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Interference effects in polarization bremsstrahlung on a multi-atomic chain


  M. Ya. Amusia [1, 2]  ,  V. I. Matveev [3]  
 [1] Racah Institute of Physics, the Hebrew University, Jerusalem, ISRAEL
[2] A. F. Ioffe Physical-Technical Institute, St. Petersburg, RUSSIA
[3] M. V. Lomonosov Northern (Arctic) Federal University, Arkhangelsk, RUSSIA

We have considered the Polarization or Atomic Bremsstrahlung (AB) [1] generated in the process of scattering of a fast charge particle on a linear chain of isolated atoms. The specific feature of AB is that the radiation is generated by the varying in direction and size dipole moment induced in the target atom by the incoming projectile. The specific feature of AB is that its intensity, contrary to the case of ordinary bremsstrahlung (OB) is independent upon projectile mass. However, even for electrons as projectiles the intensity of AB rapidly increases with the growth of emitted photon frequency ω. At typical atomic frequencies ω the intensity of AB becomes bigger than that of OB even for electrons as projectiles. Note that for incoming ions OB is suppressed as compared to AB by the factor (m/M)2<<1, where m and M are electron and ion masses, respectively.

In case of multi-atomic targets, one must take into account that the projectile interacts with several atoms simultaneously, inducing a common time-dependent dipole moment. As a concrete target, we choose a linear chain of equally spaced atom with interatomic distance d. Using the approach developed in [2] for ion-chain scattering, we obtained intensity and angular distribution of the polarization bremsstrahlung spectrum for arbitrary number N of atoms in the chain. We demonstrate that the interference of photon radiation amplitudes leads to impressive alteration of the spectral angular distributions of AB on the target atomic chain as compared to that on an isolated atom. The effect of the chain is presented by a simple factor

η = {[sin(Nωd/v) sin(Nkd)]/[sin(Nωd/v) sin(kd)]}2, 

where kd = kdt with t being the cosine of the direction between the chain axis and emitted photon momentum k= ω/c; v is the speed of the projectile. We see that photons are emitted predominantly orthogonal to the chain axis.

The result allows generalization for the cases when the target is a plane formed of chains. Of special interest is the case when chains form a tube. Essential difference is expected when the projectile goes inside and outside this tube.

 [1] M. Ya. Amusia, Radiation Physics and Chemistry, 75, 1232, 2006.

[2] V. I. Matveev and D. U. Matrasulov, JETP Letters, 96, 700, 2012