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

Avraham Gover

Tel Aviv University

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 [1]

The FEL is based upon the ORGAD RF_-LINAC at the Schlesinger Accelerator Center in Ariel (Fig. 2), and is operated by the FEL center of Ariel and Tel-Aviv universities. It is a compact RF gun accelerating to energies between 3.5 and 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, that bunch duration is less than half a period of the radiation (289 femto-seconds). This produces superradiance, a phenomenon where the electrons emit in phase with each other. In this situation the radiation field emitted by the electrons add up. Thus, the total energy of the radiation is proportional to the square of the number of the electrons and not to the number of electrons as in conventional spontaneous emission.

This principle provides a significant advantage over THz FEL schemes based on simulated amplification of spontaneous emission (SASE) [2]. Since in our case we have about N=108 electrons, the total energy emitted is N2 =1016 times the 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 is the same enhancement factor that was obtained by exponential growth in a SASE FEL with a much longer wiggler and higher beam energy [2]. Thus comparable THz radiation energies (we measured at first attempt ~30 nJoul/pulse) can be obtained with a very compact accelerator and a short wiggler.

In the framework of our FEL user center of the Ministry of Science, we aim to apply our special THz source to provide high energy tunable radiation to users in a wide range of disciplines in biology, chemistry, material research and medicine.

 

Reference

  1. 1. A. Gover et al, Superradiant and stimulated-superradiant emission of bunched electron beams. Reviews of Modern Physics, 91(3), 035003.‏

  2.  M. Krasilnikov et al “First Lasing of the THz SASE FEL at PITZ” International FEL Conference, Trieste, August 22, 2022, MOA08

 

 

 

    

Fig 1                                                                 Fig 2

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