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Title: Single Mode Wavelength-Tunable Thulium Fiber.
Creator: Shin, Dong Jin, Richardson, Martin, Schulzgen, Axel, Amezcua Correa, Rodrigo, University of Central Florida
Abstract / Description: Thulium fiber lasers have the broadest emission wavelength bandwidth out of any rare-earth doped fiber lasers. The emission wavelength starts from 1.75(&)#181;m and ends at around 2.15(&)#181;m, covering a vast swath of the eye safe wavelength region and intersecting with a large portion of mid-infrared atmospheric transmission window. Also, thulium fiber lasers provide the highest average output power of any other rare-earth doped fiber lasers in these wavelength regimes, making them...
Show moreThulium fiber lasers have the broadest emission wavelength bandwidth out of any rare-earth doped fiber lasers. The emission wavelength starts from 1.75(&)#181;m and ends at around 2.15(&)#181;m, covering a vast swath of the eye safe wavelength region and intersecting with a large portion of mid-infrared atmospheric transmission window. Also, thulium fiber lasers provide the highest average output power of any other rare-earth doped fiber lasers in these wavelength regimes, making them uniquely suited for applications such as remote sensing. At the moment, high power beam propagation of continuous wave laser through the atmosphere in the mid-infrared range is yet to be investigated anywhere. In particular, the effects of atmospheric water vapors on the thulium fiber laser propagation are unknown and are of great research interest. This dissertation identifies the stringent requirements in constructing a high power, single frequency, wavelength tunable, continuous wave thulium fiber laser with the aim of using it to study various atmospheric transmission effects. A fine spectral control scheme using diffraction gratings is explored and improvements are made. Moreover, a fiber numerical simulation model is presented and is used for designing and implementing the thulium fiber laser system. The current limitations of the implemented system are discussed and an improved system is proposed. This will lay the foundation for the future high power atmospheric propagation studies.
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Date Issued: 2018
Identifier: CFE0007372, ucf:52084
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007372

Title: Power Scaling of High Power Solid State Lasers.
Creator: Oh, Bumjin, Richardson, Martin, Soileau, MJ, Chini, Michael, University of Central Florida
Abstract / Description: The solid-state laser is one of the most widely used lasers in scientific research and industrial applications. This thesis describes detailed investigations of two modern architectures of high power cw solid-state lasers, a 20 W diode-pumped Yb:YAG thin disc laser and 300 W diode-pumped Nd:YAG rod laser. With the thin disc laser architecture, the signal beam must fit to the pump area on the disc defined by the multi-pass diode pump configuration. The beam propagation, beam diameter, phase...
Show moreThe solid-state laser is one of the most widely used lasers in scientific research and industrial applications. This thesis describes detailed investigations of two modern architectures of high power cw solid-state lasers, a 20 W diode-pumped Yb:YAG thin disc laser and 300 W diode-pumped Nd:YAG rod laser. With the thin disc laser architecture, the signal beam must fit to the pump area on the disc defined by the multi-pass diode pump configuration. The beam propagation, beam diameter, phase and thermal effects for various cavity configurations are investigated theoretically and experimentally. In addition, the internal loss, small signal gain, and thermal lensing effect are essential properties to construct the laser system but usually unknown. The theories and methodologies to obtain these properties are presented and the experimental results are compared. In a second phase of the project, the multi-mode and single-mode operation of a high power diode-pumped rod laser system are examined and compared to the thin disc system. Thermal effects on the phase, beam quality and brightness are examined and future applications and improvements considered.
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Date Issued: 2018
Identifier: CFE0007232, ucf:52221
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007232

Title: High Energy, High Average Power, Picosecond Laser Systems to Drive Few-Cycle OPCPA.
Creator: Vaupel, Andreas, Richardson, Martin, Delfyett, Peter, Schulzgen, Axel, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description: The invention of chirped-pulse amplification (CPA) in 1985 led to a tremendous increase in obtainable laser pulse peak intensities. Since then, several table-top, Ti:sapphire-based CPA systems exceeding the 100 TW-level with more than 10 W average power have been developed and several systems are now commercially available. Over the last decade, the complementary technology of optical parametric chirped-pulse amplification (OPCPA) has improved in its performance to a competitive level. OPCPA...
Show moreThe invention of chirped-pulse amplification (CPA) in 1985 led to a tremendous increase in obtainable laser pulse peak intensities. Since then, several table-top, Ti:sapphire-based CPA systems exceeding the 100 TW-level with more than 10 W average power have been developed and several systems are now commercially available. Over the last decade, the complementary technology of optical parametric chirped-pulse amplification (OPCPA) has improved in its performance to a competitive level. OPCPA allows direct amplification of an almost-octave spanning bandwidth supporting few-cycle pulse durations at center wavelengths ranging from the visible to the mid-IR. The current record in peak power from a table-top OPCPA is 16 TW and the current record average power is 22 W. High energy, few-cycle pulses with stabilized carrier-envelope phase (CEP) are desired for applications such as high-harmonic generation (HHG) enabling attoscience and the generation keV-photon bursts.This dissertation conceptually, numerically and experimentally describes essential aspects of few-cycle OPCPA, and the associated pump beam generation. The main part of the conducted research was directed towards the few-cycle OPCPA facility developed in the Laser Plasma Laboratory at CREOL (University of Central Florida, USA) termed HERACLES. This facility was designed to generate few-cycle pulses in the visible with mJ-level pulse energy, W-level average power and more than 100 GW peak power. Major parts of the implementation of the HERACLES facility are presented.The pump generation beam of the HERACLES system has been improved in terms of pulse energy, average power and stability over the last years. It is based on diode-pumped, solid-state amplifiers with picosecond duration and experimental investigations are presented in detail. A robust system has been implemented producing mJ-level pulse energies with ~100 ps pulse duration at kHz repetition rates. Scaling of this system to high power ((>)30 W) and high peak power (50-MW-level) as well as ultra-high pulse energy ((>)160 mJ) is presented. The latter investigation resulted in the design of an ultra-high energy system for OPCPA pumping. Following this, a new OPCPA facility was designed termed PhaSTHEUS, which is anticipated to reach ultra-high intensities.Another research effort was conducted at CELIA (Univerist(&)#233; de Bordeaux 1, France) and aimed towards a previously unexplored operational regime of OPCPA with ultra-high repetition rates (10 MHz) and high average power. A supercontinuum seed beam generation has been established with an output ranging from 1.3 to 1.9 ?m and few ps duration. The pump beam generation has been implemented based on rod-type fiber amplifiers producing more than 37 W average power and 370 kW peak power. The utility of this system as an OPCPA pump laser is presented along with the OPA design.The discussed systems operate in radically different regimes in terms of peak power, average power, and repetition rate. The anticipated OPCPA systems with few-cycle duration enable a wide range of novel experimental studies in attoscience, ultrafast materials processing, filamentation, LIBS and coherent control.
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Date Issued: 2013
Identifier: CFE0004952, ucf:49570
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004952

Title: Plasma Dynamics of Laser Filaments.
Creator: Reyes, Danielle, Richardson, Martin, Gaume, Romain, Chini, Michael, University of Central Florida
Abstract / Description: Laser filamentation is a complex phenomenon occurring for pulses with peak power above a critical value. A filament is a dynamic self-guided structure characterized by several unique qualities, which include a beam with a high-intensity core surrounded by an energy reservoir, a weakly ionized plasma channel, and supercontinuum generation. Several of the proposed applications for filamentation utilize the plasma channel, such as for assisted electric discharge and microwave guiding. However,...
Show moreLaser filamentation is a complex phenomenon occurring for pulses with peak power above a critical value. A filament is a dynamic self-guided structure characterized by several unique qualities, which include a beam with a high-intensity core surrounded by an energy reservoir, a weakly ionized plasma channel, and supercontinuum generation. Several of the proposed applications for filamentation utilize the plasma channel, such as for assisted electric discharge and microwave guiding. However, filament properties are highly influenced by the physical conditions under which they are formed. A host of studies have been conducted to further characterize filaments, but much work still remains in order to understand their complex behavior. This work presents an accurate and direct measurement of the electron density based on an interferometric technique. The impact of different initial parameters on filament spatio-temporal dynamics in air is investigated, concentrating primarily on their influence on the plasma. For comparison of the experiment with theory, the plasma decay is modeled by a system of kinetic equations that takes into account three-body and dissociative electron recombination reactions.
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Date Issued: 2017
Identifier: CFE0006646, ucf:51222
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006646

Title: Design and Verification of a Multi-Terawatt Ti-Sapphire Femtosecond Laser System.
Creator: Roumayah, Patrick, Shah, Lawrence, Richardson, Martin, Amezcua Correa, Rodrigo, University of Central Florida
Abstract / Description: Ultrashort pulse lasers are well-established in the scientific community due to the wide range of applications facilitated by their extreme intensities and broad bandwidth capabilities. This thesis will primarily present the design for the Mobile Ultrafast High Energy Laser Facility (MU-HELF) for use in outdoor atmospheric propagation experiments under development at the Laser Plasma Laboratory at UCF. The system is a 100fs 500 mJ Ti-Sapphire Chirped-Pulse Amplification (CPA) laser, operating...
Show moreUltrashort pulse lasers are well-established in the scientific community due to the wide range of applications facilitated by their extreme intensities and broad bandwidth capabilities. This thesis will primarily present the design for the Mobile Ultrafast High Energy Laser Facility (MU-HELF) for use in outdoor atmospheric propagation experiments under development at the Laser Plasma Laboratory at UCF. The system is a 100fs 500 mJ Ti-Sapphire Chirped-Pulse Amplification (CPA) laser, operating at 10 Hz. Some background on the generation of very high intensity optical pulses is also presented, alongside an overview of the physics of filamentation. As part of the design of MU-HELF, this thesis focuses on a novel approach to manage the large amount of dispersion required to stretch the pulse for CPA utilizing a custom nonlinear chirped Volume Bragg Grating (VBG) as a pulse stretcher matched to a traditional Treacy compressor. As part of this thesis, the dispersion of the CPA system was thoroughly modeled to properly design the chirped VBG and fabricated VBGs were characterized using a scanning spectral interferometry technique. The work demonstrates the feasibility of using a compact monolithic pulse stretcher in terawatt class CPA lasers.
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Date Issued: 2017
Identifier: CFE0006651, ucf:51241
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006651

Title: Filament Wavefront Evolution.
Creator: Thul, Daniel, Richardson, Martin, Shah, Lawrence, Baudelet, Matthieu, University of Central Florida
Abstract / Description: Filamentation is a complex process that gives rise to many nonlinear interactions. However, the fundamentals of filament formation and propagation can be explained in terms of two dominant mechanisms: Kerr self-focusing and plasma defocusing. The first to occur, self-focusing, is responsible for an increase in irradiance through beam collapse. This process requires sufficient initial peak power, on the order of gigawatts for near infrared beams in air. Plasma defocusing then arrests the...
Show moreFilamentation is a complex process that gives rise to many nonlinear interactions. However, the fundamentals of filament formation and propagation can be explained in terms of two dominant mechanisms: Kerr self-focusing and plasma defocusing. The first to occur, self-focusing, is responsible for an increase in irradiance through beam collapse. This process requires sufficient initial peak power, on the order of gigawatts for near infrared beams in air. Plasma defocusing then arrests the collapse process once the irradiance reaches the ionization threshold of the medium. These two pro-cesses balance each other in an extended plasma channel known as a filament. A beam's collapse behavior is strongly influenced by the initial beam conditions, espe-cially in applications that require power scaling to terawatt levels where the Kerr effect is more pronounced. Therefore, understanding and controlling the collapse process is essential in this regime. For this reason, an exploration of the wavefront evolution of filamenting beams is of great interest and the topic of this thesis, which has three parts. First, it reviews the filamentation process and describes characteristics of filaments. Next, experimental measurements of the wavefronts of filamenting beams are given in two separate regimes. The first regime is the Kerr self-focusing that takes place before beam collapse is arrested. This data is then contrasted with wavefront measurements within a filament after collapse has occurred.
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Date Issued: 2017
Identifier: CFE0006808, ucf:51804
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006808

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: 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: LASER FILAMENT INTERACTION WITH AEROSOLS AND CLOUDS.
Creator: Jeon, Cheonha, Richardson, Martin, Vanstryland, Eric, Baudelet, Matthieu, Sigman, Michael, University of Central Florida
Abstract / Description: A high powered ultrashort laser pulse can propagate as a diffraction-free self-channeled structure called a filament, created by a combination of nonlinear processes. With its ability to convey extremely high intensity beams to distant targets, many applications such as remote sensing, cloud seeding, and discharge guiding are potentially possible. However, one of the main challenges of outdoor field applications is the laser propagation through the atmosphere where pressure fluctuations and...
Show moreA high powered ultrashort laser pulse can propagate as a diffraction-free self-channeled structure called a filament, created by a combination of nonlinear processes. With its ability to convey extremely high intensity beams to distant targets, many applications such as remote sensing, cloud seeding, and discharge guiding are potentially possible. However, one of the main challenges of outdoor field applications is the laser propagation through the atmosphere where pressure fluctuations and concentrations of aerosols may be present. The rationale behind the work presented in this dissertation is to evaluate the robustness of the filamentation, measure the interaction losses as well as understanding the modifications to (i) filament length (ii) supercontinuum generation, and (iii) the beam profile along propagation through perturbed media.Detailed studies of the interaction of a single filament with a single water droplet are presented. In addition, preliminary results on filament propagation through a cloud of aerosols are discussed. The effect of pressure on the beam profile along propagation and on the supercontinuum generated by the filament is studied. This document provides valuable insight into the complex nonlinear processes affecting the formation, propagation and post propagation of filaments under adverse atmospheric conditions.
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Date Issued: 2016
Identifier: CFE0006530, ucf:51368
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006530

Title: High Average Power Nanosecond Pulsed Tm:Fiber Laser for Pumping an Optical Parametric Oscillator.
Creator: Abdulfattah, Ali, Richardson, Martin, Shah, Lawrence, Delfyett, Peter, University of Central Florida
Abstract / Description: Thulium-doped fiber lasers operating with wavelengths in the vicinity of 2 (&)#181;m are useful for several emerging applications including generating mid-IR light via nonlinear frequency conversion. In this study we describe the design and construction of a thulium fiber laser system comprising a master oscillator and a power amplifier. The first stage is a Q-switched, thulium-doped photonic crystal fiber oscillator utilizing an acousto-optic modulator to produce 65-80 nanosecond pulses. A...
Show moreThulium-doped fiber lasers operating with wavelengths in the vicinity of 2 (&)#181;m are useful for several emerging applications including generating mid-IR light via nonlinear frequency conversion. In this study we describe the design and construction of a thulium fiber laser system comprising a master oscillator and a power amplifier. The first stage is a Q-switched, thulium-doped photonic crystal fiber oscillator utilizing an acousto-optic modulator to produce 65-80 nanosecond pulses. A diffraction grating in the cavity provides wavelength tunability from 1.8 (-) 2?m. The oscillator produced up to 3 W of average power and 150 (&)#181;J pulse energies, corresponding to 2.3 kW peak powers. The amplifier stage consists of a large mode area, thulium-doped, step-index fiber seeded with powers up to 2 W from the oscillator. An output energy of 700 (&)#181;J with 81 ns pulse width, was achieved at a wavelength of 1.9 (&)#181;m. The effect of the fiber holder temperature on the amplifier performance relative to output pulse energy and seed wavelength was also studied. As a part of this thesis, a methodology has been developed to thoroughly characterize Tm:fiber amplifier performance. This has been the subject of prior work by several research groups, however, this work explicitly focuses on the precise characterization of absorbed pump power, pump bleaching, and extracted amplified energy for a range of input seeds power, pulse energy, and wavelength in order to better understand amplifier performance.
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Date Issued: 2016
Identifier: CFE0006240, ucf:51065
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006240

Title: Pulsed Tm-Fiber Laser for Mid-IR Generation.
Creator: Kadwani, Pankaj, Richardson, Martin, Abouraddy, Ayman, Schulzgen, Axel, Peale, Robert, University of Central Florida
Abstract / Description: Thulium fiber lasers have attracted interest based on their long emission wavelength and large bandwidth (~1.8 (-) 2.1 (&)#181;m) relative to more established ytterbium and erbium fiber lasers. In addition, Tm:fiber lasers offer the potential for high efficiencies (~60 %) and high output power levels both in cw as well as pulsed regimes. These attributes are useful particularly in applications such as remote sensing, materials processing and mid-infrared generation. This dissertation...
Show moreThulium fiber lasers have attracted interest based on their long emission wavelength and large bandwidth (~1.8 (-) 2.1 (&)#181;m) relative to more established ytterbium and erbium fiber lasers. In addition, Tm:fiber lasers offer the potential for high efficiencies (~60 %) and high output power levels both in cw as well as pulsed regimes. These attributes are useful particularly in applications such as remote sensing, materials processing and mid-infrared generation. This dissertation describes the development of novel nanosecond pulsed thulium fiber laser systems with record high peak power levels in order to pump nonlinear mid-infrared generation. The peak power scaling in thulium fiber lasers requires new fiber designs with ultra large mode field area (MFA). Two different classes of prototype thulium doped photonic crystal fibers (PCF) were investigated for high peak power generation. The first prototype is a flexible-PCF with 50 ?m core diameter, and the second is a rod-type PCF with 80 ?m diameter core. A robust single stage master oscillator power amplifier (MOPA) source based on flexible-PCF was developed. This source provided narrow linewidth, tunable wavelength, variable pulse duration, high peak power, and high energy nanosecond pulses. The PCF-rod was implemented as a second stage power amplifier. This system generated a record level of ~1 MW peak power output with 6.4 ns pulse-duration at 1 kHz repetition rate. This thulium doped PCF based MOPA system is a state of the art laser source providing high quality nanosecond pulses. The single stage MOPA system was successfully implemented to pump a zinc germanium phosphide (ZGP) crystal in an optical parametric oscillator (OPO) cavity to generate 3 - 5 (&)#181;m wavelengths. The MOPA source was also used to demonstrate backside machining in silicon wafer. The PCF based laser system demonstrated an order of magnitude increase in the peak power achievable in nanosecond thulium doped fiber laser systems, and further scaling appears possible. Further increases in the peak power will enable additional capabilities for mid-IR generation and associated applications.
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Date Issued: 2013
Identifier: CFE0005100, ucf:50739
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005100

Title: Photothermal Lensing in Mid-Infrared Materials.
Creator: Cook, Justin, Richardson, Martin, Shah, Lawrence, Gaume, Romain, University of Central Florida
Abstract / Description: A thorough understanding of laser-materials interactions is crucial when designing and building optical systems. An ideal test method would probe both the thermal and optical properties simultaneously for materials under large optical loads where detrimental thermal effects emerge. An interesting class of materials are those used for infrared wavelengths due to their wide spectral transmission windows and large optical nonlinearities. Since coherent sources spanning the mid-wave and long-wave...
Show moreA thorough understanding of laser-materials interactions is crucial when designing and building optical systems. An ideal test method would probe both the thermal and optical properties simultaneously for materials under large optical loads where detrimental thermal effects emerge. An interesting class of materials are those used for infrared wavelengths due to their wide spectral transmission windows and large optical nonlinearities. Since coherent sources spanning the mid-wave and long-wave infrared wavelength regions have only become widely available in the past decade, data regarding their thermal and optical responses is lacking in literature.Photothermal Lensing (PTL) technique is an attractive method for characterizing the optical and thermal properties of mid-infrared materials as it is nondestructive and can be implemented using both continuous wave and pulsed irradiation. Analogous to the well-known Z-scan, the PTL technique involves creating a thermal lens within a material and subsequently measuring this distortion with a probe beam. By translating the sample through the focus of the pump laser, information can be obtained regarding the nonlinear absorption, thermal diffusivity and thermo-optic coefficient. This thesis evaluates the effectiveness and scope of the PTL method using numerical simulations of low loss infrared materials. Specifically, the response of silicon, germanium, and As2Se3 glass is explored. The 2 ?m pump and 4.55 ?m probe beam geometries are optimized in order to minimize experimental error. Methodologies for estimating the thermal diffusivity, nonlinear absorption coefficient and thermo-optic coefficient directly from the experimentally measured PTL signal are presented. Finally, the ability to measure the nonlinear absorption coefficient without the need for high-energy or ultrashort optical pulses is demonstrated.
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Date Issued: 2017
Identifier: CFE0006730, ucf:51885
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006730

Title: Laser Filamentation Interaction with Materials for Spectroscopic Applications.
Creator: Weidman, Matthew, Richardson, Martin, Schulzgen, Axel, Christodoulides, Demetrios, Sigman, Michael, University of Central Florida
Abstract / Description: Laser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work has shown a quasi-constant filament-induced mass ablation along a 35 m propagation distance. The mass ablated was sufficient for the application of...
Show moreLaser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work has shown a quasi-constant filament-induced mass ablation along a 35 m propagation distance. The mass ablated was sufficient for the application of laser filamentation as a sampling tool for plasma based spectroscopy techniques. Within the scope of this study, single-shot ablation was compared with multi-shot ablation. The dependence of ablated mass on the number of pulses was observed to have a quasi-linear dependence on the number of pulses, advantageous for applications such as spectroscopy. Sample metrology showed that both physical and optical material properties have significant effects on the filament-induced ablation behavior. A relatively slow filament-induced plasma expansion was observed, as compared with a focused beams. This suggests that less energy was transferred to the plasma during filament-induced ablation. The effects of the filament core and the energy reservoir on the filament-induced ablation and plasma formation were investigated. Goniometric measurements of the filament-induced plasma, along with radiometric calculations, provided the number of emitted photons from a specific atomic transition and sample material.This work has advanced the understanding of the effects of single filaments on the ablation of solid materials and the understanding of filament-induced plasma dynamics. It has laid the foundation for further quantitative studies of multiple filamentation. The implications of this work extend beyond spectroscopy and included any application of filamentation that involves the interaction with a solid material.
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Date Issued: 2012
Identifier: CFE0004616, ucf:49940
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004616

Title: Microstructure and Chemistry Evaluation of Direct Metal Laser Sintered 15-5 PH Stainless Steel.
Creator: Coffy, Kevin, Sohn, Yongho, Coffey, Kevin, Richardson, Martin, University of Central Florida
Abstract / Description: 15-5PH stainless steel is an important alloy in the aerospace, chemical, and nuclear industries for its high strength and corrosion resistance at high temperature. Thus, this material is a good candidate for processing development in the direct metal laser sintering (DMLS) branch of additive manufacturing. The chemistry and microstructure of this alloy processed via DMLS was compared to its conventionally cast counterpart through various heat treatments as part of a characterization effort....
Show more15-5PH stainless steel is an important alloy in the aerospace, chemical, and nuclear industries for its high strength and corrosion resistance at high temperature. Thus, this material is a good candidate for processing development in the direct metal laser sintering (DMLS) branch of additive manufacturing. The chemistry and microstructure of this alloy processed via DMLS was compared to its conventionally cast counterpart through various heat treatments as part of a characterization effort. The investigation utilized optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffractometry (XRD), energy dispersive X-Ray spectroscopy (EDS) and glow discharge atomic emission spectrometry (GDS) techniques. DMLS processed samples contained a layered microstructure in which the prior austenite grain sizes were relatively smaller than the cast and annealed prior austenite grain size. The largest of the quantifiable DMLS prior austenite grains had an ASTM grain size of approximately 11.5-12 (6.7?m to 5.6?m, respectively) and the cast and annealed prior austenite grain size was approximately 7-7.5 (31.8?m to 26.7?m, respectively), giving insight to the elevated mechanical properties of the DMLS processed alloy. During investigation, significant amounts of retained austenite phase were found in the DMLS processed samples and quantified by XRD analysis. Causes of this phase included high nitrogen content, absorbed during nitrogen gas atomization of the DMLS metal powder and from the DMLS build chamber nitrogen atmosphere. Nitrogen content was quantified by GDS for three samples. DMLS powder produced by nitrogen gas atomization had a nitrogen content of 0.11 wt%. A DMLS processed sample contained 0.08 wt% nitrogen, and a conventionally cast and annealed sample contained only 0.019 wt% nitrogen. In iron based alloys, nitrogen is a significant austenite promoter and reduced the martensite start and finish temperatures, rendering the standard heat treatments for the alloy ineffective in producing full transformation to martensite. Process improvements are proposed along with suggested future research.
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Date Issued: 2014
Identifier: CFE0005317, ucf:50507
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005317

Title: Specialty Fiber Lasers and Novel Fiber Devices.
Creator: Jollivet, Clemence, Schulzgen, Axel, Moharam, Jim, Richardson, Martin, Mafi, Arash, University of Central Florida
Abstract / Description: At the Dawn of the 21st century, the field of specialty optical fibers experienced a scientific revolution with the introduction of the stack-and-draw technique, a multi-steps and advanced fiber fabrication method, which enabled the creation of well-controlled micro-structured designs. Since then, an extremely wide variety of finely tuned fiber structures have been demonstrated including novel materials and novel designs. As the complexity of the fiber design increased, highly-controlled...
Show moreAt the Dawn of the 21st century, the field of specialty optical fibers experienced a scientific revolution with the introduction of the stack-and-draw technique, a multi-steps and advanced fiber fabrication method, which enabled the creation of well-controlled micro-structured designs. Since then, an extremely wide variety of finely tuned fiber structures have been demonstrated including novel materials and novel designs. As the complexity of the fiber design increased, highly-controlled fabrication processes became critical. To determine the ability of a novel fiber design to deliver light with properties tailored according to a specific application, several mode analysis techniques were reported, addressing the recurring needs for in-depth fiber characterization. The first part of this dissertation details a novel experiment that was demonstrated to achieve modal decomposition with extended capabilities, reaching beyond the limits set by the existing mode analysis techniques. As a result, individual transverse modes carrying between ~0.01% and ~30% of the total light were resolved with unmatched accuracy. Furthermore, this approach was employed to decompose the light guided in Large-Mode Area (LMA) fiber, Photonic Crystal Fiber (PCF) and Leakage Channel Fiber (LCF). The single-mode performances were evaluated and compared. As a result, the suitability of each specialty fiber design to be implemented for power-scaling applications of fiber laser systems was experimentally determined.The second part of this dissertation is dedicated to novel specialty fiber laser systems. First, challenges related to the monolithic integration of novel and complex specialty fiber designs in all-fiber systems were addressed. The poor design and size compatibility between specialty fibers and conventional fiber-based components limits their monolithic integration due to high coupling loss and unstable performances. Here, novel all-fiber Mode-Field Adapter (MFA) devices made of selected segments of Graded Index Multimode Fiber (GIMF) were implemented to mitigate the coupling losses between a LMA PCF and a conventional Single-Mode Fiber (SMF), presenting an initial 18-fold mode-field area mismatch. It was experimentally demonstrated that the overall transmission in the mode-matched fiber chain was increased by more than 11 dB (the MFA was a 250 ?m piece of 50 ?m core diameter GIMF). This approach was further employed to assemble monolithic fiber laser cavities combining an active LMA PCF and fiber Bragg gratings (FBG) in conventional SMF. It was demonstrated that intra-cavity mode-matching results in an efficient (60%) and narrow-linewidth (200 pm) laser emission at the FBG wavelength.In the last section of this dissertation, monolithic Multi-Core Fiber (MCF) laser cavities were reported for the first time. Compared to existing MCF lasers, renown for high-brightness beam delivery after selection of the in-phase supermode, the present new generation of 7-coupled-cores Yb-doped fiber laser uses the gain from several supermodes simultaneously. In order to uncover mode competition mechanisms during amplification and the complex dynamics of multi-supermode lasing, novel diagnostic approaches were demonstrated. After characterizing the laser behavior, the first observations of self-mode-locking in linear MCF laser cavities were discovered.
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Date Issued: 2014
Identifier: CFE0005354, ucf:50491
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005354

Title: High resolution time-resolved imaging system in the vacuum ultraviolet region.
Creator: Jang, Yuseong, Richardson, Martin, Moharam, Jim, Likamwa, Patrick, University of Central Florida
Abstract / Description: High-power debris-free vacuum ultraviolet (VUV) light sources have applications in several scientific and engineering areas, such as high volume manufacturing lithography and inspection tools in the semiconductor industry, as well as other applications in material processing and photochemistry.For the past decades, the semiconductor industry has been driven by what is called "Moore's Law". The entire semiconductor industry relies on this rule, which requires chip makers to pack transistors...
Show moreHigh-power debris-free vacuum ultraviolet (VUV) light sources have applications in several scientific and engineering areas, such as high volume manufacturing lithography and inspection tools in the semiconductor industry, as well as other applications in material processing and photochemistry.For the past decades, the semiconductor industry has been driven by what is called "Moore's Law". The entire semiconductor industry relies on this rule, which requires chip makers to pack transistors more tightly with every new generation of chips, shrinking the size of transistors. The ability to solve roadmap challenges is, at least partly, proportional to our ability to measure them. The focus of this thesis is on imaging transient VUV laser plasma sources with specialized reflective imaging optics for metrology applications. The plasma dynamics in novel laser-based Zinc and Tin plasma sources will be discussed. The Schwarzschild optical system was installed to investigate the time evolution of the plasma size in the VUV region at wavelengths of 172 nm and 194 nm. The outcomes are valuable for interpreting the dynamics of low-temperature plasma and to optimize laser-based VUV light sources.
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Date Issued: 2014
Identifier: CFE0005352, ucf:50492
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005352

Title: High flux isolated attosecond pulse generation.
Creator: Wu, Yi, Chang, Zenghu, Richardson, Martin, Christodoulides, Demetrios, Rahman, Talat, University of Central Florida
Abstract / Description: This thesis outlines the high intensity tabletop attosecond extreme ultraviolet laser source at the Institute for the Frontier of Attosecond Science and Technology Laboratory.First, a unique Ti:Sapphire chirped pulse amplifier laser system that delivers 14 fs pulses with 300 mJ energy at a 10 Hz repetition rate was designed and built. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two stage Ti:Sapphire chirped pulse power amplifier with mJ-level white light...
Show moreThis thesis outlines the high intensity tabletop attosecond extreme ultraviolet laser source at the Institute for the Frontier of Attosecond Science and Technology Laboratory.First, a unique Ti:Sapphire chirped pulse amplifier laser system that delivers 14 fs pulses with 300 mJ energy at a 10 Hz repetition rate was designed and built. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two stage Ti:Sapphire chirped pulse power amplifier with mJ-level white light pulses from a gas filled hollow core fiber. It is the highest energy level ever achieved by a broadband pulse in a chirped pulse amplifier up to the current date.Second, using this laser as a driving laser source, the generalized double optical gating method is employed to generate isolated attosecond pulses. Detailed gate width analysis of the ellipticity dependent pulse were performed. Calculation of electron light interaction dynamics on the atomic level was carried out to demonstrate the mechanism of isolated pulse generation.Third, a complete diagnostic apparatus was built to extract and analyze the generated attosecond pulse in spectral domain. The result confirms that an extreme ultraviolet super continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The extreme ultraviolet pulse energy was ~100 nJ at the exit of the argon gas target.
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Date Issued: 2013
Identifier: CFE0005075, ucf:49949
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005075

Title: Femtosecond Filament Interaction as a Probe for Molecular Alignment.
Creator: McKee, Erik, Richardson, Martin, Baudelet, Matthieu, Chang, Zenghu, University of Central Florida
Abstract / Description: Femtosecond laser filamentation is a highly nonlinear propagation mode. When a laser pulse propagates with a peak power exceeding a critical value Pcr (5 GW at 800 nm in air), the Kerr effect tends to collapse the beam until the intensity is high enough to ionize the medium, giving rise to plasma defocusing. A dynamic competition between these two effects takes place leaving a thin and weakly ionized plasma channel in the trail of the pulse. When an ultrafast laser pulse interacts with...
Show moreFemtosecond laser filamentation is a highly nonlinear propagation mode. When a laser pulse propagates with a peak power exceeding a critical value Pcr (5 GW at 800 nm in air), the Kerr effect tends to collapse the beam until the intensity is high enough to ionize the medium, giving rise to plasma defocusing. A dynamic competition between these two effects takes place leaving a thin and weakly ionized plasma channel in the trail of the pulse. When an ultrafast laser pulse interacts with molecules, it will align them, spinning them about their axis of polarization. As the quantum rotational wave packet relaxes, the molecules will experience periodic field-free alignment. Recent work has demonstrated the effect of molecular alignment on laser filamentation of ultra-short pulses. Revival of the molecular alignment can modify filamentation parameters as it can locally modify the refractive index and the ionization rate. In this thesis, we demonstrate with simulations and experiments that these changes in the filament parameters (collapse distance and filament plasma length) can be used to probe molecular alignment in CO2.
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Date Issued: 2013
Identifier: CFE0005033, ucf:50000
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005033

Title: Phase-locking Stability of a Quasi-single-cycle Pulse.
Creator: Bodnar, Nathan, Richardson, Martin, Chang, Zenghu, Delfyett, Peter, University of Central Florida
Abstract / Description: There is increasing interest in the generation of very short laser pulses, even down to attosecond (10-18 s) durations. Laser systems with femtosecond pulse durations are needed for these applications. For many of these applications, positioning of the maximum electric field within the pulse envelope can affect the outcome. The peak of the electric field relative to the peak of the pulse is called the Carrier Envelope Phase (CEP). Controlling the position of the electric field becomes more...
Show moreThere is increasing interest in the generation of very short laser pulses, even down to attosecond (10-18 s) durations. Laser systems with femtosecond pulse durations are needed for these applications. For many of these applications, positioning of the maximum electric field within the pulse envelope can affect the outcome. The peak of the electric field relative to the peak of the pulse is called the Carrier Envelope Phase (CEP). Controlling the position of the electric field becomes more important when pulse duration approaches single-cycle.This thesis focuses on the stabilization of a quasi-single-cycle laser facility. Improvements to this already-established laser facility, HERACLES (High Energy, Repetition rate Adjustable, Carrier-Locked-to-Envelope System) described in this thesis include a stabilized pump line and the improvement in CEP stabilization electronics. HERACLES is built upon an Optical Parametric Chirped Pulse Amplification (OPCPA) architecture. This architecture uses Optical Parametric Amplification (OPA) as the gain material to increase the output energy of the system. OPA relies on a nonlinear process to generate high gain (106) with ultra-wide bandwidth. Instabilities in the OPA driving pump energy can create dynamically fluctuations in the final OPCPA output energy. To reduce these fluctuations two key upgrades were implemented on the pump beam. Both were major improvements in the stability. Firstly, an improved regenerative amplifier design reduced beam pointing fluctuations. Secondly, the addition of a pump monitoring system with feedback-control eliminated long-term power drifts. Both enhanced the OPA pulse-to-pulse and long-term stability.To improve the stability in measuring CEP drifts, modification of the feedback electronics was needed. The modification consisted of integrating noise reduction electronics. This novel noise reducer uses a similar process to a super-heterodyne receiver. The noise reducer resulted in 60 dB reduction of out-of-band noise. This led to increased signal quality with cleaner amplification of weaker signals. The enhanced signal quality led to more reliable long-term locking. The synthetically increased signal-to-noise ratio allows locking of the CEP frequency below the typically requirements. This integration allows relaxed constraints on the laser systems.The optics and electronics of a high-power, quasi-single cycle laser facility were improved. This thesis included the stabilization of the pump line and the stabilization of the CEP. This work allows for new long-duration experiments.
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Date Issued: 2013
Identifier: CFE0004654, ucf:49908
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004654

Title: Peak Power Scaling of Nanosecond Pulses in Thulium based Fiber Lasers.
Creator: Gaida, Christian, Richardson, Martin, Shah, Lawrence, Amezcua Correa, Rodrigo, University of Central Florida
Abstract / Description: Thulium based fiber lasers represent a promising alternative for pulse energy scaling and highpeak power generation with ytterbium based systems at 1 micrometer. Advantages of thulium arise fromthe operation at longer wavelengths and a large gain bandwidth (1.8-2.1 micrometer). Nonlinear effects,such as self phase modulation, stimulated Raman scattering and stimulated Brillouin scattering generally limit peak power scaling in fiber lasers. The longer wavelength of thulium fiber lasersand...
Show moreThulium based fiber lasers represent a promising alternative for pulse energy scaling and highpeak power generation with ytterbium based systems at 1 micrometer. Advantages of thulium arise fromthe operation at longer wavelengths and a large gain bandwidth (1.8-2.1 micrometer). Nonlinear effects,such as self phase modulation, stimulated Raman scattering and stimulated Brillouin scattering generally limit peak power scaling in fiber lasers. The longer wavelength of thulium fiber lasersand large mode field areas can significantly increase the nonlinear thresholds. Compared to 1 micrometer systems, thulium fiber lasers enable single mode guidance for two times larger mode field diameterin step index fibers. Similar behavior is expected for index guiding thulium doped photonic crystalfibers.In this work a novel thulium doped rod type photonic crystal fiber design with large mode field diameter (>50 micrometer) was first characterized in CW-lasing configuration and then utilized as finalamplifier in a two stage master oscillator power amplifier. The system generated MW-level peakpower at 6.5ns pulse duration and 1kHz repetition rate. This world record performance exemplifiesthe potential of thulium fiber lasers to supersede ytterbium based systems for very high peak powergeneration in the future.As part of this work a computer model for the transient simulation of pulsed amplification inthulium based fiber lasers was developed. The simulations are in good agreement with the experimentalresults. The computer model can be used for efficient optimization of future thulium basedfiber amplifier designs.
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Date Issued: 2013
Identifier: CFE0004845, ucf:49699
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004845

laser (9)	+ -
Laser (7)	+ -
EUV (5)	+ -
Plasma (5)	+ -
Filamentation (4)	+ -

laser plasma (4)	+ -
EUVL (3)	+ -
Femtosecond (3)	+ -
Nonlinear Optics (3)	+ -
OPCPA (3)	+ -
Optics (3)	+ -
Spectroscopy (3)	+ -
Thulium (3)	+ -
femtosecond (3)	+ -
fiber laser (3)	+ -
laser filamentation (3)	+ -
nonlinear optics (3)	+ -
tin (3)	+ -
Chirped Pulse Amplification (2)	+ -
Extreme Ultraviolet (2)	+ -
High Power Laser (2)	+ -
Laser Plasma (2)	+ -
Lithography (2)	+ -
PCF (2)	+ -
Spectrometer (2)	+ -
Ultrafast (2)	+ -
Ultrafast laser (2)	+ -
VUV (2)	+ -
chalcogenide (2)	+ -
fiber lasers (2)	+ -

Richardson, Martin (58)	+ -
University of Central Florida (58)	+ -
Shah, Lawrence (12)	+ -
Schulzgen, Axel (10)	+ -
Delfyett, Peter (8)	+ -

Amezcua Correa, Rodrigo (7)	+ -
Baudelet, Matthieu (7)	+ -
Chang, Zenghu (6)	+ -
Gaume, Romain (6)	+ -
Christodoulides, Demetrios (4)	+ -
Shivamoggi, Bhimsen (4)	+ -
Sigman, Michael (4)	+ -
Moharam, Jim (3)	+ -
Andrews, Larry (2)	+ -
Barbieri, Nicholas (2)	+ -
Bodnar, Nathan (2)	+ -
Chini, Michael (2)	+ -
Chow, Louis (2)	+ -
Likamwa, Patrick (2)	+ -
Phillips, Ronald (2)	+ -
Rahman, Talat (2)	+ -
Richardson, Kathleen (2)	+ -
Sincore, Alex (2)	+ -
Sisken, Laura (2)	+ -
Sundaram, Kalpathy (2)	+ -
Szilagyi, John (2)	+ -
Vanstryland, Eric (2)	+ -
Abdolvand, Reza (1)	+ -
Abdulfattah, Ali (1)	+ -
Abouraddy, Ayman (1)	+ -

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