Active spectral shaping with polarization encoding of chirped pulses in Ti:Sapphire amplifiers

Up to date, the majority of the existing petawatt class lasers are based on Ti: Sapphire (Ti:Sa) because of the wide emission spectrum, high thermal conductivity and loose requirement of the pump laser parameters [1]. However, petawatt systems with pulse duration considerably less than 25 fs are not yet available due to the gain narrowing effect which limits the achievable bandwidth [2]. The most widely used methods for overcoming gain narrowing are based on spectral shaping by inducing spectral losses (e.g. Dazzler), optical parametric amplification in the frontend and post compression. Unfortunately, critical all of them have imperfections, which limit their application. Polarization Encoded (PE) amplification in Ti: Sa was proposed to amplify pulses with spectral bandwidth supporting a few cycle duration even for final amplifiers of PW-level laser systems without energy losses, and the proof-of-principle experiments were recently reported [3]. A PE amplifier can preserve the bandwidth effectively during amplification by exploiting the difference between the π- and σ-emission cross-sections in a Ti: Sa medium, simultaneously the profile of the output spectrum can be conveniently shaped to either asymmetric red-, blue-shifted, or a symmetrically broad, only by rotating two λ/2 plates. These two features make the PE amplifier attractive for ultrashort high power laser systems.