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Development and applications of a picosecond VUV/x-ray streak cameraLamb, M. J. January 1981 (has links)
No description available.
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Optical method for liquid sorption measurements in paperFabritius, T. (Tapio) 17 April 2007 (has links)
Abstract
This thesis presents an effective optical method for measuring liquid sorption into paper. From the two tested methods, based on a streak-camera and optical coherence tomography (OCT), the last-mentioned proved very promising for investigating dynamical paper-liquid interactions as spatially and temporally dependent processes.
The streak-camera measurements were performed to explore the relationship between paper properties and light migration in dry and refractive index matched paper in general. Based on streak-camera measurements, a novel procedure for determining the average refractive index of cellulose fibre tissue was also presented here. In addition, the streak camera method lent itself to paper porosity determination.
Results of the performed OCT measurements proved that liquids cannot penetrate into paper before filling the pores and pits of the paper surface. As a liquid penetrated into paper, the border between the wetted and dry area could be investigated in the depth direction. The liquid penetration velocity seemed to be slower at the beginning and end of the process. Liquid absorption into paper fibres could be investigated concurrently. For the first time, the location and moment of structural changes in paper could be determined during wetting, and the effect of three different coexistent subprocesses related to paper wetting could be detected. OCT only fell short of detecting the effect of liquid migration along fibres.
Despite the limitations of the utilized method (resolution, probing depth and depth scanning rate), the obtained OCT measurement results are very promising for the development of an effective paper wetting measurement device for industrial applications. Even if this thesis focused on paper wetting, it is reasonable to assert that the presented ideas and obtained results have more general value in terms of explaining liquid penetration into porous structures and offer an alternative method of evaluating that process.
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Development of Plasma Assisted Ignition for Wave Rotor Combustion TurbineRavichandra R. Jagannath (5929814) 15 August 2019 (has links)
Gas turbines are important for power generation and aircraft engines. Over thepast century, there has been improvements in components of the gas turbine such ascompressors, turbines and nozzles, but very little progress has been made in combustor technology. The combustion still occurs at constant pressure and the only changes made are in terms of its design and mixing of fuel and air streams. These design changes have only allowed minimal improvements in gas turbine efficiency. To achievea substantative improvement in efficiency, it is required to make a technology change such as the introduction of constant volume combustion.<div><br></div><div>In this work, one such constant volume combustion device in the form of wave rotor combustion is studied and further developed for use in gas turbines. Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. In addition, there is also confined high speed turbulent deflagration. If the blades are curved, then the flow undergoes angular momentum change from inlet to outlet, generating shaft work. This will allow maximum extraction of work potential from the wave rotor. In addition, an attempt is made to check the applicability of plasma assisted ignition for wave rotors. </div><div><br></div><div>A computational tool is developed to understand physics of non-axial channelwave rotors. The governing equations are formulated in one dimension through a passage average approach. Shaft work is estimated using conservation of angular momentum and enrgy to verify the working of numerical model. The model shows increase in shaft work with increase in blade curvature, but as the angle is increased, the possibility of ignititing the reacting mixture becomes difficult since it is hard tomove the mixture towards the ignition port. </div><div><br></div><div>An alternate ignition source using plasma discharges is investigated through experiments. Two experiments are developed, one to make ultrafast measurements of plasma properties such as gas heating and lifetime of electronically excited molecules, and a second experiment to understand ignition characteristics of a pin to ring electrode configuration. The experiments show that excited nitrogen which reacts with molecular oxygen to form atomic oxygen is short lived and forms oxygen atoms extremely rapidly. This rapid formation of oxygen atoms assists in fast ignition. The ignition experiment with pin to pin electrode showed that even though there is fast ignition, the propagation speed does not change significantly with pulse repetition frequency. Ignition with pin to ring electrode showed fast ignition and increase inflame speed with pulse repetition frequency. Results show that plasma discharge can be used as an ignition source for wave rotors but will need further investigation.</div><div><br></div><div>The development of computational tool and plasma discharge experiments has provided a solid base for future efforts in wave rotor combustion and design of full scale non-axial wave rotor combustor experiment.</div>
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Photon migration in pulp and paperSaarela, J. (Juha) 07 December 2004 (has links)
Abstract
The thesis clearly demonstrates that photon migration measurements allow characterization of pulp and paper properties, especially the fines and filler content of pulp, and the basis weight, thickness and porosity of paper.
Pulp and paper are materials with a worldwide significance. Their properties strongly depend on the manufacturing process used. For efficient process control, the employed monitoring and measuring has to be fast. Therefore it is worthwhile to try to develop new approaches and techniques for such measurements. Recent advancements in optics offer new possibilities for such development.
If two samples have different optical properties their photon migration distributions are different. The measurement of a photon migration distribution allows some features between two optically slightly dissimilar samples to be distinguished. Some simple measurements, which only yielded the photons' average time of flight, were made with an oscilloscope and a time-of-flight lidar. More precise measurements yielding photon pathway distribution or some selected characteristics like light pulse rise time, broadening, or fall time were measured with a streak camera. Two methods to assess photon path length distribution were introduced: particle determination with simulation, and streak camera with deconvolution.
The basic properties for pulp are consistency and fines content and for paper the basic properties are thickness, basis weight and porosity. The influence on photon migration caused by changes in these basic properties was determined.
As pulp and paper are rarely very basic, an additional property was demonstrated for both materials. For pulp it was the content of filler talc, and for paper it was the use of beaten pulp as a raw material. These additional properties were also distinguishable.
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Untersuchungen zum Lumineszenzverhalten des Aluminiumnitrids und der Aufbau einer Kurzzeit-Lumineszenz-Spektroskopie-Apparatur / Investigations of the luminescence behaviour of aluminium nitride and the construction of a short time luminescence apparatusKoppe, Tristan 05 July 2017 (has links)
No description available.
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[pt] CARACTERIZAÇÃO E APLICAÇÕES DO CHAVEAMENTO ÓPTICO ULTRARRÁPIDO DE CAVIDADES SEMICONDUTORAS / [en] CHARACTERIZATION AND APPLICATIONS OF THE ULTRAFAST ALLOPTICAL SWITCHING OF SEMICONDUCTOR MICROCAVITIESGUILHERME MONTEIRO TORELLY 21 May 2020 (has links)
[pt] Este trabalho descreve teoria, simulação e caracterização óptica de
microcavidades semicondutoras utilizadas para a mudança de cor de pulsos de luz
e geração de pulsos ultra-curtos. Amostras foram fabricadas por MBE com GaAs e
AlAs em estruturas compostas de dois espelhos de Bragg e um espaçador de GaAs,
formando cavidades de Fabry-Pérot. Espectros de refletância e transmitância foram
simulados com o Método da Matriz de Transferência, considerando modelos
realísticos para as propriedades ópticas dos materiais. A caracterização óptica foi
realizada por FTIR e experimentos de Ring-Down utilizando uma streak camera.
Fatores de qualidade maiores que 10(5)
foram observados, correspondendo a tempos
de armazenamento da luz maiores que 100 ps. Experimentos de troca de cor da luz
em uma configuração de pump and probe foram realizados. A geração de pulsos
ultra-curtos com cavidades em micropilar foi estudada. Para caracterizá-las, foram
empregados o chaveamento óptico de cavidades e a microfotoluminescência
resolvida no tempo. O processo completo, ultrarápido, de chaveamento dos modos
ressonantes de uma cavidade semicondutora foi claramente observado de maneira
inédita. / [en] This work describes the theory, simulation and optical characterization of
semiconductor microcavities used to change the color of light and generate ultrashort pulses. Samples were fabricated by MBE with GaAs and AlAs in structures
composed of two Bragg mirrors and a GaAs spacer, creating Fabry-Pérot cavities.
Reflectance and transmittance spectra were simulated with the transfer-matrix
method considering realistic models of the materials optical properties. Optical
characterization was performed using FTIR spectroscopy and Ring-Down
experiments with a streak camera. Quality factors in excess of 10(5) were observed,
corresponding to storage times larger than 100 ps. Color-change experiments using
a pump and probe optical setup were performed. The generation of ultra-short
pulses with micropillar cavities was investigated. Time-resolved microphotoluminescence and optical cavity switching were employed to characterize the
cavities. The complete ultrafast process of switching resonant modes of a
semiconductor cavity using all-optical free carrier injection has been clearly
observed for the first time.
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Contribution à l'étude des électrons solvatés dans l’eau et les alcools et des processus radiolytiques dans les carbonates organiques par radiolyse impulsionnelle picoseconde / Contribution to the study of solvated electrons in water and alcohols and of radiolytic processes in organic carbonates by picosecond pulse radiolysisTorche, Fayçal 13 July 2012 (has links)
Le travail présenté dans cette thèse, s’inscrit dans le domaine d'étude de l'interaction des rayonnements ionisants avec les liquides polaires. Bénéficiant de l’accélérateur d'électrons picoseconde ELYSE, les études ont été menées en utilisant les techniques de la radiolyse impulsionnelle associées à la spectrophotométrie d’absorption résolue en temps dans le domaine de la picoseconde. Ce travail est réparti sur deux chapitres distincts. Le premier aborde l’étude la variation temporelle du rendement radiolytique de l’électron solvaté dans l'eau et les alcools simples. Grâce au système de détection original monté sur l’accélérateur ELYSE, composé d’une lampe flash spécialement conçue pour cette détection et d’une streak-camera utilisée pour la première fois en spectroscopie d’absorption, il a été possible d'enregistrer la totalité du déclin du rendement radiolytique de l’électron solvaté d’une façon continue dans un intervalle de temps allant de la dizaine de picoseconde à quelques centaines de nanoseconde. La capture de l’électron solvaté par le méthylviologène, a été mise à profit pour réévaluer le coefficient d’extinction molaire du spectre d'absorption de l’électron solvaté dans l’eau et l’éthanol à partir des points isobestiques qui apparaissent à l'intersection des spectres d'absorption de l’électron solvaté qui disparaît et du méthylviologène qui se forme au cours de la réaction.Le deuxième chapitre est consacré à l’étude des carbonates organiques liquides, tels que le diméthyle carbonate (DMC), le diéthyle carbonate (DEC) et le propylène carbonate (PC). Cette famille de carbonate qui n’a jamais été étudiée auparavant par radiolyse pulsée, entre dans la composition des électrolytes des batteries notamment au lithium. Les études ont été focalisées sur le PC au vu de ces caractéristiques physico-chimiques, notamment sa constante diélectrique très élevée (64) et son très fort moment dipolaire de 4,9 D. Les premiers résultats ont été obtenus d’abord sur des solutions aqueuses contenant du propylène carbonate afin d'observer les réactions de réduction et d'oxydation du PC par les espèces radiolytiques de l'eau (électron solvaté et radicaux OH). Puis après l’identification (spectrale et cinétique) de l’espèce formée par interaction avec le radical OH comme étant le radical PC• résultant de l'abstraction d'un H de la molécule de PC et l’espèce formée par interaction avec l’électron aqueux comme étant l'anion PC-, d’autres mesures ont été effectuées dans le liquide pur ainsi qu’en présence de certains intercepteurs d’électrons (biphényle, anthracène, naphtalène). Elles ont permis d'accéder au rendement radiolytique de PC- ainsi qu'à l'évaluation de son potentiel redox. Les premiers résultats sur le DEC et le DMC sont aussi exposés dans cette partie, portant dans un premier lieu sur le solvant pur et puis en présence de biphényle. / This work is part of the study area of the interaction of radiation with polar liquids. Using the picosecond electron accelerator ELYSE, studies were conducted using the techniques of pulse radiolysis combined with absorption spectrophotometry Time-resolved in the field of a picosecond.This work is divided into two separate chapters. The first study addresses the temporal variation of the radiolytic yield of solvated electron in water and simple alcohols. Due to original detection system mounted on the accelerator ELYSE, composed of a flash lamp specifically designed for the detection and a streak-camera used for the first time in absorption spectroscopy, it was possible to record the time-dependent radiolytic yields of the solvated electron from ten picoseconds to a few hundred nanoseconds. The scavenging of the electron solvated by methyl viologen, was utilized to reevaluate the molar extinction coefficient of the absorption spectrum of solvated electron in water and ethanol from isobestic points which corresponds to the intersection of the absorption spectra of solvated electron which disappears and methyl viologen which is formed during the reaction.The second chapter is devoted to the study of liquid organic carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC) and propylene carbonate (PC). This family of carbonate wich compose the electrolytes lithium batteries, has never been investigated by pulse radiolysis. The studies were focused on the PC in the light of these physicochemical characteristics, including its very high dielectric constant (64) and its strong dipole moment of 4.9 D. The first results were obtained on aqueous solutions containing propylene carbonate to observe the reactions of reduction and oxidation of PC by radiolytic species of water (solvated electron and OH radicals). Then, after the identification (spectral and kinetic) of the species formed by interaction with the OH radical as the PC• radical resulting from the abstraction of a H from the molecule of PC and the species formed by the interaction with electron as the anion aqueous PC-, other measurements were made in the pure liquid and in the presence of some electron interceptors (biphenyl, anthracene, naphthalene). They give access to the radiolytic yield of PC- and the evaluation of its redox potential. The first results of the DEC and the DMC are also outlined in this section, the pure solvent and then in the presence of biphenyl.
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Ultrafast structural dynamics in 4Hb-TaSe2 observed by femtosecond electron diffractionErasmus, Nicolas 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis the structural dynamics, upon photo-excitation, of the charge-densitywave
(CDW) material 4Hb-TaSe2 is investigated on the time-scale of atomic motion
and simultaneously on the spatial-scale of atomic dimensions.
CDW materials have been of interest since their discovery in the 1970’s because of their
remarkable non-linear and anisotropic electrical properties, gigantic dielectric constants,
unusual elastic properties and rich dynamical behaviour. Some of these exotic
properties were extensively investigated in thermal equilibrium soon after their discovery
but only recently have ultrafast techniques like femtosecond spectroscopy become
available to study their out-of-equilibrium behaviour on the time-scale of atomic
motion. By studying their behaviour on this time-scale a more in-depth understanding
of their macroscopic properties can be gained. However, to do investigations on the
atomic time-scale and simultaneously directly observe the evolution of the atomic arrangements
is another challenge. One approach is through the previously mentioned
technique of femtosecond pump-probe spectroscopy but converting the usual ultrashort
optical probing source to an ultrashort electron or x-ray source that can diffract
off the sample and reveal structural detail on the atomic level. Here, the femto-to-picosecond out-of-equilibrium behaviour upon photo-excitation in
4Hb-TaSe2 is investigated using an ultrashort electron probe source. Two variations
of using an electron probe source are used: conventional scanning Femtosecond Electron
Diffraction (FED) and a new approach namely Femtosecond Streaked Electron
Diffraction (FSED). The more established FED technique, based on femtosecond pumpprobe
spectroscopy, is used as the major investigating tool while the FSED technique,
based on ultrafast streak camera technology, is an attempt at broadening the scope of
available techniques to study structural dynamics in crystalline material on the subpicosecond
time-scale.
With these two techniques, the structural dynamics during the phase transition from
the commensurate- to incommensurate-CDW phase in 4Hb-TaSe2 is observed through
diffraction patterns with a temporal resolution of under 500 fs. The study reveals
strong coupling between the electronic and lattice systems of the material and several
time-constants of under and above a picosecond are extracted from the data. Using
these time-constants, the structural evolution during the phase transition is better understood
and with the newly gained knowledge, a model of all the processes involved
after photo-excitation is proposed. / AFRIKAANSE OPSOMMING: In hierdie tesis word die strukturele dinamika van die lading-digtheid-golf (LDG) materiaal
4Hb-TaSe2 ondersoek op die tydskaal van atomiese bewegings en gelyktydig op
die ruimtelikeskaal van atomiese dimensies.
LDG materie is al van belang sedert hul ontdekking in die 1970’s as gevolg van hul
merkwaardige nie-lineêre en anisotrope elektriese eienskappe, reuse diëlektriese konstantes,
ongewone elastiese eienskappe en ryk dinamiese gedrag. Sommige van hierdie
eksotiese eienskappe is omvattend ondersoek in termiese ewewig kort na hul ontdekking,
maar eers onlangs is dit moontlik deur middle van ultravinnige tegnieke
soos femtosekonde spektroskopie om hulle uit-ewewigs gedrag te bestudeer op die
tydskaal van atomiese beweging. Deur die gedrag op hierdie tydskaal te bestudeer
kan ’n meer insiggewende begrip van hul makroskopiese eienskappe verkry word.
Om ondersoeke in te stel op die atomiese tydskaal en gelyktydig direk die evolusie
van die atoom posisie te waarneem is egter ’n moeilike taak. Een benadering is deur
middle van femtosekonde “pump-probe” spektroskopie maar dan die gewone optiese
“probe” puls om te skakel na ’n electron of x-straal puls wat van die materiaal kan
diffrak en dus strukturele inligting op die atomiese vlak kan onthul. Hier word die femto-tot-pico sekonde uit-ewewig gedrag in 4Hb-TaSe2 ondersoek met
behulp van elektron pulse. Twee variasies van die gebruik van ’n elektron bron word
gebruik: konvensionele “Femtosecond Electron Diffraction” (FED) en ’n nuwe benadering,
naamlik, “Femtosecond Streaked Electron Diffraction” (FSED). Die meer gevestigde
FED tegniek, wat gebaseer is op femtosekonde “pump-probe” spektroskopie,
word gebruik as die hoof ondersoek metode terwyl die FSED tegniek, wat gebaseer is
op die ultra vinnige “streak camera” tegnologie, ’n poging is om beskikbare tegnieke
uit te brei wat gebruik kan word om strukturele dinamika in materie te bestudeer op
die sub-picosekonde tydskaal.
Met behulp van hierdie twee tegnieke, word die strukturele dinamika tydens die fase
oorgang van die ooreenkomstige tot nie-ooreenkomstige LDG fase in 4Hb-TaSe2 deur
diffraksie patrone met ’n tydresolusie van minder as 500 fs waargeneem. Die studie
toon ’n sterk korrelasie tussen die elektroniese sisteem en kristalrooster. Verskeie
tydkonstantes van onder en bo ’n picosekonde kon ook uit die data onttrek word en
gebruik word om die strukturele veranderinge beter te verstaan. Hierdie nuwe kennis
het ons in staat gestel om ’n model van al die betrokke prosesse voor te stel.
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Ultrafast electron diffraction : source development, diffractometer design and pulse characterisationKassier, Gunther Horst 12 1900 (has links)
Thesis (PhD (Physics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Ultrafast Electron Diffraction (UED) is a rapidly maturing field which allows investigation of the
evolution of atomic arrangement in solids on timescales comparable to the vibrational period of
their constituent atoms (~10-13 s). The technique is an amalgamation of conventional high energy
electron diffraction methods and pump-probe spectroscopy with femtosecond (1 fs = 10-15 s) laser
pulses. Ultrafast pulsed electron sources generally suffer from limitations on the attainable electron
number per pulse (brightness) due to Coulomb repulsion among the electrons. In this dissertation,
the design and construction of a compact UED source capable of delivering sub-300 fs electron
pulses suitable for diffraction experiments and containing about 5000 electrons per shot is
described. The setup has been characterised by measurement of the transverse beam size and
angular spread, and through recording and analyzing an electron diffraction pattern from a titanium
foil. Measurement of the temporal duration of fs electron pulses is not trivial, and a specialised
compact streak camera operating in accumulation mode has been developed as part of this study. A
sub-200 fs temporal resolution has been achieved, and the dependence of temporal duration on
electron number per pulse was investigated for the current UED source. The observed trends
correlate well with detailed electron bunch simulations. In order to investigate ultrafast processes on
samples that cannot be probed repeatedly, it becomes necessary to significantly increase the
brightness of current state of the art compact sources such as the one constructed in the present
study. UED sources employing electron pulse compression techniques offer this possibility.
Traditional pulse compression schemes based on RF cavities, while simple in principle, pose
significant technical challenges in their realisation. The current thesis describes two novel UED
pulse compression methods developed by the author: achromatic reflectron compression and pulsed
cavity compression. Both concepts are expected to be easier to realise than conventional RF
compression. Detailed simulations predict that such sources can attain a brightness improvement of
more than one order of magnitude over compact sources that do not employ compression
techniques. In addition, such sources show much promise for the attainment of pulse durations in
the sub-100 fs range. / AFRIKAANSE OPSOMMING: Ultra vinnige elektron diffraksie is ‘n meettegniek wat tans in die proses is om vinnige ontwikkeling
te ondergaan. Die tegniek het ten doel om strukturele omsettingsprosesse op ‘n lengteskaal van
atoombindings en ‘n tydskaal van die vibrasie periode van atome in materie, ongeveer 10-13 s, te
ondersoek. Dit word bewerkstellig deur die spasieresolusievermoë van gewone hoë energie elektron
diffraksie met die tydresolusievermoë van femtosekonde (1 fs = 10-15 s) laserspektroskopie te
kombineer. Die aantal elektrone per puls (intensiteit) van ultravinnige gepulsde elektronbronne
word beperk deur die Coulomb afstootingskragte tussen die elektrone. Hierdie dissertasie beskryf
die ontwerp en konstruksie van ‘n kompakte ultravinnige elektron bron. Die elektronpulse wat
geproduseer word bevat tot 5000 elektrone per puls met ‘n tyd durasie van minder as 300 fs, en is
geskik vir diffraksie eksperimente. Die aparaat is gekarakteriseer deur die volgende metings:
elektronpulsdiameter, straaldivergensie, en ‘n titaan foelie se statiese diffraksie patroon. Dit is nie
triviaal om die durasie van femtosekonde elektronpulse te meet nie, en n spesiale kompakte
akkumulerende “streak camera” is vir die doeleindes van hierdie projek onwikkel. Die tydresolusie
van hierdie “streak camera” is beter as 200 fs, en die afhanklikheid van die pulsdurasie wat deur die
ultravinnige elektron bron geproduseer word as n funksie van die elektrongetal per puls is met
behulp van hierdie toestel bepaal. Die resultate klop redelik goed met gedetaileerde simulasies van
die elektron puls dinamika. Die karakterisasie van monsters wat nie herhaaldelik gemeet kan word
nie vereis verkieslik ‘n nog hoër pulsintensiteit as wat met huidige bronne bereik kan word. ‘N
verdere doelstelling is dus om ultravinnige elektron bronne te ontwikkel wat pulse met meer
elektrone per puls kan genereer. Dit kan bewerkstellig word deur bronne wat van elektron puls
kompressie tegnieke gebruik maak. Die tradisionele manier waarop dít gedoen word is deur middel
van n kontinu gedrewe radio frekwensie holte. Hierdie metode gaan egter gepaard met aanmerklik
hoë tegniese uitdagings. Om hierdie rede het die outeur twee alternatiewe puls kompressie konsepte
ontwikkel: akromatiese reflektron kompressie and gepulsde holte kompressie. Albei konsepte sal
waarskeinlik makliker wees om te realiseer as die tradisionele radio frekwensie kompressie, en is
deur middel van gedetaileerde simulasies geverifiseer. Hierdie simulasies voorspel dat die
intensiteit van genoemde bronne met ten minste n grooteorde meer kan wees as wat tans met
kompakte ultravinnige elektron bronne moontlik is. Verder blyk dit dat sulke bronne n pulsdurasie
van minder as 100 fs kan bereik.
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Ultrafast Cooperative Phenomena in Coherently Prepared Media: From Superfluorescence to Coherent Raman Scattering and ApplicationsGombojav, Ariunbold 2011 May 1900 (has links)
Technological progress in commercializing ultrafast lasers and detectors has allowed realization of cooperative processes on an ultrashort time scale, which demand a re-evaluation of the conventional cooperative phenomena with a new insight. Ultrafast cooperative phenomena in coherently prepared media and various applications of superfluorescence and coherent Raman scattering are studied in this dissertation. In particular, a simple theoretical testimony on analogy between a cooperative emission and coherent Raman scattering is presented by offering an opportunity to perform parallel research on these two processes from a unified point of view.
On one hand, the superfluorescent pulse with a time duration of a few tens of picoseconds (ps) from alkali metal vapor is observed for the first time, even though cooperative phenomena in atomic vapor have been extensively studied for more than five decades. A dense rubidium vapor pumped by ultrashort (100 femtosecond, fs) pulses allows a realization of the ultrafast superfluorescence while a time-resolved study of superfluorescence is accomplished by using a streak camera with 2 ps time resolution. Experimental research on quantum nature of cooperative emissions has been “frozen” over the years (three decades) possibly because of the technical difficulties. Quantum fluctuations of superfluorescence development are explored experimentally by taking advantage of the ultra fast streak camera. Presumable applications of the superfluorescent pulse in e.g., a remote sensing, and an ultraviolet upconversion of the input infrared laser pulse are presented. The quantum interference due to different excitation pathways is revealed by the temporal coherent control technique while observing interferometric signals from alkali metal vapors.
On the other hand, a new spectroscopic technique based on ultrafast coherent Raman scattering is developed. The key advantage of the presented technique is to suppress the non-resonant background noise which usually obscures possible applications of the other conventional coherent Raman techniques in practice. A reduction of the background noise is achieved by shaping and delaying the third pulse which probes the coherence of the medium (i.e., an enhancement of specific vibrations of the target molecules in unison) firstly prepared by two broadband pulses. We demonstrate a robustness and superiority of signal-to-noise ratio of the developed technique by identifying as few as 10000 bacterial spores at a single laser shot level.
Finally, several comparative studies between cooperative and uncooperative processes are presented. A picosecond cooperative phenomenon in a three-photon resonant medium induced by a single as well as two-color ultrashort pulses is investigated. A time-resolved study shows that a picosecond cooperative effect is crucial in the well-established fields of resonant-enhanced multiphoton ionizations and harmonic generations. We also present a quantitative analysis for spontaneous versus broadband coherent Raman scattering on pyridine molecules. The spontaneous Raman signal is enhanced by 5 orders as a result of cooperative phenomena.
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