Development and characterisation of a tunable laser source in the vacuum ultraviolet

[摘要] ENGLISH ABSTRACT: Four-wave frequency mixing in a metal vapour medium is a technique that is used togenerate small bandwidth, frequency tunable coherent vacuum ultraviolet radiation forspectroscopic applications. The theory of nonlinear optics, applied to sum-frequencygeneration in a magnesium vapour medium at moderate input laser intensity, describesthe requirements for optimal conversion efficiency accurately. The microscopicrequirement - a sufficiently large third order susceptibility - is met by employing the 3s²_3s3d two-photon resonance of atomic magnesium to enhance the susceptibility for sum-frequencygeneration. The macroscopic requirement for the constructive interference ofthe sum-frequency contributions generated in different volume elements (termed thephase matching condition) can be met by using a two-component gaseous medium ofmagnesium vapour and krypton gas. In an experimental setup phase matching requireshigh homogeneity of the medium, very stable temperature conditions and the ability tofine tune the krypton magnesium pressure ratio. These conditions can be met in a crossedconcentric heat pipe oven by relying on the properties of a dynamic liquid-vapour phaseequilibrium. Results obtained with two similar experimental setups for four-wavefrequency mixing in magnesium vapour confirm the theoretical predictions and show thatthe technically simple setup functions as an efficient laser source of tunable vacuumultraviolet radiation.

[发布机构] Stellenbosch University