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The lateral displacement between the microlens arrays can realize the rapid deflection of a beam; however, in this process, crosstalk beams will inevitably occur between the microlens units, which will affect the imaging quality of the system. For this reason, we propose a crosstalk elimination design method based on the combination of multilayer stop arrays, establish a simulation model, use a geometric optical object image relationship to trace the characteristic light of a single group of microlenses, analyze the relationship between the structural parameters of the microlens array and the stop array size, and comprehensively discuss the light transmission of the microlens array under various conditions. An example of an infrared system is simulated using the optical design analysis software Fred, verifying the effectiveness of this design method in suppressing the crosstalk beams generated in the dynamic transmission process, ensuring independent propagation between microlens units, and realizing crosstalk-free imaging.

Recently, we developed a simple theoretical model for the estimation of the irradiance distribution at the focal plane of commercial off-the-shelf (COTS) camera lenses in case of laser illumination. The purpose of such a model is to predict the incapacitation of imaging sensors when irradiated by laser light. The model is based on closed-form equations that comprise mainly standard parameters of the laser dazzle scenario and those of the main devices involved (laser source, camera lens and imaging sensor). However, the model also includes three non-standard parameters, which describe the scattering of light within the camera lens. In previous work, we have performed measurements to derive these typically unknown scatter parameters for a collection of camera lenses of the Double-Gauss type. In this publication, we compare calculations based on our theoretical model and the measured scatter parameters with the outcome of stray light simulations performed with the optical design software FRED in order to validate the reliability of our theoretical model and of the derived scatter parameters.

Stray light, such as sunlight, moonlight, and earth-atmosphere light, can bring about light spots in backgrounds, and it affects the star detection of star sensors. To overcome this problem, this paper proposes a star detection algorithm (CMLCM) with multidirectional local contrast based on curvature. It regards the star image as a spatial surface and analyzes the difference in the curvature between the star and the background. It uses a facet model to represent the curvature and calculate the second-order derivatives in four directions. According to the characteristic of the star and the complex background, it enhances the target and suppresses the complex background by a new calculation method of a local contrast map. Finally, it divides the local contrast map into multiple 256 × 256 sub-regions for a more effective threshold segmentation. The experimental results indicated that the CMLCM algorithm could effectively detect a large number of accurate stars under stray light interference, and the detection rate was higher than other compared algorithms with a lower false alarm rate.

The phase induced intensity noise (PIIN) may seriously reduce the signal-to-noise ratio (SNR) of continuous-wave coherent Doppler lidar (CW-CDL), thereby limiting its performance in practical applications. In this paper, we propose to use optical frequency domain reflectometry (OFDR) technique to locate the PIIN sources and evaluate their intensities. According to the OFDR information, we demonstrate that the PIIN in our CW-CDL system is mainly induced by the crosstalk of polarization beam splitter. Then, the PIIN is reduced by setting fiber delay line, polarization control, and AR-coating. Finally, a wind Doppler signal at a distance of 80 meters is obtained on a clear day, and a typical SNR of 19.4 dB is achieved.

Waveguide technology has great prospects of development in optical see-through near-eye displays with larger field of view, lower thickness and lighter weight than other conventional optical technologies. However, the stray light is usually inevitable in current optical design and manufacturing, causing a poor imaging quality. In this paper, the principle and structures of stray light generation are analyzed, and the causes are discussed by non-sequential ray-tracing with mass precision calculation. From the ray-tracing, the suppression of stray light by optimizing design and manufacturing are achieved. A 2 mm-thickness geometrical waveguide with partially reflective mirror array is designed. The field of view of the optimized geometrical waveguide reaches 47° with 10 mm at exit pupil diameter and 20 mm at eye relief.

The laser four-quadrant detection system is an important part of laser guided weapons. The accurate evaluation of its performance in the design stage is conducive to the iteration and optimization of the design scheme. The simulation model of the four-quadrant detection system was established based on LitghtTools. Through the establishment of target model, optical system model and four-quadrant detector model, the system could be effectively simulated. Combined with principle of four-quadrant detection system, the sum-difference amplitude of angle deviation could be obtained; the stray light of the system could also be simulated to evaluate the impact of stray light on system; in addition, it could also simulate the laser speckle effect and analyze the influence of speckle characteristics on the sum-difference amplitude. Therefore, the modeling and simulation based on LitghtTools provided an accurate basis for design optimization. Finally, the simulation model was verified by experiments. The sum-difference amplitude of the simulation is basically the same as that of the experiment in the range of ± 15°.

Aiming at the problem that diffraction effect of digital micro-mirror device (DMD) has serious influence on system imaging, the stray light generated by DMD device was studied. Firstly, based on the rigorous coupled wave theory, the DMD diffraction model was constructed and the effects of different bands and incident angles on its diffraction efficiency were analyzed. It was concluded that the diffraction effect of DMD was more obvious in the long-wave infrared band, and the diffraction effect of DMD was more significant with the increase of incident angle. Secondly, the generation methods of diffracted stray light of DMD in the projection system was analyzed. By changing the number of F in the system, the incident angle was controlled, and then the energy proportion of stray light generated by the diffraction effect of DMD was calculated. Finally, the curve of the optical system with different number of F at different wavelengths along with the diffraction effect was obtained. The results show that the larger the F number, the smaller the influence of DMD diffraction effect on stray light.

We introduce a new approach to reduce uncorrelated background signals from fluorescence imaging data, using real-time subtraction of background light. This approach takes advantage of the short fluorescence lifetime of most popular fluorescent activity reporters, and the low duty-cycle of ultrafast lasers. By synchronizing excitation and recording, laser-induced multiphoton fluorescence can be discriminated from background light levels with each laser pulse. We demonstrate the ability of our method to – in real-time – remove image artifacts that in a conventional imaging setup lead to clipping of the signal. In other words, our method enables imaging under conditions that in a conventional setup would yield corrupted data from which no accurate information can be extracted. This is advantageous in experimental setups requiring additional light sources for applications such as optogenetic stimulation.

In this article, we design and demonstrate new angled multimode interference (MMI) couplers in silicon-on-insulator that allow arbitrary selection of coupling ratios, while simultaneously achieve low-chromaticity response and improved fabrication variations tolerance. The proposed couplers rely on paired-interference design approach in tandem with a new angled multi-mode junction to mitigate chromatic aberration and geometry-induced waveguide modal shift in conventional angled MMI coupler design. Test devices with footprint of 4.8 μ m × 75 μ m showed full coupling ratio range addressability with insertion loss below 1.2 dB. Spectral responses across the extended C band (1525 nm – 1575 nm) were also characterized, where coupling ratio varied by less than 2.3% across the spectral region of interest. Furthermore, coupler characteristics variations against line-width and thickness deviations are numerically analyzed, demonstrating robustness within typical fabrication tolerances.

Traditionally, there is a trade-off between the numerical aperture and field of view for a microscope objective. Diffractive lens arrays (DLAs) with overlapping apertures are used to overcome such a problem. A spot array with an NA up to 0.83 and a pitch of 75 µm is produced by the proposed DLA at a wavelength of 488 nm. By measurement of the fluorescence beads, the DLA-based confocal setup shows the capability of high-resolution measurement over an area of 3 m m × 3 m m with a 2.5 × 0.07 N A objective. Further, the proposed fluorescence microscope is insensitive to optical aberrations, which has been demonstrated by imaging with a simple doublet lens.

A freeform pushbroom hyperspectral imager design was investigated as a combination of a freeform reflective triplet imager and a freeform reflective triplet spectrometer used in double-pass. The design operates at about F/2 with a 15-degree cross-track field-of-view and a 30 mm entrance pupil diameter. The design process led to achieving a small volume of less than 2 liters that fits comfortably within a 3U CubeSat geometry, exemplifying the compactness of this hyperspectral imager. We report the freeform sag departures and maximum slopes of the freeform surfaces, as well as the manufacturing tolerances together with an evaluation of the system stray light, all of which highlight the feasibility of a design in this class to be manufactured. This design uniquely positions itself on the landscape of compact hyperspectral imagers.

An advanced Dyson imaging spectrometer in the near ultraviolet-visible-near infrared region was designed, fabricated, and evaluated. A lens with reflective coating on the back surface is applying to replace the traditional lens-reflecting grating combination. The design concept and fabrication and alignment methods as well as the results of evaluations of the proposed spectrometer are described in detail. The advanced imaging spectrometer achieves high resolution in both spectral and spatial direction and low stray light at a high numerical aperture in the working waveband. The performance of this modified porotype is analyzed and evaluated. Results show the spectrometer is well suited for the remote sensing of the ocean color as well as for various agriculture and vegetation-related applications.

In this study, a low-noise Fabry–Perot interference-based method is promoted to measure the longitudinal uniformity of the distance between six pairs of opposite silica–air interfaces within the core of a seven-cell hollow-core photonic bandgap fiber. The experimental results demonstrate that the precision of the method is improved to the subnanometer scale. Based on the test results, a model is established to study the effect of the longitudinal uniformity of the core structure on the fiber loss, and the simulation results indicate that the fiber loss could reach ∼22.73 dB/km, which is consistent with the practical loss value.

A 300 mm×500 mm large-area echelle grating with groove density of 79 grooves/mm is fabricated for the spectrometer of the fiber array solar optical telescope (FASOT). This paper focusses on measurement methods of the grating performance. We present a method to evaluate the grating’s stray light intensity, which is measured to a level of 10−4. The directly measured grating efficiency is approximately 90% of the designed value, and an indirect measurement method based on the grating groove profile is proposed. Based on the Rayleigh criterion and the grating diffraction wavefront, a physical optics method and a geometric grating method are proposed and are used to calculate the actual grating resolving power; the calculated results exceed 95% of the grating’s theoretical resolving power. These results show that the CIOMP-6 ruling engine has sufficient precision to fabricate high-quality, large-area echelle gratings.

The interferometric signals produced in conventional dual-comb laser ranging require femtosecond lasers with long-term f_CEO stability, and are limited to an upper sampling rate by radio-frequency aliasing considerations. By using cross-polarized dual combs and two-photon detection we demonstrate carrier-phase-insensitive cross-correlations at sampling rates of up to 12x the conventional dual-comb aliasing limit, recording these in a digitizer-based acquisition system to implement ranging with sub-100-nm precision. We then extend this concept to show how the high data burden of conventional dual-comb acquisition can be eliminated by using a simple microcontroller as a ns-precision stopwatch to record the time intervals separating the two-photon cross-correlation pulses, providing real-time and continuous LiDAR-like distance metrology capable of sub-100 nm precision and dynamic acquisition for unlimited periods., Comment: 9 pages, 6 figures

A new, to the best of our knowledge, multi-purpose spectral-polarizing beam splitter (SPBS) design is described that simultaneously isolates multiple identical reflected and transmitted polarized passbands to permit passive simultaneous polarimetry in a common instantaneous field of view (FOV). The SPBS design can be implemented in wavelength regions between ∼ 260 n m and ∼ 1700 n m and consists of fewer than 30 layers. Degree of linear polarization values are ∼ 0.99 . FOV area coverage in a swath as wide as 6° is accomplished by object space scanning. A polarization calibrator/stability monitor source is integrated with the optical system. Estimated system polarimetric error is < 2 % . Applications range from biomedical instrumentation to remote sensing.

Quantum-illumination-inspired single-pixel imaging (QII-SPI) or computational ghost imaging protocol is proposed to improve image quality in the presence of strong background and stray light. According to the reversibility of the optical path, a digital micro-mirror device acts as a structured light modulator and a spatial light filter simultaneously, which can effectively eliminate 50% of stray light. Accompanied by a 6 dB gain of detection signal-to-noise ratio under an equivalent loss condition, our scheme only requires a simple and minor modification on the placement of the single-pixel detector based on the original SPI system. Since QII-SPI will obtain almost the same reconstruction results as the passive SPI technology in principle, one can, therefore, adjust the placement position of the detector, without exchanging the relative position of the detector and the light source to realize the flexible conversion of the SPI system from active to passive. Also, this work initially discusses the influence of relative coherence time on Hadamard-based SPI driven by a thermal source. This work brings new insights into the optical path design of the SPI technology, paving the way for the practical application of active SPI in stray light environments.

We investigate the three-beam conjugate enhanced micro-vibration detection system. We introduce a conjugate light to the classical dual-beam heterodyne laser vibrometer to generate the three-beam interference. Detection of the micro-vibration signal is then enhanced by matching the power and phase of conjugate light and measured light. We also present the basic principle of three-beam conjugate enhanced micro-vibration detection and the conjugate enhancement conditions. Moreover, the expressions of micro-vibration signal amplitude amplification and resolution enhancement are derived and compared with the demodulation amplitude and limited resolution of classical dual-beam laser vibrometer. Experiments and numerical results further verify the amplitude amplification and resolution enhancement of the three-beam conjugate enhanced micro-vibration system. The archived results indicate that this system is especially suitable for the high-resolution detection of weak vibration targets, e.g., micro-nano structures.

A fabrication method for large-area gratings with uniform duty without using a spatial beam modulator is introduced in this study. The inhomogeneity of gratings caused by flaws of the lens and stray light was solved by controlling exposure time within an appropriate range and selecting a suitable beam expansion aperture in the optical path. A model for representing this process was established by analyzing the effects of exposure and development time length, and experimental results exhibited good agreement with the simulation results. Finally, a grating with a period of 550 nm, a uniform duty cycle, and a diameter larger than 30 mm was achieved using a Mach–Zehnder interferometer optical path without a spatial beam modulator. The uniformity of this grating was observed via atomic force microscopy, and the results were highly desirable.

In terms of the shortcomings of defect detection based on the electroluminescence of conventional silicon solar panels, which can only be performed under darkroom conditions, a defect detection system that can work under the Sun with any irradiance in all weather is designed. The system electrifies solar panels through a modulated current source, uses high frame rate InGaAs area array detectors for image data acquisition, and transmits images via CameraLink. Using these image data as data sources, a defect display algorithm model is designed. Through experiments, it can effectively collect the defect information of solar panels within the range of 0.2 to 1300 W / m 2 of sunlight irradiance. Based on this, according to the relationship of the modulated phase difference between the defective points and the nondefective points found in the experiment, an enhancing algorithm for image saliency is proposed. The results show that this algorithm can reduce background interference in an effective way and improve the contrast of defects displayed under high irradiance.

A wide-field imaging spectrometer based on a grating prism is proposed. The grating and prism parameters are discussed to balance spectral distortion over the entire band. The design method of the grating-prism (GP) dispersive module and the catadioptric optics of the spectrometer are discussed in detail. A high optical speed (F/2.4) and long slit (29.4 mm) visible and near-infrared design with high image quality and small distortion is presented. The results show that the optical performance of the GP imaging spectrometer is excellent. The tolerance analysis indicates that the GP spectrometer can be easily manufactured and implemented. The prototype has been tested in the laboratory and outdoors, and the results confirmed that the design will be useful in the fields of aeronautics and astronautics.

In their September 2020 paper [Appl. Opt. 59, 7585 (2020)APOPAI0003-693510.1364/AO.401602], Purschke et al. report UV-C transmittance measurements of N95 filtering facepiece respirators (FFRs), including the 3M 1860, which is one of the most widely used FFRs. We have also measured the transmittance of this FFR in our two separate laboratories with multiple FFR samples, and we have obtained transmittance values similar to one another, but very different from what Purschke et al. reported for two of the four FFR layers.

In low-Earth orbit, the already existing population of small and medium debris (between 1 cm and several dozens of cm) is a concrete threat to operational satellites. A space-based laser space debris removal (SLDR) system that can remove hazardous debris around selected space assets appears to be a flexible and effective project. To achieve high-precision tracking and emitting, the optical system of the SLDR mission includes a target-detection telescope and emitting telescope, adopting a common light path structure. The optical design results, system performance, tolerance budget, and detailed stray light control design are presented in this paper. The large-aperture off-axis two-mirror beam-narrowing system characteristics are also discussed in terms of stray light control. This paper will present the lateral-displacement (LD) setting, two-stage fore baffle design, black baffle surface selection, and opening direction of the telescope door. The results showed that the stray light elimination reaches a 10 − 9 order, meeting design requirements.

Radio absorptive materials (RAMs) are key elements for receivers in the millimeter-wave range. For astronomical applications, cryogenic receivers are widely used to achieve a high-sensitivity. These cryogenic receivers, in particular the receivers for the cosmic microwave background, require that the RAM has low surface reflectance ($\lesssim 1\%$) in a wide frequency range (20--300 GHz) to minimize the undesired stray light to detectors. We develop a RAM that satisfies this requirement based on a production technology using a 3D-printed mold (named as RAM-3pm). This method allows us to shape periodic surface structures to achieve a low reflectance. A wide range of choices for the absorptive materials is an advantage. We survey the best material for the RAM-3pm. We measure the index of refraction ($n$) and the extinction coefficient ($\kappa$) at liquid nitrogen temperature as well as at room temperature of 17 materials. We also measure the reflectance at the room temperature for the selected materials. The mixture of an epoxy adhesive (STYCAST-2850FT) and a carbon fiber (K223HE) achieves the best performance. We estimate the optical performance at the liquid nitrogen temperature by a simulation based on the measured $n$ and $\kappa$. The RAM-3pm made with this material satisfies the requirement except at the lower edge of the frequency range ($\sim$20 GHz). We also estimate the reflectance of a larger pyramidal structure on the surface. We find a design to satisfy our requirement., Comment: 8 pages, 10 figures

14 pags., 8 figs., 2 tabs., The bidirectional scattering-surface reflectance distribution function (BSSRDF) is the function that describes the variation of the radiance of the elementary areas of a surface with respect to the directionally incident radiant flux on that surface. Measurements of the BSSRDF are important for characterizing the translucency of objects and for obtaining those optical parameters affecting volume scattering. However, to date, no traceable measurements of this function are available, since, likely due to its technical complexity, no standard measurement procedure has been established. We have developed a primary facility for measuring the BSSRDF based on a gonio-spectrophotometer with spatial resolution in the collection, spectral resolution in the irradiation, and angular resolution both for irradiation and collection directions. The BSSRDF of twelve homogeneous and translucent samples (with controlled values for the mean diameter of the scattering particles and their concentration) have been measured with relative uncertainties below 3% inside the irradiated area. Some results are shown and commented. This primary facility will allow the BSSRDF scale to be transferred to other instruments., Comunidad de Madrid (S2018/NMT-4326-SINFOTON2-C); European Association of National Metrology Institutes (18SIB03); Ministerio de Economía, Industria y Competitividad, Gobierno de España (MCIU/AEI/FEDER,UE) PGC2018-096470-B-I00

In this work, we present an ultra-fast line-field optical coherence elastography system (LF-OCE) with an 11.5 MHz equivalent A-line rate. The system was composed of a line-field spectral domain optical coherence tomography system based on a supercontinuum light source, Michelson-type interferometer, and a high-speed 2D spectrometer. The system performed ultra-fast imaging of elastic waves in tissue-mimicking phantoms of various elasticities. The results corroborated well with mechanical testing. Following validation, LF-OCE measurements were made in in situ and in in vivo rabbit corneas under various conditions. The results show the capability of the system to rapidly image elastic waves in tissues.

We report a simple concept to implement a single-wavelength beam steering based on a liquid-cladded one-dimensional (1D) optical phased array (OPA). The beam steering was realized by modifying the waveguide mode effective index through replacing the liquid upper claddings. A prototype of a 32-channel liquid-cladded OPA was fabricated and characterized. Owing to the high refractive index range of liquids ( > 0.625 ), a maximum steering angle of > 10 ∘ was achieved with the liquid range from 1.0 to 1.63 at a wavelength of 940 nm. Moreover, the liquid-cladded OPA reveals a quasi-continuous beam steering range of > 29 ∘ by combining the liquid cladding tuning and discrete wavelength tuning of λ = 785 n m , 852 nm, and 940 nm. Further integration with optofluidic systems offers the OPA potential for low power consumption and all-fluidic beam steering operating at a single wavelength.

The nonlinear residual intensity modulation (RIM) in a multifunction integrated optic circuit (MIOC), mainly caused by the recoupling of the stray light of the TE mode to the output fiber, can impact the stability of a fiber-optic gyroscope (FOG). Theoretically, the polarization extinct ratio (PER) of the MIOC can be utilized to evaluate the nonlinear RIM. To suppress the nonlinear RIM, we have constructed an anti-reflection layer consisting of rough treatment and absorption coating on the bottom of the MIOC. Compared with the traditional design, the MIOC presents a lower nonlinear RIM about an order of magnitude (from 6 × 10−4 to 8 × 10−5), which has been verified by both theoretical simulation and practical experiments. As well as, the PER of the MIOC is improved with this design. The MIOC design proposed in this article has good potential in the applications of high-accuracy FOGs.

Dispersion problem has always constrained the development of see-through near-eye displays with diffractive waveguide. Here, we propose a design method and optical systems for achromatic surface microstructure composed with a triple-carved-sub-grating. The triple-carved-sub-grating with specified period is designed based on rigorous coupled wave theory, corresponding to Red, Green and Blue (RGB) wavelengths, respectively, with diffraction efficiencies of 1st(-1st) orders reach 47.5% under TE polarization. The surface microstructure with period of 18.9um is realized by integrating the three sub-gratings together, and it is verified numerically that the diffractive angle of RGB wavelengths is 35{\deg} and the crosstalk is less than 4.5% under the normal incidence of TE polarization, which imply the surface microstructure diffracts the certain RGB wavelengths achromatically. Via proper duplication it could be utilized as the combining optics of diffractive-waveguide near-eye display and head-up display because of its light and compact features., Comment: 5 pages, 1 figure

We present a way to prevent stray light generated from draft facets of Fresnel lens. Fresnel lens has distinctive shape that induces stray light. The draft facets can generate as much as 8% of stray light, deteriorating performance of optics. To prevent such stray light, we fabricated light-shielding film on draft facets and edges of Fresnel lens. First, we investigated structure and material of the shielding film. We then studied optimal laser source which can perform the precise processing, and found that laser ablation by picosecond laser works the best. Finally, we demonstrated the fabrication of light-shielding film on draft facets of Fresnel lens by experiment, and verified the elimination of stray light.

Well-defined Fe3O4@SiO2 composite colloidal particles decorated with Ag nanoparticles were successfully synthesized through a simple chemical approach. These particles self-assembled into 1D chain-like photonic structures under the induction of magnetic field and diffract tunable structural colors. The hue and brightness of the structural colors are related to Ag nanoparticles deposited on the particles surface and its brightness increases with the increase of Ag concentration. This phenomenon could be the result of the superposition of photonic bandgap formed by photonic crystals and possible plasmonic property, as well as capability in absorbing stray light of Ag nanoparticles. As-prepared Fe3O4@SiO2@Ag colloidal particles have great potential to be applied in many crucial areas such as color displaying, biological detection and anti-counterfeiting technology.

We present a firmly arranged dielectric regular hexagonal pyramid array to generate lattice light sheets with high conversion efficiency and low stray light. Both the size and working distance of the lattice light sheets can be modulated by changing the structural parameters. We experimentally recorded the lattice light sheets illumination, which is consistent with the corresponding simulation. To evaluate the imaging quality, we compared the light field generated with and without structure by using polystyrene fluorescent microspheres. This study provides a potential method for the building of light sheet fluorescence microscopy with high resolution and low phototoxicity.

Quality assurance of finished pharmaceuticals is a necessity in ensuring the safety of consumers. There is a need for low-cost and portable rapid screening methods of pharmaceuticals in resource limited areas. Recent advances in technology have made handheld and low-cost diffuse reflectance spectrometers available to the public. While these handheld spectrometers offer advantages over benchtop spectrometers, the accuracy and repeatability must be assessed before these instruments can be used for quality assurance screening. Here, five handheld spectrometers of the same model were purchased, where an in-house installation qualification and operational qualification (IQOQ) was subsequently established for the instruments. Wavelength and photometric accuracy (and repeatability), spectroscopic noise, stray light, and bandpass were assessed between instruments. Results were found to be consistent between the spectrometers, passing IQOQ procedures, and were determined to be ready for field use. Once the handheld spectrometer’s performance was verified, a practical and low-cost daily performance verification was established using common high density polyethylene vial caps on location in South Africa, Thailand, and the United States. A Mahalanobis distance-based classifier found the five spectrometers to be in agreement.

The small-angle optical particle counter (OPC) can detect particles with strong light absorption. At the same time, it can ignore the properties of the detected particles and detect the particle size singly and more accurately. Reasonably improving the resolution of the low pulse signal of fine particles is key to improving the detection accuracy of the small-angle OPC. In this paper, a new adaptive filtering method for the small-angle scattering signals of particles is proposed based on the recursive least squares (RLS) algorithm. By analyzing the characteristics of the small-angle scattering signals, a variable forgetting factor (VFF) strategy is introduced to optimize the forgetting factor in the traditional RLS algorithm. It can distinguish the scattering signal from the stray light signal and dynamically adapt to the change in pulse amplitude according to different light absorptions and different particle sizes. To verify the filtering effect, small-angle scattering pulse extraction experiments were carried out in a simulated smoke box with different particle properties. The experiments show that the proposed VFF-RLS algorithm can effectively suppress system stray light and background noise. When the particle detection signal appears, the algorithm has fast convergence and tracking speed and highlights the particle pulse signal well. Compared with that of the traditional scattering pulse extraction method, the resolution of the processed scattering pulse signal of particles is greatly improved, and the extraction of weak particle scattering pulses at a small angle has a greater advantage. Finally, the effect of filter order in the algorithm on the results of extracting scattering pulses is discussed.

A miniaturized immersed imaging spectrometer possessing long slit and large relative aperture is proposed. It is integrated monolithically with three concentric optical components. Through the chief ray tracing, we analyzed its astigmatism characteristic and then deduced the anastigmatic condition for long slit. Meanwhile, it is athermal by matching the suitable lens materials to compensate thermal defocus. Based on the anastigmatic and athermal conditions, we have designed a miniaturized VNIR immersed imaging spectrometer and developed the prototype. Its slit is 48 mm long and it is optically fast with an F-number of 2.5. The new form shows about 12 times smaller in volume than the classic Offner-Chrisp imaging spectrometer and weighs only 2 kg, and has excellent thermal adaptability while temperature changes between -40 °C and 60 °C. Meanwhile, fabrication of core elements and gluing process of the immersed imaging spectrometer are presented. Test results of the prototype show superior performance with high imaging quality and small smile and keystone distortions. Such miniaturized immersed imaging spectrometer will greatly improve the performance and reduce the costs of wide swath hyperspectral remote sensing, and is desirable for usage on small plane or satellite platforms.

We report on a thin-disk multipass amplifier delivering azimuthally polarized, 7.8 ps short, laser pulses at an average power and with pulse energies of up to 1.7 kW and 5.8 mJ, respectively. High polarization purity was achieved by compensating for the arbitrary linear phase shifts that are introduced by tilted optical elements.

Microscopic variations in material stiffness play a vital role in cellular scale biomechanics, but are difficult to measure in a natural 3D environment. Brillouin microscopy is a promising technology for such applications, providing non-contact label-free measurement of longitudinal modulus at microscopic resolution. Here we develop heterodyne detection to measure Brillouin scattering signals in a confocal microscope setup, providing sensitive detection with excellent frequency resolution and robust operation in the presence of stray light. The functionality of the microscope is characterized and validated, and the imaging capability demonstrated by imaging structure within both a fibrin fiber network and live cells.

The sidelobe phenomenon of acousto-optic tunable filter (AOTF)-based hyperspectral imaging is the result of the phase mismatching condition, which will reduce the quality of hyperspectral imaging data. This phenomenon can be observed in two specified scenes, namely, high brightness panchromatic target imaging and high brightness monochromatic target imaging. In this paper, the acousto-optic interaction in these two scenes is discussed using the phase matching condition. As a follow-up work of the previous related research, this paper studies laser interference in AOTF imaging, which is a typical example of the second case. A method to remove laser sidelobes in AOTF-based hyperspectral imaging is proposed, which combines a series of procedures including laser point extraction, reverse imaging before AOTF, ray tracing in AOTF, forward imaging process after AOTF, and laser elimination. Experimental results have verified the effectiveness of the proposed method.

Off-axis three-mirror anastigmat (TMA) telescopes provide excellent correction of aberrations over a large field-of-view in one direction. In a push broom configuration, this lightweight and compact optical configuration enables high-performing imaging. Moreover, passive multi-spectral acquisition can be achieved using a filter stack positioned at the detector vicinity. Stray light is a typical limiting factor for instrument performance and its control is specific to the type of optical configuration. We describe the stray light control and analysis methods in an off-axis TMA. The design intends to control first-order scattering from non-optical surfaces and to block straight shots. This is achieved through usage of elements such as apertures and baffles, both internal and external to the instrument. It will be demonstrated that the aperture stop is a critical element, whose stray light contribution can be controlled with V-groove vanes. Impact of mirrors roughness, a manufacturing physical limitation, is evaluated by modeling the bidirectional scattering distribution function and computing the stray light distribution at the detector for point-like source illumination. We show that the scattering on the different mirrors broaden differently the spot size, as the successive mirrors focus or expand the scattered rays differently. Finally, the ghost reflections inside the filter stack are evaluated and we show that there is no cross-talk between the different channels.

Using 3D-printed n-faced pyramid lenses, we generate a series of structured diffraction free terahertz (THz) beams. Based on angular spectrum theory, analytical solutions of the output THz beams from these lenses can be obtained. Furthermore, we experimentally realize these non-diffraction THz beams, showing that the measured results are consistent with theory. It is believed that our structured non-diffraction THz beams can be used in THz imaging with large depth of focus.

The application range of hyperspectral imaging is subject to the operational system platform especially relies on the core imaging spectrometer. With a rising practical requirement of extensive remote sensing recently, the traditional method of two or multiple separate imaging submodules combined has obviously brought inevitable shortages in certain cases such as mineral detection or environmental monitoring, etc. Not only is the whole imaging system somewhat so large in physical size and so high in weight that it has an objective influence on convenience as well as flexibility in actual operation, but also each independent instrument has unique optical parameters and assembling matrices after fabrication and alignment which is against the image consistency. Instead of common image correction and data processing, the essential solution is to set up a broadband integrative system platform. This paper introduces a new prototype of imaging spectrometer in the visible and near-infrared (VNIR) to short-wave infrared (SWIR) region. Different from most existing research-based and commercial VNIR to SWIR imaging spectrometers, it is designed as broadband integration of a single core module. The main optical system consists of a collimating mirror, a central dispersive spherical prism, a converging mirror and two plane mirrors on the sides, which is similar to the normal convex grating spectrometer of three-concentric-mirror (Offner) configuration. The imaging spectrometer has relatively high imaging quality and satisfactory instantaneous field of view (IFOV) with a fairly compact internal structure benefiting from the integrated design and conscientious fabrication. The approach not only avoids extra expense and alignment complexities of multiple spectrometers but also enhances radiometric stability and reduces stray light and polarization effects. Relative performance tests are performed in various specific environment and validating imaging experiments are represented on schedule to demonstrate the expectant effectiveness of the whole system.

Gratings with low diffracted wavefront errors are crucial in many applications. Existing methods to reduce the diffracted wavefront errors of holographically produced gratings mainly address misalignment errors during exposure system adjustment, leaving the inevitable residual errors of collimation lenses uncorrected. The broad-beam scanning exposure method was recently proposed to fabricate gratings with large size and low stray light. We explore its ability to reduce the diffracted wavefront errors caused by both system misalignment and lens errors. During the exposure, the substrate translates in the direction perpendicular to the grating lines to pass through the exposure area, so the aberrations over different parts of the interference field along the scanning path are averaged. We prove the validity of this method by a theoretical analysis and numerical simulations. The averaging effect on different aberrations and with different scanning lengths is discussed. The peak-valley values of diffracted wavefront errors of gratings fabricated with an exposure field of defocus aberration and a more complicated aberration were reduced by 42.5% and 50%, respectively.

The optical properties of microlens arrays may be significantly affected by the optical crosstalk effect between adjacent lenses. Recently, this issue has triggered increasing attention in the scientific community. In this study, an integrated microlens array (MLA) consisting of self-aligning convergent waveguides of microlenses was fabricated. The optical crosstalk effect does not influence the performance of such system. Based on the self-focusing effect principle, self-writing of the waveguide array was achieved in a photosensitive polymer. The light collection and guiding performance of the MLA with and without thermal cross-linking treatment was analyzed in depth. The relation between the stray light and the filling rate of the MLA shows that a high filling rate decreases the optical crosstalk. Finally, an integrated MLA with a large area, high uniformity, and excellent optical performance was fabricated.

We have developed an SI-traceable narrow-band tunable radiance source based on an optical parametric oscillator (OPO) and an integrating sphere for the calibration of spectroradiometers. The source is calibrated with a reference detector over the ultraviolet/visible spectral range with an uncertainty of < 1 % . As a case study, a CubeSat spectroradiometer has been calibrated for radiance over its operating range from 370 nm to 480 nm. To validate the results, the instrument has also been calibrated with a traditional setup based on a diffuser and an FEL lamp. Both routes show good agreement within the combined measurement uncertainty. The OPO-based approach could be an interesting alternative to the traditional method, not only because of reduced measurement uncertainty, but also because it directly allows for wavelength calibration and characterization of the instrumental spectral response function and stray light effects, which could reduce calibration time and cost.

Light absorption by the water column plays an important role in the spatial and temporal distribution of light attenuation, mixed layer heating, primary productivity, and phytoplankton biomass in the water column. The absorption properties of water components are the main influences of the underwater light field and surface spectrum. The study of the absorption properties of the water body contributes to the understanding of its optical properties and the remote sensing inversion of water quality parameters. The effects of light source polarization on the spectral absorption coefficient measurements of colored dissolved organic matter (CDOM) and total particulate matter (TPM) in water were investigated by measuring the polarization of the light source in a UV-Vis spectrophotometer. The results show that the light source of the UV-Vis spectrophotometer is significantly polarized, but the effect of the polarization of the light source on the measurement of the spectral absorption coefficients of CDOM and TPM in water is very small and almost negligible.

We report on a joule-level, 1047 nm Nd:YLF master oscillator power amplifier laser with near-diffraction-limited beam quality. The master oscillator and two-stage two-pass amplifier were all-flashlamp-pumped. The laser produced 2 J output pulses with 3 ns duration at 10 Hz pulse repetition rate. High beam quality was achieved by using a liquid stimulated Brillouin scattering mirror and additional astigmatism compensation.

Pupil expansion using waveguide propagation and pupil replication has been a popular method of developing head-up displays and near-to-eye displays. This paper examines one of the limits of pupil replication, which involves projecting images at a finite distance through a single waveguide by holographic optical elements and seeing the image doubling artifact. A Zemax model and a demonstrator were developed to determine the cause of image doubling. A relationship between the designed outcoupled image distance of a waveguide, pupil size, optical path length, and angle of image doubling is established. In waveguide pupil replication, the internally propagating light should be close to collimated to mitigate image doubling. We also provide a solution to project the image at different distances, which is an important factor for some applications, such as automotive head-up display and the seamless integration of augmented reality information with the natural environment.