Enhanced spectral resolution of high-order harmonics by the coherent sum of dipole spectra

Abstract

A numerical probing technique is proposed that can resolve the spectral structures of high-order harmonics obtained from the solutions of the Schrodinger equation. This method can accurately locate the high harmonics in the frequency domain, which otherwise might be impossible due to the intricate structures:of midplateau harmonics in the short drive pulse regime. Resolved fine spectra reveal that the high harmonics contain several components whose phases have different intensity dependences, in accordance with the prediction of semiclassical approaches. The present technique is applied to the measurement of the harmonic blueshift induced by intense femtosecond pulses.