Correlations between the standard and alternative definitions of the beam quality factor

Strauss, Hencharl Johan (2005-04)

Thesis (MSc)--University of Stellenbosch, 2005.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/16619
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