Efficient generation of THz pulses with high energy was demonstrated by optical rectification of 785-fs laser pulses in lithium niobate using tilted-pulse-front pumping. The enhancement of conversion efficiency by a factor of 2.4 to 2.7 was demonstrated up to 186 μJ THz energy by cryogenic cooling of the generating crystal and using up to 18.5 mJ/cm2 pump fluence. Generation of THz pulses with more than 0.4 mJ energy and 0.77% efficiency was demonstrated even at room temperature by increasing the pump fluence to 186 mJ/cm2. The spectral peak is at about 0.2 THz, suitable for charged-particle manipulation.

THz pulses with more than 0.4 mJ energy were generated with 0.77% efficiency by optical rectification of 785-fs laser pulses in LiNbO 3 using tilted-pulse-front pumping. The spectral peak is at about 0.2 THz, suitable for charged-particle manipulation.

Optical rectification of ultrashort laser pulses in LiNbO 3 by tilted-pulse-front excitation is a powerful way to generate near single-cycle terahertz (THz) pulses. Motivated by various applications, calculations were carried out to optimize the THz peak electric field strength. The results predict THz output with peak electric field strength on the MV/cm level in the 0.3-1.5 THz frequency range by using optimal pump pulse duration of about 500 fs, optimal crystal length, and cryogenic temperatures for reducing THz absorption in LiNbO 3 . The THz electric field strength can be increased further to tens of MV/cm by focusing. Using optimal conditions together with the contact grating technique THz pulses with 100 MV/cm field strength and energies on the tens-of-mJ scale are feasible.

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Near-and far-field beam profiles were measured for THz pulses generated in LiNbO 3 by optical rectification of 200 fs pulses with a tilted pulse front. The variation of the THz beam size and a dramatically increasing divergence angle with increasing pump fluence were observed in the (horizontal) plane of the pulse front tilt. No significant variation was observed in the vertical direction. The reason for the observed nonlinear beam distortion is the shortening of the effective interaction length for THz generation caused by the combined effect of pump spectral broadening and angular dispersion in the tilted pulse front geometry. Our results indicate that nonlinear THz beam distortion effects have to be taken into account when designing intense THz sources and related experiments.