A dissertation submitted to the Faculty Of Science in partial fulfilment of the
requirements for the degree of
Master of Science by research only
in the School of Physics, University of the Witwatersrand, Johannesburg. July 11, 2017. / A discrete Q-switched laser that gives a side-lobed single pulse as a laser output was
implemented; followed by studying energy extraction e ciencies and pulse characterisation.
The aim was to help design a passively Q-switched laser that gives a smooth single pulse of
optimum energy as a laser output. The smoothness feature in a single pulse is important in
some applications such as range nding. The concepts are demonstrated both experimentally
and numerically; the latter using Fox-Li approach to modeling resonator modes with
the Fresnel's integral for the system under study.
In the rst two chapters, fundamentals of how a laser works and the spatial mode development
are studied. In chapter 1, the principles of a laser are discussed: absorption,
spontaneous and stimulated emission. Also, di erent types of pumping sources and resonator
con gurations that can be used are discussed. In chapter 2, the focus is on developing spatial
modes of a laser. The fundamental and high order modes are discussed together with their
propagation laws. Then a numerical method is used to nd the eigenmodes of an arbitrary
resonator con guration. This numerical method is used to simulate propagation of a fundamental
mode and the simulation results are compared to analytical propagation laws. Then,
this numerical method is used to simulate a laser resonator. The eigenmode of the lowest
loss in the resonator was found.
In chapters 3 and 4, experimental work is done on a Q-switched laser where the focus is
on the overall laser performance. In chapter 3, Q-switched laser output energies are studied
for di erent combinations of Q-switch transmission values and output coupler re
ectivities.
In addition, the in
uence of spatial modes on a Q-switched pulse shape and pulse width are
studied, taking into account beam divergence. In chapter 4, conclusions and future work are
presented. In future work, the knowledge of spatial mode in
uence on pulse shape, pulse
width and beam divergence from chapter 3 is exploited. Then particular resonator con guration
that gives optimised output results (Q-switched laser output energy, beam divergence,
pulse shape and pulse width) is chosen. On that particular resonator, di erent Q-switch
transmission values are studied, but now looking only at beam divergence and pulse width.
Also, some suggestions on further improving laser performance are given. / LG2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/24990 |
| Date | January 2017 |
| Creators | Madlala, Bigboy |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (x, 69 pages), application/pdf |
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