High power ultrashort pulse lasers (USPLs) are important for material modifications on the micron scale with minimal or precisely controllable heat effects, cataract surgery, atmospheric diagnostics, especially in remote sensing, etc. In particular the LIDAR method has become a powerful technique to monitor atmospheric parameters and has helped to understand a variety of atmospheric phenomena. We propose to use transverse mode selection in large aperture master oscillator followed by coherent beam combining approach in order to increase the energy of ultra-short pulse lasers without chirped pulse amplification. This approach is based on the advances in volume Bragg gratings technology development. We recently succeeded in recording of multiple transmitting Bragg gratings inside a single plate of PTR glass. Recording of gratings with orthogonal planes of diffraction allowed transverse mode selection for two axes simultaneously and therefore allows single transverse mode operation of multimode solid state lasers. It gives us additional opportunity to use large aperture glass/crystal gain media and high power pump diodes keeping the high beam quality. The use of multiplexed transmitting gratings with parallel planes of diffraction will be used for coherent combining of several large aperture oscillators.
Benefit: Our new Phase I proposal is to demonstrate a compact high power USPL without chirped pulse amplification. Scaling the power is supposed to be done by dramatic increase of pulse energy emitted by a master oscillator and coherent beam combination of several sub-systems. This progress is enabled by a new type of VBGs i. e. double transmitting VBGs that provide 2D transverse mode selection of lasers with large aperture gain elements. Monolithic design of multiplexed VBGs allows compactness and reliability of the UFPL system. This new project will include application of both RE doped glasses and crystals for development of laser systems in eye safe wavelength region (from 1.5 to 2 um). The proposed approach will provide dramatic increase of pulse energy and average power without chirped pulse amplification and therefore improve reliability of laser systems that should be used in harsh conditions of medical, inductrial or military applications. In the framework of the Phase II, if awarded, the detailed design for compact, high power USPL system and its subsystems will be provided. Based on the results obtained the Phase I of the project, the research activity within the Phase II will be devoted to the integration and miniaturization of the laser design, development of prototype for NAVY evaluation. Moreover, detailed design drawings and full description of system components will be delivered. Commercial application includes, laser systems for cataract removal surgery, study of living structures, LIDAR application. Federal Government application will include high energy USPL systems for hazards detection, remote control, filament generation, etc.
Keywords: Ultrashort Pulses, Ultrashort Pulses, PTR glass, Non-Chirped amplification., Transmitting Bragg Gratings, Multiplexed Bragg gratings
