Towards high power broad-band OPCPA at 3000 nm

Abstract: High-energy femtosecond laser pulses in the mid-infrared (MIR) wavelength range are essential for a wide range of applications from strong-field physics to selectively pump and probe low energy excitations in condensed matter and molecular vibrations. Here we report a four stage optical parametric chirped pulse amplifier (OPCPA) which generates ultrashort pulses at a central wavelength of 3000 nm with 430 $\mu$J energy per pulse at a bandwidth of 490 nm. Broadband emission of a Ti:sapphire oscillator seeds synchronously the four OPCPA stages at 800 nm and the pump line at 1030 nm. The first stage amplifies the 800 nm pulses in BBO using a non-collinear configuration. The second stage converts the wavelength to 1560 nm using difference frequency generation in BBO in a collinear geometry. The third stage amplifies this idler frequency non-collinearly in KTA. Finally, the fourth stage generates the 3000 nm radiation in a collinear configuration in LiIO$_3$ due the broad amplification bandwidth this crystal provides. We compress these pulses to 65 fs by transmission through sapphire. Quantitative calculations of the individual non-linear processes in all stages verify that our OPCPA architecture operates close to optimum efficiency at minimum absorption losses, which suggests that this particular design is very suitable for operation a high average power at multi kHz repetition rates.