Generation of tuneable narrowband terahertz pulses using large-area photoconductive antennas

Photoconductive antennas, driven by ultrafast optical pulses, are frequently used as broadband terahertz sources. Due to water vapour absorption in ambient air, these sources are less suitable for free space imaging or addressing small spectral regions. Amongst other techniques, narrow-band THz generation via difference frequency generation in ZnTe crystals [1] and photoconductive antennas [2] were demonstrated, the latter reaching frequencies of only 900 GHz. In this work we generate tuneable narrow-band terahertz pulses from a large-area photoconductive antenna by means of difference frequency generation with two up to 3.3 ps long time-delayed chirped optical pulses. The source is a 250 kHz regenerative Ti:sapphire amplifier. It’s output is split into three beams, where one is compressed for field resolved detection. The other two pulses are sent to a Michelson interferometer and get – with an adjustable time delay – recombined and are focussed on the antenna.
By using this technique we generated THz pulses tuneable from 0.35 to 2.5 THz with adjustable spectral widths (FWHM) of 200 to 500 GHz.