Researching On High-order Harmonic Related Problems

High-order-harmonic generation(HHG)results from the interaction of ultrashort laser pulses with matter.It is vital for the generation of the attosecond pulses,the acquisition of electronic structure information,and the acquisition of dynamic information of the target material(atoms,molecules,solid,nanomaterials).In our paper,the interaction of strong field with material is studied by the methods of Lewenstein in theory and experiment.It mainly includes the following four parts:(1)We carry out the theoretical calculation of the high harmonics produced by zthe atom.And the relationship between high harmonic spectrum and incident laser wavelength and laser field intensity is studied.The result shows that the longer the wavelength,the smaller the intensity of the harmonics,and the cutoff is creasing.However,the higher of the intensity of laser,the grater the intensity of the harmonics,and the cutoff is creasing.(2)We carry out the theoretical derivation of HHG produced by the strong laser field of the oxygen molecule,and the expression of HHG strength is given.(3)It can be seen from the expression of the high harmonics that the precise numerical calculation of the integer order complex Bessel function is key component.Based on the relation of inverse recursion,we write the code of the Bessel function of complex quantity.This is a ready-made algorithm assembly that doesn't have.(4)In the calculation of high order harmonic spectrum,multiple Bessel functions are involved and infinite sums of order are included.So what is the problem that we have to solve is that the Cut-off of position in the actual numerical computation.In this paper,we analyzed the effect on Bessel function from the order number of Bessel function and the argument,and the relationship between the number of cutoff orders and the number of cases is given under the required precision conditions.Outlook: Based on the derived expressions and the key problems of solved solutions,a high order harmonic spectrum of oxygen is programmed and analyzed.