High-speed adaptive deformable lens for boosting an high-energy optical parametric amplifier

ntense ultrafast laser sources in the mid-IR have attract ed in the recent years lot of attention in strong-field physics. A possible implementation for such sources relies in : a) the generation of a short IR seed by intra-pulse difference frequency generation (DFG) of a broadband con tinuum generated in an hollow-core fiber (HCF); b) optical parametric amplification (OPA) of the seed to the mJ level [1]. This approach yields a major advantage, namely the passive stabilization of the carrier-envel ope phase (CEP) owing to the DFG process, enabling applications like the generation of isolated attosecond pul ses in the soft X-rays. Nevertheless the CEP stability performances are limited with respect to those achieva ble with active stabilization techniques. Moreover, OPA setups require a very good beam quality as well as a robus t stability of the pumping source and this can hinder the scalability towards higher pulse energies. Here we report on the first application of adaptive optics (AO) to the stabilization of an high-energy parametric source, based on the scheme described above and pumped by a 1 kHz, 10 mJ, 25 fs Ti:Sapph laser. The AO system is based on an Hartmann-Shack wavefront sensor (WFS) and a multi-actuator deformable lens [2] placed in the collimated beam before the focusing sec tion of the HCF, allowing to correct aberrations up to the 4th order. The WFS is optically conjugated to the deformable lens by means of a simple telescope. A CPU- based control system allows to perform a closed-loop correction at 200 Hz accounting for system aberrations, mechanical vibrations and turbulence.