Generation of terahertz pulses by photoionization of electrically biased air

We present an experimental demonstration of the generation of far-infrared (terahertz) pulses by photoionization of electrically biased air with amplified laser pulses. The current surge following photoionization of the air with an applied bias field of 10.6 kV/cm leads to the emission of THz pulses with an intensity which can be almost as high as that of THz pulses radiated from a large-area intrinsic-field GaAs emitter. The spectra peak at higher frequency than those of biased large-area GaAs emitters.