Tunable Multi-frequency And Weak Lines Study Of TEA CO₂ Laser

The tunable TEA CO₂ laser is very useful in many fields. This paper focuses on tunable multi-frequency and weak lines output of TEA CO₂ laser, and the theoretical and experimental work has been carried out.After investigating thoroughly the tune devices of infrared and CO₂ lasers at home and abroad, we summarize the application history and current situation of CO₂ tune devices. Then the scheme of grating line selection is chosen to realize tuning of TEA CO₂ laser in this paper. Then we analyse the principle and method of obtaining multi-frequency and weak lines output in theory.Double-frequency and triple-frequency output laser groups in regular band have been obtained with adoption of a parallel grating-grating cavity and the double-frequency and triple-frequency laser output is very useful to isotope separation of multi-frequency infrared laser. The double-frequency groups are 11 groups of 00°1-10°0 band's P branch, 8 groups of 00°1-10°0 band's R branch, 8 groups of 00°1-02°0 band's P branch and the triple-frequency groups are 7 groups of 00°1-02°0 band's R branch. In our experiment each double-frequency or triple-frequency output laser has fine space overlap and time-synchronization, and the laser is tunable with a wide region. Laser is exported beside one of the gratings approximately along cavity axis and it is convenient to application. Besides, the energy ratio among lines also has well tunable ability. This laser can get other triple-frequency and four-frequency laser output through the methods of improving the gain parameter and cavity design. Thus it can meet the requirement of some materials' double (or multi) frequency excitation and isotope separation. Our TEA CO₂ laser has simple structure and only two gratings are used to realize the multi-frequency laser output. In other TEA CO₂ laser experiment, triple-frequency output is obtained by three gratings or a few lasers, which is expensive. Obviously our study is very significant.The 11μm lines of TEA CO₂ laser are very important to silicon film deposited by laser-plasma, silicon isotope study, multi molecular selective excitation, selective multiphoton dissociation and atmospheric pollutant detection. The study of the 11μm weak lines (sequence band lines and hot band lines) is very short in home. Adopting the two grating cavity and lengthening the gain region of the discharge chamber, we study the output character of the TEA CO₂ weak lines. We successfully observe six weak lines near 11μm, one isotope line (wavelength 11005nm) and the other lines (wavelength 11013nm and 11015.5nm) with 16% CO₂, 21% N₂, 63% He at total pressure of 430*133.3Pa. The six weak lines are the P17 line of 001 -110 band and the P19,P21, P2,P25,P26 of 011-030 band. We study the output characteristic of P19 line of 011-030 band (wavelength 10973.5nm) and the other line (wavelength 11013 nm). The pulse width of weak lines is 400ns around. While the centre of grating is in the axis of the discharge chamber, the maximal energy output appears. The maximal energy is several hundred mJ. The tunable multi-frequency and weak lines output of TEA CO₂ laser is realized successfully in this paper, and the theoretical conclusion about double-grating cavity accords with the experiment result.