Modelling of end-pumped Ho:YLF amplifiers
Date
2013-03
Authors
Journal Title
Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
This work is a thesis regarding the energy scaling of end-pumped Ho:YLF amplifiers. The work
includes: a brief review of laser physics and models, the development of a suitable three dimensional
time resolved numerical model, a parametric study of double pass ampli ers simulated using the model,
comparison between the simulation and the experimental results of a double pass ampli er system,
and simulation of a high energy single pass ampli er.
A three dimensional time resolved numerical model of an end-pumped ampli er was developed. A
rate equation model was used to simulate the absorption and emission of light, energy transfer upconversion,
and spontaneous emission within the gain medium. In the traveling wave approximation the
propagation of light through the gain medium was modelled with the use of a split step method that
included di raction and gain.
A parametric study was performed to nd the design parameters for an end-pumped two pass ampli-
er. Limited optimisation of several ampli er parameters was performed. The study focused on the
optimisation of the energy per pulse through changes to the following parameters: crystal length, laser
beam size, pump beam sizes, and pump wavelength. The nal design speci cations for an experimental
system were for a 100 mm long 0.5 % (atm.) doped Ho:YLF gain medium, pump and seed beams
with spot sizes with e ective beam sizes of 1 mm and 0.95 mm respectively and a pump wavelength
of 1892 nm. The simulation predicted pulse energies above 480 mJ when seeded by a 55 mJ pulse at
repetition rates of 50 Hz.
The experimentally realised system with similar design parameters produced the highest reported energy,
330 mJ, from an end-pumped Ho:YLF ampli er. Comparison between the simulation and the
experimental results showed signi cant deviation. The deviation was explained by the e ect of parameters
not included previously in the simulation. These parameters were the power of the continuous component of the seed beam, and the energy transfer upconversion rate. Limitations and delity of
the numerical model with respect to the experimental system are discussed, notably the model of the
highly divergent pump beam was simplistic.
Preliminary simulation results of a high energy single pass ampli er predict that energy scaling in
Ho:YLF follows linearly with respect to pump power and that in the ideal case, multi-Joule operation
is possible at 50 Hz with optical to optical e ciencies of 19%.
Description
Thesis (MSc)--Stellenbosch University, 2013.
Keywords
Holmium amplifiers, Rate equations, Scalar diffraction, Numerical modelling, Dissertations -- Physics, Theses -- Physics