High order dispersion control for femtosecond CPA lasers

Taking advantage of the temperature dependence of the refractive index, an arrangement is proposed for thermal control of dispersion of a chirped pulse amplification (CPA) laser. A glass slab, inserted into the Fourier plane of a stretcher or a compressor, having a spatially varying temperature profile across the beam ensures continuous variation of the spectral phase shift of the pulses. Model calculations are carried out to investigate the feasibility of the arrangement. As a demonstration, simple temperature profiles are created which compensate for the material dispersion of the thermal slab. In a proof of principle experiment it is proved that changes of spectral phase of femtosecond pulses follow the spatially varying temperature profile of a BK7 slab inserted into the compressor of a CPA system. Such a thermal slab is lossless, has a large spectral range, introduces no pixellation and exhibits a high damage threshold. Since it is easy to build into either the stretcher or the compressor of existing CPA lasers, it may become a promising candidate for high order dispersion compensation of high-power femtosecond laser systems. © 2007 Springer-Verlag.