Development of broad spectrum technologies for high energy chirped pulse amplification
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We have developed several broad-spectrum technologies for high-intensity chirped pulse amplification. We present the design and performance of two 20 TW laser systems. THOR is a Ti:sapphire, 10 Hz, ultra-fast laser that produces femtosecond pulses with a peak intensity of 18.4 TW. The laser operates near the bandwidth limit of the medium maintaining sufficient spectrum to produce 38 fs pulses. This equates to a near transform limited time-bandwidth product of 0.490. The second laser system was developed to study broad-spectrum pulse amplification in mixed Neodymium-doped laser glasses. Our efforts were to produce a multi-Joule laser with sufficient bandwidth to compress near 100 fs using mixed-glasses in the final amplifier. We present the GHOST laser with modeling and experimental analysis of the precise gain ratios between the mixed glasses. GHOST examines the bandwidth limit of the mixed-glass architecture in order to produce the broadest amplified spectrum with the shortest compressed pulsewidth. The laser has a total gain of 4x109 with a net gain of 260 from glass. The measured optimum gain ratio of 3.3 (G[subscript phos]/G[subscript sil]) produced 14.4 nm (FWHM) of bandwidth with a 103 fs pulsewidth. This constitutes a time-bandwidth product of 0.398. Additionally we have investigated two novel laser glasses in an effort to generate high energy (>1 kJ), broad spectrum pulses from a chirped-pulse amplification Nd:glass laser. Both glasses have significantly broader spectra (>38 nm FWHM) than currently available Nd:phosphate and Nd:silicate glasses. We present calculations for small signal pulse amplification to simulate spectral gain narrowing. The technique of spectral shaping using mixed-glass architecture with an optical parametric chirped-pulse amplification front-end is evaluated. Our modeling shows amplified pulses with energies exceeding 10 kJ with sufficient bandwidth to achieve 120 fs pulse widths are achievable with the use of the new laser glasses. With further development of current technologies, a laser system could be scaled to generate one exawatt in peak power. Finally we report controlled enhancement of optical third harmonic generation from hydrodynamically expanding clusters of noble gas atoms several hundred femtoseconds following ionization and heating by ultrashort pump pulses.