Download or read book Investigation of Carrier Dynamics and Nonlinear Effects in Quantum Cascade Lasers Using Femtosecond Mid IR Pulses written by Sheng Liu and published by . This book was released on 2011 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ultrafast Mid Infrared Dynamics in Quantum Cascade Lasers written by and published by . This book was released on 2010 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report summarizes the entire research period. In this program, we performed experiments using a femtosecond mid-infrared pump-probe system implemented for QCL samples operating at 4.6 and 5.3 m. We employed femtosecond time-resolved pump-probe measurements to probe the nature of the transport through the laser structure via the dynamics of the gain. The gain recovery was determined by the time-dependent transport of electrons through the cascade heterostructure; as the laser approaches and exceeds threshold, the gain recovery shows a dramatic reduction due to the onset of quantum stimulated emission. Since the electron transport through each state in the cascade is determined by the state lifetime, the transport in a cascade laser is driven by the photon density in the cavity. The gain recovery is qualitatively different from that in conventional atomic, molecular and interband semiconductor lasers due to the superlattice transport in the cascade. We also studied the effects of pulse propagation in the laser, including group velocity dispersion and coherent pulse reshaping due to ultrafast Rabi flopping of the gain medium.

Download or read book Nonlinear Photonics in Mid infrared Quantum Cascade Lasers written by Louise Jumpertz and published by Springer. This book was released on 2017-08-31 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents the first comprehensive analysis of quantum cascade laser nonlinear dynamics and includes the first observation of a temporal chaotic behavior in quantum cascade lasers. It also provides the first analysis of optical instabilities in the mid-infrared range. Mid-infrared quantum cascade lasers are unipolar semiconductor lasers, which have become widely used in applications such as gas spectroscopy, free-space communications or optical countermeasures. Applying external perturbations such as optical feedback or optical injection leads to a strong modification of the quantum cascade laser properties. Optical feedback impacts the static properties of mid-infrared Fabry–Perot and distributed feedback quantum cascade lasers, inducing power increase; threshold reduction; modification of the optical spectrum, which can become either single- or multimode; and enhanced beam quality in broad-area transverse multimode lasers. It also leads to a different dynamical behavior, and a quantum cascade laser subject to optical feedback can oscillate periodically or even become chaotic. A quantum cascade laser under external control could therefore be a source with enhanced properties for the usual mid-infrared applications, but could also address new applications such as tunable photonic oscillators, extreme events generators, chaotic Light Detection and Ranging (LIDAR), chaos-based secured communications or unpredictable countermeasures.

Download or read book Optical Measurement on Quantum Cascade Lasers Using Femtosecond Pulses written by Hong Cai and published by . This book was released on 2014 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum cascade lasers (QCLs) as the state-of-the-art mid-infrared (mid-IR) coherent sources have been greatly developed in aspects such as output power, energy efficiency and spectral purity. However, there are additional applications of QCLs in high demand, namely mode-locking, mid-IR modulation, etc. The inherent optical properties and ultrafast carrier dynamics can lead to solutions to these challenges. In this dissertation, we further characterize QCLs using mid-IR femtosecond (fs) pulses generated from a laser system consisting of a Ti:sapphire oscillator, a Ti:sapphire regenerative amplifier, an optical parametric amplifier and a difference frequency generator.

Download or read book Mid infrared Quantum Cascade Lasers for Chaos Secure Communications written by Olivier Spitz and published by Springer Nature. This book was released on 2021-05-15 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: The mid-infrared domain is a promising optical domain because it holds two transparency atmospheric windows, as well as the fingerprint of many chemical compounds. Quantum cascade lasers (QCLs) are one of the available sources in this domain and have already been proven useful for spectroscopic applications and free-space communications. This thesis demonstrates how to implement a private free-space communication relying on mid-infrared optical chaos and this requires an accurate cartography of non-linear phenomena in quantum cascade lasers. This private transmission is made possible by the chaos synchronization of two twin QCLs. Chaos in QCLs can be generated under optical injection or external optical feedback. Depending on the parameters of the optical feedback, QCLs can exhibit several non-linear phenomena in addition to chaos. Similarities exist between QCLs and laser diodes when the chaotic dropouts are synchronized with an external modulation, and this effect is known as the entrainment phenomenon. With a cross-polarization reinjection technique, QCLs can generate all-optical square-waves. Eventually, it is possible to trigger optical extreme events in QCLs with tilted optical feedback. All these experimental results allow a better understanding of the non-linear dynamics of QCLs and will extend the potential applications of this kind of semiconductor lasers.

Download or read book Dispersion Dynamics of Quantum Cascade Lasers written by and published by . This book was released on 2016 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: A key parameter underlying the efficacy of any nonlinear optical process is group velocity dispersion. In quantum cascade lasers (QCLs), there have been several recent demonstrations of devices exploiting nonlinearities in both the mid-infrared and the terahertz. Though the gain of QCLs has been well studied, the dispersion has been much less investigated, and several questions remain about its dynamics and precise origin. In this work, we use time-domain spectroscopy to investigate the dispersion of broadband terahertz QCLs, and demonstrate that contributions from both the material and the intersubband transitions are relevant. We show that in contrast to the laser gain--which is clamped to a fixed value above lasing threshold--the dispersion changes with bias even above threshold, which is a consequence of shifting intersubband populations. In conclusion, we also examine the role of higher-order dispersion in QCLs and discuss the ramifications of our result for devices utilizing nonlinear effects, such as frequency combs.

Download or read book Third Generation Femtosecond Technology written by Hanieh Fattahi and published by Springer. This book was released on 2016-08-23 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis offers a thorough and informative study of high-power, high-energy optical parametric chirped pulse amplifications systems, the foundation of the next generation of femtosecond laser technology. Starting from the basics of the linear processes involved and the essential design considerations, the author clearly and systematically describes the various prerequisites of the nonlinear optical systems expected to drive attosecond physics in the coming decade. In this context, he gives an overview of methods for generating the broadband and carrier-envelope-phase stable seed pulses necessary for producing controlled electric-field waveforms in the final system; provides a guide to handling the high-power, high-energy pump lasers required to boost the pulse energy to the desired operating range; describes the design of the nonlinear optical system used to perform the amplification, including modes of operation for ultra-broadband infrared-visible pulses or narrowband (yet still ultrafast) pulses tunable over multiple octaves; and finally presents a prospective high-energy field synthesizer based upon these techniques. As such, this work is essential reading for all scientists interested in utilizing the newest generation of ultrafast systems.

Download or read book Femtosecond Laser Filamentation written by See Leang Chin and published by Springer Science & Business Media. This book was released on 2010-03-10 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book attempts to give a discussion of the physics and current and potential applications of the self-focusing of an intense femtosecond laser pulse in a tra- parent medium. Although self-focusing is an old subject of nonlinear optics, the consequence of self-focusing of intense femtosecond laser pulses is totally new and unexpected. Thus, new phenomena are observed, such as long range lam- tation, intensity clamping, white light laser pulse, self-spatial ltering, self-group phase locking, self-pulse compression, clean nonlinear uorescence, and so on. Long range propagation at high intensity, which is seemingly against the law of diffraction, is probably one of the most exciting consequences of this new sub- eld of nonlinear optics. Because the intensity inside the lament core is high, new ways of doing nonlinear optics inside the lament become possible. We call this lamentation nonlinear optics. We shall describe the generation of pulses at other wavelengths in the visible and ultraviolet (UV) starting from the near infrared pump pulse at 800 nm through four-wave-mixing and third harmonic generation, all in gases. Remotely sensing uorescence from the fragments of chemical and biological agents in all forms, gaseous, aerosol or solid, inside the laments in air is demonstrated in the labo- tory. The results will be shown in the last part of the book. Through analyzing the uorescence of gas molecules inside the lament, an unexpected physical process pertaining to the interaction of synchrotron radiation with molecules is observed.

Download or read book Optimization of Optical Nonlinearities in Quantum Cascade Lasers written by Jing Bai and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nonlinearities in quantum cascade lasers (QCL's) have wide applications in wavelength tunability and ultra-short pulse generation. In this thesis, optical nonlinearities in InGaAs/AlInAs-based mid-infrared (MIR) QCL's with quadruple resonant levels are investigated. Design optimization for the second-harmonic generation (SHG) of the device is presented. Performance characteristics associated with the third-order nonlinearities are also analyzed. The design optimization for SHG efficiency is obtained utilizing techniques from supersymmetric quantum mechanics (SUSYQM) with both material-dependent effective mass and band nonparabolicity. Current flow and power output of the structure are analyzed by self-consistently solving rate equations for the carriers and photons. Nonunity pumping efficiency from one period of the QCL to the next is taken into account by including all relevant electron-electron (e-e) and longitudinal (LO) phonon scattering mechanisms between the injector/collector and active regions. Two-photon absorption processes are analyzed for the resonant cascading triple levels designed for enhancing SHG. Both sequential and simultaneous two-photon absorption processes are included in the rate-equation model. The current output characteristics for both the original and optimized structures are analyzed and compared. Stronger resonant tunneling in the optimized structure is manifested by enhanced negative differential resistance. Current-dependent linear optical output power is derived based on the steady-state photon populations in the active region. The second-harmonic (SH) power is derived from the Maxwell equations with the phase mismatch included. Due to stronger coupling between lasing levels, the optimized structure has both higher linear and nonlinear output powers. Phase mismatch effects are significant for both structures leading to a substantial reduction of the linear-to-nonlinear conversion efficiency. The optimized structure can be fabricated through digitally grading the submonolayer alloys by molecular beam epitaxy (MBE).

Download or read book Carrier Dynamics in Mid Infrared Quantum Well Lasers Using Time Resolved Photoluminescence written by Steven M. Gorski and published by . This book was released on 2002-03-01 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research in mid-infrared laser technology has uncovered numerous applications for commercial and government use. A limiting factor for mid- infrared semiconductors is nonradiative recombination, which is a process that produces excess heat without emitting a photon. Nonradiative recombination mechanisms occur over a short time period and difficult to measure. Growth methods have significantly reduced the nonradiative recombination in some materials. The objective of this research is to further the understanding of how quantum well structures impact carrier recombination. InAsSb/InAlASb and InAs/ GaInSb quantum well structures were studied with time-resolved photoluminescence utilizing upconversion, a non-linear wave mixing technique. This research reports Shockley-Read-Hall, radiative, and Auger recombination coefficients at 77k. The luminescence rise times of type I and type II structures are also compared. The number of states available within the quantum well was found to dictate how quickly carriers were able to recombine radiatively. Finally, spectral data was taken to examine the spectral decay of the luminescence. Carrier temperatures were extracted from the spectral data. Type I structures were found to have hotter carrier temperatures and higher Auger coefficients than type II structures.

Download or read book Nonlinear Effects in Quantum Cascade Lasers written by Johannes Gambari and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2692 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Quantum Radiation in Ultra Intense Laser Pulses written by K. Felix Mackenroth and published by Springer. This book was released on 2014-06-11 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: Scientific advances and several technical breakthroughs have led to a remarkable increase in available laser intensities over the past decades. In available ultra-intense laser fields, photon fluxes may become so high that free charge carriers interact coherently with several of the field's photons. In this thesis such nonlinear interactions are investigated for the prime example of radiation emission by electrons scattered from intense laser pulses of arbitrary temporal structure. To this end, nonlinear quantum field theory is employed taking the interaction with the laser into account exactly. After an in-depth introduction to classical particle dynamics as well as quantum field theory in nonlinearly intense laser fields the emission of one and two photons is explicitly analyzed. The results are then translated to viable technical applications, such as a scheme for the determination of the carrier-envelope phase of ultra-intense laser pulses and a proposal for detecting the strongly suppressed two-photon signal.

Download or read book Quantum Cascade Lasers Based on Intra cavity Frequency Mixing written by Min Jang and published by . This book was released on 2012 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum cascade lasers (QCLs) operate due to population inversion on intersubband in unipolar mutiple-quantum-well (MQW) heterostructure. QCLs are considered one of the most flexible and powerful light semiconductor sources in the mid- and far-infrared (IR) wavelength range, covering most of the critical spectral regions relevant to IR applications. InGaAs/InAlAs/InP QCLs are the only semiconductor lasers capable of continuous wave (CW) operation at room temperature (RT) in the spectral range 3.4-12 micron. This dissertation details the development of RT QCLs based on passive nonlinear coupled-quantum-well structures monolithically integrated into mid-IR QCLs to provide a giant nonlinear response for the pumping frequency. The primary focus of short-wavelength approach in this dissertation is to develop of RT InGaAs/InAlAs/InP QCLs for lamda=2.5-3.7 micron region, based on quasi-phase-matched intracavity second harmonic generation (SHG) associated with intersubband transition. Intersubband optical transition can be engineered by the choice of quantum well and barrier thicknesses to provide the appropriate energy levels, optical dipole matrix elements, and electron scattering rates amongst other parameters. Thus, aside from their linear optical properties, resonant intersubband transitions in coupled QW's can also be designed to produce nonlinear optical medium with giant nonlinear optical susceptibilities. In long-wavelength region, at high temperature, the population inversion is reduced between the upper and lower laser levels due to the longitudinal optical (LO) phonon scattering of thermal carriers in the upper laser state and the thermal backfilling of carriers into the lower laser level from the injector state. This dissertation aims to improve an alternative approach for THz QCL sources based on intra-cavity difference frequency generation (DFG) in dual-wavelength mid-IR QCLs with a passive nonlinear structure, designed for giant optical nonlinearity. Further studies describe that Cerenkov DFG scheme allows for extraction of THz radiation along the whole length of the laser waveguide and provides directional THz emission in 1.2-4.5 THz range. An important requirement for many applications, like chemical sensing and molecular spectroscopy, is single-mode emission. We demonstrate single-mode RT DFG THz QCLs operation in 1-5 THz region by employing devices as integrated dual-period DFB lasers, where efficient solid state RT sources do not exist.

Download or read book Index to Theses with Abstracts Accepted for Higher Degrees by the Universities of Great Britain and Ireland and the Council for National Academic Awards written by and published by . This book was released on 2006 with total page 678 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mid Infrared and Terahertz Quantum Cascade Lasers written by Dan Botez and published by Cambridge University Press. This book was released on 2023-09-14 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt: Learn how the rapidly expanding area of mid-infrared and terahertz photonics has been revolutionized in this comprehensive overview. State-of-the-art practical applications are supported by real-life examples and expert guidance. Also featuring fundamental theory enabling you to improve performance of both existing and future devices.

Download or read book Harmonic States in Quantum Cascade Lasers written by Mithun Roy and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum cascade lasers (QCLs) are unipolar lasers where lasing transition and carrier transport occur between subbands that result from multiple nanometer-thick quantum wells and barriers formed by the conduction band edges of a semiconductor heterostructure. Since their inception in 1994, QCLs have undergone tremendous improvements with respect to output power, frequency range covered, and maximum operating temperature. As a result, they have become a prominent source of light emitting in the mid- and far-infrared regions of the electromagnetic spectrum. Multimode behavior of QCLs was a focus of many past works. In a recent comprehensive study, it was found that, if the pumping is increased gradually from threshold, QCLs enter into a harmonic state regime, which is characterized by the lasing of side modes that are separated from each other by multiples of free spectral range (FSR). With a further increase in the pumping, finally, transition into the familiar single-FSR-spaced regime (dense state regime) occurs. Unlike the dense state regime, the harmonic state regime of QCLs has not gone through intense scrutiny, as it is a relatively recent discovery. In this thesis, a theoretical investigation into the harmonic state regime of QCLs is performed. The work is based on Maxwell's equation and the density matrix (DM) formalism. The two-level DM equations, although commonly employed, ignore many important details of complex carrier transport through a QCL structure. Therefore, here, a three-level DM formalism is employed, which takes into account phenomena such as resonant tunneling and carrier scattering between the three states. The thesis is mainly divided into two parts. In the first part, starting from the DM-Maxwell equations, an analytical expression for the instability gain of the side modes is derived. This expression can explain the appearance of harmonic states in QCLs. Using this analytical expression, the effects of group velocity dispersion on the harmonic states are studied. In the second part, multimode behavior of QCLs is analyzed using a more general model than that used in the first part. In particular, openness (non-unity facet reflectivity) of the cavity is considered, which was not taken into account in previous works that used the modal expansion method to study QCLs. Using the theory, it is shown that the coating of a facet can be used to excite harmonic states with different mode spacing. Such a control over the generation of harmonic states could make QCLs invaluable for applications such as microwave and terahertz generation, picosecond pulse generation in the mid-infrared frequency range, and broadband spectroscopy.