| Chemical oxygen iodine laser (COIL) is the shortest wavelength, high-power chemical laser. Its output wavelength is1.315μm, a transition wavelength of atomic iodine. High power、excellent beam quality and low-loss Transmission by an optical fiber make COIL suitable for industry processing. High-peak-power pulse laser have obvious advantages in the laser drilling, cutting and welding. To realize the pulsed operation of high-power COIL is very significance.To achieve pulse operation of COIL high density of iodine atom is instantaneously produced through iodide dissociation excited by pulse discharge and photolysis, and one can use the method of Q-switched modulation in supersonic COIL. The gas component is CH3I-O2-N2which is discharged by high-voltage pulse and turns to low-temperature plasma, at the same time iodine atoms are produced. The excited iodine atoms (the upper laser level) are populated by a nearly resonant energy transfer from the electronically excited molecular oxygen in the singlet delta state O2(1△g) to iodine atoms. Population inversion of iodine atom between excited state and ground state is created, and lasing in optical resonator. The key problems of the research are to obtain stable and uniform large volume glow discharge in a mixed gas which includes some kinds of electronegative gas (CH3I, O2, Cl2et al) and to explore inner mechanism of the plasma and chemical dynamic during laser output. The influence of electrode structure, pre-ionization methods and electric circuit on large volume glow discharge is investigated. According to the structural similitude of CH3I and CF3I, one-dimensional fluid model is developed to study the pulsed discharge in CF3I-He mixture. A pre-mixed model for a pulsed chemical oxygen-iodine laser is presented to discuss the effect of gain temperature and gas composition on laser energy and pulse duration The influence of variation of iodine flow rate on laser energy and laser pulse duration is very sensitive in the research of Q-switched modulation of COIL, so real-time on-line measurement of iodine flow rate is very necessary. For the problem of contamination on the diagnostic windows in measuring iodine flow rate by means of absorption spectra, the reasons are analyzed and the corresponding approaches are presented.Experimental studies of stable and uniform large volume glow discharge are carried out by means of Rogowski-like electrode combined with side-free spark pre-ionization, side-sliding discharge pre-ionization and surface-sliding discharge pre-ionization. Compared of the discharge photos and laser output, it can be concluded that the stability and uniform of sliding discharge pre-ionization is superior to that of free-spark pre-ionization. Side UV pre-ionization is not suitable for large-aperture gas discharge because of the localized spatial diffusion of UV light. A kind of area array sliding pre-ionization is presented to solve the problem of large aperture gas discharge. The integrated design of pre-ionization and electrode result in the better stability and reliability than that of mesh electrode. The electrode can be magnified to any size in two dimensions in theory. The key design parameters of the electrode are investigated. The results show that utilization efficiency of UV light generated by area array sliding discharge is obvious higher. Using peaking capacitor (Cp) can reduce the inductance of discharge circuit and improve peak value of discharge voltage and current. It makes electric energy in storage capacitor (Cs) injecting plasma rapidly. A series of pulse laser output experiments is carried out by means of different electrode and pre-ionization method. The effect of discharge parameters, gas composition, gas pressure, PO2T value and output coupling on laser characteristics is investigated. Area-array sliding pre-ionization shows good performance in stability and energy of pulse laser. Single laser energy is up to4.3J through optimizing the experiment parameters, chemical efficiency is11%, specific volume energy is2.1J, electric efficiency is50-60%.In the pre-mixed lasing model for a pulsed chemical oxygen-iodine laser the dependence of species concentration and optical parameters (output coupling and cavity length) on single pulse energy and pulse duration is studied. Increasing iodine atom density is an effective approach to increase laser energy and reduce pulse duration. The optimal iodine density for laser energy and laser peak power is different. Under the different cavity length, the optimal output coupling to obtain the maximum laser energy is also different. The pulsed discharge in CF3I-He mixture has the glow-plasma features with the sheath region and the bulk-plasma region. Iodine atom is produced main through the collision dissociation process of electron with CF3I. The produced iodine atom density can reaches the order of1015mole cm-3and the iodine atom density increases with the pulsed voltage amplitude and pulsed width. Keeping the total pressure of mixture gas unchanged, the mixture ratio of CF3I and helium plays a significant role in discharge and only in appropriate mixture ratio can the produced iodine atom density reach the maximal value. At the different applied voltage amplitudes, the optimal mixture ratio to obtain the maximum iodine atom concentration is also different. Compared the theoretical results with experimental data partial theoretical results and tendency are consistent with experimental results.According to the characteristics of iodine vapor corrosivity and supplying, a real time measurement of iodine flow rate based on dualwavelength absorption spectroscopy is presented to solve the problem of contamination on the diagnostic windows. The wavelength that isn’t absorbed by iodine vapor is used to monitor the optical losses due to contamination and aerosol scattering. Another wavelength that is absorbed by iodine vapor is applied to monitor the total optical losses. It can easily eliminate the influence of the serious contamination and aerosol scattering on the measurement of iodine flow rate and obtain a reliable iodine flow rate. The unique design of absorption cell solves the condensation of iodine vapor on the diagnostic windows. |
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