The projectile beam coherence effects occurring in ion-atom collisions are analyzed on the basis of the recent theory of Karlovets et al. [Phys. Rev. A 92, 052703 (2015)] developed for the elastic scattering of wave packets of particles off a potential field. This theory is generalized to estimate the loss of coherence for inelastically scattered projectiles in ionizing collisions. The results obtained by the suggested model are compared with experimental data for the ionization of hydrogen atoms and molecules by 75-keV proton impact. Significantly improved agreement is observed between the theory and experiment. DOI: 10.1103/PhysRevA.93.032702 In a recent work Karlovets et al.[1] investigated theoretically the scattering of wave packets of nonrelativistic particles off a potential field. The authors derived a simple general expression that determines the number of scattering events for the case when the incident particle beam is a wave packet of arbitrary form but with its mean momentum strongly centered at a given value p i . Furthermore, they considered the example when the wave packet is scattered off randomly distributed potential centers. By averaging the number of events over the impact parameter between the potential center and the wave packet axis, they derived a formula for the effective cross section that reproduces the one obtained by previous authors (see, e.g., [2,3]where dσ /d | q i →q f is the differential cross section for the elastic scattering in an angle θ = arccos(q i ·q f ). Furthermore, by writing (k) = ⊥ (k ⊥ ) (k ), with strongly centered on p i , they obtainedKarlovets et al. carried out sample calculations for the case of electron impact, applying the Born approximation. They considered the collisions of a Gaussian wave packeton a Gaussian potential as well as on the hydrogen atom. Here σ ⊥ is the averaged transverse size of the wave packet. As a remarkable result, they found that the angular distributions of the effective cross section broaden with the decrease of σ ⊥ . [4] could control the coherence properties of the ion beam and thereby demonstrate the effect of the projectile coherence on the angular distribution of the scattered protons. The principle of the experiment is based on the van Cittert-Zernike theorem according to which the transverse coherence length r (the diameter of the area of coherence) of a source of waves at a distance L is of the order of λ/kα, where λ is the wavelength, α is the angular diameter of the source, and k is a dimensionless constant.Egodapitiya et al. used a well-collimated nearly monochromatic [< 1 eV full width at half maximum (FWHM)] proton beam that crossed a molecular hydrogen beam. The measured quantity was the doubly differential cross section (DDCS) for the ionization as a function of the scattering angle θ and the energy loss of the protons. The measurements were made at two coherence length values corresponding to two values of the distance between the target and the last aperture of the collimator, L = 6.5 and 50 cm. The diameter of t...

We analytically and numerically investigate the emission of high-order harmonic radiation from model solids by intense few-cycle midinfrared laser pulses. In single-active-electron approximation, we expand the active electron's wave function in a basis of adiabatic Houston states and describe the solid's electronic band structure in terms of an adjustable Kronig-Penney model potential. For high-order harmonic generation (HHG) from MgO crystals, we examine spectra from two-band and converged multiband numerical calculations. We discuss the characteristics of intra-and interband contributions to the HHG spectrum for computations including initial crystal momenta either from the point at the center of the first Brioullin zone (BZ) only or from the entire first BZ. For sufficiently high intensities of the driving laser field, we find relevant contributions to HHG from the entire first BZ. Based on numerically calculated spectra, we scrutinize the cutoff harmonic orders as a function of the laser peak intensity and find good qualitative agreement with our analytical saddle-point-approximation predictions and published theoretical data.