Generation of non-integer high-order harmonics and significant enhancement of harmonic intensity*

Abstract

High-order harmonics from helium atom in the orthogonally two-color (OTC) laser field are investigated by solving the two-dimensional time-dependent Schrödinger equation. Non-integer high-order harmonics are obtained in some ratio of frequencies of two components. Pure odd and even harmonics from atoms could be separated in two components by adjusting the ratio of frequencies in OTC scheme, and the resolution of harmonics is improved at the same time. The physical mechanism is explained by the periodicity of dipole. With the same intensity of the incident laser, the intensity of the high-order harmonics from the OTC field scheme is improved by three orders of magnitude compared to the monochromatic laser field scheme. A theoretical scheme is provided for experimentally achieving improving energy resolution and separation of pure odd and even harmonics in atoms. Also, we provide a means for improving harmonic intensity.