Observation of coherent millimeter and submillimeter emission from a microtron-driven Cherenkov free-electron laser

Abstract

We report the observation of coherent emission from a Cherenkov free-electron laser driven by a 5-MeV radio-frequency microtron. Power up to 50 W in pulses of 4-fis duration has been generated at the wavelengths of 1.6 and 0.9 mm using two different dielectric-loaded waveguides.PACS numbers: 42.55.Tb, 41.70.+t Slow-wave structures, which achieve velocity synchronism between the propagating wave and the interacting electron beam, are considered as potential candidates for the generation of power in the millimeter and submillimeter regions of the spectrum, since they overcome many of the problems related to the excitation of microwave cavities with dimensions of the order of the wavelength.A number of experiments exploiting the emission of Cherenkov radiation in dielectric-loaded waveguides have been performed in the past, x mainly in the millimeter region utilizing electron beams at energy < 1 MeV. In this type of device a beam of relativistic electrons passes at grazing incidence above the surface of a dielectric-loaded waveguide, exciting TM-like surface waves. 2 The longitudinal component of the evanescent electric field causes a bunching of the electrons, which give rise to stimulated emission. 3 In the synchronism condition for a single-slab geometry 2 the radiation is emitted at a wavelength given by X=27tdy(e-l)/e(1)in the approximation y^>\, X^>d y where d is the film thickness, e its dielectric constant, and y the relativistic factor of the electrons. The coupling efficiency C between a single electron and the TM wave is expressed by an exponential behav-2

Optical emission from a high-refractive-index waveguide excited by a traveling electron beam

“…25 Conventional Cherenkov lasers utilize a cylindrical dielectric waveguide, whose refractive index is approximately 1.2, to decrease the velocity v opt of the electromagnetic wave to that of the electron beam, v e . [5][6][7][8][9][10] However, in our scheme, a slab waveguide made of a semiconductor crystal with a high refractive index, such as 3.5, is used to more effectively reduce v opt .…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] These devices utilize the kinetic energy of an electron beam in a vacuum, and the condition required to obtain the radiation and to amplify the electromagnetic wave is that the velocities of the electron beam and the electromagnetic wave coincide. Therefore, these devices can operate, in principle, over a very wide frequency range extending from the microwave to the x-ray regions of the electromagnetic spectrum.…”

FIR optical cavity oscillation is observed with the AT&T Bell Laboratories free-electron laser

“…O.5GIA calibration for the undulator was measured at an early stage in the hardware development and was measured for increasing field so that the effect of saturation of the K parameter has not been detennined directly. u(l+K2) (1) 2's?…”

“…The steering of the electron beam through the undulator is most efficient for fields such that the betatron wavelength ? is nearly equal to the length of the undulator, where ffyAu (1) Undulator field tuning of 10% about this value does little to alter the electron beam trajectory thus facilitating tuning the FEL output. We will attempt to operate the FEL at a smaller K value where ?w = 2L.…”

Enhanced Coherent Emission of Terahertz Radiation by Energy-Phase Correlation in a Bunched Electron Beam

“…The most frequently used one is the so-called magnetic undulator, a device consisting of an alternate disposition of magnets along the beam propagation axis producing transverse oscillations of the electrons, which is employed in free electron lasers (FELs) [7]. Other free electron devices are the Cherenkov FEL, based on the interaction with a dielectric loaded waveguide [8], and the metal grating FEL, based on the Smith-Purcell effect [9].…”