The thallium mercury excimer and its potential as a laser

Abstract

Normalized fluorescence measurements of the thallium mercury band emission at 4590 and 6560 Å show that these bands have great promise for excimer laser action. The use of mercury as a broadening gas results in potential wells approximately four times as deep as those of the corresponding thallium xenon states. This effect, which is probably due to mercury’s high polarizability, leads to excimer band emission which is about a factor of 100 times more intense than that for thallium xenon at a given perturber gas density. Using the density dependence of the molecular fluorescence intensity, the molecular formation rate constant of the thallium mercury B 2Σ1/2 well is estimated to be 2.0×10−31 cm6/sec. It appears that the ideal laser operating conditions should be about 1019 Hg/cm3, 1016 Tl/cm3, and 6×1019 He or Ar/cm3. Under these conditions, at 720°C, an excited state Tl density of 3×1014/cm3 will result in a stimulated emission coefficient of about 1% per centimeter at either 4590 or 6560 Å. If successful, this laser will be most appropriate for high average power, rather than high peak power, because of the limitations imposed on the peak power by the molecular formation and thermalization rates. Tests of low power arc discharge in thallium iodide and mercury show that the kinetics and spectra of the excimer are apparently unaffected by the substitution of the salt for the pure metal. The use of such salts could lower the required operating temperature to around 350°C.