We describe a new four-wave rectification method for the generation of intense, ultrafast terahertz (THz) pulses from gases. The fundamental and second-harmonic output of an amplified Ti:sapphire laser is focused to a peak intensity of ~5×10<sup>14</sup>W/cm <sup>2</sup> . Under these conditions, peak THz fields estimated at 2 kV/cm have been observed; the measured power spectrum peaks near 2 THz. Phase-dependent measurements show that this is a coherent process and is sensitive to the relative phases of the fundamental and second-harmonic pulses. Comparable THz signals have been observed from nitrogen and argon as well as from air.
© 2000 Optical Society of America
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(260.3090) Physical optics : Infrared, far
(320.7110) Ultrafast optics : Ultrafast nonlinear optics
(320.7160) Ultrafast optics : Ultrafast technology
D. J. Cook and R. M. Hochstrasser, "Intense terahertz pulses by four-wave rectification in air," Opt. Lett. 25, 1210-1212 (2000)