Gain and transient absorption profiles for the iodine monofluoride 490-nm and iodine monochloride 430-nm bands under discharge excitation

The optical gain and transient absorption spectra for the IF 490-nm and ICl 430-nm bands have been measured in discharge-excited He, CF₃I and NF₃ or CCl₄ gas mixtures using a flashlamp - pumped, tunable dye laser. For the IF blue-green band, gain in excess of 1.0% cm ^-1 was observed over the entire 479-498-nm wavelength interval. Peak optical gain coefficients of ∼3.0% cm^-1 and 1.3% cm^-1 were observed for IF at 490.7 nm and ICl at 431.3 nm, respectively. For both molecules, strong absorption in the vicinity of the wavelength of maximum gain was identified as being due to the He (2p¹P₁) excited species. The addition of Ne or Ar to the gas mixture was found to substantially reduce the He (¹P₁) density, thereby improving the IF small-signal gain-to-absorption ratio as well as the temporal width of the gain pulse.