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Analysis and Design of Non-Hermitian Optical Systems
Title
Analysis and Design of Non-Hermitian Optical Systems.
Creator
Kazemi Jahromi, Ali, Abouraddy, Ayman, Christodoulides, Demetrios, Likamwa, Patrick, Chini, Michael, University of Central Florida
Abstract / Description
From a very general perspective, optical devices can be viewed as constructions based on the spatial engineering of the optical index of refraction. Sculpting the real part of the refractive index produces the wide variety of known passive optical devices, such as waveguides, resonators, gratings, among a plethora of other possibilities for managing the transport of light. Less attention has been directed to engineering the imaginary part of the refractive index (-) that is responsible for...
Show moreFrom a very general perspective, optical devices can be viewed as constructions based on the spatial engineering of the optical index of refraction. Sculpting the real part of the refractive index produces the wide variety of known passive optical devices, such as waveguides, resonators, gratings, among a plethora of other possibilities for managing the transport of light. Less attention has been directed to engineering the imaginary part of the refractive index (-) that is responsible for optical gain and absorption (-) in conjunction with the real part of the refractive index. Optical gain is the building block of amplifiers and lasers, while optical absorption is exploited in photovoltaic devices, photodetectors, and as dopants in lasing media. Recently, the field of non-Hermitian photonics has emerged in which the new opportunities afforded by the spatial engineering of the optical gain and loss in an optical device are being exploited. Indeed, the judicious design of such active devices can result in counterintuitive physical effects, new optical functionalities that enable unexpected applications, and enhanced performance of existing devices.In this work, we have theoretically and experimentally demonstrated four different non-Hermitian arrangements exhibiting novel non-trivial features. First, we show that the direction of energy flow can be controlled inside an active cavity by tuning the optical gain. Reversing the direction of the energy flow within the cavity (-) such that Poynting's vector points backwards towards the source (-) takes place when the cavity gain exceeds a certain threshold value, which we have named 'Poynting's threshold'. To realize this effect, we have employed a fiber-based arrangement that allows for unambiguous determining of the direction of the energy flow within the cavity. Second, we have studied the implication of Poynting's threshold with respect to spectral reflection from an active cavity. Surprisingly, the reflection at Poynting's threshold becomes spectrally flat and is guaranteed to attain unity reflectivity while maintaining non-zero transmission. In other words, at Poynting's threshold, the cavity becomes a 'transparent perfect mirror'. We have realized this effect in an on-chip active waveguide device and in an optical-fiber-based system. Third, we have examined a parity-time (PT) symmetric fiber-based cavity consisting of two coupled sub-cavities, one of which contains gain and the other loss. In contrast to all previous on-chip PT-symmetric micro-devices, the exotic features of such a system may be expected to vanish when the length of the cavity is extremely large (exceeding 1 km in our experiments) due to the strong fluctuations in the optical phase. Nevertheless, we have found that some of the central features of such a system survive; e.g., loss-induced enhancement of lasing power is still observable. Finally, we have demonstrated (-) for the first time (-) the interferometric perfect absorption of light in a weakly absorbing (erbium-doped) fiber system. Additionally, we verified that this coherent effect is the most efficient configuration with respect to utilizing the absorbing species in the medium.
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Date Issued
2018
Identifier
CFE0007206, ucf:52271
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007206
Power Scaling of High Power Solid State Lasers.
Title
Power Scaling of High Power Solid State Lasers.
Creator
Oh, Bumjin, Richardson, Martin, Soileau, MJ, Chini, Michael, University of Central Florida
Abstract / Description
The solid-state laser is one of the most widely used lasers in scientific research and industrial applications. This thesis describes detailed investigations of two modern architectures of high power cw solid-state lasers, a 20 W diode-pumped Yb:YAG thin disc laser and 300 W diode-pumped Nd:YAG rod laser. With the thin disc laser architecture, the signal beam must fit to the pump area on the disc defined by the multi-pass diode pump configuration. The beam propagation, beam diameter, phase...
Show moreThe solid-state laser is one of the most widely used lasers in scientific research and industrial applications. This thesis describes detailed investigations of two modern architectures of high power cw solid-state lasers, a 20 W diode-pumped Yb:YAG thin disc laser and 300 W diode-pumped Nd:YAG rod laser. With the thin disc laser architecture, the signal beam must fit to the pump area on the disc defined by the multi-pass diode pump configuration. The beam propagation, beam diameter, phase and thermal effects for various cavity configurations are investigated theoretically and experimentally. In addition, the internal loss, small signal gain, and thermal lensing effect are essential properties to construct the laser system but usually unknown. The theories and methodologies to obtain these properties are presented and the experimental results are compared. In a second phase of the project, the multi-mode and single-mode operation of a high power diode-pumped rod laser system are examined and compared to the thin disc system. Thermal effects on the phase, beam quality and brightness are examined and future applications and improvements considered.
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Date Issued
2018
Identifier
CFE0007232, ucf:52221
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007232
Plasma Dynamics of Laser Filaments
Title
Plasma Dynamics of Laser Filaments.
Creator
Reyes, Danielle, Richardson, Martin, Gaume, Romain, Chini, Michael, University of Central Florida
Abstract / Description
Laser filamentation is a complex phenomenon occurring for pulses with peak power above a critical value. A filament is a dynamic self-guided structure characterized by several unique qualities, which include a beam with a high-intensity core surrounded by an energy reservoir, a weakly ionized plasma channel, and supercontinuum generation. Several of the proposed applications for filamentation utilize the plasma channel, such as for assisted electric discharge and microwave guiding. However,...
Show moreLaser filamentation is a complex phenomenon occurring for pulses with peak power above a critical value. A filament is a dynamic self-guided structure characterized by several unique qualities, which include a beam with a high-intensity core surrounded by an energy reservoir, a weakly ionized plasma channel, and supercontinuum generation. Several of the proposed applications for filamentation utilize the plasma channel, such as for assisted electric discharge and microwave guiding. However, filament properties are highly influenced by the physical conditions under which they are formed. A host of studies have been conducted to further characterize filaments, but much work still remains in order to understand their complex behavior. This work presents an accurate and direct measurement of the electron density based on an interferometric technique. The impact of different initial parameters on filament spatio-temporal dynamics in air is investigated, concentrating primarily on their influence on the plasma. For comparison of the experiment with theory, the plasma decay is modeled by a system of kinetic equations that takes into account three-body and dissociative electron recombination reactions.
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Date Issued
2017
Identifier
CFE0006646, ucf:51222
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006646
Characterization and Application of Isolated Attosecond Pulses
Title
Characterization and Application of Isolated Attosecond Pulses.
Creator
Chini, Michael, Chang, Zenghu, Saha, Haripada, Chow, Lee, Schulzgen, Axel, University of Central Florida
Abstract / Description
Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few...
Show moreTracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few-cycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on as-yet unprecedented timescales.In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for state-resolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics (-) on timescales shorter than the laser cycle (-) are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagnetically-induced absorption and transparency, and two-color multi-photon absorption to (")dark(") states of the atom. These features are observed in both bound states and quasi-bound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems.The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 15-25 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV (-) comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a world-record-breaking 67 as pulse.
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Date Issued
2012
Identifier
CFE0004781, ucf:49802
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004781