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Terahertz radiation in an optical-field-induced ionization in air with a pulsed electrostatic field

We have demonstrated that the terahertz radiation can be generate by the burst current produced by a laser created ionization front, which is induced an optical-field-induced ionization in air with a pulsed electric field. The peak frequency of the radiation spectrum depends on the rise time of the OFI. The central frequencies of the radiation are observed to be 0.2 and 0.04 THz at the pulse durations of 50 and 300 fs (FWHM), respectively. The power of the linearly polarized THz radiation is linearly increased with the square of the electrostatic field strength applied to the capacitors.