Acquisition And Analysis System Of Attosecond Transient Absorption Spectroscopy Based On Tunable High-order Harmonics

High-order harmonic generation(HHG)provide a unique method for generating ultrafast coherent XUV light sources,and are the main means of obtaining desktop extreme ultraviolet light sources today because of their small size,high stability,and tunability.The study of the spectroscopic and spatio-temporal properties of high harmonic emission and the study of the electron dynamics based on high harmonic light sources can provide a deeper understanding of the microscopic quantum world.The high harmonics themselves have good coherence and very short pulse time characteristics,and tuning the energy of discrete-level subharmonics can expand the application range and practical value of harmonic sources.Under the XUV light source with wide energy coverage,the dynamics of the target atomic or molecular system on the attosecond scale can be obtained through the technique of attosecond transient spectroscopy and the automated acquisition program based on LabView software.Firstly,under the development environment of LabView software,we programmed the acquisition and analysis program of transient absorption spectra independently,and adopted the structure of "state machine" to process different experimental requirements,and then the experimental data can be acquired through the coordination between software and hardware to improve the experimental efficiency and reduce human errors.Because the attosecond measurement has strict requirements for the stability of the experimental environment,we also built a closed-loop stabilization system based on the perfect experimental equipment,which can stabilize the relative phase of the interference fringe at 28 as by real-time monitoring of the phase change of the common-line 532 nm continuous light interference fringe and timely feedback adjustment of the experimental optical path,under the test of the stabilization system for about 80 minutes.Under the acquisition and analysis procedure with the stabilization system,we broadened the energy spectrum width of the Ne gas harmonics by high harmonic tuning,and performed a delayed scan of the attosecond transient absorption spectrum of the 2s2 p energy level of the He atom by the pump-probe optical path in the range of 55 fs.With the change of the delay time of the two beams at the same probe intensity,a regular oscillation of the harmonic order above 60 e V can be observed.oscillation.Second,we experimentally introduced dispersion by adjusting the relative position of the grating in the compression stage of the femtosecond laser system,and compared the XUV spectra of Ne and He as harmonic generating gases,and found that they have the same offset direction in energy.From the experimental results,it is clear that under certain experimental conditions it is possible to perform higher harmonic tuning by changing the chirp of the femtosecond laser pulse to achieve continuous tuning.Theoretically,the harmonic spectra of Ne under different chirp conditions were calculated using single-atom response simulations,and a similar energy transfer phenomenon was found when compared with the experimental results.