Generation of intense tunable picosecond pulses in the far-infrared

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Abstract
Continuously tunable far-infrared (FIR) picosecond pulses have been generated from 20 to 200 cm−1 through the parametric interaction of two visible pulses. Pulse energies were generated up to 3 nJ, which are sufficient for time-resolved spectroscopy. The quantum efficiency of 0.1–0.3% was surprisingly constant over this frequency range considering the large variations in FIR absorption, diffraction, and phonon resonance enhancement. The depletion of the visible pulse and the dependence of the FIR energy on pump power were typical of a saturated process. However, the FIR energy showed unexpectedly large pulse-to-pulse fluctuations. Understanding the origin of these fluctuations may lead to substantial improvements in the average efficiency.