Precision high-power solid state laser diagnostics for target-irradiation studies and target-plane irradiation modeling

摘要

Abstract: A 0.74-m aperture laser diagnostic system has been designed and built and is an operational part of target irradiation experiments being conducted at the Nova Two Beam facility at Lawrence Livermore National Laboratory. These experiments examine the effects of laser beam conditioning on laser-plasma interaction, and include the use of full-aperture (0.74-m diameter) distributed phase element optics for fundamentally altering the irradiance distribution at either the second or third harmonic wavelengths of the Nova Nd:Glass laser system. The two beam laser diagnostic system (TBLDS) provides the suite of laser diagnostics essential to interpreting the results of these studies: (1) full-aperture energy measurement, (2) near-field imaging of planes up to 15 m ahead of the target chamber focusing lens, (3) far-field imaging of equivalent target planes within 5 mm on either side of `best focus', (4) time-resolved power measurement using 10 to 20-ps resolution streak camera systems, and (5) spectral measurement using a 1-m grating spectrometer with option for temporal streaking. The diagnostic is also equipped with a self-referencing interferometer for measuring the wavefront at various near-field planes; however, this feature is still under activation. The diagnostic system can flexibly handle either the fundamental, second or third harmonic wavelengths on alternate laser pulses, and an energy range of 50 Joules/pulse to 12.5 kJ/pulse. In this paper the design of the TBLDS, and present results from ongoing measurements of the Nova irradiance without wavefront modifications are discussed. The authors' numerical simulation techniques for modeling the laser irradiance at the target plane are also reviewed.!