In this Letter, the feasibility of the high laser damage threshold liquid crystal spatial light modulator (LC-SLM) based on gallium nitride (GaN) transparent conductive electrode is proved. The laser induced damage threshold (LIDT) is measured, and a high LIDT reflective optical-addressed liquid crystal light valve (OALCLV) based on GaN is designed and fabricated. The proper work mode of the OALCLV is determined, and the OALCLV obtained a maximum reflectivity of about 55%, an on-off ratio of 55:1 and image response is demonstrated.
Speckle noise in digital holography has a great influence on image quality, and one of the reasons for the formation of speckle noise is that the degree of coherence for the reference light and the object light is too high and unnecessary noise is introduced to the recorded hologram. In this paper, the spatial depolarization and the temporal domain depolarization are analyzed to reduce the speckle noise. The spatial depolarization utilizes the depolarization performance of the depolarizer. By adding a quartz depolarizer to the object light, the linearly polarized light in the object light becomes randomly polarized light, thereby reducing the degree of coherence with the reference light, realizing the suppression of speckle noise, and by utilizing the characteristics of pupil parameters towards the depolarization degree, it is to realize the control for the degree of coherence. The temporal domain depolarization uses two quarter-wave plates and adjustable liquid crystal to realize the depolarization superposition. By controlling the phase delay of the liquid crystal phase variable retarder, the multi-depolarization accumulation in a short time is realized, and the experimental results show that this method preserves the detail portion of the image while better removing speckle noise. Finally, the Non-Local Means filtering algorithm is used to make the reconstructed image smoother. The method proposed in this paper has great applicable value for improving the image quality of digital holography system. INDEX TERMS Digital holography speckle noise, depolarization, quartz depolarizer, liquid crystal.
In this paper, Feature Engineering (FE) was applied to Landslide Susceptibility Mapping (LSM), while the most suitable conditioning feature dataset and analysis method were tested and analyzed. Tianshui city was taken as the study area, three types of geohazard (collapse, landslide, and unstable slopes) were used, while a total of twenty-three conditioning features were generated; two dimensionless methods (normalization and standardization) were tested afterward. Four Random-Forest-based (RF-based) feature selection methods using different indicators (Gini Impurity, GI; Out of Bag Accuracy, OOBA) were proposed and tested separately. The LSMs of four models were carried out under the guidance results of FE, namely Classification and Regression Tree (CART), Random Forest (RF), Logistic Regression (LR), and Support Vector Machine for Classification (SVC). For feature enhancement, standardization had significant advantages over normalization. All RF-based methods were proven effective, lifting the AUC by 0.01~0.02. The RF model achieved the highest LSM accuracies, respectively, 0.949 (landslide), 0.957, and 0.949 (unstable slopes), improved by 0.008 (landslide), 0.005 (collapse), and 0.013 (unstable slopes). This proved that the FE helped to improve LSM and can help to decide the dominant conditioning factors for regional geohazards.
In this paper, we propose a fast interference spectral imaging system based on liquid crystal (LC) relaxation. The path delay of nematic LC during falling relaxation is used for the scanning of the optical path. Hyperspectral data can be obtained by Fourier transforming the data according to the path delay. The system can obtain two-dimensional spatial images of arbitrary wavelengths in the range of 300–1100 nm with a spectral resolution of 262 cm−1. Compared with conventional Fourier transform spectroscopy, the system can easily collect and integrate all valid information within 20 s. Based on the LC, controlling the optical path difference between two orthogonally polarized beams can avoid mechanical movement. Finally, the potential for application in contactless and rapid non-destructive optical component defect inspection is demonstrated.
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