Millijoule level ultra broad brand amplification of 20 femtosecond pulses using birefringent filters

Summary form only given. In order to bring chirped pulse amplification (CPA) to its limit several issues still need to be solved. Among them is a reliable way of fighting gain narrowing in the amplifiers. We show here that a birefringent filter can compensate for gain narrowing in typical regenerative amplifiers. This set up is used to amplify sub-20 fs pulses to the millijoule level.