The Dependence Of High-order Harmonic Efficiency With Wavelength In Crystals Driven By Laser Field

The interaction between strong laser and atoms,molecules and other substances involves many novel physical phenomena,which is the focus and frontier of physics research.With the rapid development of femtosecond technology,the high-order harmonics generated by atoms and molecules in the strong laser field have been widely applied and important research value.For example,the high-order harmonics are one of the important means of synthesizing super-strong attosecond pulse(1as=10^-18s).In recent years,people's research objects have been gradually transitioning from atoms and molecules to solids.In 2011,scientists obtained the first experimental study of the high-order harmonics emitted by crystals,and in the following years,a large number of theoretical studies on the strong laser-crystal interactions emerged,trying to explain the generation mechanism of the high-order harmonics emitted by crystals.The generation mechanism of atomic and molecular high-order harmonics can be explained by the semi-classical"three-step"model.Due to the high density and periodic structure of crystal,the generation mechanism of high order harmonic emission is still in the exploration stage.A large number of experiments show that the high order harmonics produced by the crystal have higher intensity,and how to improve the harmonic emission efficiency of the crystal is also a hot research.In this article,by simulating the dynamic process of laser driven crystal generating high-order harmonic,we study the emission efficiency of high-order harmonic generation?HHG?varies with wavelength driven by long monochrome laser.It is found that,when the laser intensity and harmonic energy range were the same,the emission efficiency of the first plateau does not change obviously with wavelength,but the emission efficiency of the second plateau increases with wavelength,and then analyze the wavelength dependence of the emission efficiency of the second plateau.In addition,the influence of different wavelength laser field in crystal driven is further explained by combining the energy band structure of crystal and tunneling of electrons between different bands.