Generation and characterization of tunable mid-infrared femtosecond pulses

In this Chapter we describe the design of an optical parametric amplifier that allows the generation of infrared laser pulses suitable for ultrafast nonlinear spectroscopy on the OH-stretching mode of water molecules. Mid-infrared femtosecond pulses, tunable in the range of 2800-3800 cm with sub-100 fs duration and ~15 μJ energy are produced by an optical parametric amplifier driven at 1 kHz by 750 mJ, 800-nm pulses from a Ti:Sapphire amplifier. In this setup, tunable low-energy femtosecond pulses in the near infrared are generated by continuum amplification in β-barium borate, and subsequently the near-infrared pulses are amplified in two stages in potassium titanyl phosphate pumped by 800 nm radiation to produce intense mid-infrared pulses. A novel method is used to characterize the ultrashort IR pulses. The technique utilizes a frequency-resolved pump–probe geometry common in the applications of ultrafast spectroscopy. Part of the work as presented in this Chapter is covered by the following papers: 1. S. Yeremenko, A. Baltuška, M.S. Pshenichnikov, and D.A. Wiersma, “The criterion of pulse reconstruction quality based on Wigner representation” Appl. Phys. B70, 109-117 (2000). 2. S. Yeremenko, A. Baltuška, F. de Haan, M.S. Pshenichnikov, and D.A. Wiersma, “Frequency-resolved pump-probe characterization of femtosecond IR pulses” Opt. Lett. 27, 1171-1173 (2002).