Investigation Of High-order Harmonic Generation For Atoms Exposed To A Two-color Laser Field Using The Quantitative Rescattering Theory

When atoms(or molecules) are exposed to an intense laser field, high-order harmonic generation(HHG) can be observed. This is a very important nonlinear optical phenomenon. Lots of experimental results show that HHG spectra show a unique plateau structures. HHG has many potential applications for obtaining coherent sources of radiation in XUV and soft X-ray regions. The preferred light source of obtaining attosecond pulse is HHG. Therefore, the study of HHG has been the hot topic in recent years. At present, there are several main methods of studying HHG, namely, the strong field approximation(SFA) theory, quantitative rescattering(QRS) theory, the numerical solution of the time-dependent Schr?dinger equation(TDSE) and the time-dependent density functional theory(TDDFT). However, it is confirmed that the SFA fails to give the accurate harmonics in the lower plateau region. TDSE is more accurate but time-consuming. The QRS1 theory overcomes the above shortcomings. When atoms are exposed to a linearly polarized single-color laser pulses, HHG spectra obtained from the QRS agree very well with those from the TDSE and the experimental data. The main investigations are listed as follows:We extend the QRS theory to study the HHG of Ar, Ne and Xe atoms exposed to a linearly polarized two-color laser pulse. Firstly, we extract the returning electron wave packets from TDSE, scaled H, SFA for Ar. Secondly, we calculate the HHG yields from the TDSE, QRS1, QRS2, SFA for Ar, Ne and Xe atoms. Our results show that using the QRS theory to study the harmonic emitted spectrum is valid in two-color laser field. The wave packet is largely independence of the target structure and the shape of wave packet depends on the laser parameters only. We can see that QRS1 are not only less time consuming, and the results are accurate. At the same time,there are sharp spike in the spectrum of harmonic which are calculated by QRS1.Although the QRS2 results are more accurate, the QRS2 calculations are time-consuming and the computational time is almost close to that of the TDSE.