Abstract

Several opto-electronic techniques utilizing femtosecond laser pulses have been recently developed to generate broadband THz pulses in free space [1-3]. One method is the use of high speed photoconducting micro-strip antennas [2]. Our approach is the optical rectification of fs-Iaser pulses in a highly nonlinear organic crystal. A time-dependent polarisation is created in the crystal via the electro-optic effect. This induced polarisation is proportional to the intensity of the excitation pulse and results in the radiation of electromagnetic waves with THz bandwidth [1,3]. We use the organic salt dimethyl amino 4-N-methylstilbazolium tosylate (DAST) as a THz-emitter because of its high nonlinear optical susceptivility χ⁽²⁾. The rectified field emitted from DAST is 185 times larger than that from a LiTaO_J crystal [3]. The source of the ultrashort optical pulses was a cw-Ar+- Iaser pumped, mode-locked Ti:sapphire laser at a repetition rate of 76 MHz and a pulse duration of 100 fs at a central wavelength of 850 nm.

© 1996 Optical Society of America