A simple optical spectral calibration technique for pulsed THz sources

We have quantified the sensitivity of a simple method to measurethe frequency spectrum of pulsed terahertz (THz) radiation. The THzpulses are upconverted to the optical regime by sideband generation in a zinctelluride (ZnTe) crystal using a continuous wave (cw) narrow-bandwidthnear-infrared laser. A single-shot spectral measurement of sideband pulseswith a high resolution spectrometer directly provides the spectral informationof the THz pulses without the need of adjustable elements in thedetection setup. This method has been applied at the free electron laserFELIX, where, for a wavelength of 150 μm (2 THz), pulse trains of5 μs duration with an integrated energy of 800 nJ, as well as single pulseswith an energy as low as 13 nJ could be characterized on a single-shot basis.