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Among different inorganic and organic polarizer elements, thin-film light polarizers occupy a special place because of their flexibility, ease of integration into any optoelectronic circuit, and good functioning in the visible and near-infrared spectral range and can compete with Glan and Nicolas volumetric prisms. This paper presents the results of a study on how carbon-based nanoparticles influence on the basic properties of a well-known PVA-based polymer matrix, using which it is possible to obtain good transparency for parallel light components. An accent is made on graphene oxide nanoparticles, which are used as PVA sensitizers. It was shown for the first time that the structuring of PVA with graphene oxides allows an increased transmittance of the parallel light component to be obtained, saving the transmittance of the orthogonal one. Moreover, the graphene network can increase the mechanical strength of such thin-film PVA-based polarizers and provoke a change in the wetting angle. These advantages make it possible to use graphene oxide-structured thin-film light polarizers based on a PVA matrix as an independent optoelectronic element. Some comparative results for polarizers based on PVA-C70 structures are shown as well. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) reconstruction of objects using the polarization properties of diffuse light on the object surface has become a crucial technique. Due to the unique mapping relation between the degree of polarization of diffuse light and the zenith angle of the surface normal vector, polarization 3D reconstruction based on diffuse reflection theoretically has high accuracy. However, in practice, the accuracy of polarization 3D reconstruction is limited by the performance parameters of the polarization detector. Improper selection of performance parameters can result in large errors in the normal vector. In this paper, the mathematical models that relate the polarization 3D reconstruction errors to the detector performance parameters including polarizer extinction ratio, polarizer installation error, full well capacity and analog-to-digital (A2D) bit depth are established. At the same time, polarization detector parameters suitable for polarization 3D reconstruction are provided by the simulation. The performance parameters we recommend include an extinction ratio ≥ 200, an installation error ∈ [−1°, 1°], a full-well capacity ≥ 100 K e − , and an A2D bit depth ≥ 12 bits. The models provided in this paper are of great significance for improving the accuracy of polarization 3D reconstruction. [ABSTRACT FROM AUTHOR]

In this paper, we present a project of a multi-channel wide-field optical sky monitoring system with high temporal resolution—Small Aperture Imaging Network Telescope (SAINT)— mostly built from off-the-shelf components and aimed towards searching and studying optical transient phenomena on the shortest time scales. The instrument consists of twelve channels each containing 30 cm (F/1.5) GENON Max objectives mounted on separate ASA DDM100 mounts with pointing speeds up to 50 deg/s. Each channel is equipped with a 4128 × 4104 pixel Andor Balor sCMOS detector and a set of photometric g r i z filters and linear polarizers. At the heart of every channel is a custom-built reducer-collimator module allowing rapid switching of an effective focal length of the telescope—due to it the system is capable of operating in either wide-field survey or narrow-field follow-up modes. In the first case, the field of view of the instrument is 470 square degrees (39 sq.deg. for a single channel) and the detection limits (5 σ level at 5500 Å) are 12.5, 16.5, 19, 21 with exposure times of 20 ms, 1 s, 30 s and 20 min, correspondingly. In the second, follow-up (e.g., upon detection of a transient of interest by either a real-time detection pipeline, or upon receiving an external trigger) regime, all telescopes are oriented towards the single target, and SAINT becomes an equivalent to a monolithic 1-meter telescope, with the field of view reduced to 11 ′ × 11 ′ , and the exposure times decreased down to 0.6 ms (1684 frames per second). Different channels may then have different filters installed, thus allowing a detailed study—acquiring both color and polarization information—of a target object with the highest possible temporal resolution. The telescopes are located in two pavilions with sliding roofs and are controlled by a cluster of 25 computers that both govern their operation and acquire and store up to 800 terabytes of data every night, also performing its real-time processing using a dedicated fast image subtraction pipeline. Long-term storage of the data will require a petabyte class storage. The operation of SAINT will allow acquiring an unprecedented amount of data on various classes of astrophysical phenomena, from near-Earth to extragalactic ones, while its multi-channel design and the use of commercially available components allows easy expansion of its scale, and thus performance and detection capabilities. [ABSTRACT FROM AUTHOR]

Terahertz (THz) technology offers a variety of applications in label-free medical diagnosis and therapy, majority of which rely on the effective medium theory that assumes biological tissues to be optically isotropic and homogeneous at the scale posed by the THz wavelengths. Meanwhile, most recent research discovered mesoscale ( ∼ λ ) heterogeneities of tissues; λ is a wavelength. This posed a problem of studying the related scattering and polarization effects of THz-wave–tissue interactions, while there is still a lack of appropriate tools and instruments for such studies. To address this challenge, in this paper, quantitative polarization-sensitive reflection-mode THz solid immersion (SI) microscope is developed, that comprises a silicon hemisphere-based SI lens, metal-wire-grid polarizer and analyzer, a continuous-wave 0.6 THz ( λ = 500 µm) backward-wave oscillator (BWO), and a Golay detector. It makes possible the study of local polarization-dependent THz response of mesoscale tissue elements with the resolution as high as 0.15 λ . It is applied to retrieve the refractive index distributions over the freshly-excised rat brain for the two orthogonal linear polarizations of the THz beam, aimed at uncovering the THz birefringence (structural optical anisotropy) of tissues. The most pronounced birefringence is observed for the Corpus callosum, formed by well-oriented and densely-packed axons bridging the cerebral hemispheres. The observed results are verified by the THz pulsed spectroscopy of the porcine brain, which confirms higher refractive index of the Corpus callosum when the THz beam is polarized along axons. Our findings highlight a potential of the quantitative polarization THz microscopy in biophotonics and medical imaging. [ABSTRACT FROM AUTHOR]

A 3 × 3 Mueller matrix polarimeter, as one of the primary polarization measurement tools, has attracted intensive interest in various fields of polarization optics. In this paper, from a novel viewpoint with more mathematical analysis of the basic configuration and the working performance of a 3 × 3 Mueller matrix polarimeter, we systematically study the relationship between Mueller matrix measurement errors with the configuration and characteristics of polarizers in the polarimeter. We figure out that, mathematically, there is an optimal orientation angle configuration (0°, 60°, and 120°) of polarizers, which inherently ensures a minimal relative measurement error in general. Moreover, we interpret the internal source of such a robust error resistance under this optimized configuration mathematically for the first time. Simulation and practical experiments show the effectiveness of our mathematical analyses, and compared to the frequently used orientation angle configuration, the average relative error is reduced by up to 32% under such an optimized configuration. [ABSTRACT FROM AUTHOR]

Spectral imaging detection using acousto-optical tunable filters (AOTFs) faces a significant challenge of low throughput due to the traditional design that only receives a single polarization light. To overcome this issue, we propose a novel polarization multiplexing design and eliminate the need for crossed polarizers in the system. Our design allows for simultaneous collection of ±1 order light from the AOTF device, resulting in a more than two-fold increase in system throughput. Our analysis and experimental results validate the effectiveness of our design in improving system throughput and enhancing the imaging signal-to-noise ratio (SNR) by approximately 8 dB. In addition, AOTF devices used in polarization multiplexing applications require optimized crystal geometry parameter design that does not follow the parallel tangent principle. This paper proposes an optimization strategy for arbitrary AOTF devices which can achieve similar spectral effects. The implications of this work are significant for target detection applications. [ABSTRACT FROM AUTHOR]

In this paper, we report the use of crossed polarizer technique to measure the differential group delay (DGD) of few-mode optical fiber (FMF). The windowed Fourier transform (WFT) is applied in the analysis of beat length measurement in the spectral domain to obtain the dependence of DGD as a function of wavelength. The birefringence of polarization-maintaining fiber (PMF) and the DGD of FMF are measured by applying our method. We discuss the noise background, the width of DGD peaks, and the possible errors introduced in the optical path in the modified crossed polarizer technique. [ABSTRACT FROM AUTHOR]

Infrared imaging spectrometers detect and identify targets by collecting spectral and image information. However, when detecting small temperature differences and dynamic targets, the accuracy of infrared detection is reduced, the traditional scanning structure detection time is longer, the real-time performance is poor and it is easy to introduce motion artifacts. This paper proposes an infrared polarization snapshot spectral imaging system (PSIFTIS) based on a polarizer array, a lens array and a roof-shaped stepped micromirror. Polarized light can solve the problem of small-temperature-difference target recognition by characterizing the surface properties of materials. Lens arrays utilize multi-aperture imaging to achieve snapshot detection of targets. The system can obtain 4D data information, including polarization, in a single measurement cycle. This study completed the overall optical design of a PSIFTIS and an optical simulation experiment using it. Finally, a system prototype was built in the laboratory and a polarization spectrum detection experiment was carried out. The experimental results show that the PSIFTIS could accurately obtain the polarization spectrum information for the target, the spectral resolution reached 7.8 cm−1 and the Stokes measurement error was less than 5%. [ABSTRACT FROM AUTHOR]

The paper presents the application of the acousto-optic tunable filter (AOTF) in surface plasmon resonance (SPR) spectroscopy to measure the optical thickness of thin dielectric coatings. The technique presented uses combined angular and spectral interrogation modes to obtain the reflection coefficient under the condition of SPR. Surface electromagnetic waves were excited in the Kretschmann geometry, with the AOTF serving as a monochromator and polarizer of light from a white broadband radiation source. The experiments highlighted the high sensitivity of the method and the lower amount of noise in the resonance curves compared with the laser light source. This optical technique can be implemented for nondestructive testing in the production of thin films in not only the visible, but also the infrared and terahertz ranges. [ABSTRACT FROM AUTHOR]

Optical anisotropy offers an extra degree of freedom to dynamically and reversibly regulate polarizing optical components, such as polarizers, without extra energy consumption and with high modulating efficiency. In this paper, we theoretically and numerically design broadband and incident-angle-modulation near-infrared polarizers, based on the SnSe, whose optical anisotropy is quantitatively evaluated by the complete dielectric tensor, complex refractive index tensor, and derived birefringence (~|Δn|max = 0.4) and dichroism (~|Δk|max = 0.4). The bandwidth of a broadband polarizer is 324 nm, from 1262 nm to 1586 nm, with an average extinction ratio above 23 dB. For the incident-angle-modulation near-infrared polarizer, the high incident angles dynamically and reversibly modulate its working wavelength with a maximum extinction ratio of 71 dB. Numerical simulations and theoretical calculations reveal that the considerable absorption for p light and continuously and relatively low absorption of s light lead to the broadband polarizer, while the incident-angle-modulation one mainly arises from the blue shift of corresponding wavelength of p light's minimum reflectance. The proposed novel design of polarizers based on SnSe are likely to be mass-produced and integrated into an on-chip system, which opens up a new thought to design polarizing optical components by utilizing other low-symmetry materials. [ABSTRACT FROM AUTHOR]

Double narrowband induced perfect absorption in the terahertz region is achieved in a graphene–dielectric–gold hybrid metamaterial, whose physical mechanism is analyzed using the coupled-mode theory (CMT), which agreed well with the finite-difference time-domain (FDTD) simulation. This study found that the Fermi level of graphene can be adjusted to improve the absorptivity when the refractive index (RI) nd of the chosen dielectric cannot achieve a good absorption effect. In addition, the blue shift of absorption spectrum can be used in the design of dual-frequency electro-optical switches, of which the modulation degree of amplitude (MDA) can reach as high as 94.05% and 93.41%, indicating that this is a very promising electro-optical switch. Most significantly, the RI sensing performance is investigated, which shows an ultra-high absorption sensitivity SA = 4.4°/RIU, wavelength sensitivity Sλ = 9.8°/RIU, and phase shift sensitivity Sφ = 2691°/RIU. At last, an interesting finding is that the two peaks (R1 and R2) of plasmon-induced absorption (PIA) show different polarization characteristics (insensitive or sensitive) to the incident light angle; this polarization-sensitive is particularly important for the PIT/PIA-based optical polarizers. Undoubtedly, this paper is of great significance to the research and design of terahertz photonic devices and sensors. [ABSTRACT FROM AUTHOR]

Polarization and infrared imaging technology have unique advantages for various applications ranging from biology to ocean remote sensing. However, conventional combined polarization camera and infrared camera have limitations because they are constrained to single-band imaging systems with rotating polarizers and cascaded optics. Therefore, we propose a common-aperture mode based on multi-band infrared guided polarization imaging system (IGPIS) in this paper, which consists of infrared wide-area sensing and polarization features acquisition for accurate detection of ship targets. The IGPIS can provide images in visible polarization (0.45–0.76 μm), near-infrared polarization (0.76–0.9 μm), and long-wave infrared (8–12 μm) bands. Satellite attitude parameters and camera optical parameters are accurately calculated by establishing a dynamic imaging model for guidance imaging. We illustrate the imaging principle, sensors specifications and imaging performance analysis and the experimental results show that the MTF is 0.24 for visible and near-infrared, and 0.13 for long-wave infrared. The obtained multi-band images have an average gradient of 12.77 after accurate fusion. These results provide theoretical guidance for the design of common-aperture cameras in remote sensing imaging field. [ABSTRACT FROM AUTHOR]

The aim of this work was to design a kirigami-based metamaterial with optical properties. This idea came from the necessity of a study that can improve common camouflage techniques to yield a product that is cheap, light, and easy to manufacture and assemble. The author investigated the possibility of exploiting a rotation to achieve transparency and color changing. One of the most important examples of a kirigami structure is a geometry based on rotating squares, which is a one-degree-of-freedom mechanism. In this study, light polarization and birefringence were exploited to obtain transparency and color-changing properties using two polarizers and common cellophane tape. These elements were assembled with a rotating-square structure that allowed the rotation of a polarizer placed on the structure with respect to a fixed polarizer equipped with cellophane layers. [ABSTRACT FROM AUTHOR]

A terahertz time domain pulsed spectroscopy system is modified to provide fully polarimetric radiation and analysis. The operation of this polarimetry system is characterized using a birefringent, x-cut quartz crystal. The modification is based on rotating the photoconductive antennas such that both the emitted and detected polarizations are out of the plane of incidence. Subsequently, broadband wire grid polarizers are used to select the incident and detected direction of linear polarization to be either parallel with (vertical) or perpendicular to (horizontal) the plane of incidence with the sample surface. The experiments are conducted in both transmission and reflection. Depending on the frequency, the phase retardation of the incoming electric field components along the two perpendicular optical axes of the quartz crystal changes differently. This results in the polarization of the light exiting the crystal changing with frequency. As a result, multiple frequencies are identified where the crystal behaves as a near ideal quarter-, half-, or full-wave retarder. Additionally, due to the time-domain nature of the experiment, transmitted and reflected electric fields are measured after multiple consecutive reflections within the crystal. This leads to a further, complex control over the final polarization state of the signal. Finally, images of a resolution standard are obtained demonstrating the characteristics of the polarimetry system. [ABSTRACT FROM AUTHOR]

Linear gratings polarizers provide remarkable potential to customize the polarization properties and tailor device functionality via dimensional tuning of configurations. Here, we extensively investigate the polarization properties of single- and double-layer linear grating, mainly focusing on self-aligned bilayer linear grating (SABLG), serving as a wire grid polarizer in the mid-wavelength infrared (MWIR) region. Computational analyses revealed the polarization properties of SABLG, highlighting enhancement in TM transmission and reduction in TE transmission compared to single-layer linear gratings (SLG) due to optical cavity effects. As a result, the extinction ratio is enhanced by approximately 2724-fold in wavelength 3–6 μm. Furthermore, integrating the specially designed SABLG with an MWIR InAs/GaSb Type-II Superlattice (T2SL) photodetector yields a significantly enhanced spectral responsivity. The TM-spectral responsivity of SABLG is enhanced by around twofold than the bare device. The simulation methodology and analytical analysis presented herein provide a versatile route for designing optimized polarimetric structures integrated into infrared imaging devices, offering superior capabilities to resolve linear polarization signatures. [ABSTRACT FROM AUTHOR]

The birefringence response of aqueous cellulose nanocrystal (CNC) suspensions in a two-dimensional laminar flow is measured and studied. The suspensions have CNC concentrations of 1.0 wt% (weight percentage) and 1.2 wt%. Cellulose nanocrystals are optically anisotropic rod-like particles that align when subjected to local velocity gradients, whereas at rest, they remain randomly orientated by Brownian motion. The alignment causes birefringence, a phenomenon also known as flow-induced birefringence. We study the flow through an additively manufactured flow channel and measure the amount of birefringence as well as the position of the refractive index axes by using polarizers and a polarization camera. With the help of reference data published in a previous study (Lane, Rode, et al., 2022a), strain rates are derived from the birefringence measurements and compared with numerical simulations. Two flow situations are studied, a plane Poiseuille flow and the flow around a cosine-shaped constriction. The experimentally derived shear rates for the plane Poiseuille flow are consistent with theoretical and computational results. The derived strain rates for the flow around the cosine-shaped constriction show an unexpected asymmetric profile, with the strain rates in the contraction zone being larger than in the expansion zone. The averaged orientation of the CNCs in the flow is linked to the position of the refractive index axes. In the contraction zone, the CNCs tend to align parallel to the flow, whereas in the expansion zone, the CNCs tend to align perpendicular to the flow. The results of this study are discussed in the context of previous, similar studies. The asymmetric strain rate profile around the cosine-shaped constriction is thought to originate from history effects, and the alignment of the CNCs is influenced by extensional rates. [ABSTRACT FROM AUTHOR]

Significance: Polarized hyperspectral microscopes with the capability of full Stokes vector imaging have potential for many biological and medical applications. Aim: The aim of this study is to investigate polarized hyperspectral imaging (PHSI) for improving the visualization of collagen fibers, which is an important biomarker related to tumor development, and improving the differentiation of normal and tumor cells on pathologic slides. Approach: We customized a polarized hyperspectral microscopic imaging system comprising an upright microscope with a motorized stage, two linear polarizers, two liquid crystal variable retarders (LCVRs), and a compact SnapScan hyperspectral camera. The polarizers and LCVRs worked in tandem with the hyperspectral camera to acquire polarized hyperspectral images, which were further used to calculate four Stokes vectors: S0, S1, S2, and S3. Synthetic RGB images of the Stokes vectors were generated for the visualization of cellular components in PHSI images. Regions of interest of collagen, normal cells, and tumor cells in the synthetic RGB images were selected, and spectral signatures of the selected components were extracted for comparison. Specifically, we qualitatively and quantitatively investigated the enhanced visualization and spectral characteristics of dense fibers and sparse fibers in normal stroma tissue, fibers accumulated within tumors, and fibers accumulated around tumors. Results: By employing our customized polarized hyperspectral microscope, we extract the spectral signatures of Stokes vector parameters of collagen as well as of tumor and normal cells. The measurement of Stokes vector parameters increased the image contrast of collagen fibers and cells in the slides. Conclusions: With the spatial and spectral information from the Stokes vector data cubes (S0, S1, S2, and S3), our PHSI microscope system enhances the visualization of tumor cells and tumor microenvironment components, thus being beneficial for pathology and oncology. [ABSTRACT FROM AUTHOR]

Nuclear spin hyperpolarization is a quantum effect that enhances the nuclear magnetic resonance signal by several orders of magnitude and has enabled real-time metabolic imaging in humans. However, the translation of hyperpolarization technology into routine use in laboratories and medical centers is hampered by the lack of portable, cost-effective polarizers that are not commercially available. Here, we present a portable, automated polarizer based on parahydrogen-induced hyperpolarization (PHIP) at an intermediate magnetic field of 0.5 T (achieved by permanent magnets). With a footprint of 1 m2, we demonstrate semi-continuous, fully automated 1H hyperpolarization of ethyl acetate-d6 and ethyl pyruvate-d6 to P = 14.4% and 16.2%, respectively, and a 13C polarization of 1-13C-ethyl pyruvate-d6 of P = 7%. The duty cycle for preparing a dose is no more than 1 min. To reveal the full potential of 1H hyperpolarization in an inhomogeneous magnetic field, we convert the anti-phase PHIP signals into in-phase peaks, thereby increasing the SNR by a factor of 5. Using a spin-echo approach allowed us to observe the evolution of spin order distribution in real time while conserving the expensive reagents for reaction monitoring, imaging and potential in vivo usage. This compact polarizer will allow us to pursue the translation of hyperpolarized MRI towards in vivo applications further. Hyperpolarized magnetic resonance imaging (MRI) has the potential to revolutionize MRI applications, but requires large and clumsy instruments. Here, the authors present a 0.5 T benchtop system that allows to hyperpolarize, image, and spy on nuclear spins like 13C within seconds. [ABSTRACT FROM AUTHOR]

Traditional ideas about linearly polarized paraxial beam propagation along the optical axis of a uniaxial crystal suggest that at the crystal exit face, after propagation through the polarizer, the beam will form an intensity distribution in the form of a conoscopic pattern. Any violation of axial propagation was considered as a perturbation of the conoscopic pattern and was not taken into account. Nevertheless, this process opens up a wide variety of transformations of polarization singularities caused by weak perturbations. In this article, the behavior of linearly polarized low-order Laguerre–Gauss beams in a uniaxial crystal is considered. The existence of a fine structure of radiation on the output face of a uniaxial crystal and the dependence of this fine structure on the parameters of the crystal and the beam are shown. [ABSTRACT FROM AUTHOR]

Polarizers are an essential optical element for tailoring the polarization state of electromagnetic waves in a wide range of optical devices. Such polarizers, which exhibit a wide operating bandwidth and high performance, are attracting increasing attention, due to their extensive prospects for use in applications ranging from polarization imaging, to optical communications and detection, among others. However, achieving both broadband performance and ultra-high extinction ratio (ER), and that simultaneously, is still challenging in the design of effective polarizers. To tackle that demand, in this work, an Au-on-silica grating structure has been proposed as the basis of the design of a miniaturized high-efficiency polarizer that practically can cover the entire visible and near-infrared spectral ranges. The single-layer polarizer thus designed can show an ER of 60 dB in this spectral domain, and it has been shown that the geometrical parameters selected have a significant effect on the performance characteristics of the polarizer. Furthermore, an ER of ∼150 dB could be achieved merely by regulating the thickness of the grating to achieve the optimum performance. By integrating the high-performance polarizer proposed in this work with an optical fiber "meta-tip," a refractive polarizer with a value of the ER of >45 dB, and that over the entire spectral domain considered, has been demonstrated. Such an approach offers an alternative route to achieving a broadband, powerful, and flexible processing polarizer design. [ABSTRACT FROM AUTHOR]

This is different than on our widefield Zeiss system where we can mismatch the DIC parts and get serviceable, if not ideal, DIC with any mag lens. If a higher quality DIC image is needed for reference or publication, perhaps only use DIC imaging at a few timepoints, leaving brightfield for the rest. Microscopy Listserver I Do any of you have experience using less common targets for sputter coating SEM samples? Nino Karpf nino.karpf@gmail.com Is it Possible to Combine DIC with Spinning Disk Fluorescence without a Moving DIC Cube Confocal Listserver I Dear Microscopists, we bought a spinning disk confocal microscope (Yokogawa W1 + Olympus X83) and have also ordered DIC -components. Molecules will generally emit in the same polarization configuration as the excitation light polarization if they cannot rotate freely, but that only applies if the polarization is linear in the sample, which I'm not actually sure is true if the other DIC components are in place. [Extracted from the article]

Being able to probe the polarization states of light is crucial for applications from medical diagnostics and intelligent recognition to information encryption and bio-inspired navigation. Current state-of-the-art polarimeters based on anisotropic semiconductors enable direct linear dichroism photodetection without the need for bulky and complex external optics. However, their polarization sensitivity is restricted by the inherent optical anisotropy, leading to low dichroic ratios of typically smaller than ten. Here, we unveil an effective and general strategy to achieve more than 2,000-fold enhanced polarization sensitivity by exploiting an anisotropic charge trapping effect in organic phototransistors. The polarization-dependent trapping of photogenerated charge carriers provides an anisotropic photo-induced gate bias for current amplification, which has resulted in a record-high dichroic ratio of >104, reaching over the extinction ratios of commercial polarizers. These findings further enable the demonstration of an on-chip polarizer-free bionic celestial compass for skylight-based polarization navigation. Our results offer a fundamental design principle and an effective route for the development of next-generation highly polarization-sensitive optoelectronics. The direct linear dichroism photodetection without external optics is crucial for applications. Here, Jie et al. exploit the anisotropic charge trapping in organic phototransistors to achieve the dichroic ratio of 104 and to demonstrate a polarizer-free celestial compass for bio-inspired navigation. [ABSTRACT FROM AUTHOR]

In this work, we study a double-sense twisted low-birefringence Sagnac loop structure as a sound/vibration sensing device. We study the relation between the adjustments of a wave retarder inside the loop (which allows controlling the transmission characteristic to deliver 10, 100, and 300 μ W average power at the output of the system) and the response of the Sagnac sensor to vibration frequencies ranging from 0 to 22 kHz. For a 300 m loop Sagnac, two sets of experiments were carried out, playing at the same time all the sound frequencies mixed for ∼1 s, and playing a sweep of frequencies for 30 s. In both cases, the time- and frequency-domain transmission amplitudes are larger for an average power of 10 μ W , and smaller for an average power of 300 μ W . For mixed frequencies, the Fourier analysis shows that the Sagnac response is larger for low frequencies (from 0 to ∼5 kHz) than for high frequencies (from ∼5 kHz to ∼22 kHz). For a sweep of frequencies, the results reveal that the interferometer perceives all frequencies. However, beyond ∼2.5 kHz, harmonics are present each ∼50 Hz, revealing that some resonances are present. The results about the influence of the power transmission through the polarizer and power emission of laser diode (LD) on the Sagnac interferometer response at high frequencies reveal that our system is robust, and the results are highly reproducible, and harmonics do not depend on the state of polarization at the input of the Sagnac interferometer. Furthermore, increasing the LD output power from 5 mW to 67.5 mW allows us to eliminate noisy signals at the system output. in our setup, the minimum sound level detected was 56 dB. On the other hand, the experimental results of a 10 m loop OFSI reveal that the response at low frequencies (1.5 kHz to 5 kHz) is minor compared with the 300 m loop OFSI. However, the response at high frequencies is low but still enables the detection of these frequencies, yielding the possibility of tuning the response of the vibration sensor by varying the length of the Sagnac loop. [ABSTRACT FROM AUTHOR]

Background:In the diagnosis and primary health care of an individual, estimation of the pulse rate and blood oxygen saturation (SpO 2 ) is critical. The pulse rate and SpO 2 are determined by methods including photoplethysmography (iPPG), light spectroscopy, and pulse oximetry. These devices need to be compact, non-contact, and noninvasive for real-time health monitoring. Reflection-based iPPG is becoming popular as it allows non-contact estimation of the heart rate and SpO 2 . Most iPPG methods capture temporal data and form complex computations, and thus real-time measurements and spatial visualization are difficult. Method:In this research work, reflective mode polarized imaging-based iPPG is proposed. For polarization imaging, a custom image sensor with wire grid polarizers on each pixel is designed. Each pixel has a wire grid of varying transmission axes, allowing phase detection of the incoming light. The phase information of the backscattered light from the fingertips of 12 healthy volunteers was recorded in both the resting as well as the excited states. These data were then processed using MATLAB 2021b software. Results: The phase information provides quantitative information on the reflection from the superficial and deep layers of skin. The ratio of deep to superficial layer backscattered phase information is shown to be directly correlated and linearly increasing with an increase in the SpO 2 and heart rate. Conclusions: The phase-based measurements help to monitor the changes in the resting and excited state heart rate and SpO 2 in real time. Furthermore, the use of the ratio of phase information helps to make the measurements independent of the individual skin traits and thus increases the accuracy of the measurements. The proposed iPPG works in ambient light, relaxing the instrumentation requirement and helping the system to be compact and portable. [ABSTRACT FROM AUTHOR]

We present a simple experiment developed for the advanced physics instructional laboratory to calculate the Mueller matrix of a microscopic sample. The Mueller matrix is obtained from intensity-based images of the sample acquired by a polarization-sensitive microscope. The experiment requires a bright-field microscope and standard polarizing optical components such as linear polarizers and waveplates. We provide a practical procedure for implementing the apparatus, measuring the complete Mueller matrix of linear polarizers used as samples, and discuss the possibility of analyzing biological samples using our apparatus and method. Due to the simplicity of the apparatus and method, this experiment allows students to increase their knowledge about light polarization and initiate their training in optical instrumentation. [ABSTRACT FROM AUTHOR]

The properties of polarization-selective, light-guiding systems upon subwavelength nanogratings formation in the case of type II refractive index traces induced by femtosecond laser pulses in bulk fused silica were studied. Polarization-dependent scattering is analyzed both in simulation using a finite-difference, time-domain method and in experiments. We argue that the polarization-sensitive optical guiding of type II waveguides is due to polarization-dependent scattering of nanogratings. Optical designs can then be suggested where the guiding efficiency of type I traces can be combined with type II anisotropies. A low-loss waveguide polarizer is demonstrated based on the modulation of the evanescent field emerging from type I waveguides using polarization-dependent scattering of neighboring nanogratings. [ABSTRACT FROM AUTHOR]

Common transparent polymer films, such as cellophane and household tape, are frequently used as examples of birefringent materials in textbooks and classroom demonstrations. Qualitatively, birefringence is often demonstrated by layering such films between crossed-polarizers. In this work, we describe an inexpensive experimental setup for the quantitative measurement of birefringence in common household films, suitable for senior high school or undergraduate labs. Whereas traditional approaches for polarization-based classroom experiments typically use monochromatic laser light, we encourage the combined use of an incoherent incandescent light source and a portable spectrometer. In addition, we demonstrate how any concomitant thin-film interference effects can be used to separately measure the optical thickness in the most heterogeneous and uniform films. Such measurement can then be used as an independent experimental confirmation of either the film's index of refraction or its thickness, given knowledge of the other. In an effort to provide examples for the data analysis procedures as well as to investigate a range of materials, we measure the birefringence across the visible spectrum of six common household polymer films, including thin kitchen wrap, cellophane, gift basket film, and common adhesive tapes. [ABSTRACT FROM AUTHOR]

Polarizer is a key component of the liquid crystal display panel, and the optical properties mainly include transmittance, degree of polarization and chromaticity. Polarizer is made of a multilayer optical film, in which the PVA polarizing film is the core structure for realizing the polarization of the whole polarizer. PVA polarizing film is commonly manufactured through a multi-step craft, including rinsing, dyeing, stretching and correcting. The correction process has a significant impact on the final apparent color and optical properties of the polarizer. In this study, the KI concentration in the correcting tank, ranging from 1% to 3%, was systematically investigated. With the increase in KI concentration, the Raman vibration peak at 160 cm−1 representing I 5 − ions gradually weakened, while the Raman vibration peak at 110 cm−1 representing I 3 − ions gradually increased, indicating that the KI in the correcting tank changed the chemical equilibrium of polyiodide ions in PVA. Then abundant chromophore I 5 − ions were consumed and I 3 − ions generated, so that the apparent color of PVA polarizing film gradually changed from dark blue to dark gray, and the chromaticity a-value and b-value gradually increased. The change in the concentration of dichroic species ( I 5 − and I 3 − ) in PVA polarizing film had directly affected its transmittance in the visible range. From the UV-Vis transmittance spectrum of PVA polarizing film, when the I 5 − ions were consumed and I 3 − ions generated, the transmittance of PVA polarizing film in the region of 675–525 nm wavelength increased gradually while the polarization degree also increased. [ABSTRACT FROM AUTHOR]

Intensity modulators are an essential component in optics for controlling free-space beams. Many applications require the intensity of a free-space beam to be modulated at a single frequency, including wide-field lock-in detection for sensitive measurements, mode-locking in lasers, and phase-shift time-of-flight imaging (LiDAR). Here, we report a new type of single frequency intensity modulator that we refer to as a longitudinal piezoelectric resonant photoelastic modulator. The modulator consists of a thin lithium niobate wafer coated with transparent surface electrodes. One of the fundamental acoustic modes of the modulator is excited through the surface electrodes, confining an acoustic standing wave to the electrode region. The modulator is placed between optical polarizers; light propagating through the modulator and polarizers is intensity modulated with a wide acceptance angle and record breaking modulation efficiency in the megahertz frequency regime. As an illustration of the potential of our approach, we show that the proposed modulator can be integrated with a standard image sensor to effectively convert it into a time-of-flight imaging system. Optical intensity modulators are an important component in optics. Here, the authors demonstrate a type of resonant intensity modulator operating in the megahertz frequency regime with record high efficiency and use it for time-of-flight imaging. [ABSTRACT FROM AUTHOR]

In this research, we report using optical components such as cubic beam splitters, lenses, diffraction gratings, and mirrors from broken, obsolete, or disused electronic devices to implement a simultaneous polarization-based phase-shifting interferometric system. The system is composed of a polarized Mach–Zehnder interferometer (PMZI) which generates a sample pattern coupled to a 4f imaging system with a diffraction grating placed on its Fourier plane. Such a diffractive element replicates the pattern generated by the PMZI, and each replica is centered and modulated by each diffraction order generated by the grating. The corresponding individual phase shifts are controlled by placing linear polarizers with known angles in front of each replica. Experimental results are presented using several phase samples such as an oil drop, a pseudoscorpion claw, a microarthropod, and red blood cells. In addition, a comparison of the retrieved phase was conducted by employing two different phase demodulation algorithms. [ABSTRACT FROM AUTHOR]

Hyperpolarized contrast agents (HyCAs) have enabled unprecedented magnetic resonance imaging (MRI) of metabolism and pH in vivo. Producing HyCAs with currently available methods, however, is typically time and cost intensive. Here, we show virtually-continuous production of HyCAs using parahydrogen-induced polarization (PHIP), without stand-alone polarizer, but using a system integrated in an MRI instead. Polarization of ≈2% for [1-13C]succinate-d2 or ≈19% for hydroxyethyl-[1-13C]propionate-d3 was created every 15 s, for which fast, effective, and well-synchronized cycling of chemicals and reactions in conjunction with efficient spin-order transfer was key. We addressed these challenges using a dedicated, high-pressure, high-temperature reactor with integrated water-based heating and a setup operated via the MRI pulse program. As PHIP of several biologically relevant HyCAs has recently been described, this Rapid-PHIP technique promises fast preclinical studies, repeated administration or continuous infusion within a single lifetime of the agent, as well as a prolonged window for observation with signal averaging and dynamic monitoring of metabolic alterations. Magnetic resonance imaging of hyperpolarized contrast agents has enabled unprecedented imaging capabilities in a biomedical setting, but its widespread application is hindered by the time and costs associated with preparing hyperpolarized carbon-13 samples. Here, the authors demonstrate virtually-continuous production of batches of highly-hyperpolarized carbon-13 contrast agents every 15 s within an MRI system without a stand-alone polarizer. [ABSTRACT FROM AUTHOR]