Seamless Aperture Scaling of LBO crystals for High Energy Laser Applications

Based on the design of large aperture high energy laser technology developed at the national Ignition Facility (NIF), most planned IFE laser facilities need to operate at frequency converted shorter laser wavelengths. These future IFE driver lasers will have to operate at much higher average power and repetition rates than NIF while maintaining high wall plug efficiency. As compared to the current conversion crystal KDP, nonlinear crystal Lithium Tri-borate (LBO) has multiple times higher conversion efficiency, much wider angular acceptance and unparalleled Laser induced Damage Threshold (LiDT). To use LBO for these high energy Laser drivers would enable much more compact and efficient design and would save hundreds of millions of dollars in ignition IFE facilities. However, LBO is not currently available in aperture sizes large enough to be used in such high energy drivers. To grow single-crystalline LBO to large enough size is an extremely difficult, expensive, and lengthy process with myriads of risk factors leading to potentially catastrophic failure. Larger LBO boules also tend to be higher absorbing and less uniform than smaller LBO boules. An optically seamless and infinitely scalable process to increase the aperture of LBO crystals would have an enormous impact on the viability of laser driven fusion commercial energy production. Objective: To develop an optically seamless and infinitely scalable fabrication process to increase the optical aperture of LBOs used for Type I Second Harmonic Generation from IR to green. Tasks: To explore critical risk factors of diffusion bonding in various orientations of LBO. To multiply optical aperture in 2 dimensions to construct fundamental unit of a composite LBO. Measuring any optical distortion present in the composite as compared to monolithic single-crystalline LBO. High resolution testing of phase match and absorption uniformity of the composite as compared to monolithic single crystalline LBO. Commercial Applications: Historically, major technological advancements have been made possible by prerequisite advancements in materials. In the recent decades, various high energy laser facilities around the world have enabled breakthrough research in high energy density physics. Many of these facilities will make use of LBO for harmonic generation and optical parametric amplification. High energy free space communications and direct energy weapons are also looking for large aperture LBOs for frequency conversion of IR energy to the visible and UV spectrum. Inspired by the recent landmark event of achieving ignition at NIF, initiatives of future IFE power plant will make use of large aperture LBOs to realize highly efficient high repetition rate next generation laser drivers.