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

• Author / Creator

  Schoepp, Travis R.

• 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%.

• Subjects / Keywords

  • Laser Development
  • Thermal Modelling
  • Q-switching
  • Yb:CaF2
  • Rate Equation Modelling
  • Thermal Measurement
  • Ytterbium
  • Calcium Fluoride
  • Cr:YAG

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3JD5V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.