High-average-power diode-pumped Yb: YAG lasers

A scaleable diode end-pumping technology for high-average-power slab and rod lasers has been under development for the past several years at Lawrence Livermore National Laboratory (LLNL). This technology has particular application to high average power Yb:YAG lasers that utilize a rod configured gain element. Previously, this rod configured approach has achieved average output powers in a single 5 cm long by 2 mm diameter Yb:YAG rod of 430 W cw and 280 W q-switched. High beam quality (M{sup 2} = 2.4) q-switched operation has also been demonstrated at over 180 W of average output power. More recently, using a dual rod configuration consisting of two, 5 cm long by 2 mm diameter laser rods with birefringence compensation, we have achieved 1080 W of cw output with an M{sup 2} value of 13.5 at an optical-to-optical conversion efficiency of 27.5%. With the same dual rod laser operated in a q-switched mode, we have also demonstrated 532 W of average power with an M{sup 2} < 2.5 at 17% optical-to-optical conversion efficiency. These q-switched results were obtained at a 10 kHz repetition rate and resulted in 77 nsec pulse durations. These improved levels of operational performance have been achieved as a result of technology advancements made in several areas that will be covered in this manuscript. These enhancements to our architecture include: (1) Hollow lens ducts that enable the use of advanced cavity architectures permitting birefringence compensation and the ability to run in large aperture-filling near-diffraction-limited modes. (2) Compound laser rods with flanged-nonabsorbing-endcaps fabricated by diffusion bonding. (3) Techniques for suppressing amplified spontaneous emission (ASE) and parasitics in the polished barrel rods

Quasi-collinear and partially degenerate four-wave mixing: An alternative explanation of the phase-conjugation property of backward stimulated scattering

A quasi-collinear and partially degenerate four-wave mixing model is proposed to explain the optical phase-conjugation property of various types of stimulated backscattering. According to this model, after passing through a phase-disturbed medium or an aberration plate, the input pump beam can be resolved into two portions: a stronger undisturbed regular portion and a weaker phase-disturbed irregular portion. These two portions interfere with each other and create a volume holographic grating in the pumped region of the scattering medium. Only the stronger undisturbed portion of the pump field can excite an initial backward stimulated scattering beam with a regular wavefront. When the latter (as a reading beam) passes through the induced holographic grating, a diffracted wave will be created and then amplified together with the reading beam. A rigorous mathematical analysis shows that under certain conditions the combination of these two portions (the reading wave and the diffracted wave) of the backward stimulated scattering can be an approximate phase-conjugate field of the input pump field. The major theoretical conclusions are basically supported by the experimental results based on a specially designed two-beam interference setup.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45798/1/11447_2005_Article_570.pd