Generation of intense highly coherent femtosecond pulses in the mid infrared

Highly coherent mid-infrared femtosecond pulses, tunable between 2.5 and 4.4 $\mathit{\mu }\mathrm{m}$, and with an average energy and duration between 2.6 and 3.6 $\mathit{\mu }\mathrm{m}$ of 11 $\mathit{\mu }\mathrm{J}$ and 200 fs, respectively, have been produced by an optical parametric amplifier setup driven at 1 kHz by a 400-$\mathit{\mu }\mathrm{J}$, 800-nm pulse from a Ti:sapphire amplifier. In this system, first tunable moderate-energy femtosecond pulses in the near infrared are produced by continuum amplification in $\beta$-barium borate, and subsequently the near-infrared pulses are amplified and frequency mixed with 800-nm radiation in potassium titanyl phosphate to produce intense tunable mid-infrared pulses. The time–bandwidth product of the mid-infrared pulses is $0.28\pm 0.02$ over the whole high-energy tuning range. Experimental results are compared with numerical simulations and a simple model.