Study On Stable High-effective Discharge Of High Power Fast Axial Flow CO₂ Laser

The stability and efficiency of the gas discharge in fast axial flow CO2 laser play an important role in increasing the power. In order to make the gas discharge more stable and efficient, the theoretical and experimental study on the gas discharge has been done in this thesis. The contents of the thesis are arranged as follow:(1) The properties of the glow discharge have been investigated. The results show that the instability and thermal instability of the electron attachment affect the stability of the glow discharge. The methods for eliminating the instability of the glow discharge and the influencing factors of the electronic-optic efficiency have been discussed.(2) The DC excited high power switching power supply has been designed The power supply prototype has been produced, and some experiments have been done. The experimental results show that the power supply can work in the continuous wave, pulsed, superpulsed modes. The power efficiency is more than 85%. Moreover, there is no limiting resistor in the discharge, which improves the whole efficiency of the laser. The electro-optical efficiency is up to 24%with DC discharge. The flow flield characteristics of three types of discharge tubes are discussed. The experiments in 4kW fast axial flow CO2 laser have been done. The experimental results show that the discharge tube of uniform flow field compared with the discharge tube of nonuniform flow field has much more advantages in SIMMER discharge, pulsed discharge and high power discharge. When the gas flow rate ensures that the increasing temperature does not influence the efficiency of the laser, the increasing uniformity of gas flow field is much better than the increasing gas flow rate.(3) In this thesis, characteristics of the RF excited for Fast-axial flow are considered. The model of RF discharge is established. The spatial distribution curves of electron density and electrical field are gotted. Then the gas ionized intensity of the electric field and equivalent resistance are calculated. According to the results, a matching net work for RF discharge using SMITH Circle is designed.(4) In this thesis, the design of 10kW RF-excied fast axial flow CO2 laser is introduced. The parameter for each element under the optimum matching is gotten. On the condition of 36KW single source injecting, the reflection power is less than 0.6KW. When using two sources in parallel and the total injecting power is 45KW, the steady glow discharge is obtained. At this time, the output laser is up to 10KW and the highest electronic-optic efficiency is 23.5%.(5) Some methods are used to improve the laser and power stability. The power stability is less than±1.5% with discharge current feedback. To make up for the phenomenon that the power is not very stable under current feedback, we had researched on the power monitor and feedback stabilization system based on sampling from the rear mirror of the resonator. Also we analyzed the infrared laser power detection methods and commonly used detectors, proposed a low damage threshold and fast response speed detector, attenuated and homogenized the transmission light from the rear mirror with integral sphere, and used PID control for the power feedback. The linearizaliton of the power monitor system works well, and laser power stability<±0.5%.