189 research outputs found

    Bifurcation analysis and exact solutions for a class of generalized time-space fractional nonlinear Schrödinger equations

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    In this work, we focus on a class of generalized time-space fractional nonlinear Schrödinger equations arising in mathematical physics. After utilizing the general mapping deformation method and theory of planar dynamical systems with the aid of symbolic computation, abundant new exact complex doubly periodic solutions, solitary wave solutions and rational function solutions are obtained. Some of them are found for the first time and can be degenerated to trigonometric function solutions. Furthermore, by applying the bifurcation theory method, the periodic wave solutions and traveling wave solutions with the corresponding phase orbits are easily obtained. Moreover, some numerical simulations of these solutions are portrayed, showing the novelty and visibility of the dynamical structure and propagation behavior of this model

    Laser Plasma Study through Simulation and Theory

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    Department of PhysicsStimulated Raman Scattering (SRS) is a fascinating physical phenomenon that arises from the interaction between a plasma medium and high-energy laser radiation. It involves the transfer of laser energy to plasma waves, resulting in the generation of new waves and the scattering of the incident laser beam. SRS is an important phenomenon in laser plasma interaction, with various applications in fields such as laser fusion, particle acceleration, and high-energy-density physics. The SRS process begins when a high-intensity laser beam interacts with a plasma medium. The laser energy excites plasma waves, which can be longitudinal or transverse depending on the direction of the laser polarization. These waves then undergo a resonance process, where they interact with the plasma ions and transfer energy to them. As a result, new waves are generated, and the incident laser beam is scattered in a different direction. One of the most significant features of SRS is its threshold behavior. SRS only occurs when the laser intensity exceeds a certain threshold value. Below this value, the plasma waves cannot reach the resonance condition and do not transfer energy to the plasma ions. Above the threshold value, however, the plasma waves grow exponentially, leading to a rapid increase in the scattered light intensity. SRS has various applications in laser plasma interaction. In laser fusion, SRS can be a significant obstacle as it leads to the loss of laser energy and can damage the laser system. Researchers have developed various methods to mitigate SRS, such as using frequency conversion techniques, plasma shaping, and polarization smoothing. In particle acceleration, SRS can be used to generate high-energy electron beams. By controlling the laser intensity and plasma conditions, researchers can create plasma wakefields that accelerate charged particles to high energies. Plasma density diagnostics are crucial to understanding the laser plasma interaction process. One diagnostic method involves using a probe laser to measure the plasma density through the interaction with the plasma electrons. Other diagnostic methods include interferometry, Thomson scattering, and Langmuir probes. Raman scattering diagnostics are a powerful tool for measuring the plasma density in a wide range of applications. This technique relies on the inelastic scattering of light from the plasma, which results in a shift in the frequency of the scattered light. By measuring the frequency shift, researchers can determine the plasma density and gain insight into the plasma???s behavior. Overall, Raman scattering diagnostics are a powerful tool for measuring plasma density in a wide range of applications. These techniques can provide valuable insight into the plasma???s behavior and are essential for the development of advanced plasma technologies. Ongoing research continues to improve the sensitivity and accuracy of Raman scattering diagnostics, ensuring that these techniques remain at the forefront of plasma research. Plasma dipole oscillations are a type of collective motion that can occur in a plasma medium when it is excited by an external electromagnetic field. These oscillations result from the motion of the plasma electrons in response to the electromagnetic field, creating a dipole moment that oscillates at a characteristic frequency. Plasma dipole oscillations are an important phenomenon in plasma physics and have various applications, including as a radiation source for plasma diagnostics. Plasma dipole oscillations can also act as a radiation source for plasma diagnostics. When the dipole moment of the plasma oscillates, it generates electromagnetic radiation at the same frequency. This radiation can be in the THzband depending on the plasma parameters. This characteristics create new diagnostic method for plasma density. More easily usage of PDO method, we shot the laser pulse obliquely. The magnetization of the PDO induces the formation of three modes in gyrating electrons: the upper hybrid (H) mode, the right circular mode (R), and the left circular mode (L). The H-mode acts as a resonance point that prevents transmission to the vacuum, whereas X-modes can be transmitted through the plasma. The H-mode diminishes as the magnetic field increases, while X-modes become more prominent. This results in more energy being extracted from the PDO in the form of radiation. This effect is demonstrated by the effective flow, where in the weak field regime, electrons are well organized, resulting in effective longitudinal flow, while in the strong field regime, electron phases are randomized, and circular flows prevail, forming X-modes instead of H-mode.clos

    Integrated Frequency Combs for Applications in Optical Communications & Microwave Photonics

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    This dissertation reviews the advancements made in chip-scale optical frequency combs and their applications towards optical communications and optical to RF links. We review different chip-scale comb sources and in particular, chip-scale Kerr microresonator frequency combs. Then, we establish the theoretical background in nonlinear optics which allows the formation and stabilization of Kerr solitons in nonlinear cavities. We also discuss the concept of optical injection locking and in particular, multi-tone injection locking which precedes the idea of regenerative harmonic injection locking. We then go on to show the experimental work involved in soliton generation and characterization. We show efforts towards developing an on-chip massive electronic-photonic optical communications link using Kerr soliton frequency combs as equidistant optical carriers in a DWDM based system using a PAM-4 data modulation format. Potential methods for pushing the limits of communication speeds are also highlighted involving the implementation of other degrees of multiplexing such as space division multiplexing and polarization multiplexing. The second application we explore is based on the synchronization of two pulsed sources via regenerative harmonic injection locking, one with a repetition rate in the microwave regime (10s of GHz) and the other in the mm wave domain (100s of GHz). The two sources we use here are an InP based mode locked laser PIC and the Kerr microresonator. Future goals are discussed which involve techniques for the improvement in long-term stability and chip-scale integrability. This proposal envisions future work to achieve high-capacity optical communication links and optical to RF links utilizing chip-scale Kerr microresonator frequency combs

    ATHENA Research Book, Volume 2

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    ATHENA European University is an association of nine higher education institutions with the mission of promoting excellence in research and innovation by enabling international cooperation. The acronym ATHENA stands for Association of Advanced Technologies in Higher Education. Partner institutions are from France, Germany, Greece, Italy, Lithuania, Portugal and Slovenia: University of OrlĂ©ans, University of Siegen, Hellenic Mediterranean University, NiccolĂČ Cusano University, Vilnius Gediminas Technical University, Polytechnic Institute of Porto and University of Maribor. In 2022, two institutions joined the alliance: the Maria Curie-SkƂodowska University from Poland and the University of Vigo from Spain. Also in 2022, an institution from Austria joined the alliance as an associate member: Carinthia University of Applied Sciences. This research book presents a selection of the research activities of ATHENA University's partners. It contains an overview of the research activities of individual members, a selection of the most important bibliographic works of members, peer-reviewed student theses, a descriptive list of ATHENA lectures and reports from individual working sections of the ATHENA project. The ATHENA Research Book provides a platform that encourages collaborative and interdisciplinary research projects by advanced and early career researchers

    Non-Thermal Optical Engineering of Strongly-Correlated Quantum Materials

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    This thesis develops multiple optical engineering mechanisms to modulate the electronic, magnetic, and optical properties of strongly-correlated quantum materials, including polar metals, transition metal trichalcogenides, and copper oxides. We established the mechanisms of Floquet engineering and magnon bath engineering, and used optical probes, especially optical nonlinearity, to study the dynamics of these quantum systems. Strongly-correlated quantum materials host complex interactions between different degrees of freedom, offering a rich phase diagram to explore both in and out of equilibrium. While static tuning methods of the phases have witnessed great success, the emerging optical engineering methods have provided a more versatile platform. For optical engineering, the key to success lies in achieving the desired tuning while suppressing other unwanted effects, such as laser heating. We used sub-gap optical driving in order to avoid electronic excitation. Therefore, we managed to directly couple to low-energy excitation, or to induce coherent light-matter interactions. In order to elucidate the exact microscopic mechanisms of the optical engineering effects, we performed photon energy-dependent measurements and thorough theoretical analysis. To experimentally access the engineered quantum states, we leveraged various probe techniques, including the symmetry-sensitive optical second harmonic generation (SHG), and performed pump-probe type experiments to study the dynamics of quantum materials. I will first introduce the background and the motivation of this thesis, with an emphasis on the principles of optical engineering within the big picture of achieving quantum material properties on demand (Chapter I). I will then continue to introduce the main probe technique used in this thesis: SHG. I will also introduce the experimental setups which we developed and where we conducted the works contained in this thesis (Chapter II). In Chapter III, I will introduce an often overlooked aspect of SHG studies -- using SHG to study short-range structural correlations. Chapter IV will contain the theoretical analysis and experimental realizations of using sub-gap and resonant optical driving to tune electronic and optical properties of MnPS₃. The main tuning mechanism used in this chapter is Floquet engineering, where light modulates material properties without being absorbed. In Chapter V, I will turn to another useful material property: magnetism. First I will describe the extension of the Floquet mechanism to the renormalization of spin exchange interaction. Then I will switch gears and describe the demagnetization in Sr₂Cu₃O₄Cl₂ by resonant coupling between photons and magnons. I will end the thesis with a brief closing remark (Chapter VI).</p

    High-efficiency dissipative Kerr solitons in microresonators

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    The microresonator comb (microcomb) is a laser source that generates equally spaced coherent lines in the spectral domain. Having a chip-scale size and the potential of being low cost, it has attracted attention in multiple applications. Demonstrations have included high-speed optical communications, light detection and ranging, calibrating spectrographs for exoplanet detection and, optical clocks. These experiments typically rely on the generation of a dissipative Kerr soliton (DKS) --- a temporal waveform that circulates the microresonator without changing shape. However, these DKS states have thus far been limited in certain technical aspects, such as energy efficiency, which are essential for realizing commercial microcomb solutions.This thesis studies the dynamics of DKSs in microresonators aiming at developing a reliable and high-performing microcomb source. The investigation will cover DKSs found both in the normal and anomalous dispersion regime of silicon nitride microresonators. The performance of microcombs in terms of line power is numerically explored in single-cavity arrangements for telecommunication purposes. DKSs generated in linearly coupled microcavities are investigated, revealing exotic dynamics and improved performance in terms of power efficiency and DKS initiation. These studies facilitate reliable energy-efficient microcombs, bringing the technology a step closer to commercial use

    Optics of Dirac Materials and Light-matter Interaction in the Nanophotonic Systems

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    In recent years condensed matter physics is witnessing a rapid expansion of materials with (massless) Dirac fermions as low-energy excitations, with examples ranging from graphene, topological insulators to Weyl semimetals (WSMs). These materials are named Dirac materials because the low-energy quasiparticles obey the Dirac equation, regardless of their origin. They have electronic and optical properties different from the conventional metals and (doped) semiconductors, which obey the nonrelativistic Schrödinger equation leading to quadratic spectra. This dissertation is focused on the optics of Dirac materials, especially graphene and WSMs. We present systematic theoretical studies of both bulk and surface electromagnetic eigenmodes, or polaritons, in WSMs in the minimal model of two bands with two separated Weyl nodes. We derive the tensors of bulk and surface conductivity, taking into account all possible combinations of the optical transitions involving bulk and surface electron states. We show how information about Weyl semimetals’ electronic structure, such as the position and separation of Weyl nodes, Fermi energy, and Fermi arc surface states, can be unambiguously extracted from measurements of the dispersion, transmission, reflection, and polarization of electromagnetic waves. We also explore the potential of popular tip-enhanced optical spectroscopy techniques for studies of bulk and surface topological electron states in WSMs. Strong anisotropy, anomalous dispersion, and the optical Hall effect for surface polaritons launched by a nanotip provide information about Weyl node position and separation in the Brillouin zone, the value of the Fermi momentum, and the matrix elements of the optical transitions involving both bulk and surface electron states. Furthermore, from the theoretical point of view, we systematically study the inverse Faraday effect in graphene and WSMs. Both semiclassical and quantum theories are presented, with dissipation and finite-size effects included. We find that the magnitude of the effect can be much stronger in Dirac materials as compared to conventional semiconductors. Analytic expressions for the optically induced magnetization in the low-temperature limit are obtained. Additionally, we study the dynamics of strongly coupled nanophotonic systems with time-variable parameters. The approximate analytic solutions are obtained for a broad class of open quantum systems, including a two-level fermion emitter strongly coupled to a multimode quantized electromagnetic field in a cavity with time-varying cavity resonances or the electron transition energy. The coupling of the fermion and photon subsystems to their dissipative reservoirs is included within the stochastic equation of evolution approach, equivalent to the Lindblad approximation in the master equation formalism. The analytic solutions for the quantum states and the observables are obtained under the approximation that the rate of parameter modulation and the amplitude of the frequency modulation are much smaller than the optical transition frequencies. At the same time, they can be arbitrary with respect to the generalized Rabi oscillation frequency, which determines the coherent dynamics. Therefore, our analytic theory can be applied to an arbitrary modulation of the parameters, both slower and faster than the Rabi frequency, for complete control of the quantum state. In particular, we demonstrate protocols for switching on and off the entanglement between the fermionic and photonic degrees of freedom, swapping between the quantum states, and decoupling the fermionic qubit from the cavity field due to modulation induced transparency

    High-power few-cycle pulse generation towards the gigawatt frontier

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    The advent of precision spectroscopic techniques has brought about diverse opportunities in extending our understanding of fundamental physics and bio-medical sciences. This is especially true when harnessing radiation in the exotic extreme ultra-violet (XUV) and mid-infrared (IR) regions of the electromagnetic spectrum. While the former covers a multitude of atomic and molecular electronic transitions, the latter contains fundamental vibrational and rotational modes of numerous biologically-relevant molecules. Regardless of spectral range, many of the novel spectroscopic methodologies rely on the availability of broadband, waveform-controlled radiation with high brightness. The lack of suitable laser gain media in the aforementioned wavelength ranges means such radiation is conventionally generated by nonlinearly converting high-power, femtosecond laser pulses in the near-IR spectral range, such as those generated by thin-disk oscillators. However, those pulses generally have durations in the hundreds of femtoseconds — too long for the desired high peak-power and broad spectral coverage for effective nonlinear frequency conversion. Their electric waveform also varies randomly from pulse to pulse, hindering their applications to, among others, frequency-comb spectroscopy. This thesis describes the experimental development of various techniques to further compress the pulse duration, and the active stabilization of the output waveform in high-power thin-disk oscillators. It is shown that dispersion-controlled Herriott-type multipass-cells constitute an efficient means to broaden the spectral bandwidth of laser pulses with, in contrast to many other techniques, practically no degradation to the spatial beam quality. It presents the first time Herriott-cells operating in the net-negative dispersion regime have been used for spectral broadening with thin-disk oscillators. The demonstration yielded the highest broadening factor obtained from any multipass-cell broadening scheme using a single nonlinear bulk medium. Spectral broadening in the positive dispersion regime is also described. Two Herriott-cells in tandem facilitated the generation of 15.6 fs pulses with an unprecedented peak power of 463 MW — a record for a system driven directly by a laser oscillator with no amplification stages. Further compression of this dual-stage output was achieved by introducing the distributed quasi-waveguide approach. This technique enables the independent tailoring of nonlinearity and dispersion, which is essential for pulse compression towards few-optical-cycle durations. With a pulse duration of 10.8 fs and a peak and average power of 0.64 GW and 101 W, respectively, this marks the dawn of a new class of gigawatt-scale amplifier-free thin-disk laser system. The few-cycle laser pulses are shown to drive, via intra-pulse difference-frequency generation, the formation of broadband, waveform-stable mid-IR radiation with an exceptionally short cut-off wavelength. The achieved spectral extension down to 3.6 ”m (at -30 dB level), at an average output power of 7.6 mW, opens up new perspectives for extending field-resolved spectroscopy to the biologically important amide functional groups. To actively stabilize the near-IR driver laser waveform — crucial for deriving from it a frequency comb in the XUV region — a novel, power-scalable concept for controlling the carrier-envelope-offset (CEO) frequency of Kerr-lens mode-locked oscillators was developed. It yielded CEO-frequency-stable pulses with sub-90 mrad in-loop phase noise at an unprecedented average output power of 105 W. The envisioned combination of waveform control with the presented nonlinear pulse compression techniques will pave the way for a new generation of compact, low-noise frequency combs with high photon-flux in the XUV spectral range. The various advancements presented in this thesis not only mark a substantial development of the respective techniques themselves, but also represent a significant contribution to the coming-of-age of high-precision laser-based spectrometers for scientific and medical applications.Das Aufkommen hochprĂ€ziser Spektroskopiemethoden, insbesondere im extremen Ultraviolett (XUV) und im mittleren Infrarot, hat eine Vielzahl von Möglichkeiten eröffnet, unser VerstĂ€ndnis physikalischer und biomedizinischer ZusammenhĂ€nge grundlegend zu erweitern. Dabei deckt der XUV-Bereich eine große Anzahl elektronischer ÜbergĂ€nge in Atomen und MolekĂŒlen ab, wĂ€hrend das mittlere Infrarot zahlreiche fundamentale Schwingungs- und Rotationsmoden verschiedenster biologisch relevanter MolekĂŒle enthĂ€lt. UnabhĂ€ngig vom Spektralbereich sind viele dieser neuartigen Spektroskopieverfahren gleichermaßen auf die VerfĂŒgbarkeit von breitbandiger Strahlung mit einem kontrollierten Feldverlauf und einer hohen Brillanz angewiesen. Da es in den oben genannten WellenlĂ€ngenbereichen keine geeigneten LaserverstĂ€rkungsmedien gibt, wird derartige Strahlung ĂŒblicherweise durch die nichtlineare Frequenzkonversion von hochintensiven Femtosekunden-Laserimpulsen im Spektralbereich des nahen Infrarot erzeugt, wie sie beispielsweise von DĂŒnnscheibenoszillatoren generiert werden. Diese Impulse haben jedoch im Allgemeinen eine Dauer von Hunderten von Femtosekunden — zu lang, um die gewĂŒnschte hohe Spitzenleistung und breite spektrale Abdeckung fĂŒr eine effektive nichtlineare Frequenzumwandlung bereitstellen zu können. Außerdem variiert ihre elektrische Wellenform von Impuls zu Impuls nach dem Zufallsprinzip, was ihre Anwendung fĂŒr beispielsweise die Frequenzkammspektroskopie behindert. Diese Arbeit beschreibt experimentelle Entwicklungen von Methoden zur weiteren Komprimierung der Impulsdauer sowie zur aktiven Stabilisierung des elektrischen Feldverlaufs von hochintensiven DĂŒnnscheibenoszillatoren. Es wird gezeigt, dass dispersionskontrollierte Herriott-Multipasszellen ein effizientes Mittel zur Erweiterung der spektralen Bandbreite von Laserpulsen darstellen, wobei im Gegensatz zu vielen anderen Techniken nahezu keine Verschlechterung der rĂ€umlichen StrahlqualitĂ€t auftritt. Erstmalig wurde die durch einen DĂŒnnscheibenlaser getriebene spektrale Verbreiterung in einer Herriott-Zelle im negativen Dispersionsregime durchgefĂŒhrt. Die spektrale Verbreiterung erreichte dabei höhere Verbreiterungsfaktoren, als sie jemals zuvor mit einem auf Multipass-Zellen basierenden Verbreiterungsschema mit einem einzigen nichtlinearen Medium erzielt wurden. DarĂŒber hinaus wurde auch die spektrale Verbreiterung im positiven Dispersionsregime untersucht. Das Hintereinanderschalten zweier Herriott-Zellen ermöglichte die Erzeugung von 15.6 fs kurzen Impulsen mit einer zuvor unerreichten Spitzenleistung von 463 MW — ein Rekord fĂŒr ein System, das ohne weitere VerstĂ€rkerstufen direkt von einem Laseroszillator getrieben wird. Die weitere zeitliche Kompression am Ausgang dieses zweistufigen Systems wurde mit dem Ansatz eines verteilten Quasi-Wellenleiters gelöst. Diese Technik ermöglicht die unabhĂ€ngige Anpassung von NichtlinearitĂ€t und Dispersion, was fĂŒr die Impulskompression in Richtung einer Dauer von wenigen optischen Zyklen unerlĂ€sslich ist. Mit einer Impulsdauer von lediglich 10.8 fs bei einer Spitzen- und Durchschnittsleistung von 0.64 GW und 101 W markieren die erzeugten Laserimpulse den Beginn einer neuen Ära von verstĂ€rkerfreien DĂŒnnscheibenlasersystemen im Gigawattbereich. Des Weiteren wurden die beschriebenen Laserimpulse dafĂŒr genutzt, um mittels Differenzfrequenzerzeugung breitbandige und phasenstarre Strahlung im mittleren Infrarot zu erzeugen. Letztere zeichnet sich insbesondere durch ihre außergewöhnlich niedrige GrenzwellenlĂ€nge aus. Die erreichte spektrale Ausdehnung auf 3.6 ”m (auf - 30 dB-Niveau) mit einer mittleren Ausgangsleistung von 7.6 mW eröffnet neue Perspektiven fĂŒr die feldaufgelöste Spektroskopie von biologisch relevanten funktionellen Amidgruppen. Um die Wellenform des nahinfraroten Lasers aktiv zu stabilisieren — unabdingbar fĂŒr die Ableitung eines Frequenzkamms im XUV-Spektralbereich — wurde ein neuartiges und leistungsskalierbares Konzept entwickelt. Dieses erlaubt, die TrĂ€ger-EinhĂŒllenden-Frequenz von Kerr-Linsen-modengekoppelten Oszillatoren zu kontrollieren und zu stabilisieren. Das dabei erreichte Phasenrauschen lĂ€sst sich auf weniger als 90 mrad bei einer beispiellosen Durchschnittsleistung von 105 W beziffern. Die mögliche Kombination einer Feldverlaufstabilisierung mit den zuvor vorgestellten nichtlinearen Pulskompressionstechniken ebnet den Weg fĂŒr die Entwicklung einer neuen Generation kompakter oszillatorbasierter FrequenzkĂ€mme mit hohem Photonenfluss im XUV-Spektralbereich. Die zahlreichen in dieser Dissertation vorgestellten Entwicklungen beschrĂ€nken sich nicht nur auf einen Fortschritt der jeweiligen Techniken selbst, sondern liefern auch einen wichtigen Beitrag fĂŒr die zukĂŒnftige Entwicklung hochprĂ€ziser laserbasierter Spektrometer fĂŒr wissenschaftliche und medizinische Anwendungen

    Kerr-Nonlinear Microresonators and Frequency Combs: Modelling, Design, and Applications

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