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Development and Modelling of a Passively Q-switched Ytterbium Doped Calcium Fluoride Laser Open Access


Other title
Calcium Fluoride
Laser Development
Thermal Modelling
Thermal Measurement
Rate Equation Modelling
Type of item
Degree grantor
University of Alberta
Author or creator
Schoepp, Travis R.
Supervisor and department
Fedosejevs, Robert (Electrical and Computer Engineering)
Examining committee member and department
Fedosejevs, Robert (Electrical and Computer Engineering)
Jaeger, Wolfgang (Chemistry)
Tsui, Ying (Electrical and Computer Engineering)
Department of Electrical and Computer Engineering
Photonics and Plasmas
Date accepted
Graduation date
Master of Science
Degree level
A longitudinally diode-pumped, passively Q-switched Yb:CaF2 laser has been developed and characterised using a Cr:YAG saturable absorber. A peak average output power of 914 mW at a repetition rate of 1314 Hz was obtained with a slope efficiency of 20%. The output pulse energy was 0.62 mJ with a pulse width of 78.6 ns FWHM giving a peak power of 7.9 kW. Laser threshold pump power was 8.6 W. CW laser operation has also been achieved with a peak power of 6.0 W, a laser threshold pump power of 3.8 W, and a slope efficiency of 28%. At identical pump powers the maximum ratio of Q-switched to CW average output power was 0.42. The thermal response of the laser medium was also studied. Crystal face temperature profiles were recorded using a thermal camera in both CW and Q-switched configurations. Measurements were made with increasing pump power from below to above laser threshold. Temperatures were seen to rise nearly linearly with pump power except at and just above threshold where additional dynamics play a role in heat generation and transport within the crystal. The thermal simulations were found to match the experiment to within 2% for the CW configuration and within 4% for the Q-switched configuration in terms of absolute temperatures. Rate equation modelling was performed for the Q-switched Yb:CaF2 laser. Output characteristics generally matched with experiment with the largest discrepancy observed of 30%. The laser rate equation modelling took into account the temperature variation in the gain medium with changing pump power through the use of the thermal simulations. With appropriate optimisation it was found that the Q-switched peak output power could potentially be improved to the order of 200 kW with possible applications in x-ray generation for water window x-ray microscopy. Optimisation of the laser crystal cooling was also determined to be feasible with a simulated reduction in peak temperature rise of 72%.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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