1 |
Measuring the spatiotemporal electricBowlan, Pamela. January 2009 (has links)
Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009. / Committee Chair: Rick Trebino; Committee Member: Jennifer Curtis; Committee Member: John Buck; Committee Member: Mike Chapman; Committee Member: Stephen Ralph.
|
2 |
Yb-doped femtosecond lasers and their frequency doubling /Sarmani, Abdul Rahman. January 2008 (has links)
Thesis (Ph.D.) - University of St Andrews, November 2008.
|
3 |
Femtosecond cellular transfection using novel laser beam geometries /Tsampoula, Xanthi. January 2009 (has links)
Thesis (Ph.D.) - University of St Andrews, November 2009. / Restricted until 5th November 2011.
|
4 |
Yb-doped femtosecond lasers and their frequency doublingSarmani, Abdul Rahman January 2008 (has links)
Ultralow threshold, compact and highly efficient femtosecond lasers based on Yb³⁺ -doped potassium yttrium tungstate (Yb:KYW) and Yb³⁺ -doped vanadium yttrium oxide (Yb:YVO 4 ) have been demonstrated within this PhD-research project. For a continuous wave unmode-locked Yb:KYW laser a threshold as low as 101 mW was obtained with a slope efficiency of 74 %. By employing a single prism for dispersion control, the laser was tunable between 1012 nm to 1069 nm. When operated in the mode-locked regime, this laser produced transform-limited pulses having durations of 210 fs at a central wavelength of 1044 nm. Stable mode locking was observed for an optimised incident pulse fluence on the SESAM between 140 μJ/cm² to 160 μJ/cm² which was 2-3 times higher than the designed energy pulse fluence of the SESAM (70 μJ/cm² ). The employment of several combinations of chirped mirror designs for control of intracavity group velocity dispersion led to excellent results. The threshold for mode locking was satisfied for a pump power of 255 mW where the slope efficiency was measured to be 62 %. This is the most efficient SESAM-assisted femtosecond laser yet reported and the highest optical-to-optical efficiency of 37 % is exceptional. Transform- limited pulses with durations as short as 90 fs were produced in a spectral region centred on 1052 nm. The success of this research thus represents a good foundation on which to design and build more compact configurations that will incorporate just one chirped mirror for dispersion compensation. A relatively high nonlinear refractive index, n₂ , of 15 x 10⁻¹⁶ cm² /W was measured in Yb:YVO 4 and this affords particular potential for this candidate material in Kerr-lens mode locking. In fact, for operation in the femtosecond domain, the threshold power was 190 mW with a slope efficiency of 26 % and near-transform-limited pulses as short as 61 fs were generated at a centre wavelength of 1050 nm. The main objectives in developing this type of laser relate to a demonstration of high peak power operation in thin disc laser configurations. The deployment of a diode-pumped Yb:KYW femtosecond laser as a pump source for frequency doubling in a periodically-poled LiTaO₃ crystal was realised. The maximum realized output power of 150 mW corresponded to an impressive second harmonic conversion efficiency of 43 %. 225-fs duration green pulses (centred at 525 nm) were generated under the condition of strong focusing in the nonlinear crystal.
|
5 |
Control of multiphoton molecular excitation with shaped femtosecond laser pulsesXu, Bingwei. January 2008 (has links)
Thesis (PH. D.)--Michigan State University. Chemistry, 2008. / Title from PDF t.p. (viewed on Sept. 8, 2009) Includes bibliographical references (p. 134-148). Also issued in print.
|
6 |
Femtosecond Laser Written Volumetric Diffractive Optical Elements And Their ApplicationsChoi, Jiyeon 01 January 2009 (has links)
Since the first demonstration of femtosecond laser written waveguides in 1996, femtosecond laser direct writing (FLDW) has been providing a versatile means to fabricate embedded 3-D microstructures in transparent materials. The key mechanisms are nonlinear absorption processes that occur when a laser beam is tightly focused into a material and the intensity of the focused beam reaches the range creating enough free electrons to induce structural modification. One of the most useful features that can be exploited in fabricating photonic structures is the refractive index change which results from the localized energy deposition. The laser processing system for FLDW can be realized as a compact, desktop station, implemented by a laser source, a 3-D stage and focusing optics. Thus, FLDW can be readily adopted for the fabrication of the photonic devices. For instance, it has been widely employed in various areas of photonic device fabrication such as active and passive waveguides, couplers, gratings, opto-fluidics and similar applications. This dissertation describes the use of FLDW towards the fabrication of custom designed diffractive optical elements (DOE’s). These are important micro-optical elements that are building blocks in integrated optical devices including on-chip sensors and systems. The fabrication and characterization of laser direct written DOEs in different glass materials is investigated. The design and performance of a range of DOE’s is described, especially, laser-written embedded Fresnel zone plates and linear gratings. Their diffractive efficiency as a function of the fabrication parameters is discussed and an optimized fabrication process is realized. The potential of the micro-DOEs and their integration shown in this dissertation will impact on the fabrication of future on-chip devices involving customized iv DOEs that will serve great flexibility and multi-functional capability on sensing, imaging and beam shaping.
|
7 |
Fabrication Of Integrated Optofluidic Circuits In Chalcogenide Glass Using Femtosecond Laser Direct WritingAnderson, Troy P. 01 January 2010 (has links)
Femtosecond laser direct writing (FLDW) is a versatile process that uses focused femtosecond pulses to modify the physical structure of a material, which can result in a shift of optical properties such as the linear and nonlinear refractive index. If the photon energy of the femtosecond pulses lies below the material bandgap, nonlinear absorption rather than linear absorption becomes the dominant mechanism of energy transfer to the material. In this manner, a focused femtosecond pulse train can be used to fabricate functional features such as optical waveguides, diffractive optical elements, or micro-fluidic elements within the volume of a transparent medium. In this dissertation, the utility of femtosecond laser processing as a fabrication technique of optical and micro-fluidic elements in chalcogenide glasses is explored. The photo-induced modifications of optical and chemical parameters of new germanium-based Chalcogenide glasses in both bulk and thin-film form are characterized for the first time and the impact of material composition and laser fabrication parameters are discussed. The glasses are found to display an increase in volume, a decrease of the linear optical refractive index, and an increase of the nonlinear refractive index when exposed to femtosecond laser pulses. A model based on avalanche ionization and multi-photon ionization is used to describe the highly nonlinear absorption of laser light in the material and correlate the photo-induced modifications to the electron density generated during irradiation. The magnitude of the induced photomodification is shown to be dependent on laser parameters such as laser dose and repetition rate. The fabrication of microfluidic elements through both direct ablation and the preferential etching of photo-modified regions is also explored. Finally, the integration of both optical elements and fluidic elements fabricated by FLDW into a single substrate is discussed. iv TABLE OF CONT
|
8 |
Time domain pulse shaping using a genetic algorithmMori, Andrew 03 1900 (has links)
Thesis (MSc (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Through the use of complex Laser Pulse Shaping, numerous fundamental laser induced processes may be controlled as well as studied. This work serves as
an introduction into Laser Pulse Shaping, with the focus on a simple Pulse
Shaping experiment, as well as to determine whether future, more complex
processes may be similarly controlled.
A description of Laser Pulse Shaping theory is presented here, along with a
full explanation of a simple experiment to maximize second harmonic generation
(SHG) through Pulse Shaping. This experiment is simple on a theoretical
level yet complicated in both implementation as well as operation. The experimental
setup and software integration required hardware compatibility in
multiple programming languages. This work was successful in the sense that
a fully automated dispersion compensation system, accomplished through the
use of a genetic algorithm in a feedback controlled loop, was constructed and
tested.
The success of this experiment and the understanding gained in this work
has laid the foundation for further complex Pulse Shaping systems to be achieved
in future. / AFRIKAANSE OPSOMMING: Komplekse Laserpuls-vervorming kan gebruik word om verskeie fundamentele laser-geinduseerde prosesse beide te beheer asook te bestudeer. Hierdie navorsingstuk
dien as n inleiding tot Laserpuls-vervorming, spesifiek gefokus op
n eenvoudige Pulsvervormings-eksperiment. Meer komplekse Pulsvervormingsopstellings
kan toegepas word deur die kennis opgedoen in hierdie tesis.
Die teoretiese agtergrond van Laserpuls-vervormings word bespreek, tesame
met n eenvoudige eksperiment om die Tweede Harmoniek Skeppingsproses
(SHG) te maksimeer deur van Laserpuls-vervorming gebruik te maak. Die
eksperiment is teoreties eenvoudig, waar die implimentering asook bedryf meer
kompleks is. Die bedryf van die eksperiment word in 2 dele hanteer: die
hoofprogram en n Genetiese Algoritme gebruik in optimering. Die werking
van Genetiese Algoritmes asook Ultrakort Pulse (USPs) en pulskarakterisering
word ook bespreek.
Die suksesvolle opstelling van die experiment en ook die eind resultate
wat gevind is, maak dit moontlik om meer ingewikkeld komplekse laserpulsvervorming
experimente te bestudeer.
|
9 |
Spectral and temporal modulation and characterization of femtosecond ultra-short laser pulsesMbanda Nsoungui, Gaelle Carine 12 1900 (has links)
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.
|
10 |
Manipulation of short pulsesOkoye, Raphael 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: An ultra-fast laser pulse can be described in the time or frequency domain. If the timebandwidth
product of an ultra-fast pulse is not satisfied, then the pulse is stretched. Stretching
can be described in the time or frequency domain. In the time domain, it is called a chirp and
in the frequency domain, it is known as the group delay dispersion GDD. Various techniques
can be used to stretch and compress laser pulses. In this project, a prism pulse compressor used
for compressing stretched pulses was built. A 200nm supercontinnum generated in an all normal
dispersion photonic crystal fibre (ANDi-PCF) was compressed using the prism pulse compressor
from 2ps to 140fs. The experiment and physical interpretation presented in this project suggest
that a shorter pulse duration less than the measured 140fs of the compressed supercontinnum
can be obtained. / AFRIKAANSE OPSOMMING: 'n Ultra-vinnige laser puls kan beskryf word in tyd of frekwensie. As die tyd-bandwydte produk
van ‘n ultra-vinnige puls nie bevredig is nie, dan is die puls uitgerek. Hierdie uitrekking kan
beskryf word in tyd of frekwensie. In tyd word dit tjirp genoem en in frekwensie groep vertraging
dispersie. Verskeie tegnieke kan gebruik word om ‘n laser puls te rek of saam te pers. In
hierdie projek is ‘n prisma puls kompressor gebou om uitgerekte pulse saam te pers. ‘n 200nm
bre e bandwydte puls (“supercontinuum”) is gegenereer in ‘n fotoniese kristal optiese vesel wat
uitsluitlik normale dispersie toon (ANDI-PCF) en die puls is toe saamgepers met behulp van die
prisma puls kompressor van‘n oorspronklike 2ps na 140fs. Die eksperiment en fisiese interpretasie
wat in hierdie projek aangebied word dui daarop dat ‘n nog korter puls, minder as die gemete
140 fs, verkry kan word deur die bre e bandwydte puls verder saam te pers.
|
Page generated in 0.0694 seconds