Nd:YAG based laser sources for targeting applications

Abstract

The aim of the research is to improve laser system products manufactured at Selex ES which are used primarily for airborne targeting applications. This is achieved by developments to the design that prevent failures during manufacture or improve beam parameters such as divergence. A Q-switched diode-side-pumped Nd:YAG zig-zag geometry slab laser within a cross Porro prism resonator is investigated. This perturbation insensitive resonator design is used in laser systems operating over the full military environment of vibration and temperature. A number of aspects of the design are computer modelled with experimental verification, such as the effects of thermal lensing in the Nd:YAG slab, and the polarisation states in the resonator. These were used to analyse a number of issues encountered during manufacture, such as the lack of control over the polarisation state for output coupling, pre-lase causing damage to optical elements, and thermal lensing producing variations in beam quality. A number of design changes were made and, after experiments to verify improved performance, they were successfully integrated into a number of laser production programmes. The beam quality of laser systems was found to be affected by thermal lensing. A number of novel solutions were tested experimentally, which affected the thermal lens. Results of the alteration of the pump distribution in the Nd:YAG slab and the profile of conduction cooling are presented. 885 nm pumping instead of the traditional 808 nm pumping produced a reduction of the thermal lens by a factor of two from -0.1 D to -0.05 D, producing an improvement in the laser beam quality from M2 6.5 to 3.5. An enhancement in brightness of 2.2 was demonstrated using a laser resonator incorporating a deformable bimorph mirror. A new concept for a targeting laser source, which incorporated an eye-safe wavelength, was demonstrated using a common resonator intracavity OPO design. A conversion efficiency of 40% was achieved for 36 mJ output of 1573 nm eye-safe light from a 90 mJ laser at 1064 nm. The relative pointing directions of the two wavelength beams was measured to be within 250 μRad angular separation, which will be unaffected by ambient temperature variation. This level of performance is challenging to achieve in the current laser system design incorporating an extracavity OPO.