Optical Design of Astra Gemini Petawatt Amplification System

The Astra Gemini laser system is a dual-beam petawatt class CPA Ti: sapphire laser system which is being built at the Central Laser Facility as an upgrade to the existing Astra laser. Each beam will deliver 15 J in 30 femtoseconds on target (i.e. 0.5 PW), but the dual beam concept allows us not only to achieve petawatt power level on target with relatively small sizes of optics and compressor gratings, but also to access a wider range of science applications. The system is based on two multipass Ti:Sapphire amplifiers pumped by 4 beams at the second harmonic of a Nd:glass laser with an energy 25 J in each beam. The input for the amplifiers is the 1.5 J output of the existing Astra laser system stretched twice in the existing stretcher to give a 1 ns pulse length. 25 J amplified output will be compressed in vacuum grating compressors to give 0.5 PW power in each beam.