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We present a guide to the implementation and uncertainty evaluation for spectral stray light corrections according to the widely used method as proposed by Zong et al. [Appl. Opt.45, 1111 (2006)APOPAI0003-693510.1364/AO.45.001111]. The uncertainty analysis is based on the Monte Carlo approach in accordance with the Guide to the Expression of Uncertainty in Measurement (JCGM, Paris, 2008). We show that significant uncertainty contributions result from drifts of the spectrometer's dark signal and the width of the in-band region selected for shaping stray light distribution functions. Additionally, a simplified method for estimating these uncertainty contributions is presented, which does not require a complex Monte Carlo analysis. We also show that stray light correction may introduce correlations with respect to wavelength.

We present a method of various defects detection on a flat surface using a polygonal-shaped waveguide devised laser scatterometer capable of providing sub-µm precision. The optimized polygonal shape of the waveguide with double-slit aperture substantially improves the detection efficiency of scattered beam more than 10 times compared to that of the conventional circular-shaped waveguide. The scatterometer enables quantification of sub-µm lateral size and height of defects by counting the number of pixels and peak intensity, respectively. We validated the performance of the proposed inspection system by measuring a standard defective specimen and successfully apply to a pilot production line for inspection of 250×140 mm2 size glass panels providing 31,250 × 16,000 spatial resolution with the capability of a measuring time less than 10 s.

We report a frequency-multiplexing method for multi-beam photon-counting light detection and ranging (LiDAR), where only one single-pixel single-photon detector is employed to simultaneously detect the multi-beam echoes. In this frequency-multiplexing multi-beam LiDAR, each beam is from an independent laser source with different repetition rates and independent phases. As a result, the photon counts from different beams could be discriminated from each other due to the strong correlation between the laser pulses and their respective echo photons. A 16-beam LiDAR system was demonstrated in three-dimensional laser imaging with 16 pulsed laser diodes at 850 nm and one single-photon detector based on a Si-avalanche photodiode. This frequency-multiplexing method can greatly reduce the number of single-photon detectors in multi-beam LiDAR systems, which may be useful for low-cost and eye-safe LiDAR applications.

We report on the new technical realization of single-shot color digital holographic microscopy. For this application, we propose to use an original three-wavelength red, green, and blue laser based on the Nd:YAG active element with sequential parametric downconversion and upconversion of optical frequencies into red (634 nm), green (532 nm), and blue (451 nm) spectral intervals. This light source provides high-power short (∼10 ns) pulses and enables simultaneous formation of three color interference patterns in a two-path interferometer. Their registration by a color image sensor provides fast acquisition of phase delay distribution induced by the inspected object at three wavelengths without spectral tuning.

Refractive eyepiece design forms are often limited by chromatic aberrations and require a mix of glass types to achieve sufficient correction, thus they are not conducive to manufacture in volume. Reflective surfaces are inherently achromatic and can be produced in volume, but rotationally symmetric reflective surfaces are either used with lossy obscurations or are incapable of correcting rotationally variant aberrations when used in an unobscured form. Freeform optics enable unobscured reflective design forms with excellent image quality. Here, we document the design, fabrication, and assembly of an all-reflective high-end electronic viewfinder that shows the applicability of freeform surfaces to eyepiece design forms.

With the development of fluorescence microcopy, the autofluorescence effect of optical glass in microscope lenses has become an important source of stray light which decreases the contrast of the image. However, the autofluorescence effect of various types of microscope lenses has not been thoroughly discussed and the dominant factors of this effect are not clear. Currently, the most commonly used analysis method of the autofluorescence effect is based on the volume scattering model and Monte Carlo raytracing, which is extremely time-consuming due to the large number of rays that need to be traced. In our previous work, we have presented an efficient phase-space-based simulation method, which significantly accelerates the simulation of the autofluorescence effect [Appl. Opt.58, 3589 (2019)APOPAI0003-693510.1364/AO.58.003589]. Here we apply this new method on different types of microscope lenses and perform a systematic analysis of the autofluorescence effect based on the simulation results. In order to obtain an overview of the autofluorescence effect of different types of microscope lenses, more than 100 microscope lenses with different numerical aperture (NA), magnification, working distance, and immersion medium are selected and the corresponding autofluorescence contribution from each element in the lenses is calculated. Following a systematic analysis of the simulation result, we find that the autofluorescence effect of a lens is dependent on the etendue and complexity of the system, while the most critical elements are usually found in the front and rear groups. After the origins of the autofluorescence contribution from these critical lens groups have been found, possibilities to reduce the autofluorescence intensity have been investigated. Finally, effective methods to reduce the autofluorescence effect are presented and compared. The major contribution of this work is a detailed analysis of the impact of different factors on the autofluorescence effect, based on which a guideline is provided for the optical designers as well as the users to design or to select an appropriate microscope lens with low autofluorescence intensity.

The realization of on-chip microspectrometers would allow spectroscopy and colorimetry measurement systems to be readily incorporated into platforms for which size and weight are critical, such as consumer grade electronics, smartphones, and unmanned aerial vehicles. This would allow them to find use in diverse fields such as interior design, agriculture, and in machine vision applications. All spectrometers require a detector or detector array and optical elements for spectral discrimination. A single device that combines both detection and spectral discrimination functions therefore represents an ultimate limit of miniaturization. Motivated by this, we here experimentally demonstrate a novel nanostructured silicon-based photodetector design whose responsivity can be tailored by an appropriate choice of geometric parameters. We utilize a unique doping profile with two vertically stacked, back-to-back photodiode regions, which allows us to double the number of detectors in a given on-chip footprint. By patterning the top photosensitive regions of each device with two sets of interleaved vertical slab waveguide arrays of varied width and period, we define the absorption spectra (and thus responsivity spectra) of both the upper and lower photodiode regions. We then use twenty such “fishnet pixels” to form a microspectrometer chip and demonstrate the reconstruction of four test spectra using a two-stage supervised machine-learning-based reconstruction algorithm.

The thermal control system based on a combination of passive and active methods for a compact aerial camera used in the unmanned aerial vehicle system is studied. Integrated analysis and an experimental method are developed to ensure both low-power limit and high image quality of the camera. For rapid estimation of thermal behavior, we develop a thermal mathematic model based on a thermal network method that also offers an initial design reference for the active control system; then we develop a more complex integrated analysis method to analyze and optimize the thermal system, which allows us to get performance insights such as internal temperature gradient and airflow of the compact system. We also focus on analyzing the optical surface errors under thermal disturbance. Comparisons of interferometer test records and thermal-elastic simulation results are presented, and this comparison shows that the integrated optomechanical analysis method contributes to the success of optomechanical system design by ensuring thermal disturbance will not deform the optical surfaces beyond allowable limits. Finally, the design method is verified through a thermo-optic experiment.

An electrically controlled arc-electrode liquid-crystal microlens array (AE-LCMLA), with tuning and swing focus, is proposed, which can be utilized to replace the traditional mechanically controlled microlenses and also cooperate with photosensitive arrays to solve the problems of measuring and further adjusting a strong distortion wavefront. The top patterned electrode of a single LC microlens is composed of three arc-electrodes distributed symmetrically around a central microhole for constructing the key controlling structures of the LC cavity in the AE-LCMLA. All the arc-electrodes are individually controlled, and then the focal spot of each microlens can be moved freely in a three-dimensional fashion including along the optical axial direction and over the focal plane by simply adjusting the driving signal voltage applied over each arc-electrode, independently. The featured performances of the AE-LCMLA in a wavelength range of ∼501–561 nm are the driving signal voltage being relatively low (less than ∼11 Vrms), the focal length tuning range being from ∼2.54 mm to ∼3.50 mm, the maximum focus swing distance being ∼52.92 μm, and the focus swing ratio K being ∼20‰.

In the context of industry 4.0, building data clouds in manufacturing technologies is the fundamental step to approach intelligent automatic process. This new technology has proved to efficiently and effectively monitor five important responses (removal rate, texture, surface accuracy, edge-profiles and mid-spatial frequencies) with more than 95% repeatability in real time. This faster and inexpensive process can serve for the nowadays high-quality segmented telescopes. We illustrate the underlying problem by reference to a case-study - the challenge of an average manufacturing rate of 11.4 segments per month for the 39.3m optical/infrared European Extremely Large Telescope (E-ELT) project.

This paper discusses the new radiometric calibration methods and results that we have developed to apply to day/night whole sky imager data and extinction imager data. Day/night whole sky imagers detect the presence and location of clouds and categorize them by opacity. The new day and night cloud algorithms for these instruments are documented elsewhere, and these algorithms depend on the use of the new calibrations we have developed. In this paper, we document our calibration methods for determining the absolute radiance of the whole sky imager scene at each pixel in the images as well as the results of the calibrations. The extinction imagers are new systems we developed that determine beam transmittance and path extinction for horizontal paths through the atmosphere. These instruments and their algorithms are documented elsewhere, and they also depend on the new calibration results. The extinction imager algorithms only require relative radiances, as opposed to absolute radiances. The calibration steps for the two instruments are quite similar, and they include dark correction; linearity calibration, which corrects for nonlinearities in the signal versus flux relationship; absolute calibration (for the whole sky imager); and uniformity calibration, which corrects for pixel-to-pixel nonuniformities. These developments include methods for handling uniformity calibrations in a system using a fisheye lens and the calibration of both visible and short-wave IR systems. This paper presents both the new methods and results in support of the papers documenting the algorithms.

A full-field microprofilometry involving innovative image correlation was developed for profile measurement without vertical scanning. High-speed optical inspection has become critical for confirming precise dimensions in semiconductor fabrication such as microbumping in 3D stacked ICs and precision manufacturing. A digital micromirror device (DMD) is designed to serve as a point-light-source array in a quasiconfocal optical configuration and perform lateral scanning to minimize signal crosstalk between neighboring testing points. More importantly, multiple diffractive images are detected and measured with a prebuilt depth-correlated database to extract the height information of a tested surface. A 100-nm repeatability can be realized in the absence of a detector pinhole and without vertical scanning, thus achieving high-speed submicrometer-scale surface profilometry.

We introduce a monolithic Brillouin generator based on a semiconductor micropillar cavity embedding a high frequency nanoacoustic resonator operating in the hundreds of GHz range. The concept of two nested resonators allows an independent design of the ultrahigh frequency Brillouin spectrum and of the optical device. We develop an optical free-space technique to characterize spontaneous Brillouin scattering in this monolithic device and propose a measurement protocol that maximizes the Brillouin generation efficiency in the presence of optically induced thermal effects. The compact and versatile Brillouin generator studied here could be readily integrated into fibered and on-chip architectures., 9 pages, 4 figures

Laser-based infrared spectroscopic ellipsometry (SE) is demonstrated for the first time, to the best of our knowledge, by applying a tunable quantum cascade laser (QCL) as a mid-infrared light source. The fast tunability of the employed QCL, combined with phase-modulated polarization, enabled the acquisition of broadband (900–1204 cm−1), high-resolution (1 cm−1) ellipsometry spectra in less than 1 second. A comparison to a conventional Fourier-transform spectrometer-based IR ellipsometer resulted in an improved signal-to-noise ratio (SNR) by a factor of at least 290. The ellipsometry setup was finally applied for the real-time monitoring of molecular reorientation during the stretching process of an anisotropic polypropylene film, thereby illustrating the advantage of sub-second time resolution. The developed method exceeds existing instrumentation by its fast acquisition and high SNR, which could open up a set of new applications of SE such as ellipsometric inline process monitoring and quality control.

A cavity ringdown system for probing the spatial variation of optical loss across high-reflectivity mirrors is described. This system is employed to examine substrate-transferred crystalline supermirrors and to quantify the effect of manufacturing process imperfections. Excellent agreement is observed between the ringdown-generated spatial measurements and differential interference contrast microscopy images. A 2-mm diameter ringdown scan in the center of a crystalline supermirror reveals highly uniform coating properties with excess loss variations below 1 ppm.

We have focused on the optical form that is low cost while maintaining high performance for airborne application. We report the optical design as well as the alignment and test results for a push-broom imaging spectrometer. The smart architecture of the prism-grating based spectrometer ensures high uniformity and image quality. Moreover, an effective method for aligning the spectrometer is also proposed. The results of laboratory-based optical tests and a flight test confirm the easy manufacture and excellent performance. Thus, the proposed system should be suitable for use as a hyperspectral instrument that can be loaded onto airborne and unmanned aerial vehicles.

Infrared imaging provides invisible infrared pictures beyond that of normal human vision. However, common infrared imaging systems are incapable of capturing dynamical phenomena with high resolution and a wide field of view (FoV). The proposed modality purposefully selects the incident light with various instantaneous viewing angles and eventually combine them in different temporal sequences to form a larger FoV image, thus allowing one single cooled focal plane arrays to detect an area that appreciably exceeds what is possible with conventional counterparts. The primary principles of the 3.5 $\sim$∼ 5 $\mu$μm imaging system involve contracting and splitting the FoV with the optical wedges and switching the splitted FoV using the micro-lens arrays, which are realized with the secondary imaging structure. In this technique, the entire FoVs are enlarged from 15$^\mathrm{o}$o to 30$^\mathrm{o}$o both in 2-D and 3-D modality when the resolutions keep at 49 lp/mm. Proof-of-concept results demonstrate significantly our mid-infrared imaging modality performs high-quality images in the FoV of -15$^\mathrm{o}$o to 15$^\mathrm{o}$o. The present article has brought us a new class of wide FoV imaging configurations that permit the capture of moving objects in large area, which also preserves the high resolution.

The optimized design of multilayer-coated blazed gratings (MLBG) for high-flux tender X-ray monochromators was systematically studied by numerical simulations. The resulting correlation between the multilayer d-spacing and grating blaze angle significantly deviated from the one predicted by conventional equations. Three high line density gratings with different blaze angles were fabricated and coated by the same Cr/C multilayer. The MLBG with an optimal blaze angle of 1.0 degrees showed a record efficiency reaching 60% at 3.1 keV and 4.1 keV. The measured efficiencies of all three gratings were consistent with calculated results proving the validity of the numerical simulation and indicating a more rigorous way to design the optimal MLBG structure. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

In order to establish scattering measurements in material investigations for gravitational-wave detectors, we have built-up devices for measuring the hemispherical scattering distribution of materials which are planned to be used in those detectors as suppressors of scattered light. The measurement benches we have built, a hemispherical goniometer and a direct back-scatterometer, have a maximum background noise of ∼10 −4sr −1 BRDF at 1.064 μm wavelength which is the wavelength of the laser-light for our large interferometer for detecting gravitational waves, KAGRA. With these instruments, we have characterized the surface scattering of, e.g., NiP platings, metals, and different carbonaceous coatings, which are supposed to minimize the amount of scattered light in interferometers. The three most important materials for KAGRA’s construction (SiC, “Solblack”, and “VantaBlack”) are presented in this paper. Furthermore, we will try to explain the scattering distributions with the generalized Harvey-Shack model (smooth-surface approximation) which is a common method for surface-scattering calculations. At the end, we give also some valuations about the vacuum compatibility of the materials, which is important for instruments like KAGRA that work under ultra-high vacuum conditions.

Pushbroom hyperspectral imaging (HSI) has been used in many areas from air to land. However, its inherent operational drawback of the bulky slit leads to a limited field of view (FOV) and high energy consumption. Accordingly, a new and versatile HSI system is proposed by employing a smart digital micromirror device (DMD) to replace the mechanical scanning component. Moreover, tunable spatial and spectral resolution is implemented through adjusting the on-chip scanning linewidth and adopting the pixel fusion method, respectively. Meanwhile, three scanning modes including rough scanning, fine scanning, and regional scanning are achieved. These multiple choices increase the system's flexibility, universality, and intelligence, which is attractive for practically different applications, especially for military and remote sensing fields in need of a large FOV, and medical and food fields in need of tunable resolution for various samples.

Due to the interference of excitation lights and the perturbation of spattered particles, it is very difficult to detect the real-time evolution of ceramics damaged by pulsed laser. In this paper, a metrology "on-line detection of damage identification via the polarization spectrum imaging" is proposed to realize the real-time observation for damage evolution of ceramic composite irradiated by the laser. In this metrology, the detection principle is based on a mathematical model of polarization bidirectional reflectance distribution function. According to the Stokes vector analysis method, the damage law of the material surface under the continuous activating illuminations of multiple laser pulses and the increase of pulse energy is theoretically deduced and analyzed first, then the measured polarization spectra are compared with the microscopic imaging method to extract the edge texture information, and further the damage details are characterized with this metrology under the typical polarization parameters: I, Q, U, V, DOP and AOP. As a result, the damaging degree of ceramic composite irradiated by the 1064nm nanosecond pulsed laser, which is changed from the pulse power of 155.54 mJ and 14 pulses to 217.94 mJ and 1 pulse, can be identified with a series of polarization parameters in the different polarization spectrum images. These polarization parameters and their derived results reflect the physical and chemical evolutive properties including of texture orientation of the target surface that is different from other methods of damage detection. Finally, it can be concluded that this paper provides a new method for real-time detection of laser damage and lays a foundation for detection and identification under other strong light interference.

This paper describes the optical design of the High Resolution Imaging Channel (HRIC), which is part of the spectrometers and imagers for the Mercury Planetary Orbiter BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) suite, for imaging and spectroscopic investigation of Mercury. The optical design has been optimized to achieve the stringent scientific requirement of 5 m ground sampling at 400 km from the planet's surface in the harsh Mercury environment.

International audience; There has been a marked revival of interest in brillouin light scattering spectroscopy/microscopy over the last decade in regards to applications related to all optically studying the mechanical problems associated with systems of biological and medical interest. This revival has been driven by advancements in spectrometer design, together with mounting evidence of the critical role that mechanical properties can play in biological processes as well as the onset of diverse diseases. This feature issue contains a series of papers spanning some of the latest developments in the field of Brillouin light scattering spectroscopy and microscopy as applied to systems of biomedical interest.

The use of fluorescence in microscopy is a well-known technology. Due to autofluorescence in the materials of optical components, the contrast of the image is degraded. The calculation of autofluorescence is usually performed by brute-force methods such as the Monte Carlo-based volume scattering. The efficiency of calculations in this case is extremely low, and a huge number of rays must be calculated. In stray light calculations, the concept of important sampling is used to reduce computational effort. The idea is to calculate only rays, which have the chance to reach the target surface. The fluorescence conversion can be considered to be a scatter process, and therefore a modification of this idea is used here. The reduction factor is calculated by comparing the size of the illuminated phase space domain with the corresponding acceptance domain in every z plane of the lenses. The boundaries of the domains are determined by tracing the limiting rays of the light cone of the source as well as the pixel area under consideration. The small overlap of both domains can be estimated by geometrical considerations. The correct photometric scaling and the discretization of the volumes must be performed. The errors resulting from necessary approximations can be corrected without greatly increasing computational effort. The run time is reduced by a factor of 10 4 . It is shown with some practical examples of microscope lenses that the results are comparable with conventional methods. Additionally, a quasi-analytical model that describes the dependence of autofluorescence on various lens parameters is derived.

The bulkiness of common transmission spectroscopy probes prevents applicability at remote locations such as within the body. We present the fabrication and characterization of lensed fibers for transmission spectroscopy in the near-infrared. Eigenmode simulations and measurements of the coupling efficiency are presented and applied to design the setup corresponding to the sample absorption. Sensing capabilities are demonstrated on aqueous glucose samples ranged 80 to 500 mM, obtaining a mean absolute percentage error of calibration of 4.3%. With increased flexibility, transmission spectroscopic sensors at remote locations may be achievable, for example, applied to in vivo continuous glucose monitoring.

This study aims to demonstrate the effectiveness of sets of microlens arrays to homogenize and finely shape focal spots, for optimizing optical pumps of interest for Yb-doped slabs in the field of high-power lasers, or for use in materials processing and industrial applications. Homogenization basically involves optical integration in the Fourier plane of a large focusing lens, the input light source being consistently sampled. The generic capabilities of three complementary optical designs are demonstrated thanks to combining transfer-matrix computations with highly resolved ray-tracing modeling. This helps to benchmark a variety of experimental results. Fully generic trends are evidenced in terms of the shaping capabilities, for highly efficient focusing, in the form either of a single spot or of multiple sub-spots. Peak power densities as elevated as some hundreds of kW/cm2 or a few MW/cm2, respectively, may be produced by a couple of multi-kilowatt diode stacks.

Waveguide or lightguide technology has been widely used in the state-of-the-art, see-through, near-eye displays to reduce system weight and form factor. Although a few of the current products use a geometrical lightguide as an optical combiner, its design and performance assessment methods have been barely discussed. In this paper, by taking into account the factors affecting retinal image quality, we presented novel methods for quantifying and evaluating the optical performances and artifacts of geometrical lightguides based on microstructure mirror arrays, and proposed new merit functions and a novel process for systematic optimization of such lightguides. A lightguide design example implementing the evaluation and optimization methods are demonstrated, and the resulted lightguide is then further utilized as a combiner for the design of a lightweight, glasses-like, see-through, near-eye display.

A novel white compound material with spectral band pass filtering was proposed and demonstrated in the UV region for wavelengths smaller than 310 nm. This compound material can be obtained by dispersing CaF2 in polydimethylsiloxane (PDMS). Refractive index matching (RIM) of the compound material resulted in transmittance of up to 80% at RIM wavelength. In no-RIM wavelength region, refractive index difference about 0.005 could result in transmittance of down to 30% due to intense Rayleigh isotropic scattering. A good reproducibility of the transparent wavelength can be obtained with the specific CaF2 particle and PDMS matrix in this study. Meanwhile, simple calculation based on Rayleigh-Gans-Debye approximation [J. Am. Ceram. Soc.86(3), 480 (2003)] in the soft diffusion model can explain the CaF2: PDMS compound film transmittance spectrum in the UV region, and the bandwidth narrowing condition.

The structured-light vision sensor calibration approach based on planar target fails to generate reliable and accurate results due to the inaccurate localization of feature points in outdoor complex lighting environments. To address this issue, a novel high-accuracy calibration method that corrects image deviation is proposed for line-structured light vision sensor in this paper. The mathematical solution for stripe point location uncertainty is put forward and the location uncertainty of target feature points and stripe points is established. Moreover, the location deviation of all points is computed through large-scale nonlinear multi-step optimization based on the constraints of uncertainty. After compensation, the planar target based calibration method is adopted to solve the light plane equation. Both simulative and physical experiments have carried out to evaluate the performance of the proposed method and the results show that the proposed method is robust under large feature points localization deviation and can achieve the same measurement accuracy as the planar target calibration method under ideal imaging conditions, which reduces the requirements of the calibration environment, and has important practical engineering application value.

It is challenging to calibrate multiple camera-projector pairs for multi-view 3D surface reconstruction based on structured light. Here, we present a new automated calibration method for high-speed multi-camera-projector systems. The method uses printed and projected dot patterns on a planar calibration target, which is moved by hand in the calibration volume. Calibration is enabled by automated image processing and bundle-adjusted parameter optimization. We determined the performance of our method by 3D reconstructing a sphere. The accuracy is -0.03 ± 0.09 % as a percentage of the diameter of the calibration volume. Applications include quality control, autonomous systems, engineering measurements, and motion capture, such as the preliminary 3D reconstruction of a bird in flight we present here.

The star tracker plays a critical role in precision aerospace missions due to its high accuracy, absolute attitude output, and low power consumption. For an optical sensor, the problem of stray light is always an important research issue. A star energy information mining method for stray light suppression is proposed in this study. The gray-level co-occurrence matrix and k-nearest neighbor algorithm are adopted to identify the types of stray light that enter the optical system. Effective recognition of the stray light types is an important premise for the following steps. Then the parameters are optimized during background estimation. When star spots are extracted, the local differential encoding combined with Levenshtein distance filtering is conducted to eliminate the interference noise spots. The proposed algorithm can achieve accurate star spot extraction even when stray light exists in real night sky observation experiments.

Stray light is one of the factors exerting negative influences on the image quality of the head-up display based on the geometrical waveguide. Particularly, compared with the architecture used to expand a one-dimensional pupil, the geometrical waveguide expanding the two-dimensional pupil makes it difficult to remove the stray light due to the combined effect from two orthogonal directions. To overcome it, causes of stray light in the two-dimensional geometrical waveguide are analyzed based on the detailed calculation of the parameters that determine the geometry; the corresponding approach is put forward to decrease the percentage of the stray light across the eye box to below 0.1%. The relationship between the resultant combined waveguide and the projection optics is also clarified to obtain the pupil matching. The head-up display integrating the combined waveguide and the designed projection optics achieves the field of 24°×15° and the eye box of 80 mm×80 mm.

Artificially structured metallic meshes have been widely used in optical transparent devices for electromagnetic interference (EMI) shielding. Traditional meshes have drawbacks such as poor imaging quality from the centralized diffraction distribution and the inferior EMI shielding efficiency. Here, we propose a petal-shaped metallic mesh with anomalistic closed-loop pattern that can effectively improve the EMI shielding efficiency by reducing the equivalent period of the mesh and, meanwhile, suppress the stray light and achieve uniform optical diffraction. By experimentally testing the EMI shielding and diffraction performance of such mesh samples, a Ku-band shielding efficiency (SE) larger than 24 dB with the maximum SE of 32.1 dB at 12.2 GHz is obtained, which is 8 dB higher than that of the classical square mesh, and an optical transmittance as high as 73.4% is achieved at the visible wavelength of 632.8 nm. Petal-shaped metallic mesh with such excellent performance may play important roles in various applications of optical transparent windows.

Laboratory calibration is critical to ensure the precise attitude determination of star sensors. Existing laboratory star sensor calibration methods exhibit disadvantages for large-field-of-view star sensors and large amounts of calibration data. Inspired by the least-squares method and Li's method, a global refining method is proposed to overcome the inherent disadvantages by simultaneously obtaining all of the star sensor's parameters. It first employs the maximum likelihood estimation method to optimize the initial estimation of the principal point and focal length. Next, a linear least-squares solution is used to initially estimate the star sensor distortion. Taking the installation error into account, we conduct a maximum likelihood estimation to estimate the installation angles from the estimated parameters of the first two steps. Finally, we determine a globally optimal solution to refine the star sensor parameters. Compared with the traditional method and Li's method under the same conditions, both the simulation and real data results demonstrate that the proposed method is more robust and can achieve high precision. In addition, the experimental results show that the calibration method can satisfy the precision requirements for large-field-of-view star sensors.

In order to improve the measurement efficiency and measurement accuracy of corneal curvature, a high precision corneal curvature radius measurement system was designed. Based on the principle of film reflection imaging, the measurement light source (concentric circle with light-emitting diode lights) is projected onto the cornea of the human eye, and the human eye cornea with the measurement light source marker is imaged on the photodetector by an optical imaging objective lens and processed by the image processing. The height of the measurement light source on the photodetector to the center of the cornea is calculated. Finally, the method of least squares is used to find the corneal curvature radius. The system uses a double telecentric lens for the optical imaging objective lens to ensure that the optical system has a constant magnification in a certain depth of field. At the same time, low coherence interferometry technology is used to accurately measure the distance between the corneal apex and the measuring light source. The standard corneal simulated eye was tested with the designed prototype. The measurement accuracy was ±0.02 mm. The experimental results show that the high accuracy corneal curvature radius measurement system can effectively improve the accuracy of corneal curvature measurement.

We demonstrate a simple, controllable, and stable method for fabricating high fill factor cylindrical microlens array with a novel isolated thermal reflow process. In this method, microstripes with a very small gap were obtained via digital micromirror device-based lithography, then covered with polydimethylsiloxane (PDMS) solution. The prepared microstripes were isolated and were heated and reflowed to a cylindrical microlens array. During the reflow process, the semicross-linked PDMS can serve as a barrier to prevent the diameter change and the bonding of adjacent microlenses. By this special treatment, the fill factor of the cylindrical microlens array can be significantly improved. Moreover, the reflow time and temperature have very little effect on the microlens shape due to the surrounded semicross-linked PDMS. This will make our process stabler than traditional methods. The measured 3D profile is good and satisfactory, and excellent optical performance is demonstrated with the fabricated cylindrical microlens arrays. The proposed method may offer a viable route for fabrication of high fill factor microlens arrays in a very simple and stable way.

A miniaturized portable short-wave infrared imaging spectroscopy optical system is designed based on a prism-grating dispersion module. We established a prism-grating model to calculate the optimal combination of prism and grating parameters to balance spectral smile over the entire band. The design method for the telescopic system and spectroscopic system combines independent design with integrated optimization. The system's spectral smile and spectral keystone are less than 15 μm and less than half a pixel, respectively. The total optical system length is 230 mm, which meets the miniaturization requirements for airborne systems. The system's spatial resolution is 1 mrad, and its average spectral resolution is 6.2 nm. The system offers the advantages of large relative aperture, excellent imaging quality, reduced spectral smile, and spectral keystone, miniaturization, and portability.

Conventional cameras obscure the scene that is being recorded. Here, we place an image sensor (with no lens) on the edge of a transparent window and form images of the object seen through that window. This is enabled first, by the collection of scattered light by the image sensor, and second, by the solution of an inverse problem that represents the light scattering process. Thereby, we were able to form simple images, and demonstrate a spatial resolution of about 0.1 line-pairs/mm at an object distance of 150mm with depth-of-focus of at least 10mm. We further show imaging of two types of objects: an LED array and a conventional LCD screen. Finally, we also demonstrate color and video imaging.

The liquid crystal spatial light modulator (SLM) is an effective active beam-shaping device through adjusting each pixel transmittance to improve the spatial beam quality of the output laser, which can also be used as a binary optical element (BOE) with each pixel transmittance 0 or 1 to realize spatial beam shaping for high-power lasers. We present and demonstrate an efficient shaping method of the SLM used as BOE based on diffraction principle. The method can be used to control the output nearfield actively by compensating the spatial nonuniformity of transmission and amplification in the high-power laser system. Results show the output nearfield beam quality improves significantly after shaping by using this method with the fluence contrast changing from 22% to 11.3% within only two shots in the single-shot operation laser.

Measuring the deformation of building elements engulfed by flames is essential in fire research to improve safety in the event of a fire. Ideally, the measurement system should be non-contact, able to range at the millimeter to meter scale with sub-mm precision, and have sufficient speed to capture temperature-induced deformations of the target object. To date, no ranging technology has been demonstrated that meets those requirements while imaging through flames. Here, we show that coherent laser detection and ranging (LADAR) can provide three-dimensional images of objects hidden behind methane or acetylene flames with sufficiently high precision to track their deformation. The heterodyne detection of coherent frequency-modulated continuous-wave (FMCW) LADAR allows the ranging signal to be detected in the presence of strong radiation of the flames. We measure three-dimensional point clouds of diffusely scattering complex surfaces with a precision of less than 30 μm at 2-meter stand-off distance, despite soot-induced signal loss and steering (refraction) of the ranging laser by the flames. Movies of the heat-induced surface deformation of objects illustrate the temporal performance. These data show that FMCW LADAR can quantify the deformation and movement of objects in fires, when non-contact shape measurements at stand-off distances of multiple meters are crucial.

Single-angle infrared (IR) reflectance spectroscopy is a proven and effective method for determining the complex optical constants n and k of condensed matter. The modern method uses a Fourier transform IR spectrometer to record the quantitative reflectance R(ν) spectra followed by application of the Kramers–Kronig transform (KKT) to obtain the complex optical constants. In order to carry out the KKT, it is essential to measure the reflectance spectra to as high and low a frequency (wavenumber) as possible. Traditionally, the reflectance spectra of solid specimens consist of large (typically>10 mm diameter) polished single-crystal faces free of defects or voids. The requirement of a large polished face, however, is not a realistic expectation for many synthetic, geologic, or rare specimens where the size is usually small and the morphology can vary. In this paper we discuss several improvements and considerations to both the hardware and far-IR measurement protocols that lead to more accurate R(ν) values and thus to more accurate n/k values, especially for small (millimeter-sized) specimens where the R(ν) spectrum is concatenated from multiple independent R(ν) spectra from overlapping hardware/spectral domains. Specifically, the improved hardware and analyses introduced here include the following: (1) providing a set of far-IR calibration standards; (2) custom-designing and manufacturing low reflectivity, stray-light reducing sample masks for small specimens; (3) minimizing stray light interaction between the sample mask, the interferometer Jacquinot stop, and the detector; (4) optimizing the methods to “splice” together the spectra from independent domains; (5) discussing what methods one can use to obtain or calculate the important R(0 cm−1) value; (6) using a quartic relationship to extrapolate from the measured R data to R(0); and (7) accounting for the limiting effects of diffraction for the spot size at the sample mask and detector for millimeter-sized specimens, especially at the very long wavelengths. These seven considerations are all highly interconnected and are discussed in turn, as well as their strong interdependencies. This paper presents a holistic approach for determining reliable n/k values of millimeter-sized samples using single-angle reflectance in the mid- and far-IR.

Doppler optical coherence tomography (OCT) quantifies axial motion with high precision, whereas lateral motion cannot be detected by a mere evaluation of phase changes. This problem was solved by the introduction of three-beam Doppler OCT, which, however, entails a high experimental effort. Here, we present the numerical analogue to this experimental approach. Phase-stable complex-valued OCT datasets, recorded with full-field swept-source OCT, are filtered in the Fourier domain to limit imaging to different computational subapertures. These are used to calculate all three components of the motion vector with interferometric precision. As known from conventional Doppler OCT for axial motion only, the achievable accuracy exceeds the actual imaging resolution by orders of magnitude in all three dimensions. The feasibility of this method is first demonstrated by quantifying micro-rotation of a scattering sample. Subsequently, a potential application is explored by recording the 3D motion vector field of tissue during laser photocoagulation in ex-vivo porcine retina.

The current paper reports on the application of the Q-Spectrum for the characterization of mid-spatial frequencies on polished surfaces (plane, spherical, and aspheres). The Q-Spectrum based on the Forbes Qmn polynomials for freeforms allows, when taken to large radial and azimuthal orders, a robust and accurate representation of mid-spatial surface spectral footprints that otherwise cannot be faithfully identified with other methods. Evaluation of experimental data with the Q-Spectrum as well as a comparison with other methods is shown.

The hyperspectral data and 3D structural data are highly useful in botanical research. But, the two types of information are often acquired separately and hard to be combined. In this work, a novel dual-path configuration based on acousto-optical tunable filter (AOTF) is proposed to acquire an image, structural and hyperspectral information within one acquisition process by a combination of laser triangulation. Under the configuration, the hyperspectral data and the 3D structure can be matched to subpixel level after geometrical calibration. Finally, the obtainment of 3D hyperspectral information in field experiment verifies the feasibility of this imaging system.

We present a new experimental technique for measurement of the refractive index of a photonic crystal fiber (PCF) fundamental mode. We demonstrate that the phase refractive index of the PCF mode can be estimated by analyzing a phase shift of interfering adjacent longitudinal laser modes of a continuous-wave laser corresponding to a shift from constructive to destructive interference. The experimental results are in very good agreement with numerically simulated phase refractive index values.

Compact and lightweight laser absorption spectrometers for accurate trace gas measurements are of great scientific and commercial importance. In these instruments, the multipass cell (MPC) represents a critical element in terms of achievable size and sensitivity. Herein, we introduce a versatile MPC concept which unifies compactness, mechanical rigidity, and optical stability. Relying on fundamental cavity design principles and modern diamond turning techniques, we have developed a segmented circular MPC that allows efficient and interference-free beam folding. A prototype cell is presented featuring up to 10 m optical path length at a total mass of less than 200 g. Incorporated in a highly compact setup without additional beam pre-shaping optics, we demonstrate a normalized noise level of low 10−4 (2σ) at 1 Hz.

Recently, an optical waveguide display device that has light weight, high transparency, and full color has become more and more popular in the wearable augmented reality display application. But existing waveguide display devices are less than satisfactory because of cost, safety, and mass production. Therefore, a type of surface-relief optical waveguide display device is proposed in this paper. First, the geometrical relationship of a waveguide display device structure is confirmed according to the design method of the optical waveguide display device. Then, the influence of the waveguide structure for the image quality is analyzed, and the rationality of the surface-relief waveguide scheme is verified by simulation. Finally, the prototype of the surface-relief optical waveguide display device with polycarbonate materials, field of view of 38°, thickness of 4.5 mm, and transmittance of about 80% is fabricated and demonstrated.

LIGO and Virgo have opened up a new window into the local universe. But the global gravitational-wave community isn’t stopping there.

A wide-field, large-aperture, and lightweight Schmidt configuration has been studied for a space mission proposal named Extreme Universe Space Observatory free flyer (EUSO-FF). EUSO-FF will be devoted to the study of ultrahigh energy cosmic rays, i.e., with energy >5×1019 eV, through the detection of UV fluorescence light emitted by air showers in the Earth’s atmosphere. The proposed telescope has a field of view of about 50° and an entrance pupil diameter of 4.2 m. The mirror is deployable and segmented to fit the diameter of the launcher fairing; the corrector is a lightweight annular corona.

To solve the problem where the actual grating aperture decreases with an increasing scanning angle during the scanning of a three-grating monochromator, we propose an off-axis assembly method for the worm gear turntable that makes it possible to suppress this aperture reduction. We simulated and compared the traditional assembly method with the off-axis assembly method in the three-grating monochromator. Results show that the actual grating aperture can be improved by the off-axis assembly method. In fact, for any one of the three gratings, when the monochromator outputs the longest wavelength in the corresponding wavelength band, the actual grating aperture increases by 45.93%. Over the entire monochromator output band, the actual grating aperture increased by an average of 32.56% and can thus improve the monochromator's output energy. Improvement of the actual grating aperture can also reduce the stray light intensity in the monochromator and improve its output signal-to-noise ratio.