetric PL intensity modulation with respect to biasing polarity, and an efficient optical switching of an electric current in reverse bias operation. These results are explained in terms of the competing effects of the storage and the photogeneration of charge carriers in Si-nc and oxide defects, as indicated by the correlation between the PL intensity and the current flowing through the MOS devices. Moreover, the use of positively- and negatively- doped substrates in the MOS structures distinctly shows the different effects of electron injection over hole injection in Si-nc and their surrounding SiO₂ matrix. These novel optoelectrical features of Si-nc are expected to add more functionality to future all-silicon photonic and electronic ICs.

Recently, it has been shown that the photoluminescence (PL) spectrum emitted by silicon nanocrystals (Si-nc) can be modulated by means of light interference effects, when the Si-nc are produced by the implantation of Si ions in a SiO₂ film grown on Si substrate (SiO₂/Si). Optical interference must be considered for both the pump laser and the light emitted by the Silicon nanocrystals. In this study, strong variations of the PL spectrum intensity are observed as a function of the SiO₂ thickness so that a PL intensity up to three times greater than the one recorded from Si-nc embedded in fused silica has been observed. A Fresnel equation solver [1, 2] has been developed and used to model the emission spectrum of Si-nc in these structures. This model determines the normalized depth profile of emitting centers using the measured luminescence spectra of a series of samples covering a range of SiO₂ thicknesses, providing a powerful tool for the study of the Si-nc luminescence mechanism by comparing the shape of the emitter depth profile to those of Si-nc and implanted Si⁺ depth distributions.

In this work, we show results about the nonlinear optical characterization for four ionic liquids (ILs), namely 1-buthyl-3- methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-ethyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)imide ([EMIM][TF₂N]), 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIM][CF3COO]),1-buthyl-3-methylimidazolium trifluoroacetate ([BMIM][CF₃COO]), using z-scan technique.

Nonlinear effects are consequence of interaction of height intensities of energy with the matter. Self-diffraction is nonlinear effect and rings are produced. We analyzed the increase of rings due to changes in intensity of CW Ar laser that modify the nonlinear refractive index. The Carbon Nanotubes (CNTs) were dispersed on different solvents: a) water, b) ethanol, c) isoprophanol, and d) acetone. The concentrations were 10ml:1mg in all samples. The dependence between power and concentration of CNTs is shown.

We present the viability of obtaining the particle size and surface coverage in a monolayer of polystyrene particles adsorbed on a glass surface from optical coherent reflectance data around the critical angle in an internal reflection configuration. We have found that fitting a CSM to optical reflectivity curves in an internal reflection configuration around the critical angle with a dilute random monolayer of particles adsorbed on the surface can in fact provide the particle's radius and surface coverage once the particles are sufficiently large.

In this paper we have studied effect of depth etching on the Bragg gratings (BGs) realized by Focused Ions Beam. This technique has the advantage to induce a direct waveguide structuring without intermediate media, comparing to traditional methods. A reflectivity of 96% within a window centred at 1550 nm is obtained. The effect of the depth etching on the transmittance and the bandwidth at half maximum is demonstrated.

Hybrid chalcogenide/polysulfone structures are proposed for the implementation of microtapers and nonlinear couplers. In addition to high mechanical robustness, hybrid microtapers provide design advantages that enable the implementation of nonlinear couplers with low switching threshold powers.

Spatial and temporal solitons are at the core of many physical, geological, biological, transmission and information processing and other problems. However, in most cases we have focused on their steady behavior, and therefore on homogeneous media and their single soliton eigenvalues spectrum. This has been done even in the case of an all optical simultaneous loss and amplification, where we have assumed stability of those eigenvalues. However, the transient behavior has received little attention, often disregarded under a generic pulse reshaping or experimentally diafragmed as often occurs in large amplifiers. But such transient behavior can be frozen in a periodic nonhomogenous media, tandems, where such behavior corresponds to the soliton convergence in each tandem media, producing a regular but not steady behavior. We discuss the resonant pulse propagation in a two level atom media tandem, described by a real convergence and a Kerr intensity dependent nonlinearity, described by a complex convergence.

Ti³⁺:Al₂O₃ (Titanium doped sapphire or Ti:sapphire) nanoparticles were produced by the means of pulsed laser deposition (PLD) of bulk Ti:sapphire in background gas with the substrate at ambient temperature. The effect of background gas pressure and composition is studied, having a major impact on the shape, size and aggregation level of the particles. The nanoparticles were characterized by scanning and transmission electron microscopy (SEM and TEM). Preliminary results for the PLD of Cr³⁺:Al₂O₃ (ruby) nanoparticles are also presented.

Waveguides coupling have been widely studied; however, nanowaveguides of high refraction index contrast open the opportunity of studying the nonlinear dynamics of coupled waveguides, in particular those filled with metallic nanaoparticles composites. Those composites show a Quantum Mechanical Kerr Nonlinearity and a classical field amplitude nonlinearity that are compared by using a iterative WKB to introduce the field nonlinearity and based in the ensuing M matrix. The produced nonlinear supermodes show a confinement of the pulse in the waveguides and a breaking of the coupling at small and large core waveguides.

We present the characterization of a photonic crystal slab with a square lattice, whose basis elements are layered cylinders. The cylinders are conceived as glass cores and subsequent layers of two alternating media with different refractive indices, the thickness of each layer is a quarter of a tuning wavelength within the media. The band structure in the dispersion relation is computed by means of numerical simulation and compared to the band structure of a square lattice with plain cylinders, with the same size, and refractive index equal to the average index of the layered ones. We have found that the band structure shrinks to lower frequencies as the number of full periods of layers increases, although keeping the average refractive index and filling factor. This shrink occurs even when the index contrast is kept constant.

Metallic nanoparticles, of a few nanometers radii, show nonlinearities that are the object of experimental and theoretical studies, in particular in the framework of composites. A quantum mechanical analysis of such structures predict a Kerr type nonlinearity, however quite a recent publication on a classical approach has shown that a classical metallic nanoparticles composite shows a nonlinearity proportional to the electric field amplitude, not to the intensity as is in the Kerr case. The capability of filling up the core of a piece fiber with such composites open the possibility of preparing long enough pieces of fiber with such a composite as well as the straightforward drawing of a fiber doped with nanoparticles. In this work we carry on the numerical simulation on such class of fibers, with the specific aim of looking at the corresponding soliton propagation in an optical fiber with a core doped metal nanoparticles.

We present an extensive study of an Er doped Silicon Rich Silicon Oxide (SRSO) based material used for the realization of optical waveguide amplifiers in which Si-nanoclusters (Si-ncls) are formed by thermal annealing. In particular we focus our attention on the confined carrier absorption (CCA) mechanism within the Si-ncls and on the fraction of Er ions coupled to them. Experimental data are used for accurate modeling of Si-ncls sensitized EDWAs (Erbium Doped Waveguide Amplifiers) longitudinally pumped by visible broad area lasers. Although the material requires further optimization to be effectively deployed, accurate numerical simulations of Si-ncls sensitized EDWAs, based on this material and longitudinally pumped by visible broad area lasers at 660 nm, point out significant benefits provided by the nanoclusters sensitization. Our model, based on the Finite Element Method, performs the modal analysis of the guiding structure, and then allows to study the propagation of pump and signal electric fields along the waveguide amplifier; the rate equations for the coupled Er/Si-ncls system account for their coupling ratio. Numerical results, based on measured material parameters, point out that resonant pumping at 660 nm provides significant benefits in terms of gain enhancement, with respect to standard EDWAs, even at low Er/Si-ncls coupling ratio. This feature suggests that a careful design can lead to the realization of compact integrated amplifiers and lasers, compatible with CMOS technology.

A novel centralized light source OCDMA PON without wavelength filters is proposed and experimentally demonstrated. The OCDMA coded signals and the unmodulated clock pulses are polarization-multiplexed and simultaneously transmitted in the downlink. Then the received clock pulses at the ONU side are used as the source for the uplink transmission. The experiment results based on a two-user 2.5 Gb/s OCDMA system show that excellent performance can be achieved after a 20-km transmission.

The impact of cross-phase modulation in a multichannel hybrid on-off-keyed (OOK) and differential quadrature phase shift keyed (DQPSK) system is evaluated analytically. Results confirmed by simulation provide a simple method for determining induced RMS phase error.

It is possible that each light sensor pixel in the eye has the capability of measuring the distance to the part of the object in focus at the pixel. One can also construct an electronic camera where each pixel can measure the distance to the portion of the object in focus at the pixel. That is, these devices have depth perception

An analysis of the optical signal transmitted by a polarimetric sensor developed for the measurement of velocities of fluids in a capillary optical fiber is presented. It allows one to determine whether a fluid is moving in the vapor or the liquid phase.

The Brillouin spectrum narrowing phenomenon for nanosecond pulses in Brillouin Optical Time Domain Analysis (BOTDA) sensor system is demonstrated with high extinction ratio (ER > 24 dB) nanosecond pulse over short fibre length (10 m). The line width of the Brillouin spectrum is ~52 MHz for 10 ns pulse by feedback phase locking of the pump and probe waves from: 1) DFB lasers (2 MHz bandwidth) and 2) fibre lasers (5 kHz bandwidth) at the Brillouin frequency. It is found that the coherent length (inverse of the Brillouin line width in the fibre) of the Brillouin scattering process is not determined by the laser bandwidth, rather by the enhanced phonon field generated from phase locked pump and probe lasers for nanosecond pulses. For the same bandwidth of the pump and probe lasers, the line width of the Brillouin spectrum with high extinction ratio nanosecond pulses under the phase locking of the pump and probe waves is much narrower than that from the frequency locking of the pump and probe waves at the Brillouin frequency.

Anthocyanins are water soluble pigments in plants that are recognized for their antioxidant property. These pigments are found in high concentration in cranberries, which give their characteristic dark red color. The Total Anthocyanin concentration (TAcy) measurement process requires precious time, consumes chemical products and needs to be continuously repeated during the harvesting period. The idea of the digital TAcy system is to explore the possibility of estimating the TAcy based on analysing the color of the fruits. A calibrated color image capture set-up was developed and characterized, allowing calibrated color data capture from hundreds of samples over two harvesting years (fall of 2007 and 2008). The acquisition system was designed in such a way to avoid specular reflections and provide good resolution images with an extended range of color values representative of the different stages of fruit ripeness. The chemical TAcy value being known for every sample, a mathematical model was developed to predict the TAcy based on color information. This model, which also takes into account bruised and rotten fruits, shows a RMS error of less than 6% over the TAcy interest range [0-50].

Tunable diode laser spectroscopy (TDLS) is a well-established method for trace gas detection. TDLS systems usually employ edge-emitting diodes with a distributed feedback configuration. Recently long wavelength vertical cavity surface emitting lasers (VCSEL) have emerged as an alternative source for spectroscopic applications. The relatively low cost, low power requirements and large tuning range of VCSELs make them particularly attractive for portable gas detection systems. In this paper we describe a battery-operated VCSEL spectroscopy system operating near 1650 nm for methane detection. Wavelength modulation spectroscopy (WMS) is commonly used in TDLS systems to improve sensitivity. WMS in these systems is usually implemented with a hardware based lock-in amplifier. We report on the construction of a new system with software WMS and compare its operation with a conventional system. The VCSEL TDLS system is used to probe the 2v3 band of methane over an open path. The relative contributions of optical and electrical noise to the system signal to noise ratio and minimum gas detection level is presented. Finally, challenges and future design considerations in VCSEL spectroscopy are discussed.

Temporal phase shifting method, which is commonly used for characterization of the microstructures, requiring phaseshifter has inherent errors due to non-linearity. To overcome this, an Acoustic-Optic Modulated Stroboscopic Interferometer (AOMSI) was developed using the principle of Stroboscopic Interferometer. The technique utilizes the advantage of stroboscopy to create phase shifted images without requiring any component for phase shifting. Using Carré algorithm and developed AOMSI the curvature of microstructures due to residual stress was extracted. Experiments were performed on a silicon wafer to demonstrate the feasibility of the presented technique. Further, experiments were performed on a designed micro cantilever to extract surface-height information using the proposed method. To verify the accuracy of the presented method, the same micro cantilever was characterized using a WYKO surface profiler and the comparison was found to be in good agreement.