Development of a tuneable laser source in the vacuum ultraviolet and its applications to spectroscopy
Thesis (MSc (Physics))--Stellenbosch University, 2008.
Third harmonic generation (THG) in a metal vapour is a nonlinear optical interaction that facilitates the generation of light in the vacuum ultraviolet (VUV) portion of the electromagnetic spectrum. The requirement of the metal vapour 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 can be phase matched by mixing the metal vapour with a noble gas in a speci c pressure ratio. The metal vapour noble gas mixture needs to be homogeneous and its temperature needs to be constant to within less than a degree Celsius over a path length of 7 cm. These requirements are satis ed by a crossed heat pipe oven. The heat pipe oven makes use of a dynamic liquid-vapour phase equilibrium in sodium in order to maintain a constant temperature of around 800 degrees Celsius, thus facilitating the generation of a stable homogeneous medium of metal vapour and noble gas that can be used for e cient generation of VUV radiation. The development of such a VUV source using zinc vapour and the application of a similar VUV source using magnesium vapour are discussed. The VUV radiation has been applied to laser induced uorescence spectroscopy of carbon monoxide (12C16O and 13C16O). Spectral lines of 20 spin-forbidden singlet-triplet transitions of the e3 − − X1 +(5 0) band were detected and accurate experimental wavelengths determined for the rst time for ve of these lines.