This thesis contains two projects - the development of a Raman fibre amplifier system for gas sensing and the development of a fibre-in beam-out isolator for use with fibre lasers. The first project developed a fibre Raman amplifier which amplified a 10mW narrow linewidth DFB laser at 1651nm to an output power of over 2W. To achieve this high output power from a narrow linewidth Raman amplifier mechanisms to suppress stimulated Brillouin scattering had to be employed. This amplifier system was packaged into a portable 19” rack enclosure and used to demonstrate remote, single-end, tuneable diode laser spectroscopy of methane. The packaged system detected methane concentrations of 100ppm.m at over 100m during challenging field trials. Extrapolation of lab based measurements to longer distances predicts an ultimate sensitivity of the system of 100ppm.m at greater than 200m. The second project developed a Faraday isolator to be used at the output of industrial fibre lasers. The isolator had an isolation of greater than 30dB, an insertion loss of less than 0.5dB and a return loss of greater than 50dB. The isolator used a dual Faraday rotator design with a half wave plate between the rotators to compensate for thermal stress induced birefringence. Using this approach the isolation was shown to be constant to greater than 60W. The isolator was also compensated for thermal lensing by balancing the positive thermal lens produced in the Faraday rotator with a negative thermal lens in a DKDP crystal. This reduced the thermal lens of the isolator from ~9 Rayleigh length per kW intrinsic to below 2 Rayleigh lengths per kW.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:668858 |
| Date | January 2012 |
| Creators | Legg, Thomas |
| Publisher | University of Strathclyde |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25959 |
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