Speaker
Description
Terahertz (THz) frequencies (100 GHz – 10 THz, 414 µeV – 41 meV) are often part of synchrotron radiation, yet receive little attention for monitoring and control purposes. Previously, we investigated the capabilities of THz field effect transistors for beam positioning purposes of FELs and also spectrally characterized an FEL with a THz photonic spectrum analyzer at multiple THz. Here, we want to expand our monitoring capabilities to the detection of the carrier-envelope-phase (CEP) of pulsed radiation in the THz domain, a pre-requirement for CEP-stable operation. For the detection, the THz radiation is mixed with a pulsed laser in two photoconductive mixers. By inducing a slightly different time delay between the arrival times of the pulsed laser to two photoconductive mixers, the radiation is sampled at two points synchronously. Their amplitude difference gives information on the slope of the pulsed THz radiation at the selected measurement points and, therefore, on the phase. Its information may be used on a pulse-by-pulse base for active carrier-envelope-phase stabilization. Carrier-phase stability is important for applications using the THz field for excitation. If funded, DALI will be a CEP stable machine, amongst other accelerator facilities.