Investigation of the conditions governing the stimulated emission threshold of a $CF_3I$ (iodine) laser

An analysis is made of the factors influencing the time ($t'$ in which the stimulated emission threshold is reached in a $CF_3I$ laser. The dependences of the time $t'$ on the resonator losses $L$ and on the $CF_3I$ vapor pressure, applicable to a laser pumped by rectangular pulses of relatively slow amplitude, are used to derive the pressure dependence of the laser line width. The absolute value of this width is determined experimentally at pressures sufficiently low for the broadening to be of the Doppler type. The results obtained are used to calculate the pumping rate and quantum efficiency of the laser. The value of the latter quantity ($0.9\pm0.18$) demonstrates a high efficiency of recombination of the photodissociation products back into the original molecules. An experimentally verified approximation is used to develop a theory which yields the time dependence of the accumulation of metastable iodine atoms. The dependence $t'(L)$ in the nonlinear range of high values of $L$ is used to find the combination $(k_1+k_2)/k_5^{1/2}$ of the rate constants of the reactions $I^*+CF_3\overset{k_1}\longrightarrow CF_3I$, $I^*+CF_3\overset{k_2}\longrightarrow I+CF_3$, $2CF_3\overset{k_5}\longrightarrow C_2F_6$, which govern this nonlinearity. The combination is found to be $1.0\pm0.35\times 10^{-6}$ cm$^{3/2}\cdot$sec$^{-1/2}$. The results obtained indicate that the chemical pumping channels are ineffective in the case of $CF_3I$.