Thulium doped fibre lasers in continuous-wave and pulsed regimes

Coetzee, Riaan Stuart (2013-12)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/85645
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