Brendan Reagan | 20-FS-011
Optical parametric chirped pulse amplification (OPCPA) is an advantageous technique for generating high contrast, tunable, broadband pulses at wavelengths from the visible to the infrared. The Scalable High Power Advanced Radiographic Capability laser, Big Aperture Thulium laser, and other laser concepts under development by Lawrence Livermore National Laboratory are expected to employ OPCPA to produce the seed pulses that will be amplified by the main, high energy amplifiers. However, high-repetition-rate pump lasers of sufficient energy to drive Joule-level and higher OPCPA usually do not have good spatial uniformity, resulting in poorly amplified beam quality and degraded conversion efficiency.
In this feasibility study, we theoretically and experimentally investigated using a beam homogenization technique to redistribute the pump-beam energy into a more uniform pump profile and to allow us to shape the pump beam into an arbitrary beam profile, e.g., a square. We developed a model of optical parametric amplification incorporating the spectrum of angles that accompany these beam homogenization techniques and employed the model to determine the impacts on gain, efficiency, spatial profile, and bandwidth for OPCPA. We designed and manufactured a pair of the phase masks to shape an arbitrary-shaped pump beam into a uniform square profile. Using this homogenization setup, we made the first demonstration, to our knowledge, of OPCPA with a homogenized pump beam.
This work advances the Laboratory's core competency in lasers and optical science and technology, and supports Livermore's work in high-energy and high-average-power laser technologies. Advances in high average-power lasers are expected to have applications for inertial confinement fusion, basic science, accelerator technology, and industrial uses such as welding and laser peening.