High peak power Ti:sapphire lasers: temporal contrast and spectral narrowing issues

摘要

Two new schemes of chirped pulse amplification (CPA) lasers are demonstrated, which are specially designed to overcome some of the bottlenecks of the current Ti:sapphire lasers. In particular, the issues of temporal contrast and spectral narrowing of the pulse during amplification are considered. The proposed schemes are double CPA (DCPA) and the negatively- and positively-chirped pulse amplification (NPCPA). Both of them are an extension of the conventional CPA scheme to Ti:sapphire lasers of petawatt and higher power levels. The double DCPA laser includes two CPA stages with intermediate non-linear temporal pulse filtering. The method reduces substantially the background, including amplified spontaneous emission as well as pre- and post - pulses. The former is demonstrated by achieving a temporal contrast of at least 10~(10) with pulses of 20 mJ output energy and 50 fs pulse duration. The NPCPA laser scheme implements a combination of negatively- and positively-chirped pulse amplification. This method of amplification suppresses gain related spectral narrowing, typical to CPA lasers, thus supporting pulse spectrum much broader than a conventional CPA. With a NPCPA Ti:sapphire laser we have achieved laser pulses of 50 nm spectral width and 150 mJ energy without any additional spectral correction. The scheme appears as an easy and reliable solution to preserve spectral bandwidth in Ti:Sapphire lasers, especially at high power levels up to the Petawatt regime.