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Title: FEW-CYCLE PULSES AMPLIFICATION FOR ATTOSECOND SCIENCE APPLICATIONS: MODELING AND EXPERIMENTS.
Creator: Hemmer, Michael, Richardson, Martin, University of Central Florida
Abstract / Description: The emergence of mode-locked oscillators providing pulses with durations as short as a few electric-field cycles in the near infra-red has paved the way toward electric-field sensitive physics experiments. In addition, the control of the relative phase between the carrier and the pulse envelope, developed in the early 2000's and rewarded by a Nobel price in 2005, now provides unprecedented control over the pulse behaviour. The amplification of such pulses to the millijoule level has been an...
Show moreThe emergence of mode-locked oscillators providing pulses with durations as short as a few electric-field cycles in the near infra-red has paved the way toward electric-field sensitive physics experiments. In addition, the control of the relative phase between the carrier and the pulse envelope, developed in the early 2000's and rewarded by a Nobel price in 2005, now provides unprecedented control over the pulse behaviour. The amplification of such pulses to the millijoule level has been an on-going task in a few world-class laboratories and has triggered the dawn of attoscience, the science of events happening on an attosecond timescale. This work describes the theoretical aspects, modeling and experimental implementation of HERACLES, the Laser Plasma Laboratory optical parametric chirped pulse amplifier (OPCPA) designed to deliver amplified carrier-envelope phase stabilized 8-fs pulses with energy beyond 1 mJ at repetition rates up to 10 kHz at 800 nm central wavelength. The design of the hybrid fiber/solid-state amplifier line delivering 85-ps pulses with energy up to 10 mJ at repetition rates in the multi-kHz regime tailored for pumping the optical parametric amplifier stages is presented. The novel stretcher/compressor design of HERACLES, suitable for handling optical pulses with spectra exceeding 300 nm of bandwidth with unprecedented flexibility, is fully modeled and also presented in the frame of this thesis. Finally, a 3D model of the multi-stage non-collinear optical parametric amplifier is also reported. The current and foreseen overall performances of HERACLES are presented. This facility is designed to enable attosecond physics experiments, high-harmonic generation and physics of plasma studies.
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Date Issued: 2011
Identifier: CFE0003576, ucf:48931
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003576

Title: FABRICATION OF INTEGRATED OPTOFLUIDIC CIRCUITS IN CHALCOGENIDE GLASS USING FEMTOSECOND LASER DIRECT WRITING.
Creator: Anderson, Troy, Richardson, Martin, University of Central Florida
Abstract / Description: 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...
Show moreFemtosecond 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 photo- modification 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.
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Date Issued: 2010
Identifier: CFE0002978, ucf:47965
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002978

Title: Coupling of Laser Beams for Filament Propagation.
Creator: Kepler, Daniel, Richardson, Martin, Baudelet, Matthieu, Christodoulides, Demetrios, University of Central Florida
Abstract / Description: Laser filamentation is a nonlinear process involving high-energy, ultrashort pulses that create narrow, non-diffracting structures over many times the Raleigh length. While many of the characteristics of filaments can vary greatly depending on the physical parameters used to create them, they share several defining features: a high intensity core, a lower intensity cladding of photons that serves as an energy reservoir to the core, and spectral broadening into a supercontinuum. While there...
Show moreLaser filamentation is a nonlinear process involving high-energy, ultrashort pulses that create narrow, non-diffracting structures over many times the Raleigh length. While many of the characteristics of filaments can vary greatly depending on the physical parameters used to create them, they share several defining features: a high intensity core, a lower intensity cladding of photons that serves as an energy reservoir to the core, and spectral broadening into a supercontinuum. While there have been many studies on the creation and control of multiple filaments from one laser pulse and a few studies on the interaction of two single filaments, many fundamental questions concerning the nature of this interaction still exist.This thesis seeks to explore the correlation between ultrashort pulses involving spatial separation, temporal delay, and relative degree of polarization using an interferometric approach. Evaluating the beam profiles and spectrum that result from varying those parameters.
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Date Issued: 2016
Identifier: CFE0006531, ucf:51374
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006531

Title: Design and Engineering of Ultrafast Amplifier Systems.
Creator: Webb, Benjamin, Richardson, Martin, Chang, Zenghu, Delfyett, Peter, Gaume, Romain, Shah, Lawrence, Klemm, Richard, University of Central Florida
Abstract / Description: Recently, the design and engineering of ultrafast laser systems have led to an extraordinary increase in laser power and performance which have brought about advances in many fields such as medicine, material processing, communications, remote sensing, spectroscopy, nonlinear optics, and atomic physics. In this work, several ultrafast amplification techniques -- including chirped-pulse amplification (CPA), optical parametric chirped-pulse amplification (OPCPA), and divided-pulse amplification...
Show moreRecently, the design and engineering of ultrafast laser systems have led to an extraordinary increase in laser power and performance which have brought about advances in many fields such as medicine, material processing, communications, remote sensing, spectroscopy, nonlinear optics, and atomic physics. In this work, several ultrafast amplification techniques -- including chirped-pulse amplification (CPA), optical parametric chirped-pulse amplification (OPCPA), and divided-pulse amplification (DPA) -- are described and demonstrated in the design and construction of two ultrafast laser facilities. An existing Ti:Sapphire laser system was completely redesigned with an increased power of 10 TW for experiments capable of generating hundreds of laser filaments in ordered arrays. The performance of DPA above the Joule-level was investigated in a series of experiments utilizing various DPA schemes with gain-saturated amplifiers at high pulse energy. A new high energy OPCPA facility has been designed and its pump laser system constructed, utilizing the technique of DPA for the first time in a flashlamp-pumped amplifier chain and with a record combined energy of 5 Joules in a 230 ps pulse duration. The demonstrated OPCPA pump performance will allow for the generation of 50 TW quasi-single cycle 5 fs pulses at 2.5 Hz from a table-top OPCPA system.
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Date Issued: 2016
Identifier: CFE0006547, ucf:51349
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006547

Title: THE EFFECTS OF ELECTRODE GEOMETRY ON CURRENT PULSE CAUSED BY ELECTRICAL DISCHARGE OVER AN ULTRA-FAST LASER FILAMENT.
Creator: Bubelnik, Matthew, Siders, Craig, University of Central Florida
Abstract / Description: The time-resolved electrical conductivity of a short-pulse generated plasma filament in air was studied. Close-coupled metal electrodes were used to discharge the stored energy of a high-voltage capacitor and the resulting microsecond-scale electrical discharge was measured using fast current sensors. Significant differences in the time dependence of the current were seen with the two electrode geometries used. Using sharp-tipped electrodes additional peaks in the time-resolved conductivity...
Show moreThe time-resolved electrical conductivity of a short-pulse generated plasma filament in air was studied. Close-coupled metal electrodes were used to discharge the stored energy of a high-voltage capacitor and the resulting microsecond-scale electrical discharge was measured using fast current sensors. Significant differences in the time dependence of the current were seen with the two electrode geometries used. Using sharp-tipped electrodes additional peaks in the time-resolved conductivity were seen, relative to the single peak seen with spherical electrodes. We attribute these additional features to secondary electron collisional ionization brought about by field enhancement at the tips. Additional discrepancies in the currents measured leaving the high-voltage electrode and that returning to ground were also observed. Implications for potential laser-induced discharge applications will be discussed.
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Date Issued: 2005
Identifier: CFE0000447, ucf:46378
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000447

Title: EVALUATION OF THE PHOTO-INDUCED STRUCTURAL MECHANISMS IN CHALCOGENIDE GLASS MATERIALS.
Creator: Lopez, Cedric, Richardson, Kathleen, University of Central Florida
Abstract / Description: Chalcogenide glasses and their use in a wide range of optical, electronic and memory applications, has created a need for a more thorough understanding of material property variation as a function of composition and in geometries representative of actual devices. This study evaluates compositional dependencies and photo-induced structural mechanisms in As-S-Se chalcogenide glasses. An effective fabrication method for the reproducible processing of bulk chalcogenide materials has been...
Show moreChalcogenide glasses and their use in a wide range of optical, electronic and memory applications, has created a need for a more thorough understanding of material property variation as a function of composition and in geometries representative of actual devices. This study evaluates compositional dependencies and photo-induced structural mechanisms in As-S-Se chalcogenide glasses. An effective fabrication method for the reproducible processing of bulk chalcogenide materials has been demonstrated and an array of tools developed, for the systematic characterization of the resulting material's physical and optical properties. The influence of compositional variation on the physical properties of 13 glasses within the As-S-Se system has been established. Key structural and optical differences have been observed and quantified between bulk glasses and their corresponding as-deposited films. The importance of annealing and aging of the film material and the impact on photosentivity and long term behavior important to subsequent device stability have been evaluated. Photo-induced structures have been created in the thin films using bandgap cw and sub-bandgap femtosecond laser sources and the exposure conditions and their influence on the post-exposure material properties, have been found to have different limitations and driving mechanisms. These mechanisms largely depend on both structural and/or electronic defects, whether initially present in the chalcogenide material or created upon exposure. These defect processes, largely studied previously in individual binary material systems, have now been shown to be consistently present, but varying in extent, across the ternary glass compositions and exposure conditions examined. We thus establish the varying photo-response of these defects as being the major reason for the optical variations observed. Nonlinear optical material properties, as related to the multiphoton processes used in our exposure studies, have been modeled and a tentative explanation for their variation in the context of composition and method of evaluation is presented.
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Date Issued: 2004
Identifier: CFE0000196, ucf:46177
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000196

Title: NONLINEAR FEMTOSECOND NEAR INFRARED LASER STRUCTURING IN OXIDE GLASSES.
Creator: Royon, Arnaud, Richardson, Martin, University of Central Florida
Abstract / Description: Three-dimensional femtosecond laser structuring has a growing interest because of its ease of implementation and the numerous possible applications in the domain of photonic components. Structures such as waveguides, diffraction gratings, optical memories or photonic crystals can be fabricated thanks to this technique. Its use with oxide glasses is promising because of several advantages; they are resistant to flux and ageing, their chemical composition can easily be changed to fit the well...
Show moreThree-dimensional femtosecond laser structuring has a growing interest because of its ease of implementation and the numerous possible applications in the domain of photonic components. Structures such as waveguides, diffraction gratings, optical memories or photonic crystals can be fabricated thanks to this technique. Its use with oxide glasses is promising because of several advantages; they are resistant to flux and ageing, their chemical composition can easily be changed to fit the well-defined requirements of an application. They can already be found in Raman amplifiers, optical fibers, fiber lasers, and other devices. This thesis is based on two axes. The first axis consists in characterizing the linear and nonlinear optical properties of bulk vitreous materials in order to optimize their composition with a particular application in view. Within this context, the nonlinear optical properties, their physical origins (electronic and nuclear) as well as their characteristic response times (from a few femtoseconds to a few hundreds of picoseconds) are described within the Born-Oppenheimer approximation. Fused silica and several sodium-borophosphate glasses containing different concentrations in niobium oxide have been studied. Results show that the nonlinear optical properties of fused silica are mainly from electronic origin, whereas in the sodium-borophosphate glasses, the contribution from nuclear origin becomes predominant when the concentration of niobium oxide exceeds 30%. The second axis is based on the structuring of materials. Three commercially available fused silica samples presenting different fabrication conditions (therefore distinct impurity levels) and irradiated with a near infrared femtosecond laser have been studied. The laser induced defects have been identified by means of several spectroscopic techniques. They show the formation of color centers as well as a densification inside the irradiated area. Their linear refractive index and nonlinear third-order susceptibility properties have been measured. Moreover, the structuring of fused silica at the subwavelength scale into "nanogratings" is observed and the form of birefringence induced by these structures is discussed. In addition to the fused silica samples, several oxide glasses presenting very distinct chemical compositions have been studied. A sodium-borophosphate glass containing niobium oxide exhibits micro-cracks and nano-crystallites following irradiation. A silicate glass with or without a silver component reveals fluorescent rings or "nanograting" structures. A zinc phosphate glass containing silver also presents fluorescent ring structures, with a size of the order of 80 nm, well below the diffraction limit. Pump-probe microscope techniques have been performed on this glass to investigate the laser-glass interaction. The absorption mechanism is determined to be four-photon absorption. The generated free electron density is ~ 1017 cm-3, which suggests the conclusion that an electron gas rather than a plasma is formed during the laser irradiation.
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Date Issued: 2009
Identifier: CFE0002666, ucf:48200
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002666

Title: Characterization and Application of Isolated Attosecond Pulses.
Creator: Chini, Michael, Chang, Zenghu, Saha, Haripada, Chow, Lee, Schulzgen, Axel, University of Central Florida
Abstract / Description: Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few...
Show moreTracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few-cycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on as-yet unprecedented timescales.In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for state-resolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics (-) on timescales shorter than the laser cycle (-) are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagnetically-induced absorption and transparency, and two-color multi-photon absorption to (")dark(") states of the atom. These features are observed in both bound states and quasi-bound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems.The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 15-25 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV (-) comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a world-record-breaking 67 as pulse.
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Date Issued: 2012
Identifier: CFE0004781, ucf:49802
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004781

Title: Ultrafast Laser Material Processing For Photonic Applications.
Creator: Ramme, Mark, Richardson, Martin, Fathpour, Sasan, Sundaram, Kalpathy, Kar, Aravinda, University of Central Florida
Abstract / Description: Femtosecond Laser Direct Writing (FLDW) is a viable technique for producing photonic devices in bulk materials. This novel manufacturing technique is versatile due to its full 3D fabrication capability. Typically, the only requirement for this process is that the base material must be transparent to the laser wavelength. The modification process itself is based on non-linear energy absorption of laser light within the focal volume of the incident beam.This thesis addresses the feasibility of...
Show moreFemtosecond Laser Direct Writing (FLDW) is a viable technique for producing photonic devices in bulk materials. This novel manufacturing technique is versatile due to its full 3D fabrication capability. Typically, the only requirement for this process is that the base material must be transparent to the laser wavelength. The modification process itself is based on non-linear energy absorption of laser light within the focal volume of the incident beam.This thesis addresses the feasibility of this technique for introducing photonic structures into novel dielectric materials. Additionally, this work provides a deeper understanding of the light-matter interaction mechanism occurring at high pulse repetition rates. A novel structure on the sample surface in the form of nano-fibers was observed when the bulk material was irradiated with high repetition rate pulse trains.To utilize the advantages of the FLDW technique even further, a transfer of the technology from dielectric to semiconductor materials is investigated. However, this demands detailed insight of the absorption and modification processes themselves. Experiments and the results suggested that non-linear absorption, specifically avalanche ionization, is the limiting factor inhibiting the application of FLDW to bulk semiconductors with today's laser sources.
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Date Issued: 2013
Identifier: CFE0004914, ucf:49626
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004914

Title: Enhanced Ablation by Femtosecond and Nanoseond Laser Pulses.
Creator: Kerrigan, Haley, Richardson, Martin, Baudelet, Matthieu, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description: Laser ablation of GaAs by a combination of femtosecond and nanosecond pulses is investigated as a means of enhancing material removal by a femtosecond pulse in the filamentation intensity regime. We demonstrate for the first time increased ablation of GaAs by ultrafast laser pulse plasmas augmented by nanosecond pulse radiation from a secondary laser. Material removal during laser ablation is a complex process that occurs via multiple mechanisms over several timescales. Due to different pulse...
Show moreLaser ablation of GaAs by a combination of femtosecond and nanosecond pulses is investigated as a means of enhancing material removal by a femtosecond pulse in the filamentation intensity regime. We demonstrate for the first time increased ablation of GaAs by ultrafast laser pulse plasmas augmented by nanosecond pulse radiation from a secondary laser. Material removal during laser ablation is a complex process that occurs via multiple mechanisms over several timescales. Due to different pulse durations, ablation by femtosecond and nanosecond pulses are dominated by different mechanisms. Ablation can be enhanced by optimally combining a femtosecond and nanosecond pulse in time. In this work, the craters generated by combinations of pulses are investigated for inter-pulse delays ranging from -50ns to +1?s, with the fs pulse preceding the ns pulse corresponding to a positive delay. The Ti:Sapph Multi-Terawatt Femtosecond Laser (MTFL) in the Laser Plasma Laboratory (LPL) provides 50fs pulses at 800nm with intensities of 1014W/cm^2 at the sample. An Nd:YAG laser (Quantel CFR200) provides 8ns pulses at 1064nm with intensities of 109W/cm^2. Crater profilometry with white-light interferometry and optical microscopy determine the structure and surface features of the craters and the volume of material removed. Ultrafast shadowgraphy of the ejected plasma provides insight to the dual-pulse ablation dynamics. Sedov-Taylor analysis of the generated shockwave reveals the energy coupled to the sample or preceding plasma. It was found that inter-pulse delays between +40 and +200ns yielded craters 2.5x greater in volume than that of the femtosecond pulse alone, with a maximum enhancement of 2.7x at +100ns. Shadowgraphy of -40 to +40ns delays revealed that enhancement occurs when the nanosecond pulse couples to plasma generated by the fs pulse. This work provides a possible means of enhancing ablation by femtosecond filaments, which propagate long distances with clamped intensity, advancing long-range stand-off ablation
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Date Issued: 2017
Identifier: CFE0006889, ucf:51734
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006889

Title: HIGH-INTENSITY ULTRA-FAST LASER INTERACTION TECHNOLOGIES.
Creator: Bernath, Robert, Richardson, Martin, University of Central Florida
Abstract / Description: To our knowledge this is the first comprehensive study of laser-induced effects generated at intermediate distances using self-channeled femtosecond laser pulses. Studies performed were made both experimentally and theoretically with the use of novel modeling techniques. Peak laser pulse powers above 3 GW allow beam propagation without divergence for up to several kilometers. In this regime, experiments were performed at 30 meters from the laser system in a custom propagation and target range...
Show moreTo our knowledge this is the first comprehensive study of laser-induced effects generated at intermediate distances using self-channeled femtosecond laser pulses. Studies performed were made both experimentally and theoretically with the use of novel modeling techniques. Peak laser pulse powers above 3 GW allow beam propagation without divergence for up to several kilometers. In this regime, experiments were performed at 30 meters from the laser system in a custom propagation and target range, utilizing the Laser Plasma Laboratory's Terawatt laser system. Experiments included investigations of laser ablation; electromagnetic pulsed (EMP) radiation generation over the 1-18 GHz region; shockwave formation in air and solid media; optical coupling of channeled pulses into transparent media; and, conservation of energy in these interactions. The use of bursts of femtosecond pulses was found to increase the ablation rate significantly over single-pulse ablation in both air and vacuum. EMP generation from near-field focused and distance-propagated pulses was investigated. Field strengths upwards of 400 V/m/λ for vacuum focusing and 25 V/m/λ for self-channeled pulses were observed. The total field strengths over 1-18 GHz measured at distance surpassed 12 kV/m. Shockwaves generated in transparent media at 30 meters were observed as a function of time. It was found that the interaction conditions control the formation and propagation of the shock fronts into the medium. Due to the processes involved in self-channeling, significant fractions of the laser pulse were coupled into the target materials, resulting in internal optical and exit-surface damage. Basic estimations on the conservation of energy in the interaction are presented. The results of the experiments are supported by hydrodynamic plasma physics code and acoustic modeling.
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Date Issued: 2007
Identifier: CFE0001902, ucf:47497
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001902

Title: FEMTOSECOND LASER WRITTEN VOLUMETRIC DIFFRACTIVE OPTICAL ELEMENTS AND THEIR APPLICATIONS.
Creator: Choi, Jiyeon, Richardson, Martin, University of Central Florida
Abstract / Description: 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...
Show moreSince 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 DOEs that will serve great flexibility and multi-functional capability on sensing, imaging and beam shaping.
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Date Issued: 2009
Identifier: CFE0002958, ucf:47984
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002958

Title: ULTRASHORT LASER PULSE INTERACTION WITH PHOTO-THERMO-REFRACTIVE GLASS.
Creator: Siiman, Leo, Glebov, Leonid, University of Central Florida
Abstract / Description: Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%....
Show morePhoto-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ~10^12 W/cm^2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to phase-matching with a grating formed by modulation of the nonlinear refractive index of PTR glass.
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Date Issued: 2008
Identifier: CFE0002349, ucf:47804
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002349

Title: TOWARDS DIRECT WRITING OF 3-D PHOTONIC CIRCUITS USING ULTRAFAST LASERS.
Creator: Zoubir, Arnaud, Richardson, Martin, University of Central Florida
Abstract / Description: The advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are...
Show moreThe advent of ultrafast lasers has enabled micromachining schemes that cannot be achieved by other current techniques. Laser direct writing has emerged as one of the possible routes for fabrication of optical waveguides in transparent materials. In this thesis, the advantages and limitations of this technique are explored. Two extended-cavity ultrafast lasers were built and characterized as the laser sources for this study, with improved performance over existing systems. Waveguides are fabricated in oxide glass, chalcogenide glass, and polymers, these being the three major classes of materials for the telecommunication industry. Standard waveguide metrology is performed on the fabricated waveguides, including refractive index profiling and mode analysis. Furthermore, a finite-difference beam propagation method for wave propagation in 3D-waveguides is proposed. The photo-structural modifications underlying the changes in the material optical properties after exposure are investigated. The highly nonlinear processes of the light/matter interaction during the writing process are described using a free electron model. UV/visible absorption spectroscopy, photoluminescence spectroscopy and Raman spectroscopy are used to assess the changes occurring at the atomic level. Finally, the impact of laser direct writing on nonlinear waveguide applications is discussed.
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Date Issued: 2004
Identifier: CFE0000236, ucf:46252
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000236

femtosecond (7)	+ -
laser (7)	+ -
Femtosecond (3)	+ -
chalcogenide (3)	+ -
ultrafast (3)	+ -

OPCPA (2)	+ -
nonlinear optics (2)	+ -
optics (2)	+ -
CPA (1)	+ -
Current Pulses (1)	+ -
DPA (1)	+ -
EMP (1)	+ -
Femtosecond laser (1)	+ -
Filamentation (1)	+ -
IR (1)	+ -
Keldysh (1)	+ -
NIR (1)	+ -
Nonlinear Optics (1)	+ -
PMMA (1)	+ -
PTR glass (1)	+ -
Raman spectroscopy (1)	+ -
Ultrafast (1)	+ -
ablation (1)	+ -
ablation crater (1)	+ -
amplifier (1)	+ -
arsenic trisulfide (1)	+ -
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