High speed Imaging with High Power Terahertz Pulses

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High power terahertz (THz) electromagnetic pulses were generated using 1-kHz-repetition-rate high power femtosecond laser pulses, and the following results were obtained for the achievement of high speed THz imaging. High speed THz imaging was achieved by using a large (2 cm × 2 cm) electro-optic crystal and probe beam and acquiring the images with a CCD camera. Sufficiently good image quality was obtained with 30-ms accumulation. Using the present setup, spatio-temporal intensity profile on and near the focal plane was obtained, which showed for the first time an annular distribution of the THz intensity. Simulations based on diffraction integral and the Gaussian beam model showed that this phenomenon is specific for the half-cycle THz pulses. Direct observation of the THz electric field was achieved by applying the optical heterodyne detection method, which enabled better sensitivity and frequency-resolved spatial distribution studies. By observing the pump wavelength dependence of the THz waveforms emitted from GaAs and InP antennas, ultrafast intraband electron dynamics in these materials was studied.