Highly efficient mJ level laser amplifiers at 2 microns for frequency comb spectroscopy

Over the last decade, frequency comb spectroscopy have led to significant developments in view of the identification of varied species and of the understanding of the structure of matter. Highly efficient amplification of frequency comb femtosecond oscillators in the high pulse energies regime should allow future applications using this approach to Lidar-type measurements. We report on the millijoule level design of femtosecond amplifiers near 2 mu m wavelength having a great optical efficiency and compactness in order to be carrier in satellites. In addition to space applications, laser systems at 2 mu m become more and more popular because they offer elegant solutions to generate ultra-broad band super-continuum in the mid-infrared and for material processing. Our study helps to compare the optical performance of Tm:YAG, Tm:YAP and Tm:YLF crystals as active media, for designing ultrashort pulse regenerative amplifiers with a high gain and wall-plug efficiencies up to 10%. We will present our approach to ensure the conservation of the initial phase shift between the envelope and the carrier of pulses during amplification. We primarily discuss an innovative model which proposes a gradual path towards the optimization of any regenerative amplifier using crystalline thulium-based, end-pumped doped rods. This also involves the analysis of sizing criteria based on the assumption of rod-based active media, including the doping content, the length of the rod and the beam size inside.