X-RAY PHOTOIONIZATION IN THE PRESENCE OF A BICHROMATIC LASER FIELD

X-ray photoionization of hydrogen in the presence of a bichromatic las er held is considered. The expressions for the T matrix and the cross sections for the laser-assisted x-ray photoionization are presented. T he initial state is the laser-field-dressed hydrogen-atom ground state , while the final state is the improved Coulomb-Volkov wave. The gauge consistency is ensured by working in the r.E gauge. It turns out that the matrix elements (the explicit form of which is given in the Appen dix) are much simpler in this case. This enables one to consider the s ymmetry properties of the T matrix and the cross sections analytically . It was shown that the symmetry (phi+pi, pi-theta)<->(phi,theta), whe re phi is the relative phase between the laser-field components and a is the polar angle of the outgoing electron, is exact in our case. In addition to this, there are approximate symmetries phi<->-phi and phi< ->phi+pi. All these symmetries, as well as the behavior of the differe ntial and total cross sections as functions of phi, theta, and the num ber of exchanged photons, are analyzed in numerous examples. The resul ts presented show the possibility of the coherent phase control of the laser-assisted x-ray photoionization process. It was also shown that in the monochromatic case our model gives results that are in good agr eement with the results of previous work.