An iodine photoissociation laser (IPL) is Q-switched using the electro-optic effect of $LiNbO_3$ crystal. It is found that the electro-optic coefficient of the crystal $\gamma_{22}$ is $6.97 \times 10^{-6}$m/V. The FWHM of a single Q-switched pulse output is 15 ns.
Relaxation kinetics between the two sublevels of the excited state ($^2P_{\frac{1}{2}}$) of iodine atom is included in the set of rate equation for the IPL. With this kinetic medel, the gain-switched operation and the Q-switched operation of the laser oscillator are analyzed numerically and the results are compared with the experimental data of build up time, output energy, peak power, and temporal width of the laser pulse. When the pressure of the laser medium is 100 torr, we have found the relaxation time contants between the sublevels are 33 ns for the gain-switched operation and 29 ns for the Q-switched operation.
The directional amplified spontaneous emission (ASE) along the laser tube of IPL amplifier (active length: 60 cm, I.D.: 0.9 cm) is measured, and the experimental results are compared with one-dimensional ASE theory. Also, we have measured the loss of the stored energy in the IPL amplifier due to the omnidirectional ASE. The loss is found to be 13.5% for the present amplifier when the pressure of laser medium is 72 torr without buffer gas. But by adding the argon buffer gas to 210 torr, it is reduced to 4.2%.
Superradiant pulse is observed in the photodissociated iodine atoms ($^2P_{\frac{1}{2}}-^2P_{\frac{3}{2}}$ transition) in the IPL amplifier. The energy, peak intensity, build up time and time evolution of the pulse is investigated experimentally. We have found the intensity fluctuation exists in the pulse and its period depends linearly on the distance from the amplifier to the mirror which is placed behind the amplifier. This intensity fluctuation seems to be caused by the temporal variation and fluctuation of the population inversion density in the active medium of the amplifier.
A high power IPL amplifier series of 1 GW is designed and constructed. The amplifier series consists of an oscillator, two pre-amplifiers and a main amplifier. When the oscillator is operated in gain switched mode (FWHM=30 ns), the output energy of the amplifier series is 11.3 J. Therefore, the peak power of the amplifier series is about 380 MW for the capacitor charging voltage of 24.0 kV. It can reach to 1 GW by operating the oscillator in Q-switched mode (FWHM=15 ns) for the higher capacitor charging voltage.
