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(1 - 19 of 19)
- Title
- PERIODIC NONLINEAR REFRACTIVE INDEX OF CARBON DISULFIDE VAPORS.
- Creator
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Strunk, Evelyn, Hagan, David, University of Central Florida
- Abstract / Description
-
The purpose of this thesis is to explore the nonlinear refractive index of carbon disulfide vapors as opposed to its liquid form. With CS2 vapors, the vapors are less dense so they will rotate longer than liquid CS2 because there are less intermolecular interactions. The electric field of the beam causes the molecules to align with the electric field and applies a torque to the molecules. After this excitation, the molecules continue rotating. The rotations change the index of refraction of...
Show moreThe purpose of this thesis is to explore the nonlinear refractive index of carbon disulfide vapors as opposed to its liquid form. With CS2 vapors, the vapors are less dense so they will rotate longer than liquid CS2 because there are less intermolecular interactions. The electric field of the beam causes the molecules to align with the electric field and applies a torque to the molecules. After this excitation, the molecules continue rotating. The rotations change the index of refraction of the material. Continuous rotation of the molecules causes the index of refraction to be periodic which means the molecules are going through multiple revivals. I will analyze this periodic nonlinear index of refraction. However, some problems occurred while the experiment was being done as well as some issues of measuring CS2 because of white light continuum generation in the cell walls. To avoid these issues we measured the air in the lab and were able to observe the periodic change of index of refraction for O2 and N2 .
Show less - Date Issued
- 2014
- Identifier
- CFH0004619, ucf:45270
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004619
- Title
- OPTICAL PROPAGATION OF SELF-SUSTAINING WAVEFRONTS AND NONLINEAR DYNAMICS IN PARABOLIC MULTIMODE FIBERS.
- Creator
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Mills, Matthew, Christodoulides, Demetrios, Hagan, David, Dogariu, Aristide, Kaup, David, University of Central Florida
- Abstract / Description
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The aim of this thesis is to introduce my work which has generally been focused on opticalwavefronts that have the unusual property of resisting commonplace phenomena such as diffraction and dispersion. Interestingly, these special beams are found both in linear and nonlinear situations. For example, in the linear regime, localized spatio-temporal waves which resemble the spherical harmonic symmetries of the hydrogen quantum orbitals can simultaneously negotiate both diffractive and...
Show moreThe aim of this thesis is to introduce my work which has generally been focused on opticalwavefronts that have the unusual property of resisting commonplace phenomena such as diffraction and dispersion. Interestingly, these special beams are found both in linear and nonlinear situations. For example, in the linear regime, localized spatio-temporal waves which resemble the spherical harmonic symmetries of the hydrogen quantum orbitals can simultaneously negotiate both diffractive and dispersiveeffects. In the nonlinear regime, dressed optical filaments can be arranged to propagate multi-photon produced plasma channels orders of magnitude longer than expected.The first portion of this dissertation will begin by surveying the history of diffraction-free beamsand introducing some of their mathematical treatments. Interjected throughout this discussion will be several relevant concepts which I explored during my first years a CREOL. The discussion will then be steered into a detailed account of diffraction/dispersion free wavefronts which display hydrogen-like symmetries. The second segment of the document will cover the highly nonlinear process of optical filamentation. This chapter will almost entirely investigate the idea of the dressed filament, an entity which allows for substantial prolongation of this light string. I will then conclude by delving into the topicof supercontinuum generation in parabolic multimode fibers which, in the upcoming years, has great potential of becoming important in optics.
Show less - Date Issued
- 2015
- Identifier
- CFE0005977, ucf:50767
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005977
- Title
- Mesoscale Light-Matter Interactions.
- Creator
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Douglass, Kyle, Dogariu, Aristide, Abouraddy, Ayman, Hagan, David, Sugaya, Kiminobu, University of Central Florida
- Abstract / Description
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Mesoscale optical phenomena occur when light interacts with a number of different types of materials, such as biological and chemical systems and fabricated nanostructures. As a framework, mesoscale optics unifies the interpretations of the interaction of light with complex media when the outcome depends significantly upon the scale of the interaction. Most importantly, it guides the process of designing an optical sensing technique by focusing on the nature and amount of information that can...
Show moreMesoscale optical phenomena occur when light interacts with a number of different types of materials, such as biological and chemical systems and fabricated nanostructures. As a framework, mesoscale optics unifies the interpretations of the interaction of light with complex media when the outcome depends significantly upon the scale of the interaction. Most importantly, it guides the process of designing an optical sensing technique by focusing on the nature and amount of information that can be extracted from a measurement.Different aspects of mesoscale optics are addressed in this dissertation which led to the solution of a number of problems in complex media. Dynamical and structural information from complex fluids(-)such as colloidal suspensions and biological fluids(-)was obtained by controlling the size of the interaction volume with low coherence interferometry. With this information, material properties such as particle sizes, optical transport coefficients, and viscoelastic characteristics of polymer solutions and blood were determined in natural, realistic conditions that are inaccessible to conventional techniques.The same framework also enabled the development of new, scale-dependent models for several important physical and biological systems. These models were then used to explain the results of some unique measurements. For example, the transport of light in disordered photonic lattices was interpreted as a scale-dependent, diffusive process to explain the anomalous behavior of photon path length distributions through these complex structures. In addition, it was demonstrated how specialized optical measurements and models at the mesoscale enable solutions to fundamental problems in cell biology. Specifically, it was found for the first time that the nature of cell motility changes markedly with the curvature of the substrate that the cellsivmove on. This particular work addresses increasingly important questions concerning the nature of cellular responses to external forces and the mechanical properties of their local environment.Besides sensing of properties and modeling behaviors of complex systems, mesoscale optics encompasses the control of material systems as a result of the light-matter interaction. Specific modifications to a material's structure can occur due to not only an exchange of energy between radiation and a material, but also due to a transfer of momentum. Based on the mechanical action of multiply scattered light on colloidal particles, an optically-controlled active medium that did not require specially tailored particles was demonstrated for the first time. The coupling between the particles and the random electromagnetic field affords new possibilities for controlling mesoscale systems and observing nonequilibrium thermodynamic phenomena.
Show less - Date Issued
- 2013
- Identifier
- CFE0004990, ucf:49606
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004990
- Title
- Techniques for characterization of third order optical nonlinearities.
- Creator
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Ferdinandus, Manuel, Hagan, David, Vanstryland, Eric, Christodoulides, Demetrios, Hernandez, Florencio, University of Central Florida
- Abstract / Description
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This dissertation describes the development of novel techniques for characterization of nonlinear properties of materials. The dissertation is divided into two parts, a background and theory section and a technique development section.In the background and theory section we explain the origins of the nonlinear optical response of materials across many different spatial and temporal scales. The mechanisms that we are most interested in are the electronic nuclear and reorientational responses,...
Show moreThis dissertation describes the development of novel techniques for characterization of nonlinear properties of materials. The dissertation is divided into two parts, a background and theory section and a technique development section.In the background and theory section we explain the origins of the nonlinear optical response of materials across many different spatial and temporal scales. The mechanisms that we are most interested in are the electronic nuclear and reorientational responses, which occur on the range of sub-femtosecond to several picoseconds. The electronic mechanism is due to the electrons of a material experiencing a non-parabolic potential well due a strong electric field and occurs on the sub-femtosecond timescale. The nuclear or vibrational effect results from the motion of the nuclei of the atoms and typically occurs on the order of a few hundred femtoseconds. Finally the reorientational nonlinearity is due to the alignment of the molecule to the electric field, which alters the polarizability of the molecule and typically occurs on the scale of a few picoseconds. There are other mechanisms can induce nonlinear optical effects such as thermal effects and electrostriction, but these effects typically occur on much larger timescales than we are interested in, and hence will not be a major focus of this dissertation.In the nonlinear characterization techniques section, we describe previous research into the field of nonlinear optical characterization techniques, describing the techniques used to characterize the nonlinear properties of materials, their applications and limitations. We will trace the development of two recently developed techniques for nonlinear spectroscopy ? the Dual Arm Z-Scan and the Beam Deflection techniques. The Dual Arm Z-Scan technique is an enhancement of the standard Z-Scan technique that allows for the measurement of small nonlinear signals in the presence of large background signals. This technique allows for the measurement of materials under certain conditions not previously measureable using the standard Z-Scan technique, such materials with low damage thresholds, poor solubility and thin films.In addition to the Dual Arm Z-Scan, we have developed a new method for characterizing nonlinear refraction, the Beam Deflection technique, which is a variation of the photothermal beam deflection technique previously used to measure very weak absorption signals. This technique offers relative ease of use, the ability to measure the absolute magnitude and sign of both the real and imaginary parts of ?^((3)) simultaneously with high sensitivity. We fully develop the theory for materials with instantaneous and non-instantaneous nonlinearities, with nonlinear absorption and group velocity mismatch. We also demonstrate the power of this technique to separate the isotropic and reorientational contributions of liquids by examining the temporal response and polarization dependences.Lastly, we summarize our conclusions and describe two promising future research directions that would benefit from the Dual Arm Z-Scan and Beam Deflection techniques.
Show less - Date Issued
- 2013
- Identifier
- CFE0005164, ucf:50709
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005164
- Title
- Generation of high-flux attosecond pulses and towards attosecond-attosecond pump-probe experiments.
- Creator
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Wang, Yang, Chang, Zenghu, Hagan, David, Wu, Shintson, Saha, Haripada, University of Central Florida
- Abstract / Description
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At present, the energy of a single isolated attosecond pulse is limited to nanojoule levels. As a result, an intense femtosecond pulse has always been used in combination with a weak attosecond pulse in time-resolved experiments. To reach the goal of conducting true attosecond pump-attosecond probe experiments, a high flux laser source has been developed that can potentially deliver microjoule level isolated attosecond pulses in the 50 eV range, and a unique experimental end station has been...
Show moreAt present, the energy of a single isolated attosecond pulse is limited to nanojoule levels. As a result, an intense femtosecond pulse has always been used in combination with a weak attosecond pulse in time-resolved experiments. To reach the goal of conducting true attosecond pump-attosecond probe experiments, a high flux laser source has been developed that can potentially deliver microjoule level isolated attosecond pulses in the 50 eV range, and a unique experimental end station has been fabricated and implemented that can provide precision control of the attosecond-attosecond pump-probe pulses. In order to scale up the attosecond flux, a unique Ti:-Sapphire laser system with a three-stage amplifier that delivers pulses with a 2 J energy at a 10 Hz repetition rate was designed and built. The broadband pulse spectrum covering from 700 nm to 900 nm was generated, supporting a pulse duration of 12 fs. The high flux high-order harmonics were generated in a gas tube filled with argon by a loosely focused geometry under a phase-matching condition. The wavefront distortions for the driving laser were corrected by a deformable mirror with a Shack-Hartmann sensor to significantly improve the extreme ultraviolet radiation conversion efficiency due to the excellent beam profile at focus. A high-damage-threshold beam splitter is demonstrated to eliminate energetic driving laser pulses from high-order harmonics. The extreme ultraviolet pulse energy is measured to be 0.3 microjoule at the exit of the argon gas target. The experimental facilities developed will lead to the generation of microjoule level isolated attosecond pulses and the demonstration of true atto pump-atto probe experiments in near future. Finally, in experiment, we show the first demonstration of carrier-envelope phase controlled filamentation in air using millijoule-level few-cycle mid-infrared laser pulses.
Show less - Date Issued
- 2017
- Identifier
- CFE0006926, ucf:51688
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006926
- Title
- Non-Degenerate Two Photon Gain in Bulk Gallium Arsenide.
- Creator
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Turnbull, Brendan, Hagan, David, Vanstryland, Eric, Christodoulides, Demetrios, University of Central Florida
- Abstract / Description
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The purpose of this thesis is to investigate the nonlinear phenomena known as doubly-stimulated, non-degenerate two-photon emission (ND-2PE) in Gallium Arsenide (GaAs). 2PE refers to the simultaneous emission of two-photons as electrons move from the conduction band in a direct gap semiconductor to the valence band. Following the same path for describing one-photon emission (1PE) we describe 2PE as a product of the irradiance, I, and the negative of the loss which in this case is two-photon...
Show moreThe purpose of this thesis is to investigate the nonlinear phenomena known as doubly-stimulated, non-degenerate two-photon emission (ND-2PE) in Gallium Arsenide (GaAs). 2PE refers to the simultaneous emission of two-photons as electrons move from the conduction band in a direct gap semiconductor to the valence band. Following the same path for describing one-photon emission (1PE) we describe 2PE as a product of the irradiance, I, and the negative of the loss which in this case is two-photon absorption, ?_2, the negative coming from the population inversion. We attempt to observe 2PE by using a frequency non-degenerate pump-probe experiment in which a third beam optically excites a 4 (&)#181;m thick GaAs sample. We use non-degenerate beams in hopes of utilizing the 3-orders of magnitude enhancement seen in two-photon absorption (2PA) by going to extreme nondegeneracy (END) to enhance 2PE. GaAs is chosen due to the availability of the appropriate wavelengths, the maturity of the GaAs technology, its use in optoelectronic devices and its ability to be electrically pumped. During the experimental development we learn how to effectively etch and manipulate thin GaAs samples and model the transmission spectrum of these samples using thin film transmission matrices. We are able to match the measured transmission spectrum with the theoretical transmission spectrum. Here we etch the bulk GaAs left on the sample leaving only the 4 (&)#181;m thickness of molecular beam epitaxial grown GaAs plus additional layers of aluminum gallium arsenide (AlGaAs). These samples were grown for us by Professor Gregory Salamo of the University of Arkansas.Using the pump-probe experiment on the 4 (&)#181;m GaAs sample, we measure the change of the 2PA due to the presence of optically excited carriers. The goal is to reduce the 2PA signal to zero and then invert the 2PA signal indicating an increase in transmission indicative of 2PE when the population is inverted. Our results show that we achieve a 45% reduction in the 2PA signal in a 4 ?m thick GaAs sample due to the excited carriers. Unfortunately, we currently cannot experimentally determine whether the reduction is strictly due to free-carrier absorption (FCA) of our pump or possibly due to a change in the two-photon absorption coefficient. We measure the transmission of various wavelengths around the bang gap of GaAs as a function of excitation wavelength and achieve a transmittance of ~80% which we attribute to possibly be one photon gain (1PG) at 880 nm. We also go to cryogenic temperatures to concentrate the carriers near the bottom of the conduction band and improve the theoretical gain coefficient for 2PE. Unfortunately, we do not observe a measurable change in 2PA with the addition of optically excited carriers. Along with FCA of our infrared pump we suspect that the difficulties in this first set of experiments are also a result or radiative recombination due to amplified spontaneous emission reducing our free carrier density along with the fact that 4 ?m is too thick for uniform excitation. We now have 1 ?m samples from Professor Gregory Salamo which we hope will give better and more definitive results.
Show less - Date Issued
- 2013
- Identifier
- CFE0004762, ucf:49776
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004762
- Title
- Beam Deflection.
- Creator
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Münnich, Matthias, Hagan, David, Vanstryland, Eric, Dogariu, Aristide, University of Central Florida
- Abstract / Description
-
In order to fully understand the third order nonlinear optical response of materials under high irradianceexcitation it is necessary to study the temporal and polarization dependence of nonlinearrefraction and absorption. There are several existing approaches such as Z-scan and pump-probetechniques to determine those responses. As part of this work, these approaches will be briefly outlinedbefore presenting beam deflection, applied from photothermal beam deflection, as an...
Show moreIn order to fully understand the third order nonlinear optical response of materials under high irradianceexcitation it is necessary to study the temporal and polarization dependence of nonlinearrefraction and absorption. There are several existing approaches such as Z-scan and pump-probetechniques to determine those responses. As part of this work, these approaches will be briefly outlinedbefore presenting beam deflection, applied from photothermal beam deflection, as an alternativeexperimental technique to determine the nonlinear refraction with its temporal and polarizationdynamics. This technique measures the angle of the probe beam deflected via the index gradientof the material induced by strong excitation beam, to determine both the sign and magnitude of thenonlinear refraction. The temporal and tensor properties of the nonlinear refractive index can bedetermined by introducing a delay line, and by varying the polarization of the excitation and probebeam, respectively.To demonstrate the practicality of the beam deflection technique, we performed measurements onFused Silica, Carbon Disulfide and Zinc Oxide. Each of these samples shows quite different nonlinearresponses. Amorphous fused silica exhibits nonlinear refraction purely from instantaneouselectronic contribution; while Carbon Disulfide shows a much slower response, originating notonly from the electronic contribution but also from non-instantaneous nuclear movements (e.g.molecular orientation). These two contributions can be separated by varying the polarization directionof the excitation and probe beam. By introducing lock-in detection technique, a sensitivityof λ/5500 can be achieved. In Zinc Oxide, a wide-bandgap semiconductor, we measure bothnonlinear refraction and two-photon absorption simultaneously. Therefore the beam deflection isa sensitive technique, which can be used to measure the time and polarization dynamics of thenonlinear response of the material.
Show less - Date Issued
- 2013
- Identifier
- CFE0004896, ucf:49653
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004896
- Title
- Nonlinear integrated photonics on silicon and gallium arsenide substrates.
- Creator
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Ma, Jichi, Fathpour, Sasan, Hagan, David, Li, Guifang, Peale, Robert, University of Central Florida
- Abstract / Description
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Silicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range,...
Show moreSilicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 (-) 5 (&)#181;m). In this wavelength range, the omnipresent hurdle of nonlinear silicon photonics in the telecommunication band, i.e., nonlinear losses due to two-photon absorption, is inherently nonexistent. With the lack of efficient light-emission capability and second-order optical nonlinearity in silicon, heterogeneous integration with other material systems has been another direction pursued. Finally, several approaches have been proposed and demonstrated to address the energy efficiency of silicon photonic devices in the near-infrared wavelength range. In this dissertation, theoretical and experimental works are conducted to extend applications of integrated photonics into mid-infrared wavelengths based on silicon, demonstrate heterogeneous integration of tantalum pentoxide and lithium niobate photonics on silicon substrates, and study two-photon photovoltaic effect in gallium arsenide and plasmonic-enhanced structures.Specifically, performance and noise properties of nonlinear silicon photonic devices, such as Raman lasers and optical parametric amplifiers, based on novel and reliable waveguide technologies are studied. Both near-infrared and mid-infrared nonlinear silicon devices have been studied for comparison. Novel tantalum-pentoxide- and lithium-niobate-on-silicon platforms are developed for compact microring resonators and Mach-Zehnder modulators. Third- and second-harmonic generations are theoretical studied based on these two platforms, respectively. Also, the two-photon photovoltaic effect is studied in gallium arsenide waveguides for the first time. The effect, which was first demonstrated in silicon, is the nonlinear equivalent of the photovoltaic effect of solar cells and offers a viable solution for achieving energy-efficient photonic devices. The measured power efficiency achieved in gallium arsenide is higher than that in silicon and even higher efficiency is theoretically predicted with optimized designs. Finally, plasmonic-enhanced photovoltaic power converters, based on the two-photon photovoltaic effect in silicon using subwavelength apertures in metallic films, are proposed and theoretically studied.
Show less - Date Issued
- 2014
- Identifier
- CFE0005373, ucf:50441
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005373
- Title
- Absorptive and Refractive Optical Nonlinearities in Organic Molecules and Semiconductors.
- Creator
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Peceli, Davorin, Hagan, David, Vanstryland, Eric, Christodoulides, Demetrios, Belfield, Kevin, University of Central Florida
- Abstract / Description
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The main purpose of this dissertation to investigate photophysical properties, third order nonlinearity and free carrier absorption and refraction in organic materials and semiconductors. Special emphasis of this dissertation is on characterization techniques of molecules with enhanced intersystem crossing rate and study of different approaches of increasing triplet quantum yield in organic molecules. Both linear and nonlinear characterization methods are described. Linear spectroscopic...
Show moreThe main purpose of this dissertation to investigate photophysical properties, third order nonlinearity and free carrier absorption and refraction in organic materials and semiconductors. Special emphasis of this dissertation is on characterization techniques of molecules with enhanced intersystem crossing rate and study of different approaches of increasing triplet quantum yield in organic molecules. Both linear and nonlinear characterization methods are described. Linear spectroscopic characterization includes absorption, fluorescence, quantum yield, anisotropy, and singlet-oxygen generation measurements. Nonlinear characterization, performed by picosecond and femtosecond laser systems (single and double pump-probe and Z-scan measurements), includes measurements of the triplet quantum yields, excited-state absorption, two-photon absorption, nonlinear refraction and singlet and triplet-state lifetimes.The double pump-probe technique is a variant of the standard pump-probe method but uses two pumps instead of one to create two sets of initial conditions for solving the rate equations allowing a unique determination of singlet- and triplet-state absorption parameters and transition rates. The advantages and limitations of the the double pump-probe technique are investigated theoretically and experimentally, and the influences of several experimental parameters on its accuracy are determined. The accuracy with which the double pump-probe technique determines the triplet-state parameters improves when the fraction of the population in the triplet state relative to the ground state is increased. Although increased accuracy is in principle achievable by increasing the pump fluence in the reverse saturable absorption range, it is shown that the DPP is optimized by working in the saturable absorption regime.Two different approaches to increase intersystem crossing rates in polymethine-like molecules are presented: traditional heavy atom substitution and molecular levels engineering. Linear and nonlinear optical properties of a series of polymethine dyes with Br- and Se- atoms substitution, and a series of new squaraine molecules, where one or two oxygen atoms in a squaraine bridge are replaced with sulfur atoms, are investigated. A consequence of the oxygen-to-sulfur substitution in squaraines is the inversion of their lowest lying ??* and n?* states leading to a significant reduction of singlet-triplet energy difference and opening of an additional intersystem channel of relaxation. Experimental studies show that triplet quantum yields for polymethine dyes with heavy-atom substitutions are small (not more than 10%), while for sulfur-containing squaraines these values reach almost unity. Experimental results are in agreement with density functional theory calculations allowing determination of the energy positions, spin-orbital coupling, and electronic configurations of the lowest electronic transitions.For three different semiconductors: GaAs, InP and InAsP two photon absorption, nonlinear refraction and free carrier absorption and refraction spectrums are measured using Z-scan technique. Although two photon absorption spectrum agrees with the shape of theoretical prediction, values measured with picosecond system are off by the factor of two. Nonlinear refraction and free carrier nonlinearities are in relatively good agreement with theory. Theoretical values of the third order nonlinearities in GaAs are additionally confirmed with femtosecond Z-scan measurements. Due to large spectral bandwidth of femtosecond laser, three photon absorption spectrum of GaAs was additionally measured using picosecond Z-scan. Again, spectral shape is in excellent agreement with theory however values of three photon absorption cross sections are larger than theory predicts. ?
Show less - Date Issued
- 2013
- Identifier
- CFE0004735, ucf:49815
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004735
- Title
- Third Order Nonlinearity of Organic Molecules.
- Creator
-
Hu, Honghua, Vanstryland, Eric, Hagan, David, Zeldovich, Boris, Hernandez, Florencio, University of Central Florida
- Abstract / Description
-
The main goal of this dissertation is to investigate the third-order nonlinearity of organic molecules. This topic contains two aspects: two-photon absorption (2PA) and nonlinear refraction (NLR), which are associated with the imaginary and real part of the third-order nonlinearity (?(3)) of the material, respectively. With the optical properties tailored through meticulous molecular structure engineering, organic molecules are promising candidates to exhibit large third-order nonlinearities....
Show moreThe main goal of this dissertation is to investigate the third-order nonlinearity of organic molecules. This topic contains two aspects: two-photon absorption (2PA) and nonlinear refraction (NLR), which are associated with the imaginary and real part of the third-order nonlinearity (?(3)) of the material, respectively. With the optical properties tailored through meticulous molecular structure engineering, organic molecules are promising candidates to exhibit large third-order nonlinearities. Both linear (absorption, fluorescence, fluorescence excitation anisotropy) and nonlinear (Z-scan, two-photon fluorescence, pump-probe) techniques are described and utilized to fully characterize the spectroscopic properties of organic molecules in solution or solid-state form. These properties are then analyzed by quantum chemical calculations or other specific quantum mechanical model to understand the origins of the nonlinearities as well as the correlations with their unique molecular structural features. These calculations are performed by collaborators. The 2PA study of organic materials is focused on the structure-2PA property relationships of four groups of dyes with specific molecular design approaches as the following: (1) Acceptor-?-Acceptor dyes for large 2PA cross section, (2) Donor-?-Acceptor dyes for strong solvatochromic effects upon the 2PA spectra, (3) Near-infrared polymethine dyes for a symmetry breaking effect, (4) Sulfur-squaraines vs. oxygen-squaraines to study the role of sulfur atom replacement upon their 2PA spectra. Additionally, the 2PA spectrum of a solid-state single crystal made from a Donor-?-Acceptor dye is measured, and the anisotropic nonlinearity is studied with respect to different incident polarizations. These studies further advance our understanding towards an ultimate goal to a predictive capability for the 2PA properties of organic molecules. The NLR study on molecules is focused on the temporal and spectral dispersion of the nonlinear refraction index, n2, of the molecules. Complicated physical mechanisms, originating from either electronic transitions or nuclei movement, are introduced in general. By adopting a prism compressor / stretcher to control the pulsewidth, an evolution of n2 with respect to incident pulsewidth is measured on a simple inorganic molecule (-)carbon disulfide (CS2) in neat liquid at 700 nm and 1064 nm to demonstrate the pulsewidth dependent nonlinear refraction. The n2 spectra of CS2 and certain organic molecules are measured by femtosecond pulses, which are then analyzed by a 3-level model, a simplified (")Sum-over-states(") quantum mechanical model. These studies can serve as a precursor for future NLR investigations.
Show less - Date Issued
- 2012
- Identifier
- CFE0004387, ucf:49400
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004387
- Title
- Submillisecond-response blue phase liquid crystals for display applications.
- Creator
-
Chen, Kuan-Ming, Wu, Shintson, Likamwa, Patrick, Hagan, David, Fang, Jiyu, University of Central Florida
- Abstract / Description
-
With exploding growth of information exchanges between people, display has become indispensable in our daily lives. After decades of intensive research and development in materials and devices, and massive investment in manufacturing technologies, liquid crystal display (LCD) has overcome various obstacles and achieved the performance we need, such as wide viewing angle, high contrast ratio, and high resolution, etc. These excellent performances make LCD prevailed in every perspective....
Show moreWith exploding growth of information exchanges between people, display has become indispensable in our daily lives. After decades of intensive research and development in materials and devices, and massive investment in manufacturing technologies, liquid crystal display (LCD) has overcome various obstacles and achieved the performance we need, such as wide viewing angle, high contrast ratio, and high resolution, etc. These excellent performances make LCD prevailed in every perspective. Recently, with the demands of energy conservation, a greener LCD with lower power consumption is desired. In order to achieve this goal, new energy-effective driving methods, such as field sequential color display, have been proposed. However, in order to suppress color breakup the LC response time should be faster than 1 ms. To overcome this challenge, various fast-response liquid crystal modes, such as thin cell gap, low viscosity materials, overdrive and undershoot voltages, polymer stabilization, and ferroelectric liquid crystal, are under active investigations. Among these approaches, blue phase liquid crystal (BPLC) shows a greater potential with less fabrication limitations. In this dissertation, the feasibility of polymer-stabilized blue phase liquid crystal for display applications is explored starting from the building blocks of the material system, polymer-stabilization processes, test cell preparations, electro-optical (EO) properties, to suggested approaches for further improvements. Because of the nature of blue phase liquid crystals, delicate balance among system components is critically important. Besides the properties of each composition, the preparation process also dictates the EO performance of the self-assembled nano-structured BPLC composite. After the preparation of test cells, EO properties for display applications are investigated and results described. Approaches for further improvements of the EO properties are also suggested in the final part of this dissertation.
Show less - Date Issued
- 2012
- Identifier
- CFE0004243, ucf:49499
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004243
- Title
- Nonlinear Optical Response of Simple Molecules and Two-Photon Semiconductor Lasers.
- Creator
-
Reichert, Matthew, Vanstryland, Eric, Hagan, David, Likamwa, Patrick, Peale, Robert, University of Central Florida
- Abstract / Description
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This dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms...
Show moreThis dissertation investigates two long standing issues in nonlinear optics: complete characterization of the ultrafast dynamics of simple molecules, and the potential of a two-photon laser using a bulk semiconductor gain medium. Within the Born-Oppenheimer approximation, nonlinear refraction in molecular liquids and gases can arise from both bound-electronic and nuclear origins. Knowledge of the magnitudes, temporal dynamics, polarization and spectral dependences of each of these mechanisms is important for many applications including filamentation, white-light continuum generation, all-optical switching, and nonlinear spectroscopy. In this work the nonlinear dynamics of molecules are investigated in both liquid and gas phase with the recently developed beam deflection technique which measures nonlinear refraction directly in the time domain. Thanks to the utility of the beam deflection technique we are able to completely determine the third-order response function of one of the most important molecular liquids in nonlinear optics, carbon disulfide. This allows the prediction of essentially any nonlinear refraction or two-photon absorption experiment on CS2. Measurements conducted on air (N2 and O2) and gaseous CS2 reveal coherent rotational revivals in the degree of alignment of the ensemble at a period that depends on its moment of inertia. This allows measurement of the rotational and centrifugal distortion constants of the isolated molecules. Additionally, the rotational contribution to the beam deflection measurement can be eliminated thanks to the particular polarization dependence of the mechanism. At a specific polarization, the dominant remaining contribution is due to the bound-electrons. Thus both the bound-electronic nonlinear refractive index of air, and second hyperpolarizability of isolated CS2 molecules, are measured directly. The later agrees well with liquid CS2 measurements, where local field effects are significant. The second major portion of this dissertation addresses the possibility of using bulk semiconductors as a two-photon gain medium. A two-photon laser has been a goal of nonlinear optics since shortly after the original laser's development. In this case, two-photons are emitted from a single electronic transition rather than only one. This processes is known as two-photon gain (2PG). Semiconductors have large two-photon absorption coefficients, which are enhanced by ~2 orders of magnitude when using photons of very different energies, e.g., ??_a?10??_b. This enhancement should translate into large 2PG coefficients as well, given the inverse relationship between absorption and gain. Here, we experimentally demonstrate both degenerate and nondegenerate 2PG in optically excited bulk GaAs via pump-probe experiments. This constitutes, to my knowledge, the first report of nondegenerate two-photon gain. Competition between 2PG and competing processes, namely intervalence band and nondegenerate three-photon absorption (ND-3PA), in both cases are theoretically analyzed. Experimental measurements of ND-3PA agree with this analysis and show that it is enhanced much more than ND-2PG. It is found for both degenerate and nondegenerate photon pairs that the losses dominate the two-photon gain, preventing the possibility of a two-photon semiconductor laser.
Show less - Date Issued
- 2015
- Identifier
- CFE0005874, ucf:50871
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005874
- Title
- Nano and nanostructured materials for optical applications.
- Creator
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Chantharasupawong, Panit, Thomas, Jayan, Hagan, David, Kik, Pieter, Gaume, Romain, Chanda, Debashis, University of Central Florida
- Abstract / Description
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Nano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical...
Show moreNano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical applications are investigated in the context of optical limiting, three dimensional displays, and optical sensing. Nanomaterials with nonlinear optical responses are promising candidates for self-activating optical limiters. In the first part of this study, optical limiting properties of unexplored nanomaterials are investigated. A photoacoustic detection technique is developed as an alternative characterization method for studying optical nonlinearities. This was done with an indigenously developed setup for measuring the photoacoustic signals generated from samples excited with a pulse laser. A theoretical model for understanding the experimental observations is presented. In addition, the advantages of this newly developed technique over the existing methods are demonstrated. Blending optical sensitizers with photoconducting polymers and chromophores results in a polymer composite that is able to record a light grating. This composite can be used as recording media in 3D holographic display technology. Here, 2D nano materials, like graphenes, are used as optical sensitizers to improve the response time of a photorefractive polymer. The addition of graphenes to a PATPD/ECZ/7-DCST composite results in a three-fold enhancement in response time and therefore faster recording speed of the medium. The faster build-up time is attributed to better charge generation and mobility due to the presence of graphenes in the composite. Lastly, a facile nanofabrication technique is developed to produce metallic nanostructures with a tunable plasmonic response. The enhancement of the light-matter interactions due to these nanostructures in sensing an analyte is demonstrated.
Show less - Date Issued
- 2015
- Identifier
- CFE0006029, ucf:51016
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006029
- Title
- Ultrafast Mechanisms of Nonlinear Refraction and Two-photon Photochromism.
- Creator
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Zhao, Peng, Hagan, David, Vanstryland, Eric, Christodoulides, Demetrios, Hernandez, Florencio, University of Central Florida
- Abstract / Description
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Derived from a material's third-order nonlinearity, nonlinear refraction (NLR) occurs at any wavelength in any material, and may exhibit noninstantaneous dynamics depending on its physical origins. The main subject of this dissertation is to investigate the underlying mechanisms responsible for the NLR response in different phases of matter, e.g. liquids, gases, and semiconductors, by extensively using our recently developed ultrafast Beam Deflection (BD) technique. An additional subject...
Show moreDerived from a material's third-order nonlinearity, nonlinear refraction (NLR) occurs at any wavelength in any material, and may exhibit noninstantaneous dynamics depending on its physical origins. The main subject of this dissertation is to investigate the underlying mechanisms responsible for the NLR response in different phases of matter, e.g. liquids, gases, and semiconductors, by extensively using our recently developed ultrafast Beam Deflection (BD) technique. An additional subject includes the characterization of a novel two-photon photochromic molecule.In molecular liquids, the major nonlinear optical (NLO) response can be decomposed into a nearly instantaneous bound-electronic NLR (Kerr effect), originating from the real part the electronic second hyperpolarizability, ?, and noninstantaneous mechanisms due to nuclear motions. By adopting the methodology previously developed for carbon disulfide (CS2), we have measured the NLO response functions of 23 common organic solvents, providing a database of magnitudes and temporal dynamics of each mechanism, which can be used for predicting the outcomes of any other NLR related experiments such as Z-scan. Also, these results provide insight to relate solvent nonlinearities with their molecular structures as well as linear polarizability tensors. In the measurements of air and gaseous CS2, coherent Raman excitation of many rotational states manifests as revivals in the transient NLR, from which we identify N2, O2 and two isotopologues of CS2, and unambiguously determine the dephasing rate, and rotational and centrifugal constants of each constituent. Using the revival signal as a self-reference, ? is directly measured for CS2 molecules in gas phase, which coincides with the ? determined from liquid phase measurements when including the Lorentz-Lorenz local field correction. In semiconductors, the Kerr effect dominates the NLR in the sub-gap regime. Here, we primarily focus on investigating the dispersion of nondegenerate (ND) NLR, namely the refractive index change at frequency ?_a due to the presence of a beam at frequency ?_b. The magnitude and sign of the ND-NLR coefficient n_2 (?_a;?_b ) are determined for ZnO, ZnSe and CdS over a broad spectral range for different values of nondegeneracy, which closely follows our earlier predictions based on nonlinear Kramers-Kronig relations. In the extremely nondegenerate case, n_2 (?_a;?_b ) is positively enhanced near the two-photon absorption (2PA) edge, suggesting applications for nondegenerate all-optical switching. Additionally, n_2 (?_a;?_b ) exhibits a strong anomalous nonlinear dispersion within the ND-2PA spectral region, providing a large phase modulation of a femtosecond pulse with bandwidth centered near the zero-crossing frequency. Another subject of this dissertation is the characterization of a spiro-type two-photon photochromic molecule, in which F(&)#246;rster resonance energy transfer (FRET) is utilized to activate the ring-opening effect from a 2PA-donor chromophore. Evidence of energy transfer is observed via fluorescence measurements of the quantum yield, excitation spectra and anisotropy. The absorption and lifetime of the open form are measured in a dye-doped sol-gel matrix. Transient absorption measurements indicate both ring opening and closing occurs on a several picosecond time scale along with multiple transient photoproducts, from which a high FRET efficiency is measured in agreement with theoretical predictions. This efficient 2PA-FRET photochrome may be implemented into photonic devices such as optical memories. However, with a relatively small open-form absorption cross section and significant ring closing, the photochrome may not be viable for enhancing nonlinear absorption in applications such as optical limiting.
Show less - Date Issued
- 2016
- Identifier
- CFE0006517, ucf:51370
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006517
- Title
- Injection Locking of Semiconductor Mode-Locked Lasers for Long-Term Stability of Widely Tunable Frequency Combs.
- Creator
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Williams, Charles, Delfyett, Peter, Hagan, David, Likamwa, Patrick, Vanstryland, Eric, DeSalvo, Richard, University of Central Florida
- Abstract / Description
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Harmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Single frequency injection locking generates widely-spaced and tunable frequency combs from these harmonically mode-locked lasers, while stabilizing the optical frequencies. The output is stabilized long-term with the help of a feedback loop utilizing either a novel technique based on Pound-Drever-Hall...
Show moreHarmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Single frequency injection locking generates widely-spaced and tunable frequency combs from these harmonically mode-locked lasers, while stabilizing the optical frequencies. The output is stabilized long-term with the help of a feedback loop utilizing either a novel technique based on Pound-Drever-Hall stabilization or by polarization spectroscopy. Error signals of both techniques are simulated and compared to experimentally obtained signals. Frequency combs spaced by 2.5 GHz and ~10 GHz are generated, with demonstrated optical sidemode suppression of unwanted modes of 36 dB, as well as RF supermode noise suppression of 14 dB for longer than 1 hour. In addition to the injection locking of actively harmonically mode-locked lasers, the injection locking technique for regeneratively mode-locked lasers, or Coupled Opto-Electronic Oscillators (COEOs), is also demonstrated and characterized extensively.
Show less - Date Issued
- 2013
- Identifier
- CFE0004774, ucf:49805
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004774
- Title
- Particle Manipulation Via Optical Forces and Engineering Soft-Matter Systems With Tunable Nonlinearities.
- Creator
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Fardad, Shima, Christodoulides, Demetrios, Hagan, David, Amezcua Correa, Rodrigo, Likamwa, Patrick, Chen, Zhigang, University of Central Florida
- Abstract / Description
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One of the most intriguing properties of light-matter interaction is the ability of an electromagnetic field to exert mechanical forces on polarizable objects. This phenomenon is a direct consequence of the fact that light carries momentum, which in turn can be transferred to matter. Mediated by scattering, this interaction usually manifests itself as a (")pushing force(") in the direction of beam propagation. However, it is possible to judiciously engineer these optical forces, either by...
Show moreOne of the most intriguing properties of light-matter interaction is the ability of an electromagnetic field to exert mechanical forces on polarizable objects. This phenomenon is a direct consequence of the fact that light carries momentum, which in turn can be transferred to matter. Mediated by scattering, this interaction usually manifests itself as a (")pushing force(") in the direction of beam propagation. However, it is possible to judiciously engineer these optical forces, either by tailoring particle polarizability, and/or by structuring the incident light field. As a simple example, a tightly focused laser beam demonstrates strong gradient forces, which may attract and even trap particles with positive polarizability in the focal volume. The opposite occurs in the regime of negative polarizability, where particles are expelled from the regions of highest intensity. Based on this fundamental principle, one can actively shape the beam using spatial light modulators to manipulate individual objects as well as ensembles of particles suspended in a liquid. In the latter case, a modulation of the local particle concentration is associated with changes of the effective refractive index. The result is an artificial nonlinear medium, whose Kerr-type response can be readily tuned by the parameters of its constituent particles.In the course of this work, we introduce a new class of synthetic colloidal suspensions exhibiting negative polarizabilities, and observe for the first time robust propagation and enhanced transmission of self-trapped light over long distances. Such light penetration in strongly scattering environments is enabled by the interplay between optical forces and self-activated transparency effects. We explore various approaches to the design of negative-polarizability arrangements, including purely dielectric as well as metallic and hybrid nanoparticles. In particular, we find that plasmonic resonances allow for extremely high and spectrally tunable polarizabilities, leading to unique nonlinear light-matter interactions. Here, for the first time we were able to observe plasmonic resonant solitons over more than 25 diffraction lengths, in colloidal nanosuspensions.
Show less - Date Issued
- 2014
- Identifier
- CFE0005610, ucf:50239
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005610
- Title
- Cascaded plasmon resonances for enhanced nonlinear optical response.
- Creator
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Toroghi, Seyfollah, Kik, Pieter, Vanstryland, Eric, Kuebler, Stephen, Hagan, David, Belfield, Kevin, University of Central Florida
- Abstract / Description
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The continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic...
Show moreThe continued development of integrated photonic devices requires low-power, small volume all-optical modulators. The weak nonlinear optical response of conventional optical materials requires the use of high intensities and large interaction volumes in order to achieve significant light modulation, hindering the miniaturization of all-optical switches and the development of lightweight transmission optics with nonlinear optical response. These challenges may be addressed using plasmonic nanostructures due to their unique ability to confine and enhance electric fields in sub-wavelength volumes. The ultrafast nonlinear response of free electrons in such plasmonic structures and the fast thermal nonlinear optical response of metal nanoparticles, as well as the plasmon enhanced nonlinear Kerr-type response of the host material surrounding the nanostructures could allow ultrafast all-optical modulation with low modulation energy. In this thesis, we investigate the linear and nonlinear optical response of engineered effective media containing coupled metallic nanoparticles. The fundamental interactions in systems containing coupled nanoparticles with size, shape, and composition dissimilarity, are evaluated analytically and numerically, and it is demonstrated that under certain conditions the achieved field enhancement factors can exceed the single-particle result by orders of magnitude in a process called cascaded plasmon resonance. It is demonstrated that these conditions can be met in systems containing coupled nanospheres, and in systems containing non-spherical metal nanoparticles that are compatible with common top-down nanofabrication methods such as electron beam lithography and nano-imprint lithography. We show that metamaterials based on such cascaded plasmon resonance structures can produce enhanced nonlinear optical refraction and absorption compared to that of conventional plasmonic nanostructures. Finally, it is demonstrated that the thermal nonlinear optical response of metal nanoparticles can be enhanced in carefully engineered heterogeneous nanoparticle clusters, potentially enabling strong and fast thermal nonlinear optical response in system that can be produced in bulk through chemical synthesis.
Show less - Date Issued
- 2014
- Identifier
- CFE0005556, ucf:50272
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005556
- Title
- White Light Continuum for Broadband Nonlinear Spectroscopy.
- Creator
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Ensley, Trenton, Hagan, David, Vanstryland, Eric, Zeldovich, Boris, Christodoulides, Demetrios, Schulte, Alfons, University of Central Florida
- Abstract / Description
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Supercontinuum (SC) generation, oftentimes referred to as white-light continuum (WLC), has been a subject of interest for more than 40 years. From the first observation of WLC in condensed media in the early 1970s to the first observation of WLC in gases in the mid-1980s, much work has been devoted to developing a framework for understanding the complex nature of this phenomenon as well as discovering its utility in various applications. The main effort of this dissertation is to develop a...
Show moreSupercontinuum (SC) generation, oftentimes referred to as white-light continuum (WLC), has been a subject of interest for more than 40 years. From the first observation of WLC in condensed media in the early 1970s to the first observation of WLC in gases in the mid-1980s, much work has been devoted to developing a framework for understanding the complex nature of this phenomenon as well as discovering its utility in various applications. The main effort of this dissertation is to develop a WLC for the purpose of broadband nonlinear spectroscopy and use it in spectroscopic measurements. The ability to generate a high-quality, high-spectral-irradiance source of radiation confined in a single beam that spans the visible and near-infrared spectral regimes has great utility for nonlinear measurement methods such as the Z-scan technique. Using a broadband WLC instead of conventional tunable sources of radiation such as optical parametric generators/amplifiers has been shown to increase the efficiency of such measurements by nearly an order of magnitude. Although WLC generation has many complex processes involved, and complete models of the process involve highly complex numerical modeling, simple models can still guide us in the optimization of systems for WLC generation. In this dissertation the effects of two key mechanisms behind WLC generation in gaseous media are explored: self-phase modulation (SPM) and ionization leading to plasma production. The effects of SPM are largely dependent upon the third-order nonlinear refractive index, n2, of the gaseous medium whereas the effects of plasma production are dependent upon many parameters including the initial number density, ionization potential/energy, and the rate of ionization production. It is found that in order to generate a stable WLC suitable for nonlinear spectroscopy, the phase contributions from SPM and plasma production should be nearly equal. This guided our experiments in inert gases using mJ level, 150 fs-FWHM (full-width at half-maximum) pulses at 780 nm as well as 40 fs-FWHM pulses primarily at 1800 nm to create a stable, high-spectral-irradiance WLC. The generated WLC is shown to have sufficient spectral energy and spatial quality suitable for nonlinear spectroscopic measurements. In addition to extending the WLC bandwidth by using a long wavelength (1800 nm) pump source, it is found that by using a secondary weak seed pulse with a peak irradiance three orders of magnitude less than the main pulse, the spectral energy density is enhanced by more than a factor of 3 in Krypton gas for a WLC spectrum that spans over 2 octaves. Numerical simulations are presented which qualitatively describe the experimental results. The spectral enhancement of the WLC by seeding is also demonstrated for other inert gases and condensed media. Other efforts described in this dissertation include the development of the Dual-Arm Z-scan technique and its extension to measuring thin film nonlinearities in the presence of large substrate signals as well as predicting the n2 spectra of organic molecules (where we can approximate their behavior as if they were centrosymmetric) from knowledge of the one-photon and two-photon absorption spectra using a simplified sum-over-states quantum perturbative model by utilizing a quasi 3-level and quasi 4-level system.
Show less - Date Issued
- 2015
- Identifier
- CFE0005608, ucf:50264
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005608
- Title
- Two-photon absorption in bulk semiconductors and quantum well structures and its applications.
- Creator
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Pattanaik, Himansu, Vanstryland, Eric, Hagan, David, Delfyett, Peter, Schoenfeld, Winston, Peale, Robert, University of Central Florida
- Abstract / Description
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The purpose of this dissertation is to provide a study and possible applications of two-photon absorption (2PA), in direct-gap semiconductors and quantum-well (QW) semiconductor structures. One application uses extremely nondegenerate (END) 2PA, for mid-infrared (mid-IR) detection in uncooled semiconductors. The use of END, where the two photons have very different energies gives strong enhancement comapared to degenerate 2PA. This END-2PA enhanced detection is also applied to mid-IR imaging...
Show moreThe purpose of this dissertation is to provide a study and possible applications of two-photon absorption (2PA), in direct-gap semiconductors and quantum-well (QW) semiconductor structures. One application uses extremely nondegenerate (END) 2PA, for mid-infrared (mid-IR) detection in uncooled semiconductors. The use of END, where the two photons have very different energies gives strong enhancement comapared to degenerate 2PA. This END-2PA enhanced detection is also applied to mid-IR imaging and light detection and ranging (LIDAR) in uncooled direct-gap photodiodes. A theoretical study of degenerate 2PA (D-2PA) in quantum wells, QWs, is presented, along with a new theory of ND 2PA in QWs is developed. Pulsed mid-IR detection of femtosecond pulses is investigated in two different semiconductor p-i-n photodiodes (GaAs and GaN). With the smaller gap materials having larger ND-2PA, it is observed that they have better sensitivity to mid-IR detection, but unwanted background from D-2PA outweighs this advantage. A comparison of responsivity and signal-to-background ratio for GaAs and GaN in END-2PA based detection is presented. END-2PA enhancement is utilized for CW IR detection in uncooled GaAs and GaN p-i-n photodiodes. The pulsed mid-IR detection experiments are further extended to perform mid-IR imaging in uncooled GaN p-i-n photodetectors. A 3-D automated scanning gated imaging system is developed to obtain 3-D mid-IR images of various objects. The gated imaging system allows simultaneous 3-D and 2-D imaging of objects. The 3-D gated imaging system described in the dissertation could be used for examination of buried structures (microchannels, defects etc.) or laser written volumetric structures and could also be suitable for in-vivo imaging applications in biology in the mid-IR spectral region. As an example, 3-D imaging of buried semiconductor structures is presented.A theoretical study of D-2PA of QWs for transverse electric (TE) and transverse magnetic (TM) fields is carried out and an analytical expression for the D-2PA coefficient in QWs using second-order perturbation theory is derived. A theory for ND-2PA in QW semiconductor using second-order perturbation theory is developed for the first time and an analytical expression for the ND-2PA coefficient for TE, TM, and the mixed case of TE and TM is derived. The shape of the 2PA curve for the D-2PA and ND-2PA for QWs in the TE case is similar to that of bulk semiconductors. As governed by the selection rules both the D-2PA and ND-2PA curves for the TE case does not show a step-like signature for the density of states of the QWs whereas 2PA curve for the TM case shows such step like sharp features. The ND-2PA coefficient for TE, TM, and the mixed case is compared with that obtained for bulk semiconductors. Large enhancement in ND-2PA of QW semiconductors for the TM case over bulk semiconductors is predicted.
Show less - Date Issued
- 2015
- Identifier
- CFE0005684, ucf:50164
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005684
