Coherent radiation of an ultrarelativistic charged particle channelled in a periodically bent crystal

Abstract

Abstract. We suggest a new type of the undulator radiation which is generated by an ultra-relativistic particle channeled along a periodically bent crystallographic plane or axis. The electromagnetic radiation arises mainly due to the bending of the particle's trajectory, which follows the shape of the channel. The parameters of this undulator, which totally define the spectrum and the angular distribution of the radiation (both spontaneous and stimulated), depend on the type of the crystal and the crystallographic plane (axis), on the type of a projectile and its energy, and on the shape of the bent channel, and, thus, can be varied significantly by varying these characteristics.As an example, we consider the acoustically induced radiation (AIR) which is generated by ultra-relativistic particles channeled in a crystal which is bent by a transverse acoustic wave. The AIR mechanism allows to make the undulator with the main parameters varying in wide ranges, which are inaccessible in the undulators based on the motion of particles in the periodic magnetic fields and also in the field of the laser radiation. The intensity of AIR can be easily made larger than the intensity of the radiation in a linear crystal and can be varied in a wide range by varying the frequency and the amplitude of the acoustic wave in the crystal.A possibility to generate stimulated emission of high-energy photons (in kev-MeV region) is also discussed.

<title>Number of photons and brilliance of the radiation from a crystalline undulator</title>

“…Only in this limit does the radiation formed during the passage of a bunch of relativistic particles through a periodic system bear the features of undulator radiation (narrow, well-separated peaks in spectral-angular distribution) rather than those of synchrotron radiation. Hence, the following strong inequality, which entangles the period λ u and the length of a crystal L u must be met in the crystalline undulator 1,2 :…”

Bunch Coherence in Parametric X-Ray Radiation

“…It is a basic ingredient of freeelectron lasers (FEL) at optical wavelenght and "stimulated amplification of spontaneous emission" (SASE) in the X-ray domain (see [1,2] and refs therein). Other potential applications are coherent transition radiation (CTR) in the microwave [3][4][5] and X-ray (CXTR) [6,7] regions, and possibly coherent radiation of particles channeled in crystalline and nanotube undulators [8][9][10][11].…”

An electron-based crystalline undulator

“…It was shown in [2,3] that a crystalline undulator can operate provided the following conditions are met:…”

“…Since for an ultra-relativistic particle L d ∝ ε [18][19][20], it seems natural that to increase N d one can consider higher energies. However, at higher energies another limitation appears [2,3,6]. The coherence of undulator radiation is only possible when the energy loss ∆ε of the particle during its passage through the undulator is small, ∆ε ≪ ε.…”

“…A thorough analysis of the conditions (1) for the system "periodically bent crystal + ultra-relativistic positrons" was performed for the first time in [2,3] (and analyzed further in [5,6,8,9] ). The ranges of ε, a and λ for a number of crystals were established within which the operation of the crystalline undulator is possible.…”