Generation of 351 nm UV Q-switched laser beam with controllable spatial coherence

Abstract

Ultraviolet laser with controllable spatial coherence is essential for a wide range of applications. In this study, we developed a pulsed, partially spatial coherence laser source operating in the ultraviolet (UV) range through extra-cavity frequency tripling of a solid-state Nd:glass degenerate laser. The oscillating modes of the laser can be flexibly controlled by size of the spatial filter inside the laser cavity, thus modulating the spatial coherence of the UV laser. The beam pattern and focusing, speckle suppression and imaging, coherence property of the partially coherent UV laser is investigated in detail. The third-harmonic generation (THG) supports many more transverse modes than the fundamental generation and the second-harmonic generation (SHG). Compared with high coherent UV laser, low spatial coherent UV laser has better speckle suppression effect and smoother focused spot intensity distribution. The high brightness, good monochromaticity and low spatial coherence make the UV degenerate laser an attractive illumination source for inertial confinement fusion, lithography, laser processing and others.