Birefringence Retardation Research Articles

Pre-yielding and necking process of double network hydrogels revealed by sample geometry effects

Understanding the yielding and necking mechanisms of double network (DN) materials is crucial for establishing structure-property correlations. While previous studies have primarily focused on how macro-yielding behavior changes with network structure and swelling, in this work, we study the local internal damage in the pre-yielding process to unveil the yielding and necking mechanisms for typical DN gels. Through birefringence retardation imaging during tensile deformation on DN gels of various sample geometries, our findings reveal the following key points: 1) Initiation and Growth of Damage Zones: Prior to macroscopic yielding, damage zones initiate from the sample edges and gradually grow towards the sample center with elongation. 2) Rapid Propagation and Yielding: Beyond a certain stress threshold, damage zones rapidly propagate under constant loading. Two damage zones eventually merge at the sample center, resulting in yielding. 3) Intrinsic Stress Determination: The stress at this point is intrinsic and determined by the structure of the two networks. 4) Pseudo Size-Dependency: Samples with insufficient width exhibit a pseudo size-dependency of yielding stress, as yielding occurs before reaching the critical stress. To explain the origin of intrinsic yielding stress, we introduce an intrinsic effective crack length (cI) as a measure of stress concentration around the internal crack tip of the damaged zone in the first network. Beyond this length, the influence on internal stress concentration around the damage zone is effectively screened by the load-bearing effect of the stretchable second network. The estimated cI, dependent on the microstructure of the two networks, was approximately 10 times the mesh size of the first network for typical DN gels.

Frequency properties of channeled spectropolarimetry: an information theory perspective.

Channeled spectropolarimetry (CSP) has emerged as a notable technique due to its unique capacity to instantaneously measure either the polarization state of light or the Mueller matrix of a sample over a broad spectral range. Leveraging the quasi-linear relation between phase retardances of thick birefringent retarders and wavenumber, the target signal undergoes wavelength encoding. For the first time, we present a theoretical framework for the general CSP from a perspective of information theory. This framework comprehensively addresses the frequency properties of CSP, encompassing signal bandwidth, modulation frequency, sampling relationships, and filter window width during the demodulation process. Drawing from the frequency properties of CSP, we establish a theoretical foundation that informs the design of versatile CSPs and evaluates their measurement capabilities. Simulations for both Stokes CSP and Mueller CSP validate the efficacy of the proposed approach.

Polarimetric linear absolute position encoder

Abstract Optical encoders based on measurement of the axis-angle of linear polarizers offer high resolution and moderate accuracy, but are usually restricted to rotary measurement. We show that annular polymer sheet polarizer materials can be sheared into rectangular tapes, with a polarizing axis that varies linearly along the tape. This makes possible the construction of polarimetric linear absolute position encoders. We demonstrate also sheared polymer birefringent retarders, which function similarly, potentially with cost and size-flexibility advantages.

Polarimetric 360° absolute rotary encoder

Abstract Encoders of angle based on rotating polarizers suffer from 180° ambiguity due to their inherent twofold rotational symmetry. This restricts their applications in motor and machine controls. We show that the ambiguity can be resolved through a geometrical mapping from a plane to a conical surface. Seen from the local surface normal, one full rotation of the cone gives one half rotation of the polarizer axis. With appropriate transmission or reflective optics and multiphase detection, we build high resolution, moderate accuracy, absolute-angle encoders without 180° ambiguity. Polymer birefringent retarders can be used similarly.

Analysis of experimental errors in Mueller matrix channeled polarimeters.

This work analyzes the effect of experimental errors and measurement noise on Mueller matrix channeled spectropolarimeters. The main advantage of this type of polarimeter is the independence on temporal resolution, as it can be used as a snapshot polarimeter. The simulation of the polarimeters with experimental errors and two published extraction methods of the sample Mueller matrix are also presented. The Mueller matrix channeled spectropolarimeter (MMCS) setup consists of a mirrored Stokes channeled spectropolarimeter (SCS) as the polarization states generator (PSG) and a SCS as the polarization states analyzer (PSA). The SCS setup comprises two thick birefringent retarders followed by a horizontal linear polarizer. The effects of the thickness ratio of the retarders, the global retardance factor, retardance errors, axes alignment errors, and additive Gaussian noise are further studied to optimize the MMCS setups. In this work, we do not include a calibration procedure to improve the measured Mueller matrix parameters, but we study the sensitivity of the polarimeter to different configurations and error sources.

Error analysis of channeled Stokes polarimeters.

This work presents an analysis of passive polarimeters with spectral channeling, referred to as Stokes channeled spectropolarimeters (SCS). The SCS setup comprises two thick birefringent retarders, followed by a horizontal linear polarizer. The simulation of these polarimeters and two extraction methods for the incident Stokes vector is presented as well. The effects of different retarders thickness ratios, the global retardance factor, retardance errors, axes alignment error, and Gaussian noise on root mean square (RMS) errors of the recovered Stokes parameters are described. Furthermore, two different, previously published data extraction methods are presented and compared. We found the best polarimeter configurations from the cases studied, and our results suggest that a mixed extraction process, using different extraction methods for different Stokes parameters, could give better results by reducing RMS errors by about a factor of 5. It is worth mentioning that although calibration is needed to account for the effect of errors, this is out of the scope of this work.

Birefringent optical retarders from laser 3D-printed dielectric metasurfaces

Structuring light attracts continuous research effort due to its impactful applications in optical information and communications, laser material processing, optical imaging, or optical manipulation of matter. In particular, femtosecond laser direct writing of photoresists is a technology dedicated to the creation of optically isotropic free-form 3D micro-optical elements with size, spatial resolution, and surface quality that qualify to demanding integrated optics needs. Here, we report on the design, production, and characterization of dielectric metasurface birefringent optical retarders made from femtosecond laser 3D printing technology whose polarization conversion efficiency is more than 10 times larger than that previously reported Wang et al., Appl. Phys. Lett. 110, 181101 (2017)]. As the flexibility of the fabrication process allows considering arbitrary orientation of the artificially engineered optical axis, these results open up for 3D printed geometric phase optical elements.

Rewritable color nanoprints in antimony trisulfide films.

Materials that exhibit large and rapid switching of their optical properties in the visible spectrum hold the key to color-changing devices. Antimony trisulfide (Sb2S3) is a chalcogenide material that exhibits large refractive index changes of ~1 between crystalline and amorphous states. However, little is known about its ability to endure multiple switching cycles, its capacity for recording high-resolution patterns, nor the optical properties of the crystallized state. Unexpectedly, we show that crystalline Sb2S3 films that are just 20 nm thick can produce substantial birefringent phase retardation. We also report a high-speed rewritable patterning approach at subdiffraction resolutions (>40,000 dpi) using 780-nm femtosecond laser pulses. Partial reamorphization is demonstrated and then used to write and erase multiple microscale color images with a wide range of colors over a ~120-nm band in the visible spectrum. These solid-state, rapid-switching, and ultrahigh-resolution color-changing devices could find applications in nonvolatile ultrathin displays.

Recent Progress on Ultrathin Metalenses for Flat Optics.

SummaryAs technology advances, electrical devices such as smartphones have become more and more compact, leading to a demand for the continuous miniaturization of optical components. Metalenses, ultrathin flat optical elements composed of metasurfaces consisting of arrays of subwavelength optical antennas, provide a method of meeting those requirements. Moreover, metalenses have many other distinctive advantages including aberration correction, active tunability, and semi-transparency, compared to their conventional refractive and diffractive counterparts. Therefore, over the last decade, great effort has been focused on developing metalenses to investigate and broaden the capabilities of metalenses for integration into future applications. Here, we discuss recent progress on metalenses including their basic design principles and notable characteristics such as aberration correction, tunability, and multifunctionality.

Colorimetry characterization of molecular reorientation transition in thin nematic cells.

The characterization of equilibria and their transition is fundamental in dynamic systems. Experimentally, the characterization of transitions is complex due to time scales separation, the effect of thermal fluctuations, and inherent experimental imperfections. Liquid crystal devices are derived from the manipulation of the molecular reorientation and transition between them by employing external electrical and magnetic fields. Here, we investigate and determine the Fréedericksz transition using hue measurements of the transmitted light in thin nematic liquid crystal cells. Based on birefringent retardation experienced by transmitted light due to molecular reorientation, the color adjustment of the nematic liquid crystal cells under white light illumination is characterized. By monitoring the hue of the transmitted light, the bifurcation diagram is determined. As a function of the voltage frequency, the critical transition voltage is characterized. The critical voltage increases with the applied frequency.

Examination of internal stress by photoelasticity in laser cleaving of glass

Laser cleaving is a glass-cutting technique in which thermal stress induced by laser heating and cooling produces cracks in the glass. Stress measurement during the laser cleaving process is critical in elucidating the crack-propagation mechanism and solving the problems of the laser cleaving method. In this study, we measured the birefringence retardation using a high-speed polarization camera and evaluated the relevance and accuracy of the measured values by comparing them with the results of a numerical calculation. The birefringence retardation at the crack tip was also observed in the experimental process. For the experiment, a soda lime glass was cleaved using CO2 laser irradiation. Then, the birefringence retardation and azimuthal angle obtained using the polarization camera were compared with the numerical calculation results. The birefringence retardation around the crack tip corresponded with that of the deformation caused by mode I. The crack propagation was arrested when the crack tip approached the edge of the glass. The birefringence retardation observed using the polarization camera confirmed that the mode I deformation decreased as the crack approached the edge.

Residual stress birefringence of highly reflective mirrors with different numbers of layers.

Residual stress birefringence of highly reflective mirrors is a challenging problem due to its dubious origin and intricate nature. In this paper, the birefringences of highly reflective mirrors manufactured under the same deposition parameters but structured with different numbers of high- and low-refractive-index (HL) layer pairs are measured with the cavity ring-down technique by the mirror rotation method together with a differential loss approximation model. Experimental results show that birefringence retardation increases with the increasing number of HL layer pairs. Further measurements across the mirror surface indicate a non-uniform birefringence distribution, while curvature analysis of the stress-deformed surface provides more clues to the origins of birefringence.

Dedicated optical systems of the Institute of Applied Optics

The paper presents a collection of selected optical systems recently developed in the Institute of Applied Optics-INOS. The collection includes the family of techniques where the continuously modified wavelength facilitates high accuracy measurements of optical and geometrical features of the object in question i.e. the variable wavelength interferometry and confocal chromatic sensors. In addition, the paper refers to the construction of a new type of a spectrometer with rotating plasma and an illumination system supporting the road safety. Full Text: PDF ReferencesM. Pluta, Advanced Light Microscopy (Vol. 3, PWN, Elsevier, Warszawa-Amsterdam-London-New York-Tokyo, 1993). DirectLink M. Pluta, "Object-adapted variable-wavelength interferometry. I. Theoretical basis", Journal of Opt. Soc. Am., A4(11), 2107 (1987). CrossRef M. Pluta, "Variable wavelength microinterferometry of textile fibres", J. Microscopy, 149(2), 97 (1988). CrossRef M. Pluta, "On double‐refracting microinterferometers which suffer from a variable interfringe spacing across the image plane", Journal of Microscopy, 145(2), 191 (1987). CrossRef K. A. El-Farahaty, A. M. Sadik, A. M. Hezma, "Study of Optical and Structure Properties of Polyester (PET) and Copolyester (PETG) Fibers by Interferometry", International Journal of Polymeric Materials 56(7),715 (2007). CrossRef J. Galas, D. Litwin, M. Daszkiewicz, "New approach for identifying the zero-order fringe in variable wavelength interferometry", Proc. SPIE 10142, 101421R (2016). CrossRef A. Sadik, W. A. Ramadan, D. Litwin, "Variable incidence angle method combined with Pluta polarizing interference microscope for refractive index and thickness measurement of single-medium fibres", Measurement Science and Technology, IOP Publishing 14(10), 1753 (2003). CrossRef J. Galas, S. Sitarek; D. Litwin; M. Daszkiewicz, "Fringe image analysis for variable wavelength interferometry", Proc. SPIE 10445, 1044504 (2017). CrossRef D. Litwin, A. M. Sadik, "Computer-aided variable wavelength Fourier transform polarizing microscopy of birefringent fibers.", Optica Applicata 28(2), 139 (1998). DirectLink D. Litwin, J. Galas, N. Błocki, "Automated variable wavelength interferometry in reflected light mode", Proc.SPIE 6188, 61880F (2006). CrossRef M. Pluta, "Variable wavelength interferometry of birefringent retarders", Opt. Laser Technology, 19(3), 131 (1987). CrossRef K. Fladischer et al. "An ellipsoidal mirror for focusing neutral atomic and molecular beams", New journal of Physics, 12(3) 033018 (2010). CrossRef K. Fladischer et al. "An optical profilometer for characterizing complex surfaces under high vacuum conditions", Precision engineering Elsevier 32(3), 182 (2008). CrossRef A.E. Weeks et al. "Accurate surface profilometry of ultrathin wafers", Semiconductor Science and Technology", IOP Publishing, 22(9), 997 (2007). CrossRef D. Litwin et al. "Overview of the measuring systems where a continuously altered light source plays a key role: Part I", Proc. SPIE 10808, 10 8080B (2018). CrossRef D. Litwin et al. "Noise reduction in an optical emission spectrometer with rotating diffraction grating", Proc. SPIE 10142 101421Q (2016). CrossRef D. Litwin et al. "Photonics approach to traffic signs", Proc SPIE 10142 1014214, (2016). CrossRef

Spectral resolution enhanced static Fourier transform spectrometer based on a birefringent retarder array.

The principle and experimental demonstration of a spectral resolution enhanced static Fourier transform spectrometer (SESFTS) is presented. The device, which is based on a birefringent retarder array and a Wollaston prism, offers significant advantages over previous static Fourier transform (FT) implementations. Specifically, its use of an ultra-compact common-path interference structure creates a simple and robust spectral resolution enhanced spectrometer while preserving their high throughput and wide free spectral range. The operation principle of the device is explained in detail with a design example with a spectral resolution of 7 cm-1, which is nearly two orders of magnitude higher than that of a conventional static FT spectrometer with a similar CCD detector. An experimental demonstration is performed by the measurement of a gas charge lamp and three diode laser sources with a SESFTS prototype working in 400-1000 nm with an approximate 25 cm-1 spectral resolution.

Self-correction of alignment errors and retardations for a channeled spectropolarimeter.

Alignment errors of birefringent retarders and retardation errors introduced by environmental perturbations can cause significant influences on reconstructed Stokes parameters for the channeled spectropolarimeter. In this paper, we propose what we believe is a novel self-correction model that is independent of input polarization parameters to reduce the effects of alignment errors and environmental perturbations. This self-correction method can realize calibration and compensation of alignment errors and retardations simultaneously by measuring the target light in orbit. Simulation results show that alignment errors and retardations can be calibrated accurately, and the reconstructed Stokes parameters by using the presented method are more precise than by using the traditional method. The validity and feasibility of the presented method are further confirmed through experiments in the presence of alignment errors and environmental perturbations.

Babinet-bilayered geometric phase optical elements.

Geometric phase optical elements based on structured anisotropy are widely used for phase shaping via their orientational degree of freedom. To date, amplitude shaping via space-variant retardance is much less investigated, a practical reason being that the spin-orbit interaction of light couples retardance with the dynamic part of the optical phase. Inspired by the complementary diffractive elements associated with Babinet's principle, a bilayered subwavelength grating design is proposed in order to cancel out the spatial modulation of the dynamic phase usually associated with space-variant birefringent phase retardation. This concept is illustrated in the framework of single-mode Laguerre-Gauss beam shaping.

Single-shot optical recorder with sub-picosecond resolution and scalable record length on a semiconductor wafer.

We demonstrate a novel, single-shot recording technology for transient optical signals. A resolution of 0.4ps over a record length of 54ps was demonstrated. Here, a pump pulse crossing through a signal samples a diagonal "slice" of space-time, enabling a camera to record spatially the time content of the signal. Unlike related χ(2)-based cross-correlation techniques, here the signal is sampled through optically pumped carriers that modify the refractive index of a silicon wafer. Surrounding the wafer with birefringent retarders enables two time-staggered, orthogonally polarized signal copies to probe the wafer. Recombining the copies at a final crossed polarizer destructively interferes with them, except during the brief stagger window, where a differential phase shift is incurred. This enables the integrating response of the rapidly excited but persistent carriers to be optically differentiated. This sampling mechanism has several advantages that enable scaling to long record lengths, including making use of large, inexpensive semiconductor wafers, eliminating the need for phase matching, broad insensitivity to the spectral and angular properties of the pump, and overall hardware simplicity.

Broadband polarization conversion with anisotropic plasmonic metasurfaces

Metasurfaces offer exciting opportunities that enable precise control of light propagation, optical intensity, phase and polarization. Plasmonic metasurface based quarter-wave plates have been recently studied to realize the conversion between linear polarization and circular polarization. However, it is still quite challenging to directly measure the birefringent phase retardation introduced by metasurface wave plates with a reliable technique. Here, we report a high-performance broadband metasurface quarter-wave plate made of anisotropic T-shaped plasmonic antennas in near-infrared wavelength range, where the achromatic nearly 90° transmitted phase retardation through the metasurface is precisely characterized with an optical vortex based interferometric approach. Based on the measured transmission amplitude and phase of two orthogonal linear polarization components, nearly unit degree of linear polarization is extracted from the Stokes parameters, indicating excellent broadband polarization conversion between linearly and circularly polarized light through the metasurface. Our results will be an important step forward in the advancement of integrated metasurface devices for polarization conversion and beam manipulation, structured light control, as well as new spectroscopic and interferometric techniques for metasurface characterization.

Optically ambidextrous circularly polarized reflection from the chiral cuticle of the scarab beetle Chrysina resplendens.

The evolution of structural colour mechanisms in biological systems has given rise to many interesting optical effects in animals and plants. The instance of the scarab beetle Chrysina resplendens is particularly distinctive. Its exoskeleton has a bright, golden appearance and reflects both right-handed and left-handed circularly polarized light concurrently. The chiral nanostructure responsible for these properties is a helicoid, in which birefringent dielectric planes are assembled with an incremental rotation. This study correlates details of the beetle's circularly polarized reflectance spectra directly with physical aspects of its structural morphology. Electron micrography is used to identify and measure the physical dimensions of the key constituent components. These include a chiral multilayer configuration comprising two chirped, left-handed helicoids that are separated by a birefringent retarder. A scattering matrix technique is used to simulate the system's optical behaviour in which the roles of each component of the morphological substructure are elucidated by calculation of the fields throughout its depth.

Modelling the combination of birefringence retardations from strain envelopes around multiple inclusions in diamond

ABSTRACTA paleo-alluvial 0.21 ct yellow diamond (L058) from Bingara (NSW) has three inclusions of coesite (two subequant crystals and one thin plate), each under more than 3.1 GPa internal pressure as measured by Raman spectroscopy. These inclusions cause overlapping birefringent retardation stress/strain haloes in the host diamond, visible under cross-polarised light. The complicated retardation pattern is quantified by mapping targeted retardation contours (170 nm, 270 nm and 380 nm) onto a photo of the diamond. A mathematical model of retardation is developed for each inclusion, and then the combined light retardations (CLR) are calculated using radial and tangential components with spherical and elliptical geometries. The CLR model reproduces most features of the measured data, but remaining differences may be due to local release of stress/strain by two short fractures radiating from one inclusion.