We present an experimental demonstration of the generation of far-infrared
(terahertz) pulses by photoionization of electrically biased air with ampli
fied laser pulses. The current surge following photoionization of the air w
ith 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 radiat
ed from a large-area intrinsic-field GaAs emitter. The spectra peak at high
er frequency than those of biased large-area GaAs emitters. (C) 2000 Americ
an Institute of Physics. [S0003-6951(00)01229-8].