Deep Learning frameworks are gaining increased popularity in image processing tasks such as computational hyperspectral imaging. While these frameworks achieve state-of-the-art results in terms of reconstruction quality and run time, they often require massive databases of hyperspectral cubes for training the reconstruction algorithms. Unfortunately, such databases are usually hard to acquire due to complexity and cost considerations. To mitigate these challenges, we propose a method for generating a synthetic database of hyperspectral cubes in the visible range using a limited number of natural hyperspectral cubes, an unlimited number of RGB images, and a Generative Adversarial Network model. The suggested algorithm, dubbed SHS-GAN, is trained to get a query RGB image and to output a synthetic hyperspectral cube. While the spectral domain of the synthetic hyperspectral cube shares similar statistical properties as the natural hyperspectral cubes used in the training process, the SHS-GAN is trained to preserve the spatial characteristics of the query RGB image, whereas the R, G, B values provide an additional constraint along with the spectral domain. Our suggested framework was utilized for performing Snapshot Spectral Imaging (SSI) from a single monochromatic dispersed and diffused snapshot using the DD-Net reconstruction neural network. We demonstrate, by simulations and lab experiments, that enhancing the training database with synthetic data from the SHS-GAN improves the reconstruction quality of the hyperspectral cube. In addition, we share a new original database of more than 10,000 hyperspectral cubes of real objects of size 256x256x29 in the 420-700 nm visible range.

We propose a snapshot spectral imaging method for the visible spectral range using a single monochromatic camera equipped with a two-dimensional (2D) binary-encoded phase diffuser placed at the pupil of the imaging lens and by resorting to deep learning (DL) algorithms for signal reconstruction. While spectral imaging was shown to be feasible using two cameras equipped with a single, one-dimensional (1D) binary diffuser and compressed sensing (CS) algorithms [Appl. Opt.59, 7853 (2020).APOPAI0003-693510.1364/AO.395541], the suggested diffuser design expands the optical response and creates optical spatial and spectral encoding along both dimensions of the image sensor. To recover the spatial and spectral information from the dispersed and diffused (DD) monochromatic snapshot, we developed novel DL algorithms, dubbed DD-Nets, which are tailored to the unique response of the optical system, which includes either a 1D or a 2D diffuser. High-quality reconstructions of the spectral cube in simulation and lab experiments are presented for system configurations consisting of a single monochromatic camera with either a 1D or a 2D diffuser. We demonstrate that the suggested system configuration with the 2D diffuser outperforms system configurations with a 1D diffuser that utilize either DL-based or CS-based algorithms for the reconstruction of the spectral cube.

We propose a snapshot spectral imaging method for the visible spectral range using two digital cameras placed side-by-side: a regular red-green-blue (RGB) camera and a monochromatic camera equipped with a dispersive diffractive diffuser placed at the pupil of the imaging lens. While spectral imaging was shown to be feasible using a single monochromatic camera with a pupil diffuser [Appl. Opt.55, 432 (2016)APOPAI0003-693510.1364/AO.55.000432], adding an RGB camera provides more spatial and spectral information for stable reconstruction of the spectral cube of a scene. Results of optical experiments confirm that the combined data from the two cameras relax the complexity of the underdetermined reconstruction problem and improve the reconstructed image quality obtained using compressed sensing-based algorithms.

We propose designs of pupil-domain optical diffusers for a snapshot spectral imaging system using binary-phase encoding. The suggested designs enable the creation of point-spread functions with defined optical response, having profiles that are dependent on incident wavefront wavelength. This efficient combination of dispersive and diffusive optical responses enables us to perform snapshot spectral imaging using compressed sensing algorithms while keeping a high optical throughput alongside a simple fabrication process. Experimental results are reported.

Colour RGB imaging with high throughput was achieved by a monochromatic digital camera with a dispersive diffuser at its pupil. An acquired snapshot monochromatic image was converted to colour coordinates through spectra, by resorting to digital processing with a compressed sensing-based algorithm of spectral imaging. Results of optical evaluation and calibration of an optical system and colour imaging experiments are reported.

Color RGB imaging with high throughput was achieved by a monochromatic digital camera with a dispersive diffuser at its pupil. An acquired snapshot monochromatic image was converted to color coordinates through spectra, by resorting to digital processing with a compressed sensing-based algorithm of spectral imaging. Results of optical evaluation and calibration of an optical system and color imaging experiments are reported.

We propose a snapshot spectral imaging method that enables direct reconstruction of spatial maps for spectral signatures of given materials using a monochromatic image sensor. An image-plane array of dispersive shapers converts an aerial image of an object into a tailored mixture of spectral and spatial data that is sensed and digitally processed to reconstruct weight coefficients of the spectral signatures. The feasibility of the method is proven by computer simulations.

Spectral imaging (SI) refers to the acquisition of the three-dimensional (3D) spectral cube of spatial and spectral data of a source object at a limited number of wavelengths in a given wavelength range. Snapshot spectral imaging (SSI) refers to the instantaneous acquisition (in a single shot) of the spectral cube, a process suitable for fast changing objects. Known SSI devices exhibit large total track length (TTL), weight and production costs and relatively low optical throughput. We present a simple SSI camera based on a regular digital camera with (i) an added diffusing and dispersing phase-only static optical element at the entrance pupil (diffuser) and (ii) tailored compressed sensing (CS) methods for digital processing of the diffused and dispersed (DD) image recorded on the image sensor. The diffuser is designed to mix the spectral cube data spectrally and spatially and thus to enable convergence in its reconstruction by CS-based algorithms. In addition to performing SSI, this SSI camera is capable to perform color imaging using a monochromatic or gray-scale image sensor without color filter arrays.

We propose a spectral imaging method that allows a regular digital camera to be converted into a snapshot spectral imager by equipping the camera with a dispersive diffuser and with a compressed sensing-based algorithm for digital processing. Results of optical experiments are reported.

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ϕ c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10−3(Ω cm)−1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.

The method of electrophoretic deposition (EPD) was used to fabricate ion-conducting polymer-in-ceramic membranes. TGA, DSC, XRD, TOFSIMS, ESEM and AC-impedance tests were used for the characterization of the films. We found that the relative content of polyethylene oxide and LiAlO2 its the membrane depends on the type of solvent and composition of the suspension. Films deposited at 50V are smoother, conformal and more uniform than those prepared at 100, 150 and 200V. TOFSIMS positive-ion-species images showed that with increase in concentration of ceramic powder in the suspension, the deposition of PEO occurs predominantly between the LiAlO2 particles. The ionic conductivity of a composite membrane, with impregnated 0.3 M LiTFSI-PYR14TFSI ionic-liquid electrolyte is 1-3 mS/cm at 30-60 degrees C and comparable to that of commercial battery separators. The conductivity of quasi-solid plasticized PEO-in-LiAlO2 electrolyte is 0.2 mS/cm at room temperature and does not change up to 100 degrees C. When deposited on a Si anode the membrane conformally follows the contours of the rough electrode surface and provides strong mechanical integrity to the anode, enabling improved capacity of the Li/Si cell. This study paves the way for the application of a new simple EPD approach to the preparation of wide-temperature-range quasi-solid lithium-ion conducting electrolytes. (C) 2013 Elsevier Ltd. All rights reserved.

Resonance domain diffraction gratings with local periods near the wavelength may have very high diffraction efficiencies. Unfortunately, they are difficult to fabricate, especially for use with light in visible and shorter wavelengths. We present several methods for fabricating surface relief resonance domain diffraction gratings used in the visible spectral region. We also optimize the relevant fabrication parameters and compare the resulting performance for each method. For the fabrication, we resort to e-beam lithography and reactive ion etching. Characterization is performed with environmental scanning electron microscopy, atomic force microscopy, and optical measurements on representative structures. Nearly 100% Bragg diffraction efficiency can be achieved with transmission resonance domain binary gratings formed in fused silica and having a period of 0.5 mu m and a groove depth of 1 mu m. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.11.118002]

We investigate different types of structural defects in 20-30 mu m thick Yb/AI-codoped fused silica layers on a pure fused silica substrate, and show that all types of structural defects can be treated in a single laser heat treatment. Laser-induced processes of defect elimination include diffusion of micro-voids, amorphization of crystallites and roughness reduction via surface-tension-driven mass flow. The physical mechanisms for defect elimination are analyzed in terms of onset temperature and typical time of elimination. Results of such treatment include complete amorphization, reduction of surface roughness by an order of magnitude to about 15 nm, and a remarkable improvement of more than an order of magnitude in optical cross-transmittance. The treatment thus provides a possible route for producing lasers and high-power integrated optics components using silica-on-silica technology. (C) 2011 Elsevier B.V. All rights reserved.

The saturated optical absorption of multi-walled carbon nanotube (MWNT)-doped hybrid-glass composites was studied at 1064 nm with nanosecond long pulses using the Z-scan technique. Increased transmission was demonstrated for high intensity pulses. The results were modeled for the limiting cases of a slow or a fast saturable absorber, both referring to a three-level system. The ground-state absorption cross section was estimated as 2.3x10(-18) cm(2), in good agreement with that of a single carbon atom. The excited state absorption cross section for carbon nanotubes (CNTs) was estimated for the first time as 6.9x10(-19) cm(3). The absorber's density of 2.8x10(18) cm(-3) is smaller by approximately a factor of 5 compared to the nominal density of carbon atoms incorporated into the glass. This could be a result of the broad band-like states formation in the MWNTs. The above figures were obtained by assuming that the excited state decay time was longer than the pulse duration of similar to 1 ns. (C)2012 Optical Society of America

Surface-relief resonance-domain diffraction gratings with deep and dense grooves provide considerable changes in light propagation direction, wavefront curvature, and nearly 100% Bragg diffraction efficiency usually attributed only to volume optical holograms. In this paper, we present design, computer simulation, fabrication, and experimental results of binary resonance-domain diffraction gratings in the visible spectral region. Performance of imperfectly fabricated diffraction groove profiles was optimized by controlling the DC and the depth of the grooves. Indeed, more than 97% absolute Bragg diffraction efficiency was measured at the 635 nm wavelength with binary gratings having periods of 520 nm and groove depths of about 1000 nm, fabricated by direct electron-beam lithography and reactive ion etching.