The research in this project was directed, firstly towards gaining an understanding of the effect excited-state absorption (ESA) has on gain and lasing in broadly tunable Ce:LiLuF lasers and secondly towards the development of Ce:LiLuF lasers suitable for spectroscopic applications. Detailed measurements of the single-pass, small-signal gain in Ce:LiLuF were undertaken, with a gain coefficient as high as 30±1 cm<sup>-1</sup> at 309 nm, with an absorbed pump fluence of 0.46 Jcm<sup>-2</sup>. Further, the ESA in Ce:LiLuF at 261 nm and 349 nm was measured. Using both the gain and ESA results in a computer model, the effective gain cross-sections at 309 nm and 327 nm and the ESA cross-sections at 261 nm, 309 nm, 327 nm and 349 nm were determined. The ESA cross-sections were found to be of the order of 10<sup>-18</sup> cm<sup>2</sup>. The effective gain cross-section in Ce:LiLuF was found to increase with decreasing temperature. This was proposed to arise from a decrease in the ESA cross-section with decreasing temperature in the Ce:LiLuF. An in-depth parametric study of Ce:LiLuF laser operation and tunability was undertaken. The results of these studies, together with computer modelling, enabled the importance of ESA and other effects on lasing to be established. In particular, the gain competition effects and ESA were found to lead to inefficient laser operation unless σ-polarised lasing was suppressed. With polarisation selection, efficient operation was obtained, with continuous tunability between 305 nm - 335 nm. Narrow bandwidth operation of Ce:LiLuF for use in OH radical detection in the atmosphere was investigated. Narrow bandwidth operation was achieved for the first time in Ce:LiLuF using a Eittrow grating with a telescopic and prism beam expansion system. Tunable lasing between 306.5 nm and 311.5 nm was obtained, with a spectral bandwidth of 0.7 cm<sup>-1</sup>. Finally, highly efficient Ce:LiLuF lasing was achieved with a new all-solid-state, 289 nm frequency-quadrupled Raman-shifted Nd:YAG laser. Slope efficiencies as high as 62±3% were achieved. This slope is believed to be the highest obtained in any cerium laser to date. The IR-to-UV conversion efficiency was 0.41% and the UV-to-UV conversion efficiency was 41%. These high efficiencies were attributed to high pump beam quality and good mode matching.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:275472 |
| Date | January 2003 |
| Creators | Johnson, Kristie Shureen |
| Contributors | Coutts, David W. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:6e3f763c-ebb4-4959-974b-aa5ae447c51b |
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