Free electron laser with terahertz band Bragg reflectors

Abstract

Periodical Bragg structures may be considered as an effective way of controlling the electromagnetic energy fluxes and provision of spatially coherent radiation in the free electron lasers with oversized interaction space. A new scheme of terahertz band FEL with hybrid Bragg resonator is proposed consisting of advanced input Bragg mirror and traditional output Bragg mirror. An advanced Bragg mirror exploiting the coupling between the two counterpropagating modes and the quasicutoff one provides mode selection over the transverse index. The main amplification of the wave by the electron beam takes place in the regular section of the resonator. Small reflections from the output traditional Bragg mirror are sufficient for oscillator self-excitation.

Powerful terahertz free electron lasers with hybrid Bragg reflectors

“…1(a)]. Unlike previous considerations [5,6], in this paper the structure of paraxial wave beams over the y axis is not assumed to be fixed and presents a sum of modes of regular planar waveguide. This allows us to be more accurate in determining the maximum acceptable oversize factor (ratio between the gap b 0 and the wavelength ) that still maintains the coherence of radiation over the y axis.…”

“…(16) and (17) reduce to the form used in our previous paper [5,6], where we assumed that the transverse structure of propagating waves coincides with that of the TEM modes of the regular planar waveguide. Under the assumption of fixed transverse field structure, the interaction in the advanced Bragg mirror can be described by the equations…”

“…The peculiarity of the advanced Bragg structure is the absence of direct coupling between the counterpropagating paraxial waves. Instead, paraxial waves are coupled with a cutoff mode [6,7] under the following Bragg resonance condition:…”

“…Correspondingly, the frequency range in which the oscillators of this type effectively operate includes millimeter and optical (infrared) bands [1][2][3][4]. In [5][6][7] a new modification of Bragg structures was suggested that can be applied to the terahertz band free-electron lasers. The specific feature of this advanced Bragg structure (ABS) is the coupling between propagating and cutoff modes.…”

Comparitive Study of Coaxial Bragg Resonators

“…Early investigation was mainly concentrated on the planar or cylindrical Bragg structures [1][2][3][4][5][6][7][8][9][10][11][12][13]. As insertion of a corrugated inner rod into a cylindrical Bragg structure provides extra possibility to control the stop-band or pass-band, now growing attention is paid to the coaxial Bragg structures [14][15][16][17][18][19][20][21][22][23][24][25].…”