Influence mechanism of the particle size on underwater active polarization imaging of reflective targets.

Underwater active polarization imaging is a promising imaging method, however, it is ineffective in some scenarios. In this work, the influence of the particle size from isotropic (Rayleigh regime) to forward-scattering on polarization imaging is investigated by both Monte Carlo simulation and quantitative experiments. The results show the non-monotonic law of imaging contrast with the particle size of scatterers. Furthermore, through polarization-tracking program, the polarization evolution of backscattered light and target diffuse light are detailed quantitatively with Poincaré sphere. The findings indicate that the noise light's polarization and intensity scattering field change significantly with the particle size. Based on this, the influence mechanism of the particle size on underwater active polarization imaging of reflective targets is revealed for the first time. Moreover, the adapted principle of scatterer particle scale is also provided for different polarization imaging methods.

Guide to the design of broadband full polarization imager based on dispersion-compensation Savart plates.

We provide a broadband channeled, modulated full polarization imaging technology based on dispersion-compensation Savart plates in 2020. It has the advantages of being compact, using the snapshot method, and having a bandwidth of 0.132 µm. It is thus invaluable for applications in diverse fields, including remote sensing, biomedicine, and military science. However, there are a lot of angle restrictions in the system. In practice, these angles cannot achieve such high machining precision, and we use the tolerance or compensation method of errors to analyze the influence of the angle deviation. This analysis will help the system achieve better compactness and stability and provide analysis methods for systems that use crystals as its key elements.

Visibility enhancement of underwater images based on polarization common-mode rejection of a highly polarized target signal.

Underwater active polarization imaging is promising due to its effect of significantly descattering. Polarization-difference is commonly used to filter out backscattered noise. However, the polarization common-mode rejection of target signal has rarely been utilized. In this paper, via taking full advantage of this feature of Stokes vectors S2 which ably avoids interference from target light, the spatial variation of the degree of polarization of backscattered light is accurately estimated, and the whole scene intensity distribution of background is reconstructed by Gaussian surface fitting based on least square. Meanwhile, the underwater image quality measure is applied as optimization feedback, through iterative computations, not only sufficiently suppresses backscattered noise but also better highlights the details of the target. Experimental results demonstrate the effectiveness of the proposed method for highly polarized target in strongly scattering water.

Snapshot broadband polarization imaging based on Mach-Zehnder-grating interferometer.

Full polarization imaging plays an important role in remote sensing to distinguish artificial objects from the natural environment, recognizing objects in shadows and sun glint suppression. In this paper, we propose a broadband full Stokes channeled modulated polarization imaging system based on a Mach-Zehnder-grating interferometer (MZGI) with advantages such as compact size, low cost, snapshot ability, and high optical efficiency. It uses gratings to compensate for the dispersion of the carried frequency when inputting broadband light to generate interference fringes. Two detectors are assembled to the output plane to acquire the interference fringes. Each image obtained by the detectors can be individually demodulated into different Stokes parameters individually. When the two groups are combined together, the full Stokes parameters are obtained. The simulation and optical efficiency analysis demonstrate that the interference fringes can obtain the full polarization information simultaneously with high optical efficiency in broadband wavelengths.

Experimental study on the sensitive depth of backwards detected light in turbid media.

In the recent past, optical spectroscopy and imaging methods for biomedical diagnosis and target enhancing have been widely researched. The challenge to improve the performance of these methods is to know the sensitive depth of the backwards detected light well. Former research mainly employed a Monte Carlo method to run simulations to statistically describe the light sensitive depth. An experimental method for investigating the sensitive depth was developed and is presented here. An absorption plate was employed to remove all the light that may have travelled deeper than the plate, leaving only the light which cannot reach the plate. By measuring the received backwards light intensity and the depth between the probe and the plate, the light intensity distribution along the depth dimension can be achieved. The depth with the maximum light intensity was recorded as the sensitive depth. The experimental results showed that the maximum light intensity was nearly the same in a short depth range. It could be deduced that the sensitive depth was a range, rather than a single depth. This sensitive depth range as well as its central depth increased consistently with the increasing source-detection distance. Relationships between sensitive depth and optical properties were also investigated. It also showed that the reduced scattering coefficient affects the central sensitive depth and the range of the sensitive depth more than the absorption coefficient, so they cannot be simply added as reduced distinct coefficients to describe the sensitive depth. This study provides an efficient method for investigation of sensitive depth. It may facilitate the development of spectroscopy and imaging techniques for biomedical diagnosis and underwater imaging.

Compact static imaging spectrometer combining spectral zooming capability with a birefringent interferometer.

A compact static birefringent imaging spectrometer (BIS) with spectral zooming capability is presented. It based on two identical Wollaston prisms and has no slit. The most significant advantage of the BIS is that we can conveniently select spectral resolution to adapt to different application requirements and greatly reduce the size of the spectral image data for capturing, saving, transferring, and processing. Also, we show this configuration blend the advantage of a grating spectrometer and a Michelson interferometer: extremely compact, robust, wide free spectral range and very high throughput.

Study of p-SiC/n-GaN Hetero-Structural Double-Drift Region IMPATT Diode.

Nowadays, the immature p-GaN processes cannot meet the manufacturing requirements of GaN impact ionization avalanche transit time (IMPATT) diodes. Against this backdrop, the performance of wide-bandgap p-SiC/n-GaN heterojunction double-drift region (DDR) IMPATT diode is investigated in this paper for the first time. The direct-current (DC) steady-state, small-signal and large-signal characteristics are numerically simulated. The results show that compared with the conventional GaN single-drift region (SDR) IMPATT diode, the performance of the p-SiC/n-GaN DDR IMPATT proposed in this design, such as breakdown voltage, negative conductance, voltage modulation factor, radio frequency (RF) power and DC-RF conversion efficiency have been significantly improved. At the same time, the structure proposed in this design has a larger frequency bandwidth. Due to its greater potential in the RF power density, which is 1.97 MW/cm2 in this study, indicates that the p-SiC/n-GaN heterojunction provides new possibilities for the design and manufacture of IMPATT diode.

[FTIR spectroscopic investigation of normal and malignant pleomorphic adenoma].

The FTIR (Fourier transform infrared) spectra of malignant pleomorphic adenoma tissues and surrounding normal tissues were investigated using the Spectrum GX FTIR Spectrometer. The results indicate that there were differences in the Fourier transform infrared spectra between the malignant pleomorphic adenoma tissues and the surrounding normal tissues at some bands. (a) Amide I band location related to the protein in milignant pleomorhic adenoma tissues shifted to a higher wave number compared to the normal tissues, and the absorption was increased in tumor tissues. This indicates that the degree of hydrogen-bonding herein increased; (b) The peak position related to PO2(-1) group in nucleic acid shifted to a higher wave number after canceration, and the absorption was stronger in tumor tissues compared to the normal tissues; (c) The absorption of band 1 640 cm(-1) related to -CH2 group in lipid was stronger but its peak position shifting was disorder.