Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The beam quality factor (M2) of a laser is important because it describes both the quality of a laser
beam as well as its propagation. Particular applications require that the beam radii (from which the
M2 factor is determined) be defined in a specific way. The International Standards Organisation
(ISO) recently standardised the theoretically correct, but practically difficult second moment
definition of the beam radius.
This thesis aims to establish correlations between the second moment definition and other more
practical definitions. Chapter 2 presents a systematic introduction of moment theory for general
beams. Beam centre and radius definitions as well as beam classification are derived by means of
second and mixed moments. In Chapter 3 simple laser beams are modelled by means of a resonator
approach. The infinite number of solutions of this model is called Gaussian solutions, which are
found to be different for rectangular and cylindrical symmetric resonators. The zero order solution
for both symmetries is identified as the ideal solution to which all others can be compared to for
quality determinations. Chapter 4 presents different beam scanning devices, beam radius definitions
and correlations between these definitions. The theoretical basis for a new correlation theory is also
given. Chapter 5 describes programs and computations used to verify existing correlation methods
and to calculate correlation factors for a newly proposed theory. Chapter 6 presents the results of the
computations for both circular and rectangular symmetric beams. The ISO’s correlation theories are
tested first. Newly proposed correlation functions between the second moment and alternative
definitions as well as theoretical error graphs are given for various beams. A novel method to
correlate several important beam subclasses is also presented. Chapter 7 describes the experimental
setup, automation software and post processing techniques that were used to characterise a modified
CO2 TEA laser. It is further shown how the theory developed in previous chapters could be applied
to the experimental data. Chapter 8 presents the experimental results of the beam characterisation
measurements performed on two different beams that emanated from the CO2 TEA laser. Existing
and newly developed correlation theories are applied to the experimental data and the corresponding
results are compared. In Chapter 9, conclusions and suggestions with respect to the initial aims
identified in the first chapter are made. Several suggestions for future work are also made. / AFRIKAANSE OPSOMMING: Die bundel kwalitietsfaktor (M2) is baie belangrik omdat dit beide die kwaliteit en
voortplanting van ‘n laser bundel beskryf. Bundel radiusse (waarvan die M2 faktor bepaal
word) word verskillend gedefinieer vir spesifike toepassings. Die teoreties korrekte, maar
minder praktiese tweede moment definisie is onlangs deur die Internasionale Standaard
Organisasie (ISO) gestandariseer.
Hierdie tesis se hoofdoel is om die tweede moment definisie en ander meer praktiese
definisies te korreleer. Hoofstuk 2 stel die moment teorie van bundels sistematies bekend.
Dit word gewys hoe die senter en radius van ‘n bundel deur tweede en gemengde
momente gedefinieer kan word. In Hoofstuk 3 word laser bundels gemodeleer deur
middel van resonator aanslag. Die oneindige aantal oplossings wat verkry word heet
Gaussiese oplossings en is verskillend vir reghoekige en silindriese simmetriese
resonators. Dit word gewys dat die ideale bundel, waarmee alle ander bundels vergelyk
word, die zero orde oplossing van beide simmetrieë is. Hoofstuk 4 stel verskillende
bundel skanderings apparaat, bundel radius definisies en korrelasies tussen die definisies
bekend. Die teoretiese basis vir ‘n nuwe korrelasie teorie word ook gegee. Hoofstuk 5
beskryf die rekenaarprogramme en berekeninge wat gebruik word om huidige korrelasie
teorie mee te toets asook om nuwes mee te skep. Hooftuk 6 gee die resultate van die
berekeninge van die rekenaarprogramme vir beide reghoekig en silindriese simmetrie.
Die ISO se korrelasies word eerste getoets voordat nuwe teorieë bekend gestel word. In
Hoofstuk 7 word die eksperimentele opstelling, outomisasie sagteware en postprosessering
tegnieke gewys wat gebruik was om ‘n aangepaste CO2 TEA laser te
karakteriseer. Verder word dit gewys hoe die teorie wat in voorafgaande hoofstukke
ontwikkel is op eksperimentele data toegepas kan word. Hoofstuk 8 gee die
eksperimentele resultate van die bundel karakterisering van twee verskillende bundels
vanaf die CO2 TEA laser. Bestaande en nuwe korrelasie metodes word gebruik om die
bundels te korreleer en die resultate van elke metode word dan met mekaar vergelyk. In
Hoostuk 9 word afleidings gemaak. Daar word ook voorstelle gemaak vir potensiële
toekomstige werk.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16619 |
| Date | 04 1900 |
| Creators | Strauss, Hencharl Johan |
| Contributors | Von Bergmann, H.M., Rohwer, E.G., University of Stellenbosch. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 180 leaves : ill. |
| Rights | University of Stellenbosch |
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