Study On The Gain Properties Of Fast Axial Flow CO₂ Laser Amplifier

The need of high output power, short pulse width, excellent beam quality laser makes the amplifier show good future in more and more fields of the laser applications. Laser amplifier is used in substantial increase in output power, amplification of short or ultrashort pulse, and generation of special application and wavelength laser. In this thesis for the fast axial flow CO2 laser amplifier, dependence of the spatial gain distribution on the discharge current, gas flow speed, gas pressure and gas ratio have been studied, and the laser beam spots before and after amplification have been analyzed. The main research works of this paper are as following.(1) Introduce the types of laser amplifications and laser amplifiers, and compare the traveling-wave amplifier and regenerative amplifier. Then analyze the basic principle of the CO2 laser amplifier from the theory of the temperature model. Finally, introduce the basic structure and function of the main parts of the fast axial flow CO2 laser amplifier.(2) A related theoretical model of fast axial flow CO2 laser amplifier is established. Dependence of the spatial gain distribution on the discharge current and gas flow velocity have been researched in detail. The results are that gain properties of laser amplifier at different discharge current and gas flow velocity are different, and the gain on the central axis of the discharge tube is max. When the gas flow speed becomes larger, the gain coefficient gets relatively larger. When the discharge current becomes small, the gain coefficient gets relatively smaller. When the gas flow velocity increases to 160 m/s or larger, the gain coefficient is close to or larger than 1. When the discharge current increases to 50 mA or larger, the gain coefficient is close to or larger than 1.(3) The relation between gain coefficient and the discharge current, gas pressure and gas ratio have been researched in experiment. The results are that the gain performance differs at different discharge current. When the discharge current gets small, the gain tends to get saturation. For the small signal incident, the gain coefficient is close to or larger than 1. With the increase of the incident signal, gain coefficient will tend to decrease. When the gas proportion unchanged, the change of total gas pressure on the impact of the gain coefficient is smaller compared with the change of the discharge current. When the gas ratio varies, the gain distribution also changes. The gas ratio of He:CO2:N2=0.95:1.05:1.35 is the ideal ratio for the present laser amplifier. And the beam patterns of the incident and amplified laser have also been briefly analyzed.