Search

• Particle Swarm Optimization to find optimal values for image reconstruction by Phase Retrieval. • Faster convergence and better reconstruction results for 16-bit images. • Image reconstruction process is automated, eliminating the manual search of best values for reconstruction. Imaging through scattering media has become an important aspect in optical imaging. To achieve this, different approaches have been presented to recover the phase of an imaging object from its scattered speckle behind a scattering medium. However, all these algorithms require initial parameters which are obtained based on prior knowledge of the imaging object. This is impractical, as prior knowledge of the imaging object is not always available in real imaging applications. In this paper, we propose using a Particle Swarm Optimization algorithm to find these optimal parameters without requiring prior knowledge of the imaging object. These optimal values are then adopted in the Phase Retrieval algorithm based on object-modulated speckles for object image reconstruction behind a scattering medium in a single-shot imaging system. The obtention of the values for the standard deviation for Gaussian filter and the threshold control allows Phase Retrieval to converge faster and avoids the need for running the algorithm more than once in the search for the best reconstruction. [ABSTRACT FROM AUTHOR]

• Surface degradation of Ge in vacuum on different laser conditions are showed. • The influences of processing parameter and material failure behavior are analyzed. • Mechanism in damage variation with laser ablation is compared in air and vacuum. • Damage mechanism contains thermal effect, plasma shock wave and mechanical stress. Laser-induced damage of germanium (Ge) sheets plays a key role to estimate the lifetime of optical components in the vacuum and space irradiation environment. However, the dependence between the degrees of laser-induced surface damage and nanosecond pulsed irradiation remains unclear for Ge sheet. Here, we investigate damage morphology and the growth characteristic of Ge sheets under different conditions and measure the laser-induced damage threshold (LIDT) in vacuum. Our results reveal that optical reflectivity of Ge in vacuum chamber falls 92% because of the defective sites on the damaged surface. The area, the depth and the size of the damage crater increase but the hillock height and the surrounding thermal diffuse area decrease along with the increase of vacuum degree. The thermal effect, the failure effect of plasma shock wave and the mechanical stress are analyzed to be the main mechanism in the laser damage. The combined experimental and theoretical work gives an insight into the change of surface damage and material failure behavior, hence broadens the potential applications of Ge sheets in areas of laser material manufacturing and laser processing. [ABSTRACT FROM AUTHOR]

Pump-probe technique is employed to investigate the dynamic process of shock wave in water induced by femtosecond laser pulse. The time resolved shadowgraphs and holograms were obtained experimentally, and the 2-dimensional phase maps were reconstructed from holograms. From the analysis of the phase maps, the evolution process within the laser–water interaction region was described and the formation mechanism of the shock wave was discussed. [ABSTRACT FROM AUTHOR]

The recognition and classification of wire melted marks is crucial in modern fire investigation. The existing technology mainly uses physical or chemical methods to deal with wire melted marks and draws conclusions through manual observation, or manually extracts the features and train classification model, both of which consume excessive manpower and resources. The research on automatic feature extraction and recognition of wire weld marks by artificial intelligence technology is still blank. Based on the data set of wire melted mark metallographic images provided by a city fire research institute, we proposed an algorithm to recognize the type of wire melted mark metallographic images based on artificial intelligence which can help fire fighters efficiently speculate the cause of fire. In the algorithm, the TransUnet network is used to segment the melted zone by semantic segmentation to extract the melted zone containing the main features, and the mIOU reaches 92.2%. Then, the features of wire melted mark are extracted based on the melted zone image. Finally, XGBoost is used for feature modeling for classification. The F1 Score of model is 82.9%. [ABSTRACT FROM AUTHOR]

• Proposed a new sampling method for Fourier single pixel imaging, by which significant Fourier coefficients were effectively sampled at low sampling ratios, so the image resolution is greatly improved. • This method innovatively takes the use of the property that the Fourier domain images of most natural sceneries have light-rays pattern and the light rays corresponds to the borders in spatial domain. Therefore the discrete and sparse light rays enable effective sampling of high frequencies that are important for image resolution. • An analysis of randomly chosen 200 images from VOC image database proved most natural scenery images have the light rays pattern in Fourier domain. • The proposed method provides a potential direction to improve the sampling efficiency of Fourier single-pixel imaging. Fourier single-pixel imaging (FSI) technology has attracted wide attention for its high imaging efficiency and broad applicability. However, the existing sampling methods cannot effectively sample the key high-frequency Fourier coefficients with low sampling ratio. To address this problem, we propose an adaptive sampling method based on spectral energy continuity, especially in the directional distributed frequencies that correspond to the borders in the image. In this method, the significant high-frequency components are predicted from simply isometric sampled low frequencies and the generated sampling trajectory is close to the optimal. Because more important high-frequency information is sampled, the image quality at low sampling ratio is greatly improved. We demonstrate with both simulations and experiments that this sampling method is effective in suppressing noise and obtaining detailed information of the image at low sampling ratios. [ABSTRACT FROM AUTHOR]