Controlling paths of high-order harmonic generation by orthogonal two-color fields**Project supported by the National Natural Science Foundation of China (Grant Nos. 11974229, 11404204, and 11947002), the Scientific and Technological Innovation Program of Higher Education Institutions in Shanxi Province, China (Grant No. 2019L0468), the Natural Science Foundation for Young Scientists of Shanxi Province, China (Grant No. 201901D211404), and the Innovation Project

Abstract

Controlling paths of high-order harmonic generation from is theoretically investigated by numerically solving the time-dependent Schrödinger equation based on the Born–Oppenheimer approximation in orthogonal two-color fields. Our simulations show that the change of harmonic emission paths is dependent on time-dependent distribution of electrons. Compared with one-dimensional linearly polarized long wavelength laser, multiple returns are suppressed and short paths are dominant in the process of harmonic emission by two-dimensional orthogonal ω/2ω laser fields. Furthermore, not only are multiple returns weaken, but also the harmonic emission varies from twice to once in an optical cycle by orthogonal ω/1.5ω laser fields. Combining the time–frequency distributions and the time-dependent electron wave packets probability density, the mechanism of controlling paths is further explained. As a result, a 68-as isolated attosecond pulse is obtained by superposing a proper range of the harmonics.