Abstract
This paper describes techniques for high-energy laser pulse amplification in multi-PW femtosecond laser pulses. Femtosecond laser pulses can be generated and amplified in laser media with a broad emission spectral bandwidth, like Ti:sapphire crystals. By chirped pulse amplification (CPA) techniques, hundred-Joule amplified laser pulses can be obtained. Multi-PW peak-power femtosecond pulses are generated after recompression of amplified chirped laser pulses. The characteristics and problems of large bandwidth laser pulses amplification in Ti:sapphire crystals are discussed. An alternative technique, based on optical parametric chirped pulse amplification (OPCPA) in nonlinear crystals, is presented. Phase-matching conditions for broad bandwidth parametric amplification in nonlinear crystals are inferred. Ultra-broad phase matching bandwidth of more than 100 nm, able to support the amplification of sub-10 fs laser pulses, are demonstrated in nonlinear crystals, such as Beta Barium Borate (BBO), Potassium Dideuterium Phosphate (DKDP), and Lithium Triborate (LBO). The advantages and drawbacks of CPA amplification in laser crystals and OPCPA in nonlinear crystals are discussed. A hybrid amplification method, which combines low-medium energy OPCPA in nonlinear crystals with high energy CPA in large aperture laser crystals, is described. This technique is currently used for the development of 10-PW laser systems, with sub-20 fs pulse duration and more than 1012 intensity contrast of output femtosecond pulses.
Highlights
In continuous-wave, free-running and Q-switched pulsed laser oscillators, the output laser is the result of the interference of a number of longitudinal laser modes with discrete frequencies, determined by the resonance frequencies of the optical resonator, and random phase relations.Longitudinal oscillating modes are supplied by the energy accumulated on the upper laser level of the laser active medium
Ultra-broad phase matching bandwidth of more than 100 nm, able to support the amplification of sub-10 fs laser pulses, are demonstrated in nonlinear crystals, such as Beta Barium Borate (BBO), Potassium Dideuterium Phosphate (DKDP), and Lithium Triborate (LBO)
By using special techniques for the improvement of amplified pulses spectral bandwidth and spectral phase, PW laser pulses as short as 25 fs were generated in all Ti:sapphire laser systems
Summary
In continuous-wave, free-running and Q-switched pulsed laser oscillators, the output laser is the result of the interference of a number of longitudinal laser modes with discrete frequencies, determined by the resonance frequencies of the optical resonator, and random phase relations. Longitudinal oscillating modes are supplied by the energy accumulated on the upper laser level of the laser active medium For their amplification, they compete one against the other in the optical resonator. An alternative method for femtosecond laser pulses amplification, based on optical parametric amplification (OPA) in nonlinear crystals is presented in Section 3 of the paper. For high energy broad-bandwidth laser pulse amplification in nonlinear crystals, the currently used solution is the optical parametric chirped pulse amplification (OPCPA). A hybrid amplification technique, which combines the low-medium energy amplification by OPCPA in nonlinear crystals with high energy OPA in laser crystals, considered as a suitable solution for 10-PW laser systems development, is described in the Section 4 of the paper
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