Line shape of soft photon radiation generated at zero angle in an undulator with a dispersive medium

TL;DR

This paper investigates the zero-angle undulator radiation in a dispersive medium, revealing how soft photon emission can be coherent, leading to intense, quasi-monochromatic X-ray beams with potential practical uses.

Contribution

It introduces the effect of medium polarization on undulator radiation, highlighting the generation of coherent soft photons and their impact on X-ray beam properties.

Findings

Soft photons are generated at zero angle in a dispersive medium.

Coherent radiation occurs when soft photon wavelength exceeds microbunch length.

Resulting X-ray beams are intense, quasi-monochromatic, and directed.

Abstract

The problem of undulator radiation from a bunch of charged particles, taking into account a medium polarization, is considered. In a dispersive medium, at a zero angle, in addition to hard photons, soft photons are also generated. If the wavelength of the soft photons is greater than or equal to the longitudinal size of the microbunches formed during the FEL process, the microbunches radiate coherently. Consequently, the radiation of the bunch will be partially coherent. As a result, intense, quasi-monochromatic, and directed X-ray photon beams are produced, which can have wide practical applications.