Sodium line guide star laser using optical parametric oscillator

Abstract

The aim of this project is to develop a novel, high average power source of highly coherent radiation at the 589nm sodium D2 resonance line for use in creating a laser guide star for use with adaptive optics systems such as astronomical telescopes and satellite ranging. Adaptive optics is used to improve the resolution of ground base telescope by compensating the atmospheric turbulence. To achieve this it is necessary to measure and correct the distortions caused by the atmosphere on the beam. A laser guide star provides a beacon which combined with a wavefront sensor allows the effect of the atmosphere to be quantified and mechanical corrections made to the adaptive optics in the telescope to cancel those distortions. Whilst laser guide stars have been demonstrated as effective in a number of astronomical observatories, at present there is no laser technology that dominates this application. This project will demonstrate a novel approach to the creation of high average power optical sources for guide star applications. The aim of the project is to build a prototype of high average power, synchronously pumped optical parametric oscillators pumped by novel high power solid state laser technology. The Magnesium Oxide doped periodically poled Lithium Niobate was used as the nonlinear crystal for the 532nm pumped singly resonant parametric oscillator. The oscillator was pumped by 1.4W of 532nm light which was created from a 3.5W mode-locked Nd:YVO4 laser by a Lithium Triborate second harmonic generator. With a grating period of 12.05μm, the signal at the wavelength of 594nm was obtained at 150oC. There was unexpected green absorption of the crystal, which undermined the performance of the oscillator. However, from the experimental results of a Potassium Titanyl Phosphate optical parametric oscillator, it was demonstrated that highly efficient parametric oscillator can be built despite the idler absorption.