Development of a tuneable laser source in the vacuum ultraviolet and its applications to spectroscopy

[摘要] Third harmonic generation (THG) in a metal vapour is a nonlinear opticalinteraction that facilitates the generation of light in the vacuum ultraviolet(VUV) portion of the electromagnetic spectrum. The requirement of the metalvapour medium is that it has a suitably large third order nonlinear susceptibility.The third order susceptibility is further enhanced by a two photon resonance.Zinc and magnesium vapours are such nonlinear media. The THG process canbe phase matched by mixing the metal vapour with a noble gas in a speci cpressure ratio. The metal vapour noble gas mixture needs to be homogeneousand its temperature needs to be constant to within less than a degree Celsiusover a path length of 7 cm. These requirements are satis ed by a crossed heatpipe oven. The heat pipe oven makes use of a dynamic liquid-vapour phaseequilibrium in sodium in order to maintain a constant temperature of around800 degrees Celsius, thus facilitating the generation of a stable homogeneousmedium of metal vapour and noble gas that can be used for e cient generationof VUV radiation. The development of such a VUV source using zinc vapour andthe application of a similar VUV source using magnesium vapour are discussed.The VUV radiation has been applied to laser induceduorescence spectroscopyof carbon monoxide (12C16O and 13C16O). Spectral lines of 20 spin-forbiddensinglet-triplet transitions of the e3 − − X1 +(5 0) band were detected andaccurate experimental wavelengths determined for therst time forve of theselines.

[发布机构] Stellenbosch University