A millimeter and submillimeter wavelength free-electron laser

Abstract

Measurements of millimeter and submillimeter wavelength emission (240 GHz<ω/2π<470 GHz) from a free-electron laser are reported. The laser operates as a superradiant amplifier and without an axial guide magnetic field; focusing and transport of the electron beam through the wiggler interaction region are achieved by means of the bifilar helical wiggler field itself. Approximately 18 MW of rf power has been observed at a frequency of 470 GHz, corresponding to an electronic efficiency of 0.8%. Frequency spectra are measured with a grating spectrometer and show linewidths Δω/ω∼2%–4%. The experimental results are in very good agreement with nonlinear numerical simulations.

High-brightness electron guns for linac-based light sources

“…If the electron beam quality is high enough, the FEL interaction described above can take place in a single transit down the undulator, with a single bunch amplifying its own synchrotron radiation to saturation. The process is known as self-amplified spontaneous emission, or SASE, and has been demonstrated at various wavelengths from the microwave [5] to saturation in the visible [6] and UV [6,7]. There are variations on the SASE process, such as high-gain harmonic generation (HGHG) [8], and various seeding schemes intended to provide improved performance in terms of output linewidth and power stability or to reduce the electron beam quality requirements somewhat; but all rely, at some level, on the fundamental internal interaction of a single bunch with its own synchrotron light to generate coherent radiation without the need for external feedback.…”

Linac-based short wavelength fels: The challenges to be overcome to produce the ultimate x-ray source–the x-ray laser

“…First experimental tests of SASE were carried out at Livermore in 1986 with the ELF [ 101 experiment, which produced radiation at a very long wavelength ( 8 m m ) , guided in waveguides. SASE-related experiments were carried out in parallel at the Navel Research Laboratory (NRL) [ 111 at 1-2 mm and the Massachusetts Institute of Technology ( M I T ) [12] a t 600 pm. T h e theoretical understanding of the process has continually matured leading a t present t o a number of linac-based experiments a n d proposals for linac-based user facilities a t wavelengths down to Angstrom regime (see Table 3 .…”

Generation and characterization of superradiant undulator radiation

“…This process is often referred to as SASE (SelfAmplified Spontaneous Emission), and is crucial to the development of X-ray FELs (Free-Electron Lasers) which depend on such a mechanism to achieve lasing. Selfamplification has been seen previously in mm-waves [4] down to 600 pm [5]. In this mid infrared 3 to 40 pm vibrational modes Table 1.1: Definition of various IR bands.…”