Current Search: Argenti, Luca (x)
View All Items
 Title
 RESONANT ANISOTROPIC EMISSION IN RABBITT SPECTROSCOPY.
 Creator

Ghomashi, Bejan M, Argenti, Luca, Douguet, Nicolas, University of Central Florida
 Abstract / Description

A variant of RABBITT pumpprobe spectroscopy in which the attosecond pulse train comprises both even and odd harmonics of the fundamental IR probe frequency is explored to measure timeresolved photoelectron emission in systems that exhibit autoionizing states. It is shown that the group delay of both onephoton and twophoton resonant transitions is directly encoded in the energyresolved photoelectron anisotropy as a function of the pumpprobe timedelay. This principle is illustrated for a...
Show moreA variant of RABBITT pumpprobe spectroscopy in which the attosecond pulse train comprises both even and odd harmonics of the fundamental IR probe frequency is explored to measure timeresolved photoelectron emission in systems that exhibit autoionizing states. It is shown that the group delay of both onephoton and twophoton resonant transitions is directly encoded in the energyresolved photoelectron anisotropy as a function of the pumpprobe timedelay. This principle is illustrated for a 1D model with symmetric zerorange potentials that supports both bound states and shaperesonances. The model is studied using both perturbation theory and solving the timedependent Schodinger equation on a grid. Moreover, we study the case of a realistic atomic system, helium. In both cases, we demonstrate faithful reconstruction of the phase information for resonant photoemission.
Show less  Date Issued
 2018
 Identifier
 CFH2000451, ucf:45703
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFH2000451
 Title
 Theoretical Study of Negative Molecular Ions Relevant to the Interstellar and Laboratory Plasma.
 Creator

Khamesian, Marjan, Kokoouline, Viatcheslav, Argenti, Luca, Saha, Haripada, Masunov, Artem, University of Central Florida
 Abstract / Description

Recently, several negative molecular ions, CnN? (n = 1, 3, 5) and CnH? (n = 4, 6, 8), were observed in the interstellar medium (ISM). It was suggested that the anions are formed in the ISM by the process of radiative electron attachment (REA). A simple statistical model was developed in 1980's to estimate rate coefficients of the REA reactions. Some of the rate coefficients obtained in the model are consistent with the observations, the others are not. More importantly, some of the...
Show moreRecently, several negative molecular ions, CnN? (n = 1, 3, 5) and CnH? (n = 4, 6, 8), were observed in the interstellar medium (ISM). It was suggested that the anions are formed in the ISM by the process of radiative electron attachment (REA). A simple statistical model was developed in 1980's to estimate rate coefficients of the REA reactions. Some of the rate coefficients obtained in the model are consistent with the observations, the others are not. More importantly, some of the approximations employed in the model are not physically justified.The aim of this thesis is a development of a quantummechanical approach to study the process of radiative electron attachment to linear molecules of astrophysical interest. The approach is based on accurate ab initio calculations of electronic bound and continuum states of the negative ion. Cross sections and rate coefficients for formation of the following molecular negative ions by REA were determined: CN?, C2H?, C3N?, C4H?, C5N?, C6H?, and C8H?. All the calculations presented in the thesis were carried out using the MOLPRO and UK Rmatrix (Quantemol)suites of programs. Uncertainty quantification of the results, obtained for each studied system, was performed. A second process, closely related to the radiative electron attachment, photodetachment (PD), was also studied in the thesis. Photodetachment cross sections for the CnN? (n = 1, 3, 5), CnH? (n = 4, 6, 8) and C2? molecules were determined using an approach similar to the one employed for REA from the same transition dipole moment matrix elements. The obtained REA cross sections and rate coefficients were validated by comparing the present theoretical results with the experimental data from recent photodetachment experiments.The present results suggest that the observed abundance of these ions in the ISM can hardly be explained by the REA process. In other words, these anions are formed in the interstellar medium by a process different than radiative electron attachment.Dissociative electron attachment (DEA) is another process of anion formation, which could possibly explain formation of certain molecular anions in the ISM. The ClF attachment was studied using a first principle approach.A good agreement with experimental data was demonstrated.A theoretical approach to evaluate cross sections for rotational excitation of linear neutral molecules by an electron impact was developed and applied to acetylene, HCCH. The differential cross sections for eHCCH scattering were calculated between energies 0.1 eV and 10 eV. The momentum transfer cross section and eigenphases for eHCCH scattering were also calculated.
Show less  Date Issued
 2017
 Identifier
 CFE0006612, ucf:51295
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006612
 Title
 Mathematical Foundations of Adaptive Quantum Processing.
 Creator

Bonior, Daniel, Mucciolo, Eduardo, Martin, Keye, Argenti, Luca, Shivamoggi, Bhimsen, Marinescu, Dan, University of Central Florida
 Abstract / Description

Quantum information has the potential to revolutionize the way we store, process, transfer and acquire information [1,14,15,21,37]. In particular, quantum information offers exciting new approaches to secure communication, computation and sensing. However, in order to realize such technologies, we must first understand the effect that environmental noise has on a quantum system. This dissertation builds upon recent studies that have explored the underlying structure of quantum information and...
Show moreQuantum information has the potential to revolutionize the way we store, process, transfer and acquire information [1,14,15,21,37]. In particular, quantum information offers exciting new approaches to secure communication, computation and sensing. However, in order to realize such technologies, we must first understand the effect that environmental noise has on a quantum system. This dissertation builds upon recent studies that have explored the underlying structure of quantum information and the effects of qubit channels in quantum communication protocols.This work is divided into five main chapters, with Chapter 1 being a brief introduction to quantum information. We then begin Chapter 2 by defining the error function for our qubit communication protocols. From there we explore the properties of our error functions and the topological space that they form. In Chapter 3 we consider the newly patented process Adaptive Quantum Information Processing, patent number US9838141 B2; originally outlined by Martin in [23]. We restate the adaptive scheme and exemplify its application through the Prepare and Send Protocol and Quantum Key Distribution. Applying our results from Chapter 2, we obtain an expression for the adaptability of unital channels in these two protocols and classify the channels that admit the most improvement. We dedicate Chapter 4 to the derivation of gravitational noise, and show that in certain circumstances gravity results in a channel that can be maximally improved in Adaptive QKD [3,14,16]. Lastly, we study the set of error functions through the lens of domain theory. Domain theory is a subset of mathematics that was developed in order to rigorously formalize computations. The first four chapters are all consequences of past discoveries in the mathematical structure of quantum channels. In Chapter 5 we characterize the set of error functions through domain theory, extending the mathematical foundations of quantum information. [12,18,20, 22, 23,25].
Show less  Date Issued
 2018
 Identifier
 CFE0007313, ucf:52124
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0007313
 Title
 High power fiber lasers and fiber devices.
 Creator

Sanjabieznaveh, Zeinab, Amezcua Correa, Rodrigo, Chang, Zenghu, Argenti, Luca, Richardson, Martin, Schulzgen, Axel, University of Central Florida
 Abstract / Description

Fiber lasers and fiber amplifiers have experienced considerable improvements in recent years and demonstrated remarkable power scalability. However, due to high optical intensity in the core, the performance of high power fiber lasers is limited by detrimental nonlinear processes, such as fourwave mixing, selfphase modulation, stimulated Brillouin scattering, and stimulated Raman scattering. To mitigate nonlinear effects, very large mode area (LMA) fibers, which exhibit a mode field...
Show moreFiber lasers and fiber amplifiers have experienced considerable improvements in recent years and demonstrated remarkable power scalability. However, due to high optical intensity in the core, the performance of high power fiber lasers is limited by detrimental nonlinear processes, such as fourwave mixing, selfphase modulation, stimulated Brillouin scattering, and stimulated Raman scattering. To mitigate nonlinear effects, very large mode area (LMA) fibers, which exhibit a mode field diameter larger than 30 ?m have been developed. However, for larger core sizes the discrimination capabilities of conventional fiber designs decrease, consequently, LMA fibers are not strictly single mode which ultimately at high average powers results in sudden degradation of the output beam of a fiber laser or amplifier, namely, modal instability (MI). To suppress higher order modes (HOMs) in LMA fibers, various techniques have been proposed such as large pitch fibers (LPFs), differential bend loss for HOMs, leakage channel fibers, mode filtering with tapers, and chirally coupled cores. This thesis is divided into two parts. In the first two chapters, I focus on simulation, design and characterization of advanced high power fiber amplifiers. In the first chapter, I study the numerical modeling of the MI in active LMA fibers. Using a high fidelity time dependent computer model based on beam propagation method (BPM), taking laser gain and thermal effects into account, I show that engineering pump scheme is a promising technique leading to an appreciable threshold increase in a fiber amplifier. As an example I demonstrate that bidirectional pump scheme increases the instabilities threshold by a factor of ~30% with respect to the forward pump configuration. In the second chapter, I present a novel design of microstructured large pitch, LMA asymmetric rodtype fiber to achieve higher MI threshold. By eliminating mirror symmetries in the cladding of the LPF through six high refractive index germaniumdoped silica inclusions, we reduce the overlap of the LP1mlike modes with the core region, which leads to strong HOM delocalization and enhanced preferential gain for the fundamental mode in active fibers. The third and fourth chapters of this thesis are focused on allfiber mode multiplexers for communication applications. In the third chapter, I present an allfiber mode selective photonic lantern mode multiplexer designed for launching into fewmode multicore fibers (FMMCFs). This device is capable of selectively exciting LP01, LP11a and LP11b modes in a seven core configuration resulting in 21 spatial channels, with less than 38 dB crosstalk and with insertion loss below 0.4 dB. This device can be a critical component for the evolution of high capacity, highdensity space division multiplexing (SDM) transmission networks based on MCFs.In the fourth chapter, I demonstrate for the first time, an allfiber orbital angular momentum (OAM) mode multiplexer to efficiently generate and simultaneously multiplex multiple OAM modes within a broad spectral range of at least 550 nm. This innovative allfiber passive design provides simultaneous multiplexing of multiple orthogonal OAM modes in a single fiber device with low loss and at low design complexity, therefore, it is of grand utility in variety of applications in classical and modern optical studies.
Show less  Date Issued
 2017
 Identifier
 CFE0006956, ucf:51632
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006956