This PDF file contains the front matter associated with SPIE Proceedings Volume 12638, including the Title Page, Copyright information, Table of Contents, and Conference Committee list.

Research of lead-free perovskite solar cells has gained speedy and growing attention with urgent intent to eliminate toxic lead in perovskite materials. The environmental friendliness and excellent thermal stability proves of stable perovskite Cesium Tin Iodide (CsSnI₃) as one of the promising materials for their potential application in solar field. In this paper, fabrication and characterization of CsSnI₃ perovskite layer has been reported. Fabrication of CsSnI₃ perovskite layer was made by spin coating method. One step coating processed CsSnI₃ layer have characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). Optical properties of layer have investigated by Vis-NIR spectrophotometer. It reveals that CsSnI3 perovskite layer possess good absorption in the visible spectrum. XRD result confirms the crystal structure of orthorhombic phase with dominating peak at 27.5⁰ (2*Θ) corresponding (202) planes. Dense distributions of polycrystalline CsSnI₃ perovskite layer were recorded by FESEM images.

Hybrid nanocomposites are gaining significance as they offer dual enhancement of both chemical and electromagnetic enhancements. In this context, Graphene gold nanocomposites are of the suitable choice, offering dual SERS enhancement. However, the fabrication of SERS substrates involving hybrid nanomaterials is challenging due to the higher fabrication cost and repeated generation of hotspot sites. Hence, in this study, theoretical investigation on the influential parameters producing dual SERS enhancement by graphene gold nanocomposites is studied using the 2D Finite Element method analysis in COMSOL Multiphysics software. Herein, electromagnetic waves are utilized to excite the surface plasmons created at the graphene gold interface and the scattered light intensity is measured to quantify the dual SERS enhancement. The parameters influencing the enhancement including diameter and inter particle distance of the gold nanoparticles, interactions at graphene gold interface, graphene layer coating onto various substrates and thickness of the graphene layer are investigated. The scattered light intensity around the nanoparticle surface is increased in the presence of graphene layer and the effective refractive index sensitivity was optimized by choosing various substrate materials. Further, the interparticle spacing and the graphene layer coating are optimized and found ~5 nm interparticle spacing with minimum graphene layer coating of 5 nm achieved improved electric field strength around the nanocomposite surface. RI sensitivity for PMMA substrate is higher and can be used for biosensing applications. The theoretical results obtained could be of high value for the fabrication of graphene gold nanocomposite SERS substrates for achieving better sensitivity.

Kidney disease is one of the complications due to long term diabetes. This is presently identified by serum creatinine and urea. Any elevation in serum urea is also exhibited in sweat. Moreover its concentration in sweat is three times higher than serum level. Based on these facts, we developed an electro optical technique to quantify sweat urea concentration and thus relating it to kidney disease. We approached this work in two stages; at first with aqueous solution and then with sweat samples. First aqueous solutions of 14 different urea concentrations ranging from 60 mg/dL to 350 mg/dL are prepared. When urease is added to this colorless solution, ammonia is liberated. Then ammonium ion reacts with the coloring agent and gives different shades of blue color. This variation in color is sensed by electronic circuitry, where RGB lights are incident sequentially in time controlled fashion. The reflected light from the solution are picked up by the light sensor and mapped on to CIE chromaticity chart. This kind of test is also performed on sweat samples collected from the participants and allowing it to sediment for 15 minutes. The result of this study demonstrates gradual variation in colour space in CIE chromaticity chart. (towards dark green) as the concentration of urea increases. Also sweat sample of control, diabetes and diabetic kidney disease (DKD) found to lie in the range of 60 to 135 mg/dL ,136 to 250 mg/dL and above 251mg/dL respectively. This technique being simple and non-invasive could help us self-examining kidney function among diabetes.

In recent years, Fresnel lens has significantly improved solar energy consumption. The scientific community considers the imaging and non-imaging Fresnel lens as a solar concentrator. Compared to imaging, non-imaging concentrators usually have a larger acceptance angle, higher optical efficiency, and higher concentration ratios with less volume and shorter focal length. This paper summarizes the saga of the Fresnel lens for solar energy concentration technology. The optical design, fabrication methods, and challenges associated with the Fresnel lens are described in the context of numerous applications including daylighting, photovoltaic (PV), solar-powered lasers, space-concentrated PV, and hydrogen generation.

Trapping absorbing microscopic particles in air using photophoretic force has opened up an effective simple approach for three dimensional trapping in air. This trapping force is roughly 5 orders of magnitude higher than the radiation pressure force. Although there have been many works on trapping using structured light, work related to comparison of trapping force using various types of structured light do not exist. We have shown the correlation between the efficiency of photophoretic trapping with the structure in intensity profiles present in the trapping beam. Thus, we have created HG₀₀, HG₀₁ and HG₀₂ mode in our experiment using different single mode optical fibers. Here, we show that trapping efficiency increases with increase in the number of modes in the transverse profile of the trapping beam. Trapping efficiency was measured using two parameters, threshold power and trapping force in the radial direction. The combination of dark and bright spots in the trapping beam indeed enhances the efficiency of photophoretic trapping due to its thermal origin. Our work will be helpful both in exploiting the fundamentals of photophoretic force and applications in aerosol studies and particle sorting away from surfaces.

The Prototype Segmented Mirror Telescope (PSMT) is a 1.3m segmented mirror telescope that aims to develop and demonstrate the segmented mirror technology indigenously. The telescope design includes a spherical primary with seven hexagonal segments of size 500mm each and an ellipsoidal secondary. Since the telescope has a spherical primary, hence it suffers from spherical aberrations as well as large off-axis aberrations, thus limiting its field of view. In order to improve the image quality over relatively larger field, an aberration corrector is required. The Faint Object Spectrograph and Camera (FOSC) is a widely used back-end instrument for any telescope and PSMT is also supposed to be equipped with such an instrument. Therefore, we have designed the optics of the FOSC in such way that it meets dual requirements i.e. it works as a science instrument as well as an aberration corrector. The FOSC instrument consists of multi-element collimator and camera lenses and a grism is used as a dispersive element. The FOSC optics design is optimized for the visual wavelength range of 4500-8500A° and up to 10 arc-min field of view. Here, we present the optical design of the FOSC and outcome of the analysis carried out using the ZEMAX optical design software.

Oral cancer is one of the deadliest diseases around the world with varied morphological traits, hence making it difficult to manually achieve accurate classification. Further, the traditional methods of diagnosis used by clinicians can be time-consuming and prone to error. Therefore, computer-assisted histopathological image classification is of extreme importance for the detection of oral cancer. We propose an image classification model known as External Attention Transformer model based on external attention mechanism, aiming to extract discriminating fine features from oral cancer tissue sections and their normal counterparts. We have used 4946 oral histopathological images classified into two categories: normal and oral squamous cell carcinoma (OSCC). Of the total images, 2435 of them are categorized as normal and 2511 as OSCC. External attention based deep neural network model attained 96.97% classification accuracy. Sensitivity and specificity were recorded as 97.61% and 96.41% respectively. It is found that the effectiveness of artificial intelligence methods for classifying oral cancer has significantly improved in comparison to leading edge methods, and this has a potential for early oral cancer detection.

Calcium carbide has been long used as artificial fruit ripening agent. However, calcium carbide is not only highly toxic, but also carcinogenic in nature leading to its ban in the most of the countries. Furthermore, to prevent its use, various government regulatory bodies recommended adopting the natural ripening agent ethylene in artificial ripening centers. Generally, 10-150 ppm of ethylene is utilized in ripening centers. Gas sensing using optical fiber sensors is becoming increasingly important in many areas due to the advantage of fast response, high sensitivity, lower cost, possibility for remote sensing. Accordingly, in this work, we have integrated a fiber optic probe with sensing material for the detection of ethylene vapors in the permissible range. The ethylene gas is known to exhibit sensitivity towards coinage metals specifically copper (Cu). We therefore utilized Cu-salt impregnated fluorescent polymers and Cu-based metal-organicframeworks (MOFs) as sensing materials to detect ethylene in different sensing modes; fluorescence, evanescent wave absorption sensor.

Thin films are used in many applications including holography, integrated optical circuits, polarizers, low-pass filters, beam splitters, and antireflection coatings. Refractive index and thickness of thin films are important parameters to understand its optical characteristics. In this work, thickness of thin film is measured by diffraction Lloyd mirror interferometer (DLMI). This interferometer works on the principle of superimposing two diffracted waves and direct geometric waves to generate the interference pattern. In comparison to the conventional Lloyd mirror interferometer, the interference pattern obtained by proposed interferometer covers a large area due to the presence of diffracted light in almost 4π region. The main idea of this work is to check the feasibility of DLMI to measure the thickness of films in single step. Three different test samples containing different step heights are used as a Lloyd mirror. The fringe patterns obtained from intereference of direct diffracted wavefront and reflected wavefront from samples are recorded using CMOS sensor. Recorded fringe patterns were further processed to extract phase by the application of Fourier transform. The 3D and 2D line profile of retrieved phase information are utilized to find the thickness of the film. The measured values of the thin film thickness by DLMI are compared with that of a standard mechanical profilometer. The experimental findings verify the usefulness of the proposed method.

Raman spectroscopy is evolving as an indispensable tool in cancer diagnosis owing to its label-free molecular probing ability. However, subsurface tumor assessment is still challenging using Raman spectroscopy. Researchers have adopted Spatially Offset Raman Spectroscopy to facilitate subsurface analysis. Recent works have demonstrated simultaneous subsurface tumor depth and thickness prediction using in-silico Spatially Offset Raman Spectroscopy investigations. These investigations are aided by fiber optic probes providing a good signal collection interface between sample and spectrometer, remote accessibility, precise control over illumination area, and Source Detector Separation. Optimizing the optical fiber probe parameters for photon collection will improve the outcome of tumor assessment. In this work, we analyze the importance of fiber optic collection core radius in subsurface tumor depth prediction using Monte Carlo simulated Spatially Offset Raman Spectroscopy signals. Simulations are carried out for varying illumination and collection fiber core radii, depths, and tumor thicknesses. An optimal collection fiber core radius for sub-surface depth prediction is estimated with a regression model for a given illumination fiber core radius. This optimization would improve the subsurface tumor localization capabilities of Raman Spectroscopy

Mueller matrix polarimetry has the potential to diagnose different stages of pre-cancer utilizing elastic and in-elastically scattered signals from the human biological tissues. Absorption, scattering and emission of a beam, when traveling through a medium, manifest through diattenuation, polarizance and retardance, which are efficiently separated by the polar decomposition technique. The intrinsic fluorophores present in tissue imprint their characteristic signatures, reflecting corresponding changes in the dipole orientations. The Fluorescence Mueller matrix (FMM) is ideally suited to extract this information through the parameters diattenuation and polarizance, as the fluorescence adds extra depolarization and phase changes due to absorption and subsequent emission of light by tissue samples. Hence, our approach can potentially provide better results due to an enhancement in these parameters compared to only elastic scattering for diagnosing cancerous tissue.

The concept of surface plasmon resonance can be used to build the most-sensitive instruments for refractive index sensing with dielectric and metal layers which are sub-wavelength in thickness. This is demonstrated with the electric field calculations on plasmonic gratings, of both rectangular and sinusoidal profiles, on polymer layer. The finite element method is also used to find the optimal thickness of the layers and to calculate the reflection, transmission, and absorption spectra of the plasmonic gratings, to identify the wavelength range most appropriate to the application.

Marine biofouling refers to the undesirable growth and adhesion of marine organisms such as barnacles, macro-algae, microbial slimes etc. on immersed structures. Tropical ocean environment teems with microorganisms, of which some adhere, both to the static ship hull and while en-route to the destination increasing roughness. A laboratory-scale LIBS technique was used to analyse biofouling samples and its constituent common water-borne algae and bacterial species. Biofouling composition was determined by collecting samples from marine structures and vessels and analysing them in laboratories. Biofouling characterization tests were also done such as SEM analysis. The Quanta 200 FEG Scanning Electron Microscope (SEM) was used for obtaining the SEM images. The structure of quartz crystal in the biofouling samples was also determined.

The propagation dynamics of aluminium-copper colliding laser produced plasma plumes are studied by using time-gated fast imaging and optical emission spectroscopic techniques. The experiment is performed at 10-2 mbar of air ambient. Angular target geometry is employed for the efficient collision of two different laser produced plasmas. When two plasmas collide, it can either stagnate at the collision front or can interpenetrate each other. The dense layer of plasma stagnates at the interaction region called the stagnation layer. Multi species stagnation region is formed at the collision front of heterogeneous colliding laser produced plasma and its time-resolved expansion dynamics are analyzed. The emission intensities are different for the two materials. For a particular laser wavelength, the two metal targets have different thermal and optical properties and thereby different ablation rates. Al with less ablation threshold has more intense emission compare to that of Cu. Plasma parameters like electron density and electron temperature are also measured from the optical emission spectroscopic data.

Solution-processed chalcogenide glasses (ChGs) are a cost-effective and facile way of fabricating hybrid ChG-silica photonic crystal fibers (PCFs). The bulk glass preparation and the solution-processing of glass are discussed. Optimized annealing conditions are used for assessing the quality of the ChG layers inside PCF holes by using solution-processed Ge-Sb-Se glass film. Finally, the deposition of solution-based ChG layers inside the holes of PCF is demonstrated, which can be used as a platform for various sensor and all-fiber tunable device fabrication and non-linear optical (NLO) applications.

One of the most effective ways to decrease reflection losses, enhance the likelihood of light trapping, and boost light absorption is surface patterning of p-type monocrystalline Si(100). Monocrystalline silicon surfaces' reflectivity is significantly decreased by the surface texturing of pyramids. This study looked into and analyzed how much of a pyramid was produced on the top of p-type Si substrates when the etching parameters were altered during Si texturing. The light traps created by the pyramidal structures on the crystalline silicon surface improved the effectiveness of light absorption. The impact of pyramid size on percent reflectivity was examined, and it was found that the percent reflectance and pyramidal etching time had an inverse connection. The texturing procedure, which involved adjusting the amounts of sodium hydroxide (NaOH) and isopropyl alcohol (IPA), as well as the length of the etching process, were used to regulate the size of the pyramids. The optimal etching conditions in this study were found to be a solution made with 12 weight percent NaOH and 4 volume percent IPA at an etching temperature of 80°C and an etching period of 40 min for wet etching. Pyramid with etching time (40 min) are post-coated with single-and double-layered silicon nitride (Si₃N₄), their reflectivity are measured over wavelength of 380-850 nm, had the lowest average percent reflectance of the double-layered Si₃N₄ patterned Si surfaces, at 8.8%. The selection of the refractive index (n) and the thickness (t) for single (n=1.9, t=80 nm) and double layer (n=2.8 and t=38 nm for bottom layer and n=1.9, t=42 nm) Si3N4 was done according to the destructive interference condition satisfied i.e., minimum reflection for photovoltaic application.

Integrated Optic Micro ring Resonator-based sensors are suitable for lab-on-chip applications due to their smaller footprint. Optical sensors are sensitive to detecting small changes in external parameters. Simultaneous detection of multiple gases present in the atmosphere is crucial for several civilian and military applications. Integrated optic micro ring resonators are promising sensing devices. In this paper, machine learning techniques are used in the classification and detection of gases for a sensor of a Micro Ring Resonator (MRR) array . In this paper machine learning techniques are used to reduce the data to be used for the analysis and improve accuracy of the sensor. Three target gases in the proposed model are Ammonia, Methane and Carbon on each ring simulated in this work. The features and influences on wavelength, transmittance, concentration of gases, and ring radius have also been analyzed. Principal Component Analysis (PCA) and K-Clustering algorithm has been used for the classification and detection of different gases. The Davies Boulden Index is calculated as 0.57 which shows the distance between the clusters. The sensor has a sensitivity of 0.35 nm/ppm.

Self-luminescent BaMg₂V₂O₈ and Sm³⁺ doped BaMg₂V₂O₈ phosphors have been obtained by high temperature solid state reaction method. Detailed Structural and optical analysis were carried out and compare the result of pure and Sm doped samples for checking the suitability in various photonic applications. Broad emission band centered at 516 nm of BaMg₂V₂O₈ , under near UV excitation arises due to ³T₁→¹A₁ and ³T₂→²A₁ transition of (VO₄) ^3- and gives blue- green emission. Incorporation Sm³⁺ in to the luminescent host lattice leads to the enhancement of the emission intensity and color tuning ability of the host. The CIE chromaticity coordinates for BaMg₂V₂O₈ gives a blue green emission following the coordinates (x, y) as (0.29, 0.43) and for Sm³⁺ doped BaMg₂V₂O₈ show the yellow emission following the coordinates (x, y) as (0.36, 0.41).

Green leafy vegetables are indispensable in a healthy diet. They are rich in phytochemicals which play an essential role in plant growth and development. In this paper, we focus on chlorophyll a, the primary pigment in all green leafy vegetables. The results obtained from the optical absorbance and fluorescence analysis of chlorophyll molecules present in the whole leaf and its extract are used to identify and compare healthier greens that can be incorporated directly into the human diet without consuming extracted forms.

In this paper, we investigate the angular displacement measurements using the homodyne detection method in a modified-SU(2) Mach-Zehnder interferometer (MZI). Three parametric amplifiers (PAs) are used. PA’s role is to increase the number of photons and to reduce the shot-noise. We also consider quantum Fisher information (QFI) and derive expressions for single- and twoparameter cases and corresponding quantum Cramer-Rao bounds (QCRB). We find that angular displacement sensitivity exceeds the standard quantum limit (SQL) or shot-noise limit (SNL) and approaches single- and two-parameter QCRB. Finally, we investigate the impact of photon losses on the sensitivity of interferometer

In conventional interferometry, the intensity of the superposed field is observed to study the phase information of object / sample field. The schemes like Weak measurement scheme, spectral switching observes the intensity of the output field for enhancing the sensitivity of the phase measurements. A scheme to enhance the sensitivity in the measurement of path delays through spectral interferometry by observing the phase accumulated by the superposed field with respect to an additional reference beam is presented. Through the interference with additional reference beam maintained at out-of-phase condition near zero optical path delay with respect to the sample probe beam, it is shown to introduce nonlinearity in phase change measured. In the experimental demonstration, the classic low coherence spectral interferometry is used. The three-beam interference is achieved by a modified Michelson interferometer. According to the setting of initial path delay and amplitude ratio of the interfering fields, the intensity of superposed field shows spectral modulations. Spectral phase is measured from the modulations in the recorded spectral interference using Fourier transform method of fringe analysis. In the Fourier domain, a linear path delay between in the interfering beams gives a linear shift in the position of secondary peak. By filtering the secondary peak from the Fourier domain, and taking the Inverse Fourier transform, the amplitude and phase information of the interfering fields can be obtained. The proposed method maps the linear path delay to highly nonlinear phase accumulation and has the potential to enhance sensitivity of phase measurements.

Surface enhanced Raman scattering (SERS), a variant of Raman spectroscopy, is one of the most powerful analytical techniques which can be used to obtain detailed chemical information of molecules or molecular assemblies, with the potential to reach single molecule detection. It is rapid, highly sensitive, accurate and non-destructive detection technique. It finds extensive application in various fields such as: environmental monitoring, biology, defense, forensics etc. It can be observed when target analytes are present in the vicinity of a metallic surface, especially noble metals like Au or Ag, since their plasmonic resonances lie in the visible and NIR regions. We have provided a numerical design of Ag-bullseye structure that function as reproducible SERS probe in the visible frequency band by using FDTD method. The proposed pattern is robust (with respect to different design parameters) with high sensitivity ~ 10⁸, high uniformity and specificity, which assures that such substrate can be used for quantitative analysis, making SERS an indispensable tool for bio-diagnostics and bio-analysis. Surface enhanced Raman scattering (SERS), FDTD, Raman spectroscopy, nano-patterns, Raman enhancement factor (EF).

Photonic radar is found to be a promising technology as compared to conventional electrical radar, with respect to its property and limitations. Because of photonics incredible features, it is possible to upgrade the radar potential, mainly for ground-based transport tracking. Hence enhancing traffic safety and driverless automobile movement. There has been always a major requirement of low phase noise sources for various applications in radar as well as any other electronic devices ranging at higher frequencies. In this paper, Optoelectronic Oscillator (OEO) at 77 GHz has been designed and simulated with respective specifications. The OEO signal has been generated using only one single wavelength of 1550nm as input, which is fed to the modulator along with the noise source signal. The OEO and its integration with the Frequency Modulated Continuous wave (FMCW) based Photonic Radar has been performed. The designed photonic Radar has been simulated with different target scenarios with a different range, range rate, Radar Cross Section (RCS), and Angle of arrival (AOA). The target scenario has been shown in the Opti wave system using MATLAB block, where a script is written for target parameters. Also, the transmitted echo signal has been created using the time function block in the Optiwave system. The resulting beat frequency waveform for 30, 60m, and 90m has also been included. The design of OEO in this paper is having a noise floor of -110dBc/Hz. It could be further improved with the modification of sub-blocks of the system.

Detection of proteinuria in urine is an early sign of the progression of cardiovascular and chronic kidney disease. In general, colorimetry detection in urine dipsticks is carried out for a screening of proteinuria. Although low sensitivity and vision assessment has hindered its utility. Smartphone-based colorimetry detection using a urine dipstick plays an important role to estimate the concentration of albumin. Segmentation of albumin patches in urine dipstick is the first step for the automatic estimation of albumin concentration in the urine sample. Here, we present a deep learning-based object detection technique i.e. You Only Look Once (YOLOv5), for the segmentation of albumin patches from urine dipstick (Uristix Siemens) for the estimation of albumin concentration. A comparison between different segmentation techniques to accurately arrive at the region of interest has been demonstrated. Four different smartphones i.e. iPhone SE, Realme C11, Redmi 8A Dual, and Samsung Galaxy M01 were used to capture the images of the urine dipstick, at six different illumination conditions i. e. 500 Lux, 400 Lux, 300 Lux, 200 Lux, 100 Lux, and 50 Lux. The training was done using iPhone SE with eight different albumin concentrations: 10 mg/L, 20 mg/L, 40 mg/L, 80 mg/L, 160 mg/L, 320 mg/L, 640 mg/L, and 1280 mg/L. The proposed model is fast and robust and it helps minimize the effect of different light conditions and color variations across smartphone models.

Recently, the photonic nanojet-assisted fluorescence microscopic technique has been helpful in enhancing fluorescence signals of various samples at ultralow concentrations. In this technique, the fluorescence enhancement depends upon several parameters, such as the microsphere's size and refractive index, the surrounding medium's refractive index, and the excitation light's wavelength. Therefore, all these parameters' role on the enhancement is reported here.

Automotive lighting is another vast and important application of photonics. In automotive exterior lighting, there are two main division - i) To see and ii) To be seen. Headlamps are ‘to see’ functions and their performance is of prime importance. A well illuminated drive-way can give the driver a smooth driving experience without straining eyes in night-time. That, in turn, ensures safety for the driver and other road users as well. Such requirements have brought tremendous changes in this field and it developed beyond imagination in the last couple of decades. Here we discuss the history, the cutting-edge technologies and the challenges came up with it. In the end, we provide an overview of one of the novel headlamp technology , compact lightguide headlamp.

Cancer formation in breast tissue is associated with desmoplastic changes in the extracellular matrix, also accompanied by neoplastic growth. These changes alter the orientation, size, and density of cellular structures within the tissues. Features extracted from the polarized speckle images of the sample give us insights into these structural changes and can be used for diagnosis of cancer. An attempt is made to incorporate machine learning algorithms in understanding these features to classify normal versus cancerous tissues paving way for automated diagnostic procedures.

We report the efficient coupling of single photons from a single dipole source (SDS) into a single-mode fiber. Using the Finite Difference Time Domain (FDTD) method, we perform numerical simulations for different locations of the SDS with different polarizations on the optical nanofiber (ONF) and optical nanofiber tip (ONFT). Simulations predict that a maximum coupling efficiency of up to 43% is realized when the SDS with radial polarization is placed on the facet of the ONFT.

Modification of emission intensity of light emitters can have promising applications in sensing and imaging. Photonic crystals when incorporated with light emitters can lead to tuning of their emission intensity with respect to the relative positioning of the photonic bandgap and excitation or emission maxima of the light emitter. Herein we have prepared a carbon dot embedded self assembled photonic crystal structure. Their structural and optical characterizations were performed and the modification of optical emission from carbon dots when embedded in a photonic crystal matrix was analyzed using laser induced fluorescence technique.

Atmospheric turbulence plays an important role in long-range propagation of light pulses. Mid-infrared pulses can propagate in air upto hundreds of meters by forming long channels of plasma due to lower ionization losses compared to near-IR pulses. Such long filamentation channels are useful in atmospheric sensing, remote laser-induced breakdown spectroscopy (LIBS), steering and triggering of electric discharges and other long-range applications. We study the effects of atmospheric turbulence in long-wavelength infrared (LWIR) femtosecond filamentation in air. We numerically investigate the combined effects of turbulence and nonlinearity in the long-range propagation of LWIR pulses at 6 μm. We model the nonlinear response of the atmosphere by including Kerr effect, multiphoton-ionization and rotational Raman effects in air the dispersive response of several atmospheric gas species such as N2, O2, Ar, CO2 CH4 and H2O. We model the turbulence using a phase-screen model. The inhomogeneous medium is represented by a series of phase screens located at regular intervals along the propagation direction. This provides an understanding of the robustness of long range filamentation and propagation of LWIR pulses over turbulent medium which essential for several long range applications including free-space optical communication.

Herein, we report the theoretical investigation of two different types of Au-Ag alloy nanoparticles. In detail, the role of composition and localized surface plasmon damping due to the electron-surface scattering on the far field scattering spectra and near field or local electric field enhancement of the small Au-Ag alloy nanospheres and thin alloy nanoshells is studied with the help of analytical theory developed based on Bromwich formulism.

Diffuse optical tomography (DOT) is an imaging modality which utilizes an array of near infrared light source (830 nm) for tissue illumination. The multiple-scattered light is detected using a pinhole camera. There are three primary absorbers at this wavelength which includes, water, oxygenated and deoxygenated hemoglobin, all possessing relatively weak absorptions. This provides a spectral window through which we can attempt to localize absorption and scattering in the tissue. Current techniques in imaging involve use of ionizing radiation which cause harm to tissues. For better image quality, the dosage has to be increased which induces the risk of cancer. Hence, we aim to exploit the non-ionizing characteristic of near infrared radiation (NIR), a potentially harmless band to image soft tissues. In our proposed system we are reconstructing 3-D images from 2-D cone beam projections using Feldkamp, Davis and Kress (FDK) algorithm which is most widely used because of its effective spatial resolution and duration time. It can also handle truncated data in longitudinal direction. The object to be imaged is positioned on the turntable and is rotated at 180 degrees. A major requirement of the setup is to position the phantom at equal distance from the source and detector. Both the camera and the stepper motor are controlled using MATLAB and are synchronized to work simultaneously. During the initial trials we propose to develop a phantom using paraffin wax that mimics the soft tissue properties. Eventually, experimentation will be done with different phantom models to test the compatibility and efficiency of the algorithm developed.

We report the efficient single-mode coupling design using a silica/diamond nano-tip with a gold nanoparticle (AuNP). We determine coupling efficiency in the single mode regime by performing simulations for a silica/diamond nano-tip and a single dipole source (SDS) with different polarizations. We also investigate the effect of AuNP on coupling efficiency in the single-mode regime. We find the coupling efficiency of 38% and 61% for the optimum silica and diamond nano-tip radius, respectively. In the presence of the AuNP, the enactment of coupling efficiency has been found.

In the medical field, the 'optical biopsy' is considered the primary diagnostic application of light. Tissue abnormalities, such as cancerous growth, introduce changes in the target tissue's optical properties. The Polarized Monte Carlo (PMC) simulation applied to specific tissue models acts as a tool for observing these changes and helps monitor them in conjunction with experiments. In this work, we have performed PMC simulations on two-layered skin tissue models and compared the Mueller matrix parameters for normal and skin cancer conditions. These simulations are expected to help design diagnostic instruments for anomalies such as melanoma in situ.

Assessment of microcirculation is essential in evaluating the tissue condition after injury, surgery, or any vascular disease which can be performed via Laser Doppler flowmetry (LDF). LDF is a technique that uses monochromatic light to detect the shift in frequency of the light scattered back from moving scatterers in tissues. In the present work, Doppler frequency shift is calculated by Monte Carlo simulations of light-tissue interactions. The simulated results enable us to quantify the velocity of flow which could be verified using in-vitro flow models.

Insomnia is one commonly reported sleep problem especially among older adults. Presently, it is treated by oral medicines. Since it has side effects, non-invasive therapies are one better alternative. Light in the band of 650 to 700 nm wavelength stimulate the production of melatonin. Hence red light is used in controlled mechanism to induce sleep. This study aims to give a self-administered insomnia therapy by visual stimulation to stimulate the brainwave to enter the relaxed state at an early stage of sleep. A prototype is designed that consists of an eye mask with flashing-red light pair as the visual stimulation. It is mounted on an eye mask covered with double layer of cotton with controlled intensity and duration. This test is performed over 50 numbers of old adults (mean age 75 ± 50.5 years; male and female) including 20 healthy controls and 30 insomnia subjects. All the participants were given this device and sleep diary and were asked to use this every night for thirty days. At the end of the therapy sleep quality is assessed for all the participants. Power spectrum of EEG shows an increment of delta wave during night time and decrement during early morning in all subjects which indicates that quality of sleep is improved. This is further established by Cohen‟s d value and Paired T test value.

Knowledge of the refractive index structure constant profile at an astronomical site is crucial before developing a Multi-Conjugate Adaptive Optics (MCAO) system at that site. The S-DIMM+ (S-Differential Image Motion Monitor+) method proposed by Scharmer and van Werkhoven uses the images recorded by a SHWFS (ShackHartmann Wavefront Sensor) to estimate the profile. We have performed simulations of the same using simulated solar granulation images (which are the “objects”) and multiple layers of the atmosphere characterised by Kolmogorov turbulence, a telescope of given aperture and finally a SHWFS. The images formed using the SHWFS are then processed using an inversion code developed by us to get the turbulence strength profile. We found that the code was able to invert the data satisfactorily upto a height of 10 km with our system parameters.

Optical coherence tomography (OCT) has had significant success in the field of ophthalmology, where it is essential for both screening and diagnosis. Clinical ophthalmic OCT systems are primarily used as table-top instruments that requires the subject to align with the chinrest and be operated by qualified personnel. In order to perform OCT imaging on bedridden patients or on babies, a handheld model is essential. In handheld devices, eye movements and probe movements cause artifacts while recording OCT images, making interpretation and registration more difficult. As a result, there is a need for an OCT scanner with an automatic real-time eye-tracking system and a correction mechanism to compensate for such movements. This work aims at developing a scanner head employing a cutting-edge stereo edge camera equipped with an inertial measurement unit (IMU) for detecting rotations and motions with six degrees of freedom. In this work, an Intel RealSense D435i depth camera-based eye tracking is performed. A python-based code was developed to image the eye continuously, detect face landmarks with media pipe, process the eye features in each frame, identify the iris in each frame and a circle is marked over the iris which would move along with the iris. The algorithm is tested on various scenarios of face angle and head motion. The eye movement identification and tracking capability of the developed algorithm and its performance results are presented in this study.

Optical Coherence Tomography (OCT) is a non-invasive optical imaging technique capable of producing high-resolution cross-sectional 2D and 3D images of non-homogeneous samples, such as biological tissue. It is a gold standard in retinal imaging. In this work, an analytical model of the retina is developed to investigate the scientific principles of the OCT system. The Michelson interferometer configuration is modeled in Matlab using standard interferometric equations. A broadband light source centered at 840 nm with a spectral width of 46 nm with a Gaussian profile is modeled. The retina is simulated with a few layers of refractive indices based on the values reported so far in the literature. The final interferogram based on the above model and sample is obtained and analyzed in both time domain (TD) and spectral domain (SD) OCT configuration and an A-scan is generated. The A-scan obtained clearly shows the boundary between the layers with intensity dependent on the change in refractive index between layers and the amount of light available at each layer.