Hybrid Ti:Sapphire / KrF laser facility GARPUN for combined subpicosecond/nanosecond laser-matter interaction studies

Complete test of publication follows. Hybrid laser facility consisting of Ti:Sapphire front end, 3ω converter, and e-beam-pumped large-aperture KrF amplifiers is under construction to generate combined sub-picosecond/nanosecond pulses in UV spectral range at 248-nm wavelength. This is a part of the Petawatt excimer laser project started at P.N. Lebedev Physical Institute. In comparison with commonly used solid-state chirped-pulse amplifiers (CPA), KrF amplifiers have following advantages: (i) low-density gaseous matter with three orders of magnitude lower non-linear refraction index has a small value of B-integral and negligible pulse distortion; (ii) short radiation lifetime τr = 6 ns of the upper laser level of KrF(B-X) transition (with accounting for collisions τc ∼ 2 ns), that means the population inversion is recovered each 2 ns during the pumping time, which is typically τp ≥ 100 ns for technical reasons. Thus, it might be possible eliminating of very costly large-aperture compressor gratings and to amplify both short τsh << τc and long τlong ≥ τc pulses in the same amplifiers, as a short pulse does not affect the gain during the most of pumping. This gives a unique opportunity for realization of fast-ignition scheme in Inertial Confinement Fusion using large-scale KrF drivers. The Ti:Sapphire front end 'Start 248M' currently operates with the following parameters: rep rate 10 Hz, pulse energy and duration at fundamental wavelength (744 nm) > 8 mJ and < 60 fs, at 3ω (248 nm) > 0.5 mJ and < 65 fs, energy reproducibility (rms) < 3% (744 nm) and < 4% (248 nm). It consists of Kerr lens mode-locked master oscillator (< 30 fs, 80 MHz, 150 mW, wavelength centered at 740 nm) pumped by 2ω diode-pumped CW Finesse 4W Nd:YAG laser (3.5 W, 532 nm), all reflective-optics stretcher, which stretches pulses up to 200 ps, successive regenerative amplifier (10 Hz, > 0.4 mJ, 740 nm) and multi-pass amplifier (10 Hz, > 15 mJ, 740 nm), both pumped by 2ω pulsed Lotis LS-2134 Nd:YAG laser (10 Hz, 10 ns, 532 nm) with distributed energies of 5 and 70 mJ, two-gratings compressor, and 3ω converter with two BBO crystals and total efficiency 8%. EMG 150MSC Lambda Physik KrF laser is used afterwards to generate ns pulses and to amplify fs pulses in its two separate discharge chambers. Two e-beam pumped KrF amplifiers Berdysh and GARPUN with active volumes 10 x 10 x 100 and 16 x 18 x 100 cm3 are intended for amplification of both fs and ns pulses, as well as their combination. Preliminary numerical simulations predict 1.5 J, subpicosecond pulses combined with up to 100 J, nanosecond pulses.