First Light at the Israeli THz Superradiant Free Electron Laser
Ariel Nause, Aharon Friedman, Yehiel Vashdi, Eyal Farchi, Adnan Haj Yehye, Amir Weinberg, Leon Feigin, Eyal Magury, Michael Gerasimov, Paul Benishai
Schlesinger Family Center for Compact Accelerators and Radiation Sources, Ariel University, Ariel
Tel Aviv University
CHILI-2022 International Conference, Dec. 5, 2022, Tel Aviv
We report the first observation of terahertz super radiant emission from the Israeli Free Electron Laser (Fig. 1). This is the first demonstration of a THz source based on the scheme of coherent spontaneous superradiant emission by an ultra-short e-beam bunch . The first measured radiation signal of 31.10.22 (Fig. 1) corresponds to a 3.5THz beam output of 180 nano-Joul.
The Israeli superradiant FEL operates in the FEL center of Ariel and Tel-Aviv universities. It is based upon the ORGAD RF-LINAC at the Schlesinger Accelerator Center in Ariel (Fig. 2). The accelerator is a compact RF gun of accelerating energies 3.5 to 8.5 MeV. The gun is 64 cm long. It produces an electron bunch of about 100 femto-seconds. Since the frequency of the emitted radiation is 3.5 Tera Hertz, the bunch duration is shorter than half a period of the radiation (290 femto-seconds), satisfying the condition for superradiant emission. In this case all electrons in the bunch emit in phase with each other, and the total emitted radiation energy is proportional to the square of the number of the electrons N2 and not to the number of electrons N as in conventional spontaneous emission.
This principle provides a significant advantage over THz FEL schemes that are based on simulated amplification of spontaneous emission (SASE) . Since in our case we have about N=108 electrons, the total energy emitted is N2 =1016 times the spontaneous energy emitted by a single electron, that is 108 times the energy that would have been emitted from a longer electron beam at the same circumstances. This enhancement factor is comparable to the exponential gain factor attained in a SASE FEL with a much longer wiggler and higher beam energy . Increasing the beam charge by more than an order of magnitude is feasible and intended. Thus, our experiment demonstrates the feasibility of the superradiant FEL concept as an advantageous compact coherent powerful radiation source.
In the framework of our FEL user center of the Ministry of Science, we aim to apply our unique THz source to provide high energy tunable radiation to users in a wide range of disciplines in biology, chemistry, material research and medicine.
1. A. Gover et al, Superradiant and stimulated-superradiant emission of bunched electron beams. Reviews of Modern Physics, 91(3), (2019): 035003. 2. M. Krasilnikov et al “First Lasing of the THz SASE FEL at PITZ” International FEL Conference, Trieste, August 22, 2022, MOA08