Research On Gain Saturation Output Of Neon-like Argon 69.8 Nm Laser Pumped By Capillary Discharge

By summarizing and analyzing the domestic and international research progress of Ne-like Ar C line 69.8 nm laser,it is determined that the research content of this thesis mainly focuses on achieving the gain saturation of the 69.8 nm laser.In the theoretical study,the mechanism of the 69.8 nm laser has been studied in depth,and a four-level rate equation corresponding to 46.9nm and 69.8 nm laser has been established.And with the relevant level parameters,the relationship between the gain coefficients per ion density of the Ne-like Ar 46.9 nm and 69.8 nm lasers and the electron density and electron temperature are analyzed.Using one-dimensional magneto-hydrodynamics code,the plasma parameters during the Z-pinch process such as the electron temperature,electron density,and fractional abundance of Ar8+ as a function of the time and the radial of the capillary were calculated.And the relationship between the plasma parameters when the laser occurs and the experimental conditions such as the main pulse current and the initial Ar pressure is established.The influence of the main pulse current amplitude,the main pulse current rising time,and the initial pressure on the gain coefficient in the radial direction of capillary is analyzed,and the direction is specified for the experimental conditions required to achieve gain saturation.In experimental research,the relationship between the main pulse current amplitude or the initial pressure and the laser intensity with a 35 cm long capillary are researched.It is determined that the best laser output can be obtained when the main current amplitude is 14 k A and the initial pressure is 16 Pa.And then,the gain coefficients of Ne-like Ar lasers excited by 35 cm long capillary discharge are measured.The 46.9 nm laser accomplishes the gain saturation,the gain coefficient is 0.58 cm-1,and the gain length product is 19.The gain coefficient of the 69.8 nm laser is 0.40 cm-1,the gain length product is 13.2,and the laser nearly is the gain saturation.Afterwards,In order to achieve gain saturation increases the length of the gain medium;the optimum experimental parameters for laser intensity corresponding to 45 cm long capillary are studied.The optimum experimental parameters were: the main current amplitude is 13.5 k A,and the initial pressure is 15.4 Pa.Under the optimal experimental conditions,the 69.8 nm laser accomplishes the gain saturation,the gain coefficient is 0.41 cm-1,and the gain length product is 17.2.Simultaneously,the temporal characteristics and intensity distribution of Ne-like Ar 69.8 nm laser are measured.The experimental results show that the full width at half maximum of the 69.8 nm laser pulse first increases and then decreases with the increase of the initial pressure.The maximum half-width of the 69.8nm laser pulse is 1.75 ns at the initial pressure of 15.4 Pa.In the intensity distribution characteristics measurement experiment,the intensity distribution of the 69.8 nm laser is measured when the initial pressure and the plasma length is changed.The change of the initial pressure will influence the profile of the intensity distribution,while the change of the plasma length will not influence the profile of the intensity distribution except the laser intensity.The experimental results illustrate that there are one main peak in the laser intensity distribution at initial pressure 15.4 Pa,and the full width at half maximum of the main peak is 0.5 mrad.Finally,in order to obtain a higher laser output,a double-pass amplification experiment of a Ne-like Ar C line 69.8 nm laser is designed.A half cavity of double-pass amplification is built by the Si C flat mirror,the intensity of 69.8 nm double-pass amplification laser is higher 9.15 times than the intensity of single pass amplification,the beam angle of the double-pass amplification is 3.4mrad,the maximum half-width of the 69.8nm laser pulse is 2.2 ns,equivalent gain length is 85 cm,the gain length product is 34.9,the 69.8 nm laser depth gain saturated output is achieved.The temporal characteristics and spatial intensity distribution characteristics of the two-pass amplification laser are measured and compared with the single-pass amplification laser results.The reasons for the double-pass amplification of the laser beam angle and laser pulse width increasing are mainly related to the distribution of the gain medium.In summary,according to the kinetics of the 69.8 nm laser of the Ne-like Ar C line 69.8 nm laser,a calculation model of the 69.8 nm laser gain coefficient is established,and then the 69.8 nm laser gain coefficient is obtained in the plasma radial distribution,which has played a guiding role in the setting of experimental conditions.Based on the in-depth study of the optimal experimental parameters of the 69.8 nm laser,the gain saturation output of a Ne-like Ar 69.8nm laser is achieved using a 45 cm long capillary.The Si C mirror is used to perform the 69.8 nm laser double-pass amplification experiment,which greatly improves the laser output,and lays the foundation for the laser application research.