Abstract
The ASE (amplified spontaneous emission) level in a laser system consisting of an oscillator and a regenerative amplifier is very important, for example, in the interaction of an intense laser pulse and a thin foil, so a lower ASE level is always required. In this paper, we propose a new method to achieve a lower ASE level, which can be obtained by spectral matching of the seed laser beam and the ASE in a CPA (chirped-pulse amplification) Ti:sapphire laser system. In this method, two baffles are used to control the seed pulse spectrum by blocking a portion of the seed beam in a grating stretcher and it was found that the spectral matching method can reduce the temporal contrast ratio (after the regenerative amplifier) by a factor of 10 in a few hundred picosecond scale. This kind of spectral matching method is simple and it can be easily employed for other CPA laser systems to enhance the contrast ratio.
Highlights
High intensity femtosecond lasers (I>1018 W/cm2) have been developed for applications in relativistic laser-plasma researches such as the laser-plasma particle accelerations [1,2,3,4], radiation sources development [5,6,7], etc
We propose a new method to achieve a lower ASE level, which can be obtained by spectral matching of the seed laser beam and the ASE in a chirped-pulse amplification (CPA) Ti:sapphire laser system
Two baffles are used to control the seed pulse spectrum by blocking a portion of the seed beam in a grating stretcher and it was found that the spectral matching method can reduce the temporal contrast ratio by a factor of 10 in a few hundred picosecond scale
Summary
High intensity femtosecond (fs) lasers (I>1018 W/cm2) have been developed for applications in relativistic laser-plasma researches such as the laser-plasma particle accelerations [1,2,3,4], radiation sources development [5,6,7], etc. Two baffles are employed to control the seed beam spectrum in the pulse stretching stage and the modified spectrum is matched with the ASE spectrum of the regenerative amplifier (RA) without the seed pulse injection In this way, we found that the temporal contrast ratio can be enhanced by one order of magnitude while the output laser energy and pulse duration are maintained. When the bandwidth of the seed beam was smaller than that of the ASE, the intensity contrast ratio was similar to the case of Δλ = 38 nm at the long time delay of −400 ps, but improvement is observed between the delay −150 ps and −20 ps, as shown in the inset of Fig. 3 This contrast improvement by the spectral matching can be presented by low internal loss, leading to a high temporal contrast ratio.
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