Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The following work focuses on the development and characterization of efficient,
high-power, Thulium doped fibre lasers. Lasers emitting light around ~2 μm have
generated a large amount of interest owing to the range of applications requiring and
utilizing light centred on this wavelength. Laser light in this emission band is
considered “eye-safe” which makes it ideal for applications where eye-safety is
paramount. The aim of this work is to develop expertise in Thulium doped fibre
lasers. Background information relevant to the functioning of Thulium doped fibre
lasers is presented. An existing diode pumped, CW Thulium doped fibre laser is
characterized. The wavelength output as well as the efficiency of the fibre laser was
characterized for different fibre temperatures, indicating shorter wavelength output for
lower fibre temperatures. Additionally, initial results indicate that without any
wavelength control (fibre Bragg gratings, volume Bragg grating), the spectrum and
laser output is temporally unstable. The design, development and characterization of a
diode pumped, CW and Q-switched Thulium doped fibre laser is discussed. The
design process and considerations are discussed in detail. Different feedback
elements, including a volume Bragg Grating, are utilized to constitute the laser
resonator as well as two lengths of doped fibre. The CW fibre laser is characterized
with regard to its slope efficiency, spectral output, temporal behaviour, beam profile
and polarization. A maximum slope efficiency of 37 % was obtained for 6.5 metres of
active fibre, only limited by the onset of thermal damage of the fibre ends. Pulsed
mode of the fibre laser was facilitated with the aid of an Acousto Optic Modulator
(AOM). At a pulse repetition rate of 10 kHz and average power of 2 W, a maximum
pulse energy of 200 μJ is obtained with pulse durations of 77 ns. This corresponds to
a maximum peak power of 2.6 kW / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op die ontwikkeling en karakterisering van doeltreffende, hoëdrywing
vesellasers met Tulium as aktiewe ioon. Lasers met uitset golflengte rondom
~ 2 μm verwek groot akademise belangstelling gegewe die verskeidenheid praktiese
toepassings wat lig by ~ 2 μm vereis en benut. Laserlig in hierdie golflengtegebied
word beskou as "oogveilig", wat dit ideaal maak vir toepassings waar oogveiligheid
uiters belangrik is. Die doel van hierdie werk is om kundigheid in vesellasers, met
Tulium as aktiewe ioon, te ontwikkel. Agtergrondinligting met betrekking tot die
funksionering van Tulium vesellasers word eerstens bespreek. Daarna word 'n
bestaande diode-gepompde Tulium vesellaser bespreek in terme van die
karakteriseering van die uitset laser spektrum, asook die doeltreffendheid van die
vesel laser vir verskillende temperature, wat dui op korter golflengtes vir laer
temperature. Daarbenewens het die aanvanklike resultate daarop gedui dat sonder
enige golflengte beheer (vesel Bragg roosters, volume Bragg rooster), die spektrum en
uitsetdrywing tydelik onstabiel is. Die ontwerp, ontwikkeling en karakterisering van
'n diode-gepompde kontinuedrywing en Q-geskakelde Tulium vesellaser word
bespreek. Die ontwerp-proses en oorwegings word in detail bespreek. Verskillende
hoë-reflekterende elemente, insluitend 'n volume Bragg rooster, word gebruik om die
laserresonator te vorm. Twee lengtes van die aktiewe vesel word ook eksperimenteel
ondersoek. Die kontinuedrywing vesel laser word gekarakteriseer met betrekking tot
die helling van die doeltreffendheidskurwe, spektrale uitset, tydsgedrag, straalprofiel
en polarisasie. 'n Maksimum hellingsdoeltreffendheid van 37% was behaal vir 6,5
meter van 'n aktiewe vesel maar was beperk deur die aanvang van skade aan die vesel
endpunt as gevolg van hitteoorlading. Pulsering van die vesellaser is bewerkstelling
met 'n Akoesties Optiese Modulator (AOM). Teen 'n pulstempo van 10 kHz en met ‘n
gemiddelde uitsetdrywing van 2 W, was die maksimum pulsenergie van 200 μJ
verkry met pulslengte van 77 ns. Dit stem ooreen met 'n maksimum piekdrwywing
van 2,6 kW.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85645 |
| Date | 12 1900 |
| Creators | Coetzee, Riaan Stuart |
| Contributors | Rohwer, Erich G., Esser, Daniel, Neethling, Pieter, Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xii, 100 p. : col .ill |
| Rights | Stellenbosch University |
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