Development of VUV tunable laser spectroscopy techniques for characterizing calcium fluoride

[摘要] ENGLISH ABSTRACT:The large band gap (approximately 11.5-12.1 eV) and high transmission of calcium fluoride(CaF2) crystal in the ultraviolet (UV) and vacuum ultraviolet (VUV) region makes itan important material for optics for laser applications in UV. However, CaF2 degradesduring long exposure to UV irradiation due to defect generation. The formation of selftrappedexcitons (STE) is considered the first step in defect generation. In this projectthe possibility of observing STE states in CaF2 using a narrow bandwidth tunable VUVlaser source is investigated. This is the first spectroscopy study of an alkaline earth fluorideusing VUV tunable laser radiation instead of a fixed wavelength laser. The use of a VUVtunable laser source has potential for determining the energies of the STE states, which areunknown. Our main objective is addressed by developing techniques to measure absorptionspectra of pure and doped CaF2 samples, using a VUV scanning monochromator and atunable VUV laser, and by doing a literature study. The results obtained with the scanningmonochromator show absorption features in 126-180 nm range of all our samples. Thesevary for different samples and correlate with information from the supplier on the samples'fluorescence spectra. Total absorption of the VUV light by CaF2 in the 115-126 nm range isobserved. With the narrow bandwidth tunable laser light, absorption spectra were obtainedin the range of 143-146.7 nm of all our CaF2 samples. No significance peaks which can berelated to the STE states in CaF2 were observed in the VUV laser absorption spectra, butthe results are valuable to improve the technique. The conclusion is that either a differentspectral range or fluorescence detection can be investigated in future.

[发布机构] Stellenbosch University