| Compared with the concept of vacuum in classical physics,fluctuations of quantum fields are ubiquitous in the relativistic quantum field theories.In strong electromagnetic fields,quantum fluctuations give rise to effective and non-linear interactions between photons and the macroscopic electromagnetic fields.One of the most prominent non-linear optical features of the QED vacuum is vacuum birefringence.Several groups have proposed to detect vacuum birefringence by:optical lasers with a strong magnetic field,a PW optical laser with an X-ray free electron laser,and two X-ray free electron lasers.All these proposals need to be carried out in a vacuum environment.A clean vacuum environment is a prerequisite for the detection of vacuum birefringence phenomena.Radiation generated by other mechanisms when a strong field laser interacts with the plasma can lead to noise interference and affect the analysis of the results of vacuum birefringence detection experiments.Traditional industrial methods of obtaining high vacuum are limited by baking or complex vacuum equipment and are not suitable for vacuum birefringence experiments.Therefore,the concept of vacuum cleaning is proposed in this paper,i.e.using a cleaning laser to ionize the residual gas in space,applying an electrostatic field to clean the ionized charged particles out of the clean region.For the concept of vacuum cleaning,the following studies were carried out in this thesis.（1）Simulation of vacuum cleaning.According to the ADK ionization model,the charge state distribution of ions with laser intensity,and the ionization probabilities of ions with different charge states at the laser focus are obtained.Modeling the simple motion of ions under the action of electrostatic field,the effects of the applied electric field strength,and the ratio of the radius of the cleaned area to the probe area on the number of particles in the detection area were analyzed.Finally,the distribution of ion species in the ionization region was obtained.And it was determined that the number of particles in the detection area is relatively small when the delay between the cleaning pulse and the probe pulse is 6-9 ns and the electric field strength is higher than 2.5×105 V/m.This provides a reference for determining the experimental parameters.（2）Experimental setup.In accordance with the simulation data,a vacuum cleaning is constructed with the following main objectives:to generate the cleaning pulse and the probe pulse,to achieve multiple delay times between the two pulses and to detect the ion species and the cleaning results.Lastly,two pulses with multiple tunable energies and delays in the range 0-12 ns were obtained.The ion species of the peaks in the ion signal spectrum were confirmed based on the time-of-flight versus mass-to-charge ratio of the ions.（3）Experimental measurements.Two detection approaches were developed,cleaning>probeandcleaning<probe based on the magnitude of the intensity of the cleaning and probe pulses,and experiments were performed at different laser energies,electrostatic field strengths,and pulse delays.Three kinds of signal spectra were obtained,namely,the cleaning pulse alone,the detection pulse alone,and the cleaning pulse and probe pulse simultaneously but with a few nanoseconds delay.Eventually,by comparing the ion signal spectra produced when both pulses are present at the same time,with those produced by the probe pulse alone,it is found that thecleaning<probe detection scheme,equipped with a small sized cleaning pulse,results in a significant reduction in the intensity of the ion signal peaks in the high valence state by namely 80%.It is proved that vacuum cleaning experiment can realize partial cleaning in vacuum.The work in this thesis provides an experimental reference for further particle-free vacuum environments in small areas. |
