Research On Mechanism Of Producing Iodine Laser By Discharge Alkyl Iodide

The iodine laser has the merits of favorable transmission characteristic in atmosphere since its wavelength is at atmospheric window, preferable fiber transmission characteristic while it can be transmitted in silica fiber with high efficiency, strong amplified characteristic and easy to realize high power output. Comparing with other iodine lasers, discharge-excited iodine laser has the merits of higher electrical efficiency, more compacted structure and easier to use. Therefore it has good application prospect in industry processing field. The study of producing iodine laser by discharge alkyl iodides was done theoretically and experimentally in this paper.Theoretically, quantum chemistry theory was used to calculate alkyl iodide molecules of CF₃I, C₂F₅I, i-C3F7I, C₂H2F₃I and n-C₃H₄F₃I. Using MP2 method, the accurate structures of these five kinds of molecules and their positive, negative ions were presented. In the discharge-excited iodine laser, impact processes between electrons and medium are the main kinetic processes. B3LYP, MPn, QCISD and CCSD methods were used to calculate these kinetic processes accurately. The kinetic processes between electrons and these five kinds of alkyl iodide molecules include impact excitation, impact dissociation, ionization and electron attachment. Energies of these impact processes, namely molecules'excited energy, dissociation energy, ionization potential and electron affinity, were offered. To improve accuracy, the zero point vibration energy was corrected in all energy calculations and the basis set superposition error was corrected in the calculation of dissociation energy. The average electron energy of optimum population inversion of discharge-excited iodide laser can be given by the energy calculations of impact processes between electrons and alkyl iodide molecules.The kinetic model of discharge-excited iodine laser was established while the medium is CF₃I, C₂F₅I or i-C₃F₇I and the buffer gas is N₂. Detailed analysis of the kinetic process for producing iodine laser by discharge alkyl iodide was done and 29 reaction processes were considered in the model. These processes include electron impact excitation, electron impact dissociation, electron impact ionization, impact deactivation, two or three particles recombination, etc. Runge- Kutta method was adopted to solve the kinetic model and varieties of the main particle density and photon density with time were gained while the laser was operating. Variety of the peak photon density with pressure of alkyl iodide medium and buffer gas was calculated according to experiment conditions. The theoretical study of kinetic model of discharge-excited iodine laser is very instructive to the experiment research of laser oscillation.Experimentally, to extend the selecting range of discharge-excited iodine laser medium, the feasibility of alkyl iodides C₂H₂F₃I and n-C₃H₄F₃I as iodine laser medium was studied firstly by microwave excitation. The 1. 315μm emission spectrums were observed under different pressure conditions by excited C₂H₂F₃I and n-C₃H₄F₃I with microwave. Furthermore, since the gain characteristics is the necessary condition of laser oscillation, the small signal gain of discharge-excited alkyl iodide C₂H₂F₃I and n-C₃H₄F₃I was calculated theoretically and measured by experiment. The reflecting mirror method was used for small signal gain measurement. Experiment results are in good agreement with theoretical calculating results. The research of emission spectrum and small signal gain indicate that alkyl iodide C₂H₂F₃I and n-C₃H₄F₃I have the feasibility of being iodine laser medium. These studies can be the base of the laser oscillation research.Experimental system of pulsed transverse-discharge iodine laser was designed and laser output was obtained successfully using CF₃I as medium and N2 as buffer gas. The main parts of the laser such as discharging electrode, preionization electrode, resonance cavity, gas circulating and heat exchanging system, pressure detecting and controlling system, high voltage pulsed power supply were designed. After installing and debugging the system, experimental study of glow discharge was done and parameters'ranges of stable glow discharge were presented. Experimental results of laser oscillation indicate that the discharge-excited iodine laser designed by this paper can obtain laser output. The pulse energy is 0.45mJ and width is about 200ns while pressure of laser medium is 60Pa, pressure of buffer gas is 10kPa and discharge voltage is 18kV. The laser can operate repeatedly when the pulse frequency is less than 2Hz. The changes of pulse energy with discharge voltage, laser medium pressure and buffer gas pressure are presented. Experimental results are in good agreement with theoretical calculating results of kinetic model.