Bremsstrahlung from relativistic electrons is considered under conditions when some transverse direction of momentum transfer is statistically preferred. It is shown that in the dipole approximation all the medium anisotropy effects can be accumulated into a special modulus-bound transverse vector, N . To exemplify a target with N 2 ∼ 1, we calculate radiation from electron incident at a small angle on an atomic row in oriented crystal. Radiation intensity and polarization dependence on the emission angle and frequency for constant N is investigated. Net polarization for the angleintegral cross-section is evaluated, which appears to be proportional to N 2 /2, and decreases with the increase of the photon energy fraction. A prominent feature of the radiation angular distribution is the existence of an angle at which the radiation may be completely polarized, in spite of the target complete or partial isotropy -that owes to existence of an origin-centered tangential circle for polarization in the fully differential radiation probability kernel. Possibilities for utilizing various properties of the polarized bremsstrahlung flux for preparation of polarized photon beams and for probing intrinsic anisotropy of the medium are analyzed.

Radiation spectrum from high energy $e^\pm$ in a bent crystal with arbitrary curvature distribution along the longitudinal coordinate is evaluated, based on the stationary phase approximation. For a uniformly bent crystal a closed-form expression for the spectrum is derived. Features such as sharp end of spectrum and volume reflection turnover at beginning of the spectrum are discussed. The coherence length in a bent crystal appears to depend only on the crystal geometry and not on the electron or photon energies, which is essential for interpretation of the results. Estimates of non-dipole radiation and multiple scattering effects are given. The value for the crystal bending angle at which the dipole coherent bremsstrahlung theory holds best appears to be $\sim 10^{-4}\mathrm{rad}$.Comment: 15 pages, 10 figures; published versio

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For volume reflection process in a bent crystal, exact analytic expressions for positively-and negatively-charged particle trajectories are obtained within a model of parabolic continuous potential in each interplanar interval, with the neglect of incoherent multiple scattering. In the limit of the crystal bending radius greatly exceeding the critical value, asymptotic formulas are obtained for the particle mean de?ection angle in units of Lindhards critical angle, and for the final beam profile. Volume re?ection of negatively charged particles is shown to contain effects of rainbow scattering and orbiting, whereas with positively charged particles none of these effects arise within the given model. The model predictions are compared with experimental results and numerical simulations. Estimates of the volume re?ection mean angle and the final beam profile robustness under multiple scattering are performed.

Existence of different types of interference in the spectrum of radiation emitted by a doubly hard scattered electron is demonstrated. The spectrum develops oscillations in two regions: the hard, where the oscillations depend on the electron Lorentz factor, and the soft, where the oscillations depend on the electron scattering angles. This interference pattern owes to the presence of jetlike radiation configurations, formed by a piecewise-rectilinearly moving electron and the accompanying photon. The corresponding nondipole decomposition relation is derived. Notions describing proper field formation and interference, and presumably being applicable more generally, are discussed in detail.