Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Ultra-short laser pulses are useful in materials processing like melting and cutting metals,
and medical applications such as surgery and many other fields. In this study, we characterize
and control the temporal shape of the ultra-short pulses generated from a Ti:Sapphire
femtosecond laser. It operates in the near infra-red spectral region, with a centre wavelength
of 800 nm. The 4f pulse shaper is the main setup used to modulate spectral shape
and characterize the laser pulse. The shaper consists of two diffraction gratings, two cylindrical
lenses and a computer controlled liquid crystal spatial light modulator (LC-SLM).
Gratings, lenses and LC-SLM are arranged in a 4f geometry, f being the focal length of
the lenses. This setup is first analysed analytically and numerically using Fourier transform
and the results obtained are then compared to those obtained from the experiment. The
characterization of ultra-short pulses was done using three different autocorrelation techniques
such as the intensity autocorrelation, the interferometric autocorrelation, and the
pulse shaping autocorrelation which can act as interferometric autocorrelation when a nonlinear
crystal ß-barium borate (BBO) is placed exactly at the position of the experiment.
These characterization techniques are based on the interaction between the laser pulse and
a replica of it with a nonlinear crystal. The setups were implemented and measurements
using the last two techniques were successfully conducted, with the pulse duration result
in the range from 80-86 fs. / AFRIKAANSE OPSOMMING: Ultrakort laserpulse het baie nut in verskeie velde waaronder materiaalprosessering (soos
die smelt en sny van metale) en mediese toepassings (soos chirurgie) maar net twee voorbeelde
is. In hierdie studie karakteriseer en beheer ons die vorm van n ultrakort laserpuls,
afkomstig vanaf n Ti:Saffier femtosekonde laser, in tyd. Die laser straal in die nabyinfrarooi
spektrale gebied uit met n sentrale golflengte van 800 nm. Ons gebruik n sogenaamde
4f-pulsvormer om die spektrum van die laserpuls te moduleer en die laserpuls te
karakteriseer. Die vormer bestaan uit twee diffraksieroosters, twee silindriese lense en n
rekenaarbeheerde vloeibare kristal ruimtelike-lig-modulator (LC-SLM). Die diffraksieroosters,
lense en LC-SLM is in n 4f-geometrie gerangskik, met f die brandpunt van die lense.
Die opstelling is eers analities en numeries beskou deur van Fourier-transformasies gebruik
te maak waarna die resultate wat verkry is met die van n eksperiment vergelyk is.
Die karakterisering van ultrakort laserpulse was met drie verskillende outokorrelasie tegnieke
gedoen, naamlik n intensiteits-outokorrelasie, n interferometriese-outokorrelasie en n
pulsvormer-outokorrelasie. Die pulsvormer kan as n interferometriese-outokorrelator optree
indien n nie-lineêre kristal ß-bariumboraat (BBO) by die uitset van die pulsvormer geplaas
word. Hierdie karakteriseringstegnieke is gebaseer op die interaksie tussen die oorspronklike
laserpuls en n kopie van die laserpuls in n nie-lineêre kristal. Die nodige opstellings virdie metings is gemaak en die metings was suksesvol uitgevoer. Die pulslengte wat gemeet
is, is in die orde van 80-86 fs.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71883 |
| Date | 12 1900 |
| Creators | Mbanda Nsoungui, Gaelle Carine |
| Contributors | Rohwer, Erich. G., Schwoerer, Heinrich P. H., Neethling, Pieter H., 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 | xiv, 76 p. : col. ill. |
| Rights | Stellenbosch University |
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