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Characterized by its compact structure and fast response, the rotational double prisms system is broadly applicable for high-precision pointing and tracking. In particular, closed-loop tracking technology based on an image detector can overcome beam deflection errors caused by prism parameter and target-guiding errors. However, the rotations of each prism affect beam deflection angles in both the x- and y-directions by different amounts in different areas. Therefore, aimed at this problem of the tracking error being coupled to the rotation angle of the two prisms, we proposed a real-time sector selection closed-loop tracking method by inputting error value feedback from the detector and outputting the adjustment values of the prisms. This method can simultaneously close-loop the error signal in two directions and is not limited by the target distance. We established a test platform to verify the proposed method. The test results showed that the proposed method can continuously track moving targets across different areas of a field of view for an extended period. When the maximum moving speed of the target was 0.32 deg / s, the root mean square tracking error of the noncentral area was

Given the importance of the 0.1- to 1-THz range in the security detection and diagnosis of cancer, we propose a structure for graphene-based terahertz (THz) photodetectors. We use the finite-difference time-domain and mathematical methods to calculate the light absorption in the graphene layers (GLs) and the detector’s figure of merits, including responsivity and detectivity. The proposed photodetector is based on single-layer and multilayer graphene absorbers within a p-type-intrinsic-n-type (PIN) photodiode structure. This detector is designed to achieve maximum absorption at the THz frequencies by creating adjustable Fabry–Perot resonances. Results show that it has two distinct and adjustable detection peaks in THz. So we set the operating frequency to 0.35 and 0.83 THz by adjusting the geometric parameters of the device, which also fit the atmospheric windows. Despite the low number of GLs, high absorption is provided at room temperature. It has high responsivity peaks of ∼1220 AW − 1 at the frequency of 0.35 THz and 420 AW − 1 at 0.83 THz, respectively, while we have achieved these characteristics with fewer GLs than other previous detectors.

This work presents a measurement uncertainty analysis for a system designed to simultaneously capture specular in-plane and out-of-plane bidirectional reflectance distribution function (BRDF) data with high spatial resolution by augmenting the Complete Angle Scatter Instrument (CASI®) with a charge-coupled device (CCD) camera. Various scatter flux, incident flux, scatter angle, and detector solid angle uncertainty contributions are considered and evaluated based on imperfectly known system parameters. In particular, incident flux temporal fluctuation, detector noise and non-linearity, and out-of-plane aperture misalignment considerations each require significant adjustment from original CASI® uncertainty analysis, and expressions for neutral density (ND) filter, scatter angle, and solid angle uncertainties each require new formulations. Ultimately, ND filter uncertainty produces the largest contribution for the augmented system—at least when using unrefined worst-case tolerances—followed by solid angle uncertainty and pixel non-linearity. Total BRDF uncertainty and its contributing terms are compiled for several measurement scenarios, and compared with those from original analyses for single-pixel detectors. In particular, when ND filter uncertainty can be ignored or mitigated, total BRDF uncertainty values are comparable to those for the original system.

A low-cost near-infrared spectrometer based on fiber beam scanning and linear variable filter (LVF) was proposed and demonstrated. The key elements of the spectrometer include a piezoelectric driven fiber scanner, an LVF monochromator, and a single point detector. The single fiber scanner provides a new way to continuously sweep the LVF. A PIN photodiode behind the LVF monochromator can acquire more spectral information than the traditional linear array detection. The performance of the spectrometer was verified with a narrow band tunable laser and a broadband light source. With the help of a deconvolution algorithm, the spectral resolution of the proposed spectrometer is up to 0.32% of the center wavelength (≈5 nm@1550 nm).

Breast cancer is one of the leading causes of death throughout the world. Early detection of breast cancer can prevent the death of many women throughout the world. There are many methods to detect tumor in breast tissue samples. Plasmonic-based sensors are of great importance in recent optical technology. A perfect semiconductor metamaterial absorber based on surface plasmon resonance is designed, and its sensing capability to detect breast cancer is investigated using numerical simulations. The indium antimonide (InSb) is used as an optimized semiconductor in the structure and the absorption value of 99.22% is obtained. The thermal, material, optical, and geometrical tunability of the structure is investigated. The maximum refractive index sensitivity as high as 24,680 nm/RIU is obtained. Moreover, it is shown that the structure can effectively work as a breast cancer detector. Furthermore, the temperature sensitivity of the structure is also analyzed, and the ultra-high value of 10,830 nm/K is obtained for thermo-optical sensitivity of this design/device.

Image sensing has entered a new era with advancements in quantum mechanics. The infrared (IR) absorbers are the heart of this new era of image sensing. Within the IR spectra, the shortwave to mid-wave (MWIR) radiations are absorbed by IR photodetectors, whereas the MWIR to very-long wave spectrum is absorbed by IR thermal detectors. Both of these categories of image sensing cover the complete IR spectrum utilized by the applications ranging from biosensing in healthcare sector to autonomous vehicle navigation in military and space purposes. Despite having high-cost semiconductor technology with group-II–VI (mercury–cadmium–telluride) and group-III–V (indium–gallium–arsenide) dominating this IR absorbance industry for many decades, the need to have a cost-effective solution has led to an explosion in the exploration of potential materials. Two-dimensional (graphene, dichalcogenides of transition metals, and black-phosphorous) antimonite-based and group-IV/IV alloys have been found to show unprecedented absorption yield and detector properties comparable to traditional dominators with flexible fabrication methods. At the same time, the photon upconversion phenomenon that upconverts low-energy light to high-energy light has emerged as an exceptionally rich area of research in image sensing. The principle behind this concept lies in different energy transfer mechanisms (two photon absorption, triplet–triplet annihilation, cooperative energy pooling, etc.). The advancements that took place most recently in the development of IR absorbers have been reviewed in a concise way. Furthermore, the advancements in upconversion-based detection focusing on how this is evolving as a low-cost alternative for image sensing have been reviewed. Further discussion on how to anticipate a low-power, cost-effective, and light-weight image sensing system has been presented while mentioning some recent research as a proof-of-concept. We finally suggest a possible approach that could come up by synergizing the two simultaneous technologies to foresee the realization of an all-optical, low-power, and light-weight broad-range IR absorber for various applications.

The bidirectional reflectance distribution function (BRDF) is used to describe reflectances of materials by calculating the ratio of the reflected radiance to the incident irradiance. While it was found that the isotropic models maintained symmetry about ϕs = π, such symmetry was not maintained about the θs = θi axis, except for close to the specular peak. This led to the development of a data-driven metric for how isotropic a BRDF measurement is. Research efforts centered around developing an algorithm that could determine material anisotropy without having to fit to models. This algorithm was tested using high fidelity data (containing off-axis BRDFs), which was collected via a modified Complete Angle Scatter Instrument (CASI®) with a CCD array detector. The algorithm accurately characterized the degree of isotropy for four out of five materials and worked for cases where the BRDF is higher than 100 sr − 1. This algorithm is intended to improve BRDF characterization, and the applications of light curve analysis, scene generation, and remote sensing.

We present methods enabling rapid non-uniformity and range walk error correction of 3D flash LiDAR imagers that exhibit electronic crosstalk caused by simultaneously triggering too many detectors. This additional electronic crosstalk is referred to as simultaneous ranging crosstalk noise (SRCN). Using a method in which the 3D flash LiDAR imager views a checkerboard target downrange, the SRCN is largely mitigated. Additionally, processing techniques for computing the non-uniformity correction (NUC) and range walk error correction are described; these include an in-situ thermally compensated dark-frame non-uniformity correction, image processing and filtering techniques for the creation of a photo-response non-uniformity correction, and characterization and correction of the range walk error using data collected across the full focal plane array without the need for sampling or windowing. These methods result in the ability to correct noisy test validation data to a range precision of 8.04 cm and a range accuracy of 1.73 cm and to improve the signal-to-noise ratio of the intensity return by 15 to 49 dB. Visualization of a 3D scene corrected by this process is additionally presented.

We have designed a silicon detector based on an avalanche photodiode for detecting vacuum ultraviolet radiation. It was demonstrated that the detector has a photon detection efficiency superior to 0.65 electrons / photon, in the wavelength range from 114 to 170 nm, with an external quantum yield from 49 to 7000 electrons / photon at a reverse-bias voltage from 190 to 315 V, respectively. The detector’s active area diameter is 1.5 mm.

Scanning beam interference lithography (SBIL) is an advanced technology developed for manufacturing large-area diffraction grating at a nanometer-scale phase accuracy. To withstand environmental disturbances and maintain the interference fringes still relative to the substrate, SBIL requires high-precision phase control. We proposed a fringe phase control system with homodyne detection for SBIL. First, a homodyne detector is employed to achieve high-precision phase measurement, while ensuring the simplicity of the optics and high laser utilization. The time-varying nonlinear error in the measurement results is corrected by a dynamic ellipse fitting method. To reduce the latency effect, a lead controller is designed using the root locus method based on the model identification result. The lead controller considerably increases the control bandwidth while ensuring a sufficient phase margin, which further suppresses disturbances and stabilizes the interference fringes to within ∼1 / 60 of the fringe period. Wide-range phase tracking for perpendicular scanning with high accuracy is also verified through an experiment.

A laser power scale transfer technique was developed based on shape detection; using this technique, detectors can be precisely centered on laser beams, thereby significantly reducing measurement errors introduced by detector nonuniformities and misalignments. A modified imaging scheme was designed and embedded in the scale transfer setup, and the effective resolution was proven to be better than 100 μm, compatible for incident lasers with diameters under 15 mm. For different types of detectors, absolute positioning was realized using objective algorithms with repeatability errors of 7 to 13 μm, which is an improvement of over 30 times the limitation of human-vision-based positioning. Correspondingly, the relative measurement error caused by detector non-uniformity for a typical calibration was reduced by a factor of 19–40 in the scale transfer process. The proposed technique thus has the potential for detector-based optical metrological applications that are influenced by geometric accuracy.

The US Army Night Vision and Electronic Sensors Directorate’s Night Vision Integrated Performance Model (NVIPM) is a robust, comprehensive, and sophisticated model that calculates the performance of an infrared imager in the task of target acquisition. The inputs are specifics about the target, atmosphere, optics, detector, electronics, and display and the outputs are probabilities of target detection, recognition, and identification. NVIPM is complicated and takes a good bit of time to master obtaining correct answers based on numerous assumptions and modeling experience. For midwave infrared (MWIR) and longwave infrared (LWIR) sensors, past research has shown that imaging system performance is strongly related to Fλ / d, where F is the f-number, λ is the wavelength, and d is the detector pitch. Fλ / d provides a metric that relates how closely to diffraction-limited performance a sensor operates. We use the past Fλ / d work to develop a simple model that provides probability of target discrimination as a function of range that can be performed with a simple hand calculator or spreadsheet. We compare this model to the NVIPM calculations on 10 very disparate MWIR and LWIR sensors to show robust agreement. We also describe the conditions under which the simple model is valid.

A low-cost laser detection system based on coherence detection has been developed and is able to detect weak, continuous laser sources even against bright background light. The system is composed of a Mach–Zehnder interferometer with one arm modified with a piezo-mounted mirror to modulate the path length. We introduce methods to determine the laser wavelength and to extend the horizontal field of view of the detector. To widen the field of view, a cone mirror is added to the system while the additional use of a camera allows the direction of the incoming laser beam to be studied. The wavelength from three different lasers is estimated with the use of the modulation amplitude of the piezo mirror. The preliminary results demonstrate that a 360-deg horizontal field of view can be achieved and that the direction of the laser beam can be determined with an estimated angular precision of ±5 deg. Moreover, the wavelength can be determined with a precision of ±10 nm. The system trades sensitivity for a larger field of view with the resultant detection sensitivity equal to 70 nW (or 1 μW · cm − 2) at 635 nm.

Experimental demonstration of a quantum random number generator based on one single-photon avalanche diode (SPAD) detector, a T / ( T − t ) pulse-shaped laser, and an field-programmable gate array (FPGA) acquisition module is presented. An integrated laser driver drives an external laser diode at 670 nm wavelength, whereas the SPAD with a photon detection probability of 18.5% is integrated together with an active quenching-resetting circuit. The SPAD detector generates counts for the interarrival time (IAT) measurement system implemented in an FPGA, where the change of the IATs between consecutive pulses is used to derive a random bit stream. It is shown how the application of a pulse-shaped laser driver can increase the performance of the system as compared to the continuous-wave operation of the laser diode to achieve the maximum generation rate of 5 Mbps while using a single SPAD. The generated numbers pass all randomness tests of the National Institute of Standards and Technology (NIST), Dieharder, and ENT test (pseudorandom number sequence test) suits.

The performance of free-space optical (FSO) communication systems based on avalanche photodiodes (APDs) is investigated over the aggregated double generalized gamma (double GG) fading channels. The approximate average bit error rate (ABER) expression is theoretically derived in terms of the double GG distributions under moderate and strong turbulent atmospheric conditions considering thermal noise and shot noise. The union bound and Hermite polynomials are then used to estimate the ABER performance of M-ary pulse-position modulation (PPM)-based systems and orthogonal frequency division multiplexing scheme (OFDM)-based systems. The ABER performance is studied with different receiver noise temperatures, modulation orders, turbulence strengths, and average photon counts assuming plane wave and spherical wave propagations. The results show that adopting an optimal average APD gain affected by the receiver temperature minimizes the ABER value for both wave propagations. In addition, the present APD-based system offers better ABER performance than that of a PIN-based FSO system over the double GG fading channels at two receiver noise temperatures of 200 and 400 K for both the PPM and OFDM schemes. We provide a reference for FSO system design.

A simple millimeter wave and terahertz (THz) receiver scheme that uses subwavelength focusing of electromagnetic beam on the point-contact detector area with waveguide dimensions is studied. A detection system with such an optical coupling scheme is implemented, where the signal to be detected is coupled to a detector through a mesoscale dielectric particle lens based on terajet effect. We have experimentally demonstrated an enhancement of the point-contact detector sensitivity higher than 6 dB and with 1.5 times decreasing of the noise equivalent power value. The results show that the proposed method could be applied to reduce the size and increase the sensitivity of various THz systems, including imaging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, etc.

Terahertz (THz) detectors have drawn much attention and have been widely applied in imaging, spectroscopy, and sensing fields. An uncooled monolithic resonant THz thermal detector implemented in a standard 55-nm CMOS process is presented. The integration of a frequency selective metamaterial (MM) absorber coupled with an optimized proportional-to-absolute temperature (PTAT) sensor leads to an approach toward uncooled, compact, low-cost, easy-integration, and mass-production THz detectors. The theoretical analysis, design considerations, and characteristic measurements are demonstrated in detail. The proposed thermal detector is designed to resonate at 2.58 THz for the accessible THz source and the natural atmospheric window. The MM absorber achieves near-perfect absorptivity of 98.6%, and the optimized PTAT sensor obtains a high-temperature sensitivity of 10.11 mV / ° C. The calculated responsivity is 49.81 V / W at 2.58 THz with a calculated noise-equivalent power (NEP) of 0.78 μW / Hz0.5 at a modulation frequency of 3 Hz. Relatively better experimental results are obtained at 2.58 THz with a maximum responsivity of 48.3 V / W and a minimum NEP of 1.06 μW / Hz0.5.

Improved technology and emerging interferometric techniques have allowed the use of uncooled microbolometers in the long-wave infrared (LWIR; 8 to 14 μm) for hyperspectral imaging (HSI). The midwave infrared (MWIR; 3 to 5 μm) presents several advantages with respect to the LWIR for Earth and planetary science. For example, important atmospheric trace gases on Earth such as CO2 and CH4 are not masked by other atmospheric constituents in the MWIR. However, HSI in the MWIR is more challenging at ambient Earth temperatures because less radiance is available to measure. We describe how hyperspectral images in the MWIR can be acquired with an instrument using an uncooled microbolometer married to a Sagnac interferometer. Standard characterization tests are used to benchmark the performance of the microbolometer instrument with a cryogenically cooled photon detector with the same optical design. At a spectral resolution of 100 cm − 1 (17 bands between 3 and 5 μm), we measured a signal-to-noise ratio (SNR) of 100 at 30°C with the microbolometer instrument and an SNR of 50 at 50 cm − 1 (33 bands). Results from this work show that coupling microbolometers with interferometers allows for quality measurements with adequate SNR for high-temperature science applications.

A compact long-wave infrared (LWIR) channeled spectro-polarimeter (IRCSP) has been developed for integration into the NASA Earth Science Technology Office (ESTO) funded submm-wave and LWIR polarimeters project to measure the microphysical properties of cloud ice. Once deployed, the IRCSP will produce the first linear Stokes measurements ( S0 , S1 , S2 ) of upper-tropospheric cirrus clouds from 8.5 to 12.5 μm. For the first time, a compact, light-weight, and uncooled LWIR polarimeter with off-the-shelf thermal optical components is demonstrated. We report narrowband calibration measurements which quantify metrics of polarimetric system performance. The response of the system to linearly polarized light is shown to agree with both a Mueller matrix model and modulation function for narrowband calibration measurements with an R2 > 0.98 from 8 to 11 μm. The polarimetric efficiency is >0.8 from 8 to 11 μm for narrowband measurements indicating satisfactory performance of the polarization optics. Beyond 11 μm, the agreement is significantly reduced as thermal noise compounds with reduced detector response. Ultimately, the observed system performance is limited by the spectral response of the detector past 11 μm in addition to the thermal noise inherent for the measurements at room temperature.

Transverse translation-diverse phase retrieval (TTDPR), a ptychographic wavefront-sensing technique, is a viable method for freeform optical surface metrology due to its relatively simple hardware requirements, flexibility, and demonstrated accuracy in other fields. In TTDPR, a subaperture illumination pattern is scanned across an optic under test, and the reflected intensity is gathered on an array detector near focus. A nonlinear optimization algorithm is used to reconstruct the wavefront aberration at the test surface from which we can solve for surface error, using intensity patterns from multiple scan positions. TTDPR is an advantageous method for aspheric and freeform metrology because measurements can be performed without null optics. We report on the development of a concave freeform mirror measurement using this technique. Simulations were performed to test algorithmic performance as a function of various parameters, including detector signal-to-noise ratio and position uncertainty of the illumination, with

A low-cost camera-based method of detecting continuous-wave (cw) lasers has been developed at Defence Science and Technology Laboratory. The detector uses a simple optical modification to a standard color camera combined with image processing techniques to distinguish lasers from other illumination sources and measure the wavelength, direction, and irradiance of the laser light. Such a detector has applications in collecting information on aircraft laser dazzle incidents, providing the evidence required to inform on aircrew laser exposure events and to assess if engagements are eye safe. A prototype has been developed using entirely commercially available off-the-shelf (COTS) components, costing ≈£600, and assessed in laboratory conditions with the capability of measuring laser wavelengths to ±5 nm and irradiances to ±10 % . A realistic handheld laser engagement scenario, using a range of relevant wavelengths and irradiances, was simulated during the Moonraker trial where the prototype was capable of measuring laser wavelengths to an accuracy of ±10 nm and peak irradiances to ±25 % . All laser engagements were detected over a total data collection period of 9 h with zero false alarms. Comparisons were made with a COTS laser detector, which showed an equivalent performance. This technology offers a low-cost approach to cw laser detection, which is capable of extracting a range of parameters while maintaining a relatively wide field of view and angular resolution.

A trace chemical detector is described that combines external-cavity quantum cascade lasers and a mercury cadmium telluride camera to capture hyperspectral images of the diffuse reflectance from a target surface in the long-wave infrared. The system is able to generate individual hypercubes in 60 cm2 / s have been achieved. Results are presented for standoff distances ranging from 0.1 to 25 m. Hyperspectral images generated by the system are analyzed for spectral features that indicate the presence of trace surface contaminants. This approach has been found to be highly capable of detecting trace chemical residues on a wide variety of surfaces, and we present a collection of detection results to demonstrate the capabilities of this technology. Examples include the detection of 10 μg of saccharin powder on a wide range of substrates, 0.2 μg of an explosive residue on a computer keyboard, residual pharmaceuticals within a plastic baggie, and a contaminated fingerprint on cell phone case.

A quantum random number generation method based on measuring the time differences between photon detections is analyzed mathematically in terms of bit generation efficiency and bit generation rate. It was found that these two values cannot be maximized simultaneously by altering the incident photon rate of a light source with Poisson statistics, but the generation rate can be increased at the expense of efficiency. Analytical results are presented for both an idealized and a practical case. The detector’s dead time has been taken into consideration in the latter case, implying that, for certain combinations of the dead time and the measurement clock period, the generation rate becomes a two-peaked function of the incident photon rate. The theoretical results are confirmed by simulations, showing excellent agreement between the two.

For a simultaneous phase-shifting interferometer (SPSI), typically four interferograms with different phase shifts are captured at different areas on the detector target by a single-shot capture method. Prior to calculating phase distribution, the region segmentation should be conducted to obtain four separated interferograms. A registration method is also necessary to eliminate the mismatch errors between the interferograms. A spatial mismatch calibration method based on fast partial phase correlation is proposed to register the spatial positions between the phase-shifting interferograms. By tilting the reflective flat, four carrier interferograms are captured to extract four phase distributions using the Fourier transform technique. Partial phase distribution is used as match characteristics to register the interferograms rapidly by employing the correlation operation. The simulation and experimental results show that the ripple error generated by spatial mismatch is suppressed well by the proposed method.

Terahertz (THz) spectroscopy with high sensitivity is essential for biological application considering the strong absorption and scattering effects therein. As the most commonly used THz detector, the photoconductive antenna’s (PCA) response greatly relies on the properties of the substrate’s material. THz detection properties of the PCAs fabricated on low-temperature-grown GaAs (LT-GaAs) and ErAs:GaAs superlattices were compared at the sub-THz band. The detection efficiency of the PCAs with regard to incident laser power was characterized. In addition, using the PCAs as detectors, the signal-to-noise ratio (SNR) and dynamic range (DR) of a terahertz time-domain spectroscopy were quantified. The result indicates that the PCA detector with LT-GaAs has higher efficiency than the one with ErAs:GaAs. Consequently, the corresponding THz spectrometer has better SNR and DR. This result is contrary to the previous report, in which enhanced detection efficiency was observed with ErAs:GaAs-based PCA, which is probably due to the different structures of ErAs:GaAs superlattices used in the experiment.

Many optical systems are used for specific tasks such as classification. Of these systems, the majority are designed to maximize image quality for human observers. However, machine learning classification algorithms do not require the same data representation used by humans. We investigate the compressive optical systems optimized for a specific machine sensing task. Two compressive optical architectures are examined: an array of prisms and neutral density filters where each prism and neutral density filter pair realizes one datum from an optimized compressive sensing matrix, and another architecture using conventional optics to image the aperture onto the detector, a prism array to divide the aperture, and a pixelated attenuation mask in the intermediate image plane. We discuss the design, simulation, and trade-offs of these systems built for compressed classification of the Modified National Institute of Standards and Technology dataset. Both architectures achieve classification accuracies within 3% of the optimized sensing matrix for compression ranging from 98.85% to 99.87%. The performance of the systems with 98.85% compression were between an F / 2 and F / 4 imaging system in the presence of noise.

In the field of laser circumferential detection and laser imaging, there is demand for a simple and small system. A new kind of small linear laser circumferential laser radar using a single detector is proposed. The effects of surface characteristics of two typical targets (a plane and a cylinder) on echo waves of a linear laser are investigated via modeling, theoretical analysis, and an experiment. The results show that the echo waveform is affected by the detection range, target surface condition, and target size. The rising edge, broadening, and arrival time of the echo are affected by the shape of the target. Furthermore, a simple imaging method is proposed in the last part of our study using this circumferential system based on the echo characteristic studied.

The quantification of remote sensing information requires spectral radiometric calibration technology support with high accuracy, and this technology can ensure the comparability, accuracy, and long-term stability of data acquisition for sensor. Now, the calibration technique traced to the absolute cryogenic radiometer (ACR) is the trend of development. To improve the accuracy of infrared absolute spectral responsivity, a gold-plated hemisphere reflector is added to a thermopile detector with electrical substitution pins. So an infrared electrical substitution radiometer (ESR) is developed as the standard transfer detector. The spectral response linearity, uniformity, and stability of ESR are tested by electric substitution technology. We also have established a radiometric calibration system based on ACR. The combined uncertainty in the spectral responsivity of this detector from 0.7 to 20 μm is about 0.99%. The application of infrared ESR to radiometric calibration can improve the calibration accuracy of detectors through its shorter calibration chain.

The spectral and amplitude-frequency characteristics of a new pyroelectric detector based on thin tetraaminodiphenyl polycyclic polymer films with a thickness of

A common-path spatial phase shifting digital speckle pattern shearing interferometry setup is introduced for simultaneous measurement of in-plane and out-plane strain components under dynamic loading using two laser beams with different wavelengths that symmetrically illuminate the test object and a single detector. The simplicity, stability, and efficiency of the arrangement are provided by using a glass plate as a shearing device, which is capable of tuning the sensitivity continuously. The phase is recovered from a single frame by the Fourier method. In this setup, the spatial carrier frequencies can be adjusted independent of the amount of the lateral shear. Ultimately, the desired field of view can easily be achieved by simple imaging optics. To validate the feasibility and the flexibility of our technique, the proposed setup is used to evaluate the in-plane and out-plane strain maps of an aluminum plate, which is deformed under dynamic stress in its plane. The temporal phase stability of the proposed system is also investigated.

We present a method based on image pixel value to evaluate the characteristics of the corona discharge of polymer insulators. To capture the images of the solar-blind ultraviolet (SBUV) band, an ultraviolet (UV) imaging detector based on an image intensifier is designed. First, through the experiments’ results with the UV light source, the proposed method based on the image pixel value is proved to detect solar-blind signals more effectively than the photon counting method. Then, by conducting experiments with the insulator at a fixed observation distance, the corona characteristics of the insulator can be described through analyzing the images captured by the detector. Finally, the experiments at different observation distances are conducted, and the image pixel value ratios of the recorded images with certain observation distance are computed. The results reveal that the developing stages of different corona discharges can be uniquely described. Based on the method, the characteristics of a corona discharge in the SBUV band can be described accurately and objectively.

Within the last two decades, terahertz systems have become a well-established tool in scientific laboratories and industrial research and development departments. Unlike the methods of pulsed terahertz radiation that mainly rely on ultrafast optical technology, the technology behind continuous-wave terahertz sources and detectors has a long history involving many different types of technical schemes. The intent is to provide a brief review of the continuous-wave terahertz systems that are based on photomixing and current application trends in the field of terahertz technology.

We experimentally demonstrate coincidence measurements as well as g (2) ( nτ ) correlation function measurements with only one single-photon detector (SPD) with the aid of field-programmable gate array and 2 × 2 fast optical switches. Both experiments produced similar results compared to conventional experimental methods, requiring more than one SPD. When detecting correlations between multiple single photons, this technique can be employed to reduce demands for the number of SPDs and potentially would be able to offer new options to researchers and institutions requiring coincidence measurement systems with lower complexity as well as smaller form factors.

The lobster-eye optical system is widely used in the wide field of view (FOV) soft x-ray imaging device. The payload soft x-ray imager (SXI) onboard the solar wind magnetosphere ionosphere link explorer satellite will apply this technology to achieve panoramic imaging of the dayside magnetosphere. In order to optimize the imaging performance of SXI, we focus on geometric parameters optimization of a lobster-eye lens. The results show an appropriate microchannel ratio of length to width of lobster-eye optics with radius of curvature of 600 mm could be 30:1 (microchannel width of 40 μm and length of 1.2 mm). For a monochromatic parallel light source with energy of 1 keV, this combination of parameters can theoretically provide relatively large total effective area of about 15.52 cm2 and focusing efficiency of about 0.2887 along with spatial angular resolution of about 6 arc min at the center of FOV. Combined with the actual lobster-eye optics, the aberrations from deformation of the microchannel, the deviation of radius of curvature and planar detector are analyzed. For SXI with planar CCD detector, an optimum focal length could be 304.2 mm to ensure better resolution in full FOV.

We have proposed and demonstrated position-sensitive detectors based on the spectral changes in fluorescent waveguides. The first prototype is a transparent heat-shrink tubing containing an organic luminescent dye at its core. With a laser beam incident on this linear fluorescent tubing, the redshift in the photoluminescence (PL) spectrum observed at its edge increases with the distance from the incident point. The range for position sensing is 2 cm. It is extended to 280 cm by adopting a scintillating fiber in our second experiment. Two-stage conversion enables two-dimensional position detection. We have attached two linear fluorescent tubing to a planar 50 mm × 50 mm × 8 mm fluorescent waveguide. When a laser beam excites the first luminescent material at a single spot in the planer waveguide, PL photons propagate to its edges and excite the second luminescent material in the two linear waveguides. Photon division between these linear waveguides gives the first coordinate. The second coordinate is given by the redshift in the linear waveguides. We have observed that the maximum error in position estimation is 1.5 mm. Unlike the conventional semiconductor technologies, no electronic components are required for the sensor head. This robust technology might be suited for deployment in large-scale harsh environments.

Efforts to extend speckle-based focal plane array modulation transfer function measurements beyond the detector Nyquist frequency have unearthed challenging spectral estimation issues. In an attempt to better understand the task of speckle imagery spectral estimation, we explore the nuances of various estimation techniques, making comparisons using both real speckle imagery and simulated data. Parameters and features of the techniques investigated include number of image realizations, the size of image realizations, and applications of windows to speckle imagery spectral estimation. Real-world testing considerations such as laser stability and the challenge of collecting significant numbers of independent image realizations are addressed in the analysis. Results from this research show the advantage increasing the number of realizations has on estimation variance, the robustness of smaller realization segments when battling speckle field imagery spatial nonuniformities, the benefits of windowing image segments with regard to power spectral density estimation accuracy, and the impact that the increasing aperture area has on system signal-to-noise ratio.

Imaging systems can be used to obtain situational awareness in maritime situations. Important tools for these systems are automatic detection and tracking of objects in the acquired imagery, in which numerous methods are being developed. When designing a detection or tracking algorithm, its quality should be ensured by a comparison with existing algorithms and/or with a ground truth. Detection and tracking methods are often designed for a specific task, so evaluation with respect to this task is crucial, which demands for different evaluation measures for different tasks. We, therefore, propose a variety of quantitative measures for the performance evaluation of detectors and trackers for a variety of tasks. The proposed measures are a rich set from which an algorithm designer can choose in order to optimally design and assess a detection or tracking algorithm for a specific task. We compare these different evaluation measures by using them to assess detection and tracking quality in different maritime detection and tracking situations, obtained from three real-life infrared video data sets. With the proposed set of evaluation measures, a user is able to quantitatively assess the performance of a detector or tracker, which enables an optimal design for his approach.

A HgCdTe avalanche photodiode (APD) focal plane array assembly with linear mode photon-counting capability has been developed for space lidar applications. An integrated detector cooler assembly (IDCA) has been built using a miniature Stirling cooler. A microlens array has been included to improve the fill factor. The HgCdTe APD has a spectral response from 0.9- to 4.3-μm wavelengths, a photon detection efficiency as high as 70%, and a dark count rate of

Despite all the significant advances in human detection in various environmental conditions, it is still a challenging task. Most of the human detection algorithms mainly use color information, which is not robust to lighting changes and varying colors under which such a detector should operate namely day and nighttime. This problem is further amplified with infrared (IR) imagery, which only contains grayscale information. The proposed algorithm for human detection uses intensity distribution, gradient, and texture features for effective detection of humans in IR imagery. For the detection of intensity, histogram information is obtained in the grayscale channel. For extracting gradients, we utilize the histogram of oriented gradients for better information in the various lighting scenarios. For extracting texture information, center-symmetric local binary pattern gives rotational invariance as well as lighting invariance for robust features under these conditions. Various binning strategies help keep the inherent structure embedded in the features, which provide enough information for robust detection of the humans in the scene. The features are then classified using an AdaBoost classifier to provide a tree-like structure for detection in multiple scales. The algorithm has been trained and tested on IR imagery and has been found to be fairly robust to viewpoint changes and lighting changes in dynamic backgrounds and visual scenes.

Terahertz waves have unique propagation and penetration ability, and these reasons have been widely used in nondestructive testing. Compared with other terahertz imaging approaches, terahertz digital holography can retrieve both quantitative amplitude and phase information about an object wavefront in real time. A continuous-wave terahertz reflective digital holographic method is proposed for measuring the profile of covered objects. Subpixel image registration and image fusion algorithms are presented to expand the field-of-view (FOV) of the system. The validity of the proposed method is verified by the experiment using an optical pumped far-IR gas laser and a pyroelectric array detector. The profile of a metallic bookmark covered by a polytetrafluoroethylene plate is obtained. The FOV is expanded by a factor of 1.75 compared with that of a reconstruction performed employing single hologram.

Long-term robust tracking remains a challenging problem in visual object tracking. Based on the popular tracking-by-detection framework, we propose an approach named real-time long-term correlation tracking by single-shot multibox detection (RLCT-SSD), in which tracking and detection work in parallel and cooperate together. Our algorithm consists of two parts: a tracking module is expected to track in real time and accurately, whereas a detection module is responsible for verifying the tracking results at intervals, and redetecting if necessary. The detector updates the tracking module when the tracking result is unreliable. We introduce a motion model on the basis of fast discriminative scale space tracker to design our tracking module. The detection module is based on the single-shot multibox detector algorithm. To further reduce the computational cost, we use the ShuffleNet as our base network of detection. The experimental results on OTB2013 and OTB2015 demonstrate that our RLCT-SSD performs favorably against most state-of-the-art trackers and achieves long-term accurate tracking running in real time.

Spectral computed tomography (CT) can reconstruct scanned objects at different energy-bins and thus solve the multimaterial decomposition (MMD) problem. Because the linear attenuation coefficients of different basis materials may be extremely close, the decomposition problem is often ill-conditioned. Meanwhile, traditional material decompositions with image-domain algorithms are usually voxelwise based. Therefore, these algorithms rely heavily on image quality. Ring artifacts often exist in the reconstructed images of spectral CT due to the inconsistency feature of energy-resolved detectors and beam-hardening effect. Considering the enlargement of the receptive field and taking advantage of the modeling ability of convolutional neural networks in deep learning, we proposed a convolutional material decomposition algorithm to solve the MMD problem through a basis of patches instead of pixels of the spectral CT images. Simulations and physical experiments were performed to validate the proposed algorithm, and its quality was compared with a traditional MMD algorithm in the image domain. Results show that the proposed method achieves good accuracy, reduces mean squared errors by one to two orders, and exhibits robustness in the MMD of spectral CT images even in the case that obvious ring artifacts is presented.

As a signal processing theory, compressive sensing (CS) breaks through the limitations of the traditional Nyquist sampling theorem and provides the possibility to solve the high sampling rate, large data volume, and real-time processing difficulties of traditional high-resolution radar. Based on the theory of single-pixel cameras, an array detection imaging system is built, and main structural parameters are analyzed. The simulation experiment of a simple target is organized to show that the number of measurements can be reduced by achieving the parallel operation through increasing the number of detectors. When the target changes, it is found that the sparsity problem has a great influence on the number of measurements. Therefore, an improved method is proposed using the structure flexibility of fiber array and detectors, which can reduce the number of measurements simultaneously while decreasing the number of detectors, which is superior to the original method.

We describe techniques developed to optimize beam pointing control for a CubeSat laser downlink demonstration mission being developed at the MIT Space Telecommunications, Astronomy, and Radiation Laboratory. To fine-point its downlink beam, the mission utilizes an uplink beacon signal at 976 nm captured by an on-board ±5-deg field-of-view detector and tracked by a 3.6-mm commercial, off-the-shelf MEMS fast steering mirror. As these miniature actuators lack feedback sensors, the system design is augmented with an optical calibration signal to provide the mirror’s pointing feedback. We describe the system and introduce calibration algorithms utilizing the feedback signal to achieve higher fidelity beam pointing control. A demonstration in the laboratory is conducted to obtain a quantitative performance analysis using quasi-flight hardware with simulated spacecraft body pointing disturbances. Experimental results show that beacon tracking errors of only 16 μrad root-mean-square are feasible for both axes, significantly exceeding the mission pointing requirement of 0.65 mrad and indicating the feasibility of narrower beams and higher data throughputs for next-generation downlink demonstration missions.

Scanning beam interference lithography (SBIL) is an advanced large-area grating manufacturing technology. To produce gratings with nanoscale phase accuracy, the phase detector is demanded for a high precision in SBIL. A well-designed homodyne detector with a four-orthogonal detection is proposed to meet the harsh measurement requirements. However, the phase detection could suffer from periodic nonlinearity error, which changes slowly over time. A real-time correction method based on an extended Kalman filter is applied to estimate and compensate the periodic nonlinearity. The simulation results show that this method has great advantages in eliminating the time-varying periodic nonlinearity, compared with the conventional least squares fitting method. An experimental setup is also established to validate the proposed correction method.

A compact stand-off chemical detector using a Michelson interferometer has been developed and is presented. Its size is only 104 × 183 × 108 mm3 and its weight is 2.5 kg, which makes it suitable for hand-held operation. This compact detector is a minimized version of the conventional Michelson interferometer. The housing for the interferometer was designed to be divided into two parts for minimization and convenient assembly. All the optics composing the interferometer were directly fastened to the housing. The moving mirror module in the Michelson interferometer was specially designed for the small size detector. Using a symmetrically positioned linear elastic plate, the tip and tilt angle of reflected light from the moving mirror were smaller than 8 arc sec during linear back-and-fourth motion without any active alignment feedback system, which results in low noise in the interference signal. The spectra of SF6 and NH3 were measured with changing concentration and the detection limit was determined to be 46.7 and 65.2 mg / m2, respectively. Additionally, outdoor measurement was demonstrated with a distance of about 1 km.

We propose a security-enhanced optical interference-based multiple-image encryption (IBMIE) using a modified multiplane phase retrieval algorithm (MPPRA) in the Fresnel transform domain. In this IBMIE scheme, while a phase-only mask (POM) distributing randomly between [ 0 , 2π ] is fixed, the other POM is iteratively extracted based on a modified mMPPRA, and thus, multiple plaintexts are simultaneously encrypted into two POMs with different distances to the image planes. At last, the retrieved POM is pixel scrambled by chaotic pixel scrambling (CPS). During image decryption, the decrypted images can be obtained at their preset positions by an intensity detector directly. The silhouette of the original images cannot be obtained using either of the two POMs. The parameters of both CPS and Fresnel transform can serve as security keys to enhance the security. Numerical simulation is presented to demonstrate the validity of the proposed mMPPRA-based IBMIE.

This paper proposes and investigates a partial discharge (PD) detector based on fiber Bragg grating (FBG) sensor and a mandrel to detect and localize PD in power transformers. An identification of PD in the early stages is important, so using high-resolution sensor is considerable. A Teflon hollow mandrel with attached FBG is chosen as the inner transformer PD detector. The design of the sensor in terms of materials, dimensions, and the shape is chosen; it receives signal strength according to the obtained distance and angle. Standard deviation of angle data is