Efficient generation of subpicosecond terahertz radiation by phase-matched optical rectification using ultrashort laser pulses with tilted pulse fronts

We report on the generation of subpicosecond terahertz (THz) electromagnetic radiation in a nonlinear crystal by ultrashort laser pulses with a tilted pulse front. Free-space THz pulses with an energy of 98 pJ and a repetition rate of 200 kHz have been obtained by optical rectification using 2.3 muJ near-infrared laser pulses in a LiNbO3 crystal cooled down to 77 K. The emitted THz beam has a divergence smaller than 40 mrad, which is close to the diffraction limit. Spectral analysis of the generated THz beam with a Michelson interferometer reveals an approximately 1.5 THz broad asymmetric peak centered at 2 THz and a pulse duration of less than 500 fs. (C) 2003 American Institute of Physics.