High-power THz pulses based on difference-frequency generation

Frequency mixing in nonlinear crystals corresponds to one of the efficient schemes for generating coherent THz pulses from intense laser beams. Recently, difference-frequency-generation (DFG) using coherent pulses at 1 mum was investigated in a few nonlinear materials; the highest peak power generated so far is 390 W. However, the average output power was still limited to 20 muW. In order to further increase the average power, a much higher repetition must be used. In addition, mixing frequencies should be in the mid-IR rather than the near-infrared region, since the maximum power conversion efficiencies dictated by Manley-Rowe relation can be then an order of higher magnitude. The best mid-IR source is a CO₂ laser at the wavelength of around 10 mum.