Design of high-energy terahertz sources based on optical rectification

Detailed analysis of the tilted-pulse-front pumping scheme used for ultrashort THz pulse generation by optical rectification of femtosecond laser pulses is presented. It is shown that imaging errors in a pulse-front-tilting setup consisting of a grating and a lens can lead to a THz beam with strongly asymmetric intensity profile and strong divergence, thereby limiting applications. Optimized setup parameters are given to reduce such distortions. We also show that semiconductors can offer a promising alternative to LiNbO3 in high-energy THz pulse generation when pumped at longer wavelengths. This requires tilted-pulse-front pumping, however the small tilt angles allow semiconductors to be easily used in such schemes. Semiconductors can be advantageous for generating THz pulses with high spectral intensity at higher THz frequencies, while LiNbO3 is better suited to generate THz pulses with very large relative spectral width. By using optimized schemes the upscaling of the energy of ultrashort THz pulses is foreseen. (C) 2010 Optical Society of America