Macroscopic studies of short-pulse high-order harmonic generation using the time-dependent Schrodinger equation

We consider high harmonic generation by ultrashort (27-108 fs) laser pulses and calculate the macroscopic response of a collection of atoms to such a short pulse. We show how the harmonic spectrum after propagation through the medium is significantly different from the single-atom spectrum. We use single-atom data calculated by integration of the time-dependent Schrodinger equation and propose a method, based on an adiabatic approximation;:to extract the data necessary to perform a propagation calculation.