The interhalogens IF and ICl as visible oscillators or amplifiers

Abstract

The spectroscopic and kinetic properties of the interhalogens are reviewed, with emphasis on iodine-monofluoride (IF) and iodine-monochloride (ICI). The IF discharge laser has produced 140 kW, 30 ns FWHM pulses at 491 and 485 nm, and shows promise of being scalable to at least the tens of millijoules per pulse level. The optical gain and transient absorption spectra for the IF 490 nm and ICI 430 nm bands have also been studied for discharge excitation. Gain in excess of 1.0 percent.cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> was observed across the entire IF blue-green band (479-498 nm) which demonstrates the potential broad tunability of this molecular laser. For both IF and ICI, strong absorption in the vicinity of the wavelength of maximum gain was identified as being due to the He ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2p^{1}P_{1}</tex> ) excited species. Introduction of Ne or Ar to the gas mixture was found to reduce the He ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> ) density by up to 75 percent, thereby substantially improving the IF small-signal gain-to-absorption ratio as well as the temporal width of the gain pulse. Although ICI has not yet lased, its peak small-signal gain of 1.3 percent-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and the negligible background absorption measured at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda = 431.3</tex> nm in discharge plasmas make it an attractive candidate for a violet amplifier. The radiative lifetimes for the IF and ICd D' states have also been measured and are consistent with the known lifetime of the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D'\rightarrow A'</tex> ) transition. Finally, the formation kinetics of IF* and ICI* in electron beam or discharge produced plasmas and the potential and limitations of these molecules as visible lasers (or amplifiers) are discussed.