Chirped pulse waveguide amplifier.

We introduce the first ultrafast Cr:ZnS amplifier in a 34-mm-long depressed-cladding waveguide with a cross-section of up to 50 m and an excellent output beam quality of M ∼ 1.2. In a chirped pulse amplification scheme incorporating a Chirped Volume Bragg Grating stretcher/compressor, the amplifier achieves an optical gain of 75 over 15 mm, corresponding to a 12 dB/cm gain coefficient. The amplifier delivers 2.35 W of average output power in a single pass, with the amplified pulses being compressed to 235 fs. Furthermore, our numerical 3D model, which accounts for the spatial profiles of both the pump and the seed beams, reveals and describes experimental observation of what we believe to be a novel phenomenon: multimode relaxation to the fundamental transverse mode in a large-mode-area (LMA) waveguide, occurring without degradation of the effective mode volume or amplification efficiency. We also demonstrate that without stretching, the waveguided propagation in a non-centrosymmetric Cr:ZnS medium enables effective generation of multiple harmonics even for the relatively long 100-fs seed pulses, making an integrated carrier-envelope phase stabilization using 2f-3f or 3f-4f schemes within reach.