γ -Ray Beams with Large Orbital Angular Momentum via Nonlinear Compton Scattering with Radiation Reaction

Abstract

Gamma-ray beams with a large angular momentum may affect astrophysical phenomena, which calls for appropriate earth-based experimental investigations. For this purpose, we investigate the generation of well-collimated γ-ray beams with a very large orbital angular momentum using nonlinear Compton scattering of a strong laser pulse of twisted photons at ultrarelativistic electrons. Angular momentum conservation among absorbed laser photons, quantum radiation, and electrons is numerically demonstrated in the quantum radiation-dominated regime. We point out that the angular momentum of the absorbed laser photons is not solely transferred to the emitted γ photons, but due to radiation reaction shared between the γ photons and interacting electrons. The efficiency of the angular momentum transfer is optimized with respect to the laser and electron beam parameters. The accompanying process of electron-positron pair production is furthermore shown to enhance the orbital angular momentum gained by the γ-ray beam.

Semiclassical probability of radiation of twisted photons in the ultrarelativistic limit

“…The spin effects become irrelevant in this limit within the bounds of the approximations made in deriving (47). Contrary to the classical formula for radiation probability, expression (47) does not factorize into c * c, where c is determined by the particle trajectory. This is a consequence of the fact that the averaging over spin polarizations was performed and the quantum recoil was taken into account.…”

“…and substitution (152) must be performed in the definitions of a n , b n (115) and the radiation spectrum (117). The contribution of the last two terms in (47) has to be evaluated from scratch. It follows from the explicit expressions for the mode functions [(13), [33]] that for s = −1 the third term in (47) can be omitted while for s = 1 the second term can be thrown out.…”

“…The hard twisted photons can be employed to study the properties of nuclear matter by exciting higher multipole transitions in nuclei and hadrons (see, e.g., the discussion in [24,25,41,42]). Rather recently, it was shown that hard twisted photons can be generated in channeling radiation [43,44] and strong laser pulses [41,[45][46][47][48]. In Sec.…”

Accelerated-Cherenkov radiation and signatures of radiation reaction

“…The asymptotes for the low and high frequency cutoffs are given by equations (10) and (12), respectively. The peak frequency is given by equation (13) and the solid curve (both blue and red) of the spectral cutoff is given by equation (11). Here, we use the experimentally realizable parameters of ω a =5.5×10 −4 eV (a), ω a =11×10 −4 eV (b), and index of refraction n=1.5.…”

“…a recoil correction due to the emitted photon's momentum. This is particularly exciting since recent theoretical and experimental works involving high intensity lasers and channeling radiation [9][10][11][12][13] have reported the first signatures of radiation reaction which appears to have quantum aspects involved in them [14][15][16][17].…”