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| Home > Publications database > Status of high power, tunable THz FEL source at PITZ |
| Talk (non-conference) (Invited) | PUBDB-2025-04688 |
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2025
Abstract: The Photoinjector test facility at DESY in Zeuthen develops and characterizes the electron guns for FLASH and Eu-XFEL. It consists of a normal-conducting L-band RF gun cavity with a Cs2Te photocathode, which can produce beam charge up to several nC. The electron bunches can gain an energy up to ~6.5 MeV after the gun and then further acceleration, up to ~22 MeV, is possible by a booster cavity. The pulse train structure is identical to the one at Eu-XFEL. Considering all these features, the development of a prototype for an accelerator-based THz source was carried out at PITZ.The ideal THz source required for the pump-probe experiments at the Eu-XFEL should meet the following requirements: tunable frequency (0.1-20 THz), high pulse energy (μJ to mJ; depending upon frequency), narrow bandwidth (<1-10%) and possibly carrier envelope phase stable THz signal. With the current setup at PITZ, narrowband THz radiation in the 1–5 THz frequency range can be generated. Proof-of-principle experiments were done with a bunch charge of ~2.4 nC and a beam energy of ~17 MeV, corresponding to a 3 THz signal. After a challenging beam transport and matching of the space-charge dominated beam through an LCLS-I undulator, having a cross-section 11 x 5 mm and length 3.5 m, high peak and average THz pulse power were reported. THz pulse energies were measured for different effective lengths of the undulators and the so-called gain curves were obtained. The transverse profile of the THz radiation was measured using a THz camera and rms sizes as small as 300 microns were obtained. Additionally, spectral measurements were conducted using a compact broadband THz spectrometer, specifically a Fourier Transform Infrared (FTIR) spectrometer with a reflective lamellar grating. In the recent experimental campaign, 5THz signal using a flattop laser was obtained and further optimization is planned in the upcoming beam operation.
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