Mixed gauge in strong laser-matter interaction

We show that the description of laser-matter interaction in length gauge at short short and in velocity gauge at longer distances allows for compact physical modeling in terms of field free states, rapidly convergent numerical approximation, and efficient absorption of outgoing flux. The mathematical and numerical framework for using mixed gauge in practice is introduced. We calculate photoelectron spectra generated by a laser field at wavelengths of 400$\sim$800 nm from single-electron systems and from the helium atom and hydrogen molecule. We assess the accuracy of coupled channels calculations by comparison to full two-electron solutions of the time-dependent Schrodinger equation and find substantial advantages of mixed over velocity and length gauges.