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• 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]