Refinement method for compressive hyperspectral data cubes based on self-fusion.

Compressive hyperspectral images often suffer from various noises and artifacts, which severely degrade the imaging quality and limit subsequent applications. In this paper, we present a refinement method for compressive hyperspectral data cubes based on self-fusion of the raw data cubes, which can effectively reduce various noises and improve the spatial and spectral details of the data cubes. To verify the universality, flexibility, and extensibility of the self-fusion refinement (SFR) method, a series of specific simulations and practical experiments were conducted, and SFR processing was performed through different fusion algorithms. The visual and quantitative assessments of the results demonstrate that, in terms of noise reduction and spatial-spectral detail restoration, the SFR method generally is much better than other typical denoising methods for hyperspectral data cubes. The results also indicate that the denoising effects of SFR greatly depend on the fusion algorithm used, and SFR implemented by joint bilateral filtering (JBF) performs better than SRF by guided filtering (GF) or a Markov random field (MRF). The proposed SFR method can significantly improve the quality of a compressive hyperspectral data cube in terms of noise reduction, artifact removal, and spatial and spectral detail improvement, which will further benefit subsequent hyperspectral applications.

Transverse effect of superradiation due to nonlinear effect in Rb atomic medium.

We report on the investigation on the transverse effect of superradiation (SR) in Rb atomic medium by analyzing and comparing the diffraction patterns in the far-field under the circumstances that Gaussian and Bessel beam are taken as the excitation respectively. It is found that Gaussian SR shows a ring-pattern and its beam profile is closely dependent on the incident power and position of the sample cell. The experimental results are in good agreement with the simulations using semi-classical theory of SR together with spatial self-phase modulation (SPM), indicating that the transverse effect of SR is mainly attributed to its propagation in the nonlinear medium. By contrast, the beam profile of Bessel SR is hardly influenced by the input power thanks to its non-diffraction property. The comparison further confirms that the transverse effect of the SR is the result of the nonlinear effect for SR. This work provides useful information in understanding the physics behind the transverse effect of SR, which would be of significance in the applications of SR, such as enhancement on the beam quality and efficiency of the SR sources.

Restoration Method of Hadamard Coding Spectral Imager.

Hadamard coding spectral imaging technology is a computational spectral imaging technology, which modulates the target's spectral information and recovers the original spectrum by inverse transformation. Because it has the advantage of multichannel detection, it is being studied by more researchers. For the engineering realization of push-broom coding spectral imaging instrument, it will inevitably be subjected to push-broom error, template error and detection noise, the redundant sampling problem caused by detector. Therefore, three restoration methods are presented in this paper: firstly, the one is the least squares solution, the two is the zero-filling inverse solution by extending the coding matrix in the redundant coding state to a complete higher order Hadamard matrix, the three is sparse method. Secondly, the numerical and principle analysis shows that the inverse solution of zero-compensation has better robustness and is more suitable for engineering application; its conditional number, error expectation and covariance are better and more stable because it directly uses Hadamard matrix, which has good generalized orthogonality. Then, a real-time spectral reconstruction method is presented, which is based on inverse solution of zero-compensation. Finally, simulation analysis shows that spectral data could be destructed relative accuracy in the error condition; however, the effect of template noise and push error on reconstruction is much greater than that of detection error. Therefore, in addition to reducing the detection noise as much as possible, lower template noise and more accurate push controlling should be guaranteed specifically in engineering realization.

Thermally Induced Nonlinearity of Organic Solvents and Real-Time Visualization of the Nucleophilic Addition Reaction Using Spatial Cross-Phase Modulation.

We report on the study of the thermally induced nonlinear optical (NLO) properties of the commonly used organic solvents at the near-infrared range using spatial cross-phase modulation (SXPM). The results indicate that those solvents (alcohols, formic acid, and acetic acid) with -OH and -COOH functional groups have obvious NLO effect in the near-infrared range due to the third overtone absorption of the O-H band. In addition, the NLO effect of the ketones and aldehydes is enhanced when water or nitric acid is added, because the products with -OH and -COOH are generated, respectively, according to the nucleophilic addition reactions. Finally, real-time visualization of the acetone nucleophilic addition reaction is realized by monitoring the SXPM diffraction patterns' variation with time. This work not only is of importance in studying the NLO properties of the materials, e.g, interpreting the results performed in solutions and selecting suitable solvents, but also provides a simple way to visualize chemical reactions.