Radical increase of the parametric X-ray intensity under condition of extremely asymmetric diffraction

Abstract

Parametric X-ray radiation (PXR) from relativistic electrons moving in a crystal along the crystal-vacuum interface is considered. In this geometry the emission of photons is happening in the regime of extremely asymmetric diffraction (EAD). In the EAD case the whole crystal length contributes to the formation of X-ray radiation opposed to Laue and Bragg geometries, where the emission intensity is defined by the X-ray absorption length. We demonstrate that this phenomenon should be described within the dynamical theory of diffraction and predict a radical increase of the PXR intensity. In particular, under realistic electron-beam parameters, an increase of two orders of magnitude in PXR-EAD intensity can be obtained in comparison with conventional experimental geometries of PXR. In addition we discuss in details the experimental feasibility of the detection of PXR-EAD

Parametric X-ray radiation in the Smith-Purcell geometry for non-destructive beam diagnostics

“…In the Smith-Purcell geometry the angle θ B = π/4, c σ = 1, c π = cos 2θ B ≈ 0. This means that the emitted radiation will be polarized in the direction perpendicular to the plane defined by the vectors N and g. In addition, in the point where the intensity of radiation is maximal, which corresponds to q 0 = 0, the quantity α B exactly coincides with the one in the case of PXR-EAD [4]. That is…”

“…Moreover, according to Ref. [4] the number of emitted photons N PXR−EAD in this situation significantly exceeds N PXR . One can obtain the following estimation in this case N PXR−EAD = Q PXR−EAD L = 10 2 N PXR .…”

“…Following Refs. [2,4] we now estimate the number of radiated photons in both cases. Let the quantity Q PXR describes the number of photons emitted from the unit length of an electron trajectory for the transition geometry case.…”

“…The actual expression for Q PXR is not important and for our qualitative estimation we mention only that Q PXR is independent of the crystal length under the condition L abs < d [2]. In the case of PXR-EAD [4] the photons emitted from the whole length L of an electron trajectory contribute to the formation of PXR, as they are not absorbed. Moreover, according to Ref.…”

“…Recently, it was demonstrated [4] that the intensity of the radiation can be significantly increased if the grazing geometry under condition of the extremely asymmetric diffraction of the emitted photons (PXR-EAD) is employed. However, in that case the electrons were moving inside a crystal, parallel to the crystal vacuum interface.…”