Bragg selectors of transversal modes for high power lasers

The objective of this proposal is to demonstrate the novel type of mode selection for high power lasers for target tracking and interception. In Phase I, LPTI proved the concept of volume Bragg gratings (VBGs), which were recorded in photo-thermo-refractive (PTR) glass, as effective selectors of transverse modes for pulsed neodymium laser. Dramatic narrowing of angular divergence of Nd:YAG laser was shown. Recently, UCF/CREOL demonstrated emission with diffraction limited divergence from a wide stripe semiconductor laser with PTR VBG as output coupler. Those results enable achieving of low divergence for high power solid state, fiber, and semiconductor lasers. A correlation between induced absorption, scattering, and refraction will be studied, and a technology of transmitting PTR Bragg gratings will be optimized for transversal mode selection. Interrelationships between angular and spectral selectivity of volume Bragg grating (VBG) and parameters of laser resonators will be studied and optimal design for high power, low divergence operation will be determined. PTR VBGs with absolute diffraction efficiency exceeding 97% withstanding 100 kW/cm2 CW laser radiation, and 30 J/cm2 of 10 ns pulsed radiation in near IR spectral region will be demonstrated for intracavity applications.100-Watt-class lasers with sub-nanometer spectral width and diffraction limited divergence will be demonstrated.