Measuring the detuning angle distribution within the full aperture of a large-aperture potassium dihydrogen phosphate (KDP) crystal is of great engineering importance for improving its frequency conversion efficiency. To improve the measurement speed of the crystal detuning angle, we propose a measurement method based on a flattened Gaussian beam with a large divergence angle. Theoretical simulation shows that the detuning angle of the KDP crystal is linearly related to the vertical position of the maximum light intensity of the second-harmonic laser when using this method. Experimental results confirm our theoretical analysis and show a relative measurement error of 1.32%, which meet the requirements of engineering applications. This measurement method saves 96% of the measurement time of the detuning angle of a single point within the aperture of the KDP crystal, enabling us to measure more points in a limited time, thus improving the measurement accuracy of the detuning angles over the full aperture of the KDP crystals.
Large aperture frequency converters are important components of the high-power laser system. It is often composed of a cascaded KDP (Potassium Dihydrogen Phosphate) crystal and dKDP (potassium deuterium phosphate) crystal system. The effect of the stress distribution of KDP crystal on the second harmonic generation (SHG) efficiency has been studied. It is found that the phase mismatch has a linear relationship with unidirectional stress. The result of the case study shows that the stress-induced phase mismatch in the SHG process is needed to be paid more attention to in engineering.
Aiming at the requirement of illumination uniformity and backscattering suppression in laser-driven inertial confinement fusion (ICF) facilities, we propose a polarization smoothing (PS) scheme based on stress-engineered optical element that can modulate linearly polarized light into a full Poincaré beam. The unique law of modulation of the polarization state by glass window under symmetrical loads is revealed by numerical simulations, the results indicate that the glass window exhibits a fast axis orientation that rotates with the polar angle and a phase retardance that increases with the radius under more than two symmetrical pressure loads. Further optical calculations show that when the pressure of the loads and the thickness of the glass are sufficient, the window can modulate the linearly polarized light into a full Poincarébeam.
In the amplifier of the large-aperture laser facility, the laser slab will have a depolarization effect in part areas due to the mounting stress and thermal stress. The depolarization effect will degrade the polarization state of the laser so that it cannot meet the design requirements, thereby affecting the efficiency of the whole facility. At the same time, depolarization will also cause low isolation in the facility and cause unpredictable damage to the optics. Aiming at the problem of depolarization, this article proposes a method to adjust the stress distribution of the laser slab by mounting load, and then adjust the polarization state of the slab, so that the stress distribution of the glass is uniform, and the position of the glass depolarization is controlled as far from the four corners as possible and minimize the influence of depolarization effect on the laser.
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