title: Frequency modulation of high-order harmonic generation in an orthogonally polarized two-color laser field.
abstract: We have experimentally investigated the frequency modulation of high-order harmonics in an orthogonally polarized two-color laser field consisting of a mid-infrared 1800nm fundamental pulse and its second harmonic pulse. It is demonstrated that the high harmonic spectra can be fine-tuned as we slightly change the relative delay of the two-color laser pulses. By analyzing the relative frequency shift of each harmonic at different two-color delays, the nonadiabatic spectral shift induced by the rapid variation of the intensity-dependent intrinsic dipole phase can be distinguished from the blueshift induced by the change of the refractive index during self-phase modulation (SPM). Our comprehensive analysis shows that the frequency modulation pattern is a reflection of the average emission time of high-order harmonic generation (HHG), thus offering a simple method to fine-tune the spectra of the harmonics on a sub-cycle time scale.
authors: Guicun
authors: G
authors: Li
authors: Yinghui
authors: Y
authors: Zheng
authors: Xiaochun
authors: X
authors: Ge
authors: Zhinan
authors: Z
authors: Zeng
authors: Ruxin
authors: R
authors: Li