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(1 - 20 of 31)
Pages
- Title
- The ancient and modern conception of the atom.
- Creator
-
Rankin,Henry Ashly
- Date Issued
- 1927
- Identifier
- 369418, CFDT369418, ucf:5441
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/369418
- Title
- Atoms, bombs and you.
- Creator
-
Mather, Kirtley F. (Kirtley Fletcher)
- Date Issued
- 1946
- Identifier
- 360080, CFDT360080, ucf:5238
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/360080
- Title
- Authentic guide to atom bomb precautions: Based largely on official data prepared.
- Date Issued
- 1950
- Identifier
- 1927615, CFDT1927615, ucf:4870
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/1927615
- Title
- Authentic guide to atom bomb precautions: Based largely on official data prepared.
- Date Issued
- 1950
- Identifier
- 1927662, CFDT1927662, ucf:4882
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/1927662
- Title
- One world or none.
- Creator
-
Masters, Dexter, Way, Katharine 1903-, Bohr, Niels, Compton, Arthur H., Arnold, H. H., Bethe, Hans, Condon, E. U.
- Date Issued
- 1946
- Identifier
- 2683364, CFDT2683364, ucf:5059
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/2683364
- Title
- Brief guide to the atomic age.
- Creator
-
Fagley, Richard Martin
- Date Issued
- 1945
- Identifier
- 360078, CFDT360078, ucf:5236
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/360078
- Title
- Texts of speeches: On general reduction of armaments, at the United Nations General Assembly, November-December, 1946, New York City.
- Creator
-
Molotov, Vyacheslav Mikhaylovich
- Date Issued
- 1946
- Identifier
- 671338, CFDT671338, ucf:5553
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/671338
- Title
- The atomic bomb.
- Creator
-
Atomic Scientists of Chicago
- Date Issued
- 1946
- Identifier
- 369652, CFDT369652, ucf:5465
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/369652
- Title
- SYMMETRY IN THE DISSOCIATIVE RECOMBINATION OF POLYATOMIC IONS AND IN ULTRA-COLD FEW BODY COLLISIONS.
- Creator
-
Douguet, Nicolas, Kokoouline, Viatcheslav, University of Central Florida
- Abstract / Description
-
We discuss the role of symmetries in the dissociative recombinations (DR) of three polyatomic ions, namely the linear HCO+ (formyl) ion and the two highly symmetric H3+ and H3O+ (hydronium) molecular ions. Regarding the HCO+ ion, we apply a quantum mechanical treatment using the Multi-channel Quantum Defect Theory (MQDT) formalism to describe the ion-electron scattering process. Our study takes into account the Renner-Teller effect in order to model the non Born-Oppenheimer vibronic coupling...
Show moreWe discuss the role of symmetries in the dissociative recombinations (DR) of three polyatomic ions, namely the linear HCO+ (formyl) ion and the two highly symmetric H3+ and H3O+ (hydronium) molecular ions. Regarding the HCO+ ion, we apply a quantum mechanical treatment using the Multi-channel Quantum Defect Theory (MQDT) formalism to describe the ion-electron scattering process. Our study takes into account the Renner-Teller effect in order to model the non Born-Oppenheimer vibronic coupling in linear polyatomic ions. The coupling has shown to represent the main mechanism responsible for electronic capturing in highly excited Rydberg states associated with excited vibrational levels of the ionic core. We consider all internal degrees of freedom of HCO+ and obtain the dissociative cross section as a function of the incident electron kinetic energy. We have also improved the theoretical approach by including the large permanent dipole moment of HCO+ using a generalization of the MQDT formalism. To our knowledge, this is the first time the permanent dipole moment of an ion is included in a DR study. The obtained results are in good agreement with experimental data. W also study the DR of H3+ and H3O+ symmetric ions using a simplified theoretical treatment, which focuses on the key ingredient of the DR process, the electron capture in the first excited degenerate vibrational normal mode of the ions through non Born-Oppenheimer Jahn-Teller coupling. For both ions the obtained cross sections are in very good agreement with the available experimental data. Moreover, in the case of H3+, the results reproduce previous calculations from two independent theoretical studies. Finally, we investigate the role of symmetries in few body ultra-cold collisions by considering both three and four identical atoms systems. We derive allowed rearrangements of different fragments of the system, satisfying the complete symmetry of the molecular Hamiltonian. For that purpose we establish a correspondence between constants of motion of the system in different large-distance configurations and irreducible representations of the total symmetry group. Selection rules (forbidden transitions) and allowed states, which depend on the fermionic or bosonic nature of the atoms, can be derived from these results.
Show less - Date Issued
- 2010
- Identifier
- CFE0003552, ucf:48896
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003552
- Title
- The atomic age : suicide, slavery or socialism?.
- Creator
-
Levenstein, Aaron
- Date Issued
- 1946
- Identifier
- 363245, CFDT363245, ucf:5272
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/363245
- Title
- LATTICE VIBRATION STUDY OF SILICA NANOPARTICLE IN SUSPENSION.
- Creator
-
Sachdeva, Parveen, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
-
In recent years considerable research has been done in the area of "nanofluids". Nanofluids are colloidal suspensions of nanometer size metallic or oxide particles in a base fluid such as water, ethylene glycol. Nanofluids show enhanced heat transfer characteristics compared to the base fluid. The thermal transport properties of nanofluids depend on various parameters e.g. interfacial resistance, Brownian motion of particles, liquid layering at the solid-liquid interface and clustering of...
Show moreIn recent years considerable research has been done in the area of "nanofluids". Nanofluids are colloidal suspensions of nanometer size metallic or oxide particles in a base fluid such as water, ethylene glycol. Nanofluids show enhanced heat transfer characteristics compared to the base fluid. The thermal transport properties of nanofluids depend on various parameters e.g. interfacial resistance, Brownian motion of particles, liquid layering at the solid-liquid interface and clustering of nanoparticles. In this work atomic scale simulation has been used to study possible mechanisms affecting the heat transfer characteristics of nanofluids. Molecular dynamics simulation for a single silica nanoparticle surrounded by water molecules has been performed. Periodic boundary condition has been used in all three directions. The effect of nanoparticle size and temperature of system on the thermal conductivity of nanofluids has been studied. It was found that as the size of nanoparticle decreases thermal conductivity of nanofluid increases. This is partially due to the fact that as the diameter of nanoparticle decreases from micrometer to nanometer its surface area to volume ratio increases by a factor of 103. Since heat transfer between the fluid and the nanoparticle takes place at the surface this enhanced surface area gives higher thermal conductivity for smaller particles. Thermal conductivity enhancement is also due to the accumulation of water molecules near the particle surface and the lattice vibration of the nanoparticle. The phonon transfer through the second layer allows the nanofluid thermal conductivity to increase by 23%-27% compared to the base fluid water for 2% concentration of nanosilica.
Show less - Date Issued
- 2006
- Identifier
- CFE0001278, ucf:46897
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001278
- Title
- Interplay of Molecular and Nanoscale Behaviors in Biological Soft Matter.
- Creator
-
Ciaffone, Nicholas, Tetard, Laurene, Kang, Hyeran, Santra, Swadeshmukul, University of Central Florida
- Abstract / Description
-
The complexity of biological soft matter at the sub-micrometer level is fundamentally correlated to the functionalities at the larger scale. Reflecting the level of heterogeneities in the properties of systems remains challenging when probing small scales, due to the mismatch between the area surveyed with the tools offering nanoscale resolution, such as atomic force microscopy (AFM), and the scale of natural variations inherent to biology. Hence, to understand the physiological and...
Show moreThe complexity of biological soft matter at the sub-micrometer level is fundamentally correlated to the functionalities at the larger scale. Reflecting the level of heterogeneities in the properties of systems remains challenging when probing small scales, due to the mismatch between the area surveyed with the tools offering nanoscale resolution, such as atomic force microscopy (AFM), and the scale of natural variations inherent to biology. Hence, to understand the physiological and mechanical alterations that occur within a single cell relative to a cell population, a multiscale approach is necessary. In this work we show that it is possible to observe molecular, chemical and physical alterations in both plant and human cells with a multiscale approach. Biophysical and biochemical traits of cell populations are studied with Fourier Transform infrared spectroscopy (FTIR) and in turn, guide higher resolution discovery with Raman spectroscopy and nanoscale infrared spectroscopy using AFM (NanoIR) to access finer details. We illustrate this with three examples of biological soft matter systems: 1) a preliminary study of cellular interactions with naturally occurring vehicles applicable to human health, 2) a qualitative examination of antibiotics and new pesticide treatments in food crop systems, and 3) a fundamental investigation of the deconstruction mechanisms of plant cells during pre-treatments in preparation for biofuel production.
Show less - Date Issued
- 2018
- Identifier
- CFE0007395, ucf:52058
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007395
- Title
- Multiphase Flow Modeling of Molten Metal Atomization at High Gas Pressure.
- Creator
-
Hanthanan Arachchilage, Kalpana, Kumar, Ranganathan, Sohn, Yongho, Kassab, Alain, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
The high-pressure gas atomization is well known as one of the best powder manufacturing processes due to its controllability over powder size distribution. However, with the continuous improvement of new alloys, optimizing the operating parameters to maximize the yield is costly and time-consuming. Therefore, it is essential to understand the high-pressure gas atomization process and the effects of different operational parameters on the powder size distribution.Two-phase numerical...
Show moreThe high-pressure gas atomization is well known as one of the best powder manufacturing processes due to its controllability over powder size distribution. However, with the continuous improvement of new alloys, optimizing the operating parameters to maximize the yield is costly and time-consuming. Therefore, it is essential to understand the high-pressure gas atomization process and the effects of different operational parameters on the powder size distribution.Two-phase numerical simulations are performed to capture the interfacial dynamic during the atomization process and to obtain the effects of gas pressure, melt flow rate, and thermophysical properties of atomizing gas and the molten metal. The Volume of Fluid (VOF) model is used to capture the melt-gas interface, and in-house post-processing code is developed to obtain the droplet size distributions. Three-dimensional geometry of an annular-slit close-coupled gas atomizer is utilized to investigate the primary atomization process. The current grid resolution is sufficient forcapturing primary atomization and some characteristics of the secondary atomization, but it is not adequate to capture all the length scales in secondary atomization. Qualitative comparisons of the cumulative volume graphs indicate that this numerical approach is capable of capturing the trends in the atomization process as in the experiments. It is found that a combination of several interfacial instabilities governs the atomization process. Simulations corresponding to different gas pressures show that the atomizationcharacteristics remain unchanged irrespective of the gas pressure. However, it is found that the rate of the evolution and the effectiveness of the atomization process increases with the gas pressure. Three melts (aluminum, steel, and an artificial material with intermediate thermophysical properties) are used to investigate the effects of the molten metal properties and found that the rate of the atomization process decreases with increasing melt density, and the yield of the atomized powder is seen to increase. The flow characteristics remain unchanged for all three melts. The melt flow is strongly correlated with flow characteristics and interfacial instability.
Show less - Date Issued
- 2019
- Identifier
- CFE0007814, ucf:52342
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007814
- Title
- On the reduction of armaments, prohibition of the atomic weapon and on international control: speeches delivered in the Political committee at the sixth session of the United Nations General Assembly, Nobvember 24, 1951....
- Creator
-
Vyshinsky, Andrey Yanuaryevich
- Date Issued
- 1952
- Identifier
- 671334, CFDT671334
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/671334
- Title
- SELF-ASSEMBLED SUPRAMOLECULAR STRUCTURES OF CHIRAL PHOSPHOLIPIDS: STRUCTURE, MECHANICAL PROPERTIES AND PATTERNING.
- Creator
-
Mahajan, Nidhi, Fang, Jiyu, University of Central Florida
- Abstract / Description
-
Lipid molecule is well known natural building block to form different supramolecular structures with specific shape, size and functionality. In my thesis work, I have used DC8,9PC 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine), a type of chiral lipid to form the vesicles, tubules and ribbons . By using Atomic Force Microscope, I have studied the morphological features of these particular structures. Also, the mechanical properties of lipid tubules have been studied using AFM....
Show moreLipid molecule is well known natural building block to form different supramolecular structures with specific shape, size and functionality. In my thesis work, I have used DC8,9PC 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine), a type of chiral lipid to form the vesicles, tubules and ribbons . By using Atomic Force Microscope, I have studied the morphological features of these particular structures. Also, the mechanical properties of lipid tubules have been studied using AFM. Softlithography has been used to pattern the lipid vesicles and tubules into 2-dimensional and 3-dimensional ordered arrays. The structure of self-assembled hollow spherical vesicles was studied using AFM. The applications of soft lithography in patterning polymerized lipid vesicles of DC8,9PC on glass substrates are reported. It has been demonstrated that the lipid vesicles can be used as a high-molecular weight ink to be transferred from a PDMS stamp onto a glass substrate to form two-dimensional stripes with a controlled separation over a large area. By combining channel flow with dewetting within microfluidic networks, vesicles were assembled into one-dimension lines on a glass substrate. The vesicle lines can also be selectively removed from the substrate with lift-up process. The direct and precise assembly of lipid vesicles on solid substrates will open up the possibility of integrating them in biosensors and microelectronic devices. Lipid tubules and helices are other extremely interesting superstructures that have captured the imagination of scientists in disciplines from biology through material science to chemistry and physics. Lipid tubules are self-assembled hollow cylindrical structures with opened ends, composed of rolled-up bilayers. They have been used as a template for the synthesis of inorganic materials, a substrate for the crystallization of proteins, a controlled release system for drug deliver, and a colorimetric material for chemical sensors. However, due to the high aspect ratio, the formation of ordered arrays of lipid tubules on substrates still remains to be challenging. In this thesis work, the application of well-known soft lithography techniques in assembling and manipulating lipid tubules on substrates has been reported. I show that lipid nano- and microtubules can be assembled into two-dimensional (2-D) parallel arrays with controlled separations by combining fluidic alignment with dewetting, which occur within microchannels. It has also been shown that lipid tubules can be assembled into 3-D crossbar arrays with fluidic alignment, which occurs within microfluidic networks. The deposition experiments with silica colloidal particles show that the 2-D parallel-aligned tubules can be used as a template to synthesize silica films with controlled morphologies and patterns on substrates in a single-step process. Atomic force microscopy studies show that the resulting silica films replicate the shape, orientation, and pattern of aligned tubule templates. Though, the structures of the lipid tubules have been extensively studied, but very little is known about their mechanical properties. In my work, the mechanical properties of the lipid tubules of DC8,9PC were studied with atomic force microscope. The deformation of the lipid tubules with different outer diameters is directly observed in both tapping and contact modes with increasing loading forces.
Show less - Date Issued
- 2005
- Identifier
- CFE0000449, ucf:46385
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000449
- Title
- Nanoscale Spectroscopy in Energy and Catalytic Applications.
- Creator
-
Ding, Yi, Tetard, Laurene, Challapalli, Suryanarayana, Zhai, Lei, Thomas, Jayan, Lyakh, Arkadiy, Blair, Richard, University of Central Florida
- Abstract / Description
-
Emerging societal challenges such as the need for more sustainable energy and catalysis are requiring more sensitive and versatile measurements at the nanoscale. This is the case in the design and optimization of new materials for energy harvesting (solar cells) and energy storage devices (batteries and capacitors), or for the development of new catalysts for carbon sequestration or other reactions of interest. Hence, the ability to advance spectroscopy with nanoscale spatial resolution and...
Show moreEmerging societal challenges such as the need for more sustainable energy and catalysis are requiring more sensitive and versatile measurements at the nanoscale. This is the case in the design and optimization of new materials for energy harvesting (solar cells) and energy storage devices (batteries and capacitors), or for the development of new catalysts for carbon sequestration or other reactions of interest. Hence, the ability to advance spectroscopy with nanoscale spatial resolution and high sensitivity holds great promises to meet the demands of deeper fundamental understanding to boost the development and deployment of nano-based devices for real applications. In this dissertation, the impact of nanoscale characterization on energy-related and catalytic materials is considered. Firstly an introduction of the current energy and environmental challenges and our motivations are presented. We discuss how revealing nanoscale properties of solar cell active layers and supercapacitor electrodes can greatly benefit the performance of devices, and ponder on the advantages over conventional characterization techniques. Next, we focus on two dimensional materials as promising alternative catalysts to replace conventional noble metals for carbon sequestration and its conversion to added-value products. Defect-laden hexagonal boron nitride (h-BN) has been identified as a good catalyst candidate for carbon sequestration. Theoretically, defects exhibit favorable properties as reaction sites. However, the detailed mechanism pathways cannot be readily probed experimentally, due to the lack of tools with sufficient sensitivity and time resolution. A comprehensive study of the design and material processes used to introduce defects in h-BN in view of improving the catalytic properties is presented. The processing-structure-property relationships are investigated using a combination of conventional characterization and advanced nanoscale techniques. In addition to identifying favorable conditions for defect creation, we also report on the first signs of local reactions at defect sites obtained with nanoscale spectroscopy. Next, we explore avenues to improve the sensitivity and time-resolution of nanoscale measurements using light-assisted AFM-based nanomechanical spectroscopy. For each configuration, we evaluate the new system by comparing its performance to the commercial capabilities.Lastly, we provide a perspective on the opportunities for state-of-the-art characterization to impact the fields of catalysis and sustainable energy, as well as the urge for highly sensitive functional capabilities and time-resolution for nanoscale studies.
Show less - Date Issued
- 2018
- Identifier
- CFE0007751, ucf:52387
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007751
- Title
- Asteroid Surfaces: The Importance of Cohesive Forces.
- Creator
-
Jardine, Keanna, Dove, Adrienne, Tetard, Laurene, Britt, Daniel, University of Central Florida
- Abstract / Description
-
Adhesive forces play a significant role on airless bodies due to their weak gravities. Investigating adhesion at the surface of asteroids and their constituent components is vital to understanding their formation and evolution. Previous research has been done to understand the interaction of micron-sized spheres to planar surfaces and sphere-to-sphere interactions, which have been used to develop models of asteroid surfaces. Our investigation experimentally investigates adhesion through...
Show moreAdhesive forces play a significant role on airless bodies due to their weak gravities. Investigating adhesion at the surface of asteroids and their constituent components is vital to understanding their formation and evolution. Previous research has been done to understand the interaction of micron-sized spheres to planar surfaces and sphere-to-sphere interactions, which have been used to develop models of asteroid surfaces. Our investigation experimentally investigates adhesion through atomic force microscopy (AFM) measurements between JSC-1 simulant particles and several AFM tips, including a typical pyramidal gold tip and microspheres of sizes 2 (&)#181;m and 15 (&)#181;m. The samples of JSC-1 consist of three size ranges: (<) 45 (&)#181;m, 75-125 (&)#181;m, and 125-250 (&)#181;m. For each sample we looked at the magnitude and distribution of the measured adhesive forces. Results show that the pyramidal tip produced larger forces than the spherical tips generally, and the sample that produced larger forces and a larger distribution of those force was the smaller, more powder-like sample with sizes (<)45 (&)#181;m.
Show less - Date Issued
- 2018
- Identifier
- CFE0007755, ucf:52377
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007755
- Title
- Towards Scalable Nanomanufacturing: Modeling the Interaction of Charged Droplets from Electrospray using GPU.
- Creator
-
Yang, Weiwei, Deng, Weiwei, Chen, Ruey-Hung, Ilie, Marcel, University of Central Florida
- Abstract / Description
-
Electrospray is an atomization method subject to intense study recently due to its monodispersity and the wide size range of droplets it can produce, from nanometers to hundreds of micrometers. This thesis focuses on the numerical and theoretical modeling of the interaction of charged droplets from the single and multiplexed electrospray. We studied two typical scenarios: large area film depositions using multiplexed electrospray and fine pattern printings assisted by linear electrostatic...
Show moreElectrospray is an atomization method subject to intense study recently due to its monodispersity and the wide size range of droplets it can produce, from nanometers to hundreds of micrometers. This thesis focuses on the numerical and theoretical modeling of the interaction of charged droplets from the single and multiplexed electrospray. We studied two typical scenarios: large area film depositions using multiplexed electrospray and fine pattern printings assisted by linear electrostatic quadrupole focusing. Due to the high computation power requirement in the unsteady n-body problem, graphical processing unit (GPU) which delivers 10 Tera flops in computation power is used to dramatically speed up the numerical simulation both efficiently and with low cost. For large area film deposition, both the spray profile and deposition number density are studied for different arrangements of electrospray and electrodes. Multiplexed electrospray with hexagonal nozzle configuration can not give us uniform deposition though it has the highest packing density. Uniform film deposition with variation (<) 5% in thickness was observed with the linear nozzle configuration combined with relative motion between ES source and deposition substrate. For fine pattern printing, linear quadrupole is used to focus the droplets in the radial direction while maintaining a constant driving field at the axial direction. Simulation shows that the linear quadrupole can focus the droplets to a resolution of a few nanometers quickly when the inter-droplet separation is larger than a certain value. Resolution began to deteriorate drastically when the inter-droplet separation is smaller than that value. This study will shed light on using electrospray as a scalable nanomanufacturing approach.
Show less - Date Issued
- 2012
- Identifier
- CFE0004463, ucf:49333
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004463
- Title
- Deposition Thickness Modeling and Parameter Identification for Spray Assisted Vacuum Filtration Process in Additive Manufacturing.
- Creator
-
Mark, August, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
- Abstract / Description
-
To enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer...
Show moreTo enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer dynamics in the spray atomization and vacuum filtration are studied for the mass of solid particles and mass of water in differential areas, and then the thickness of a filter cake is derived. A two-loop nonlinear constrained optimization approach is used to identify the unknown parameters in the model. Experiments involving depositing carbon nanofibers in a sheet of paper are used to measure the ability of the model to mimic the filtration process.
Show less - Date Issued
- 2015
- Identifier
- CFE0005974, ucf:50788
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005974
- Title
- Characterization and Application of Isolated Attosecond Pulses.
- Creator
-
Chini, Michael, Chang, Zenghu, Saha, Haripada, Chow, Lee, Schulzgen, Axel, University of Central Florida
- Abstract / Description
-
Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few...
Show moreTracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few-cycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on as-yet unprecedented timescales.In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for state-resolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics (-) on timescales shorter than the laser cycle (-) are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagnetically-induced absorption and transparency, and two-color multi-photon absorption to (")dark(") states of the atom. These features are observed in both bound states and quasi-bound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems.The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 15-25 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV (-) comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a world-record-breaking 67 as pulse.
Show less - Date Issued
- 2012
- Identifier
- CFE0004781, ucf:49802
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004781
