Major advances in laser technology at LLE have included the demonstration of high-efficiency frequency doubling and tripling of fusion lasers1 and the development of short-pulse, chirped-pulse-amplification (CPA) lasers2 These technologies were combined a few years ago with the demonstration of 75% efficient frequency doubling of 1.6-ps laser pulses on the CPA T~ (table-top terawatt) system at LLE, in collaboration with the Australian National University (A N U) .~ Excellent agreement with simulations demonstrated that "standard" frequency conversion theory also applies in the picosecond regime, at intensities up to a few Gw/cm2. This article reports a more recent collaboration with the University of Michigan. In an extensive series of experiments, 500-fs, 1053-nm laser pulses were converted to the second harmonic in KDP crystals at intensities up to 400 Gw/cm2, with efficiencies of-80%, without any obvious damage to the crystals. This result extends the regime of validity of the theory nearly two orders of magnitude higher in intensity. Further, the results provide evidence that, at these intensities, it is necessary to include self-and cross-phase modulation in the theory. Most significant, though, may be the extension of the available wavelength range of CPA systems used for ultra-intense lasermatter interaction experiments. CPA lasers have been successfully used to generate peak laser powers in the infrared well beyond the terawatt regime.4-7 When focused, these lasers can produce intensities exceeding 1018 w/cm2, giving access to new regimes of lasermatter interaction. For solid targets irradiated at these intensities the peak-to-background intensity contrast of the laser pulse should exceed-109:1 to avoid energy deposition in a plasma created by a much longer prepulse. Second-harmonic generation (SHG) in nonlinear crystals is thus important because, aside from extending the available wavelength range, it significantly improves the contrast ratio. Indeed, high-contrast, second-harmonic laser pulses have been used to produce high-density, high-temperature plasmas that emit short x-ray pulses in the keV region.8
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.