Research On The Relative Phase Locking Of Optical Path In Attosecond Pump-Probe Experiment

Since the invention of pump-probe technology,lasers have become a key tool for researching microscopic dynamics.The ultra-short laser pulses are of extraordinary significance for exploring the motion and the structure of the molecules,atoms as well as electrons.At this stage,the attosecond pump-probe is the cutting-edge technology for researching microscopic dynamics.It is the "camera" with the highest time resolution at present,which can perform "ultra-high-speed photography" during molecular recombination and record electronic transitions,interference,etc.The attosecond pump-probe setups designing in a non-collinear way based on the Mach-Zehnder interferometer configuration can independently manipulate the character of the IR probe field and make the pump beam achieving wider reflection bandwidth,so it's especially favored by researchers.However,due to the fluctuating environmental conditions,such as airflow,mechanical vibration,and temperature,the MachZehnder interferometer is unstable.The changes in the optical path make the accuracy of the relative phase affected.To make the time resolution of the attosecond pump-probe setups more reliable,the relative phase between the pump and the probe pulse must be controlled with attosecond precision.This article focuses on the precise control of the relative phase of the attosecond pump-probe setups.A 532 nm continuous wave propagates through the Mach-Zehnder interferometer to produce interference fringes.Then the phase is extracted by the fast Fourier transform,and the proportional-integral-derivative algorithm is used to calculate the relative phase deviation for feedback control.The principle of pump-probe technology as well as the generation mechanism of interference fringes in the Mach-Zehnder interferometer system is explained.Due to the non-collinear design,the Mach-Zehnder interferometer has unique superiority in the attosecond pumpprobe setups.However,it's more susceptible to the surrounding environment,so its optical path needs to be locked.Besides,this article describes in detail the process of extracting the relative phase of the interference fringes by the fast Fourier transform.During compensating the extra optical path caused by the disturbance of the surrounding environment,the difference between the real-time interference fringe phase and the initial phase is regarded as the deviation signal.Then the proportional-integral-derivative algorithm is used to obtain the compensation value.It will be converted to a voltage signal to control the movement of Piezo Transducer,to achieve the lock of the optical path.What's more,we set the scanning function to meet the relative phase step control requirements of the attosecond pump-probe experiment.The operating of the optical path locking system in various environments is researched.By comparing the unlocking and the locking result,we analyze the influence of various factors on the stability of the system.During the verification experiment,the optical path locking system can effectively solve the problem of phase drift in various environments.With this system,the time delay between the pump and probe beams is stabilized within 17 as rms in 12 hours.To achieve long-distance optical path locking,the arm length of the system is extended to 8 meters with the result of 39as rms,which can still make the relative phase precisely controlled for actually using in attosecond pump-probe setups.The system is easy to operate and only requires a few minutes to reach a stable locked state,which can ensure high precision control of attosecond pump-probe setups.