Literatura académica sobre el tema "Lasers à Cascade Interbande"

Les lasers à cascade interbandes (ICL) fournissent des sources pour la gamme spectrale du moyen infrarouge compris entre 3 et 6 µm particulièrement efficaces en termes de consommation d’énergie. Cette gamme spectrale est particulièrement intéressante pour la détection des gaz impliqués dans l’industrie pétrochimique, car des gaz tels que le méthane, l'éthane et le dioxyde de carbone présentent une forte absorption dans cette gamme de longueur d’onde. L'identification correcte d'un gaz présent dans un échantillon nécessite des lasers avec une émission monomode et une certaine accordabilité en longueur d’onde. L'amélioration de cette plage de réglage possible avec une source laser offre de nouvelles opportunités dans des applications liées à la spectroscopie. Une alternative à ce qui est actuellement disponible dans le commerce peut être réalisée grâce à l'utilisation de guides d'ondes à fente, qui peuvent être fabriqués en utilisant de la photolithographie conventionnelle, réduisant ainsi le coût de fabrication.Deux nouveaux types d'ICL ont été conçus, fabriqués, et étudiés dans le cadre de cette thèse : un ICL à fentes à section unique et un ICL à fentes multiples accordé par Vernier (SVT). Une étude approfondie des étapes de fabrication et en particulier de la gravure sèche a été réalisée pour obtenir une gravure verticale des matériaux constituants les ICLs. Les premiers ICLs à fentes ont été fabriqués démontrant un e une émission monomode en régime continu à température ambiante avec une émission proche de 3.4 µm. Sur cette base, l'ICL SVT a été fabriqué pour étendre la plage d'accord et démontrer que l'accord par effet Vernier pouvait être mis en œuvre sur ce système de matériaux<br>Interband cascade lasers (ICLs) provide sources for the mid-infrared spectral range between 3 – 6 µm with low power consumption and efficient performance. This spectral range is of particular interest to the detection of gases involved with petrochemical processing, such as methane, ethane, and carbon dioxide due to their strong absorption in this range. Correct identification of a gas present in a sample requires single-mode emission and some tuning to match the absorption line, depending on the environmental conditions. Increasing the tuning range possible with one laser source opens up new possibilities in spectroscopic applications. An economical design alternative to what is currently commercially available can be realized through the use of slotted waveguides, which can be fabricated using photolithography, reducing the cost of fabrication.Two new types of ICLs have been designed, fabricated, and studied in this thesis: a single-section slotted ICL and a multi-section slotted Vernier tuned (SVT) ICL. An extensive study of the fabrication step and in particular dry etching was carried out to achieve vertical etching of the materials constituting the ICLs. First, the slotted ICLs were fabricated demonstrating single-mode emission in continuous wave operation at room temperature with emission close to 3.4 µm. Building from this foundation, the SVT ICL was fabricated to extend the tuning range and demonstrate that Vernier tuning could be implemented on this material system

The extension of Multi-mode Absorption Spectroscopy (MUMAS) to the infra-red spectral region for multi-species gas sensing is reported. A computationally efficient, theoretical model for analysis of MUMAS spectra is presented that avoids approximations used in previous work and treats arbitrary and time-dependent spectral intensity envelopes, thus facilitating the use of commercially available Interband Cascade Lasers (ICLs) and Quantum Cascade Lasers (QCLs). The first use of an ICL for MUMAS is reported using a multi-mode device operating at 3.7 &mu;m to detect CH₄ transitions over a range of 30 nm. Mode-linewidths are measured using the pressure-dependent widths of an isolated absorption feature in HCl. Multi- species sensing is demonstrated by measurement of partial pressures of CH₄, C₂H₂ and H₂CO in a low-pressure mixture with uncertainties of around 10&percnt;. Detection of CH₄ in N₂ at 1 bar is demonstrated using a shorter-cavity ICL to resolve spectral features in pressure-broadened and congested spectra. The first use of a QCL for MUMAS is reported using a commercially available device operating at 5.3 &mu;m to detect multiple absorption transitions of NO at a partial pressure of 2.79 &mu;bar in N₂ buffer gas. The revised model is shown to enable good fits to MUMAS data by accounting for the time-variation of the spectral intensity profile during frequency scanning. Individual mode-linewidths are derived from fits to pressure- dependent MUMAS spectra and features from background interferences due to H₂O in laboratory air are distinguished from those of the target species, NO. Data obtained at scan rates up to 10 kHz demonstrate the potential for achieving short measurement times. The development of a balanced ratiometric detection scheme for MUMAS with commercially available multi-mode lasers operating at 1.5 &mu;m is reported for simultaneous detection of CO and CO₂ showing improved SNR performance over previous direct transmission methods and suitability for a compact field-employable instrument. In addition, MUMAS spectra of CO₂ are used to derive gas temperatures with an uncertainty of 3.2&percnt; in the range 300 - 700 K.

Les peignes de fréquence optique (OFC) sont des sources de lumière cohérente qui émettent un large spectre de modes discrets parfaitement espacés, chacun avec une fréquence absolue mesurable avec la précision d'une horloge atomique.Les OFC dans l'infrarouge moyen (MIR 3-12 μm) sont récemment devenus d'un grand intérêt pour la spectroscopie moléculaire par la présence de forte absorption des modes de vibration et de rotation moléculaires dans la région des "empreintes digitales" spectroscopiques. Néanmoins, le fonctionnement de l'OFC dans la région cruciale de l'infrarouge moyen (MWIR 3-6 μm) reste nettement sous-développé par rapport aux autres parties du MIR.Dans ce travail, nous présentons une étude expérimentale approfondie d'une nouvelle génération de laser à cascade interbande (ICL) et de leur potentiel pour les OFC dans MWIR. La thèse apporte la preuve du régime OFC à la fois par spectroscopie des battements (BN) à haute fréquence, et par la nouvelle technique de reconstruction temporelle de la dynamique ultrarapide de ces lasers, celle-ci permettant de "visualiser" le contrôle du type de fonctionnement de l'OFC dans les ICL. En particulier, a été effectuer la caractérisation opto-électrique d'un ensemble d'ICL avec une gamme de géométries, dans le but d'étudier les ICL à faible dispersion de retard de groupe (GDD) à des longueurs d'onde plus longues que celles étudiées auparavant: un ICL fonctionnant à 3.8 μm avec une architecture en 2-sections, des ICL fonctionnant à 4.1 μm, et une autre génération d'ICL fonctionnant à une longueur d'onde de 4.2 μm conçue avec un gain spectral large. La formation du régime OFC et le GDD sont liées et importantes pour comprendre les mécanismes fondamentaux de la formation de l'OFC. Les ICL ont été étudiés à l'aide de la spectroscopie BN optique et électrique. Les verrouillages de mode passif (PML) (ou fonctionnement libre) et actif (AML) ont été démontrés. Pour les ICL à 2-sections, où l'ICL est divisé en une partie longue et une partie courte pour une seule cavité, l'effet exact de la petite section sur le BN a été explicité: permets de (a) contrôler très finement le GDD intracavité, (b) introduire des pertes et montrant que l'on converge vers un comportement PML. Ce travail étend l'étude au cas des ICL fonctionnant à des longueurs d'onde plus longues dans une cavité à section unique et où le GDD est censé être inférieur.Pour un ICL à 4.1 μm, il est montré qu'un BN optique puissant peut être verrouillé par injection radiofréquence (RF) à la fréquence d'un aller-retour de l'ICL, premières étapes de AML. Ce verrouillage par injection a été réalisé à l'aide d'une architecture laser à 1-section avec une très faible GDD montrant ainsi que l'adaptation du guide d'onde ICL au fonctionnement RF n'est pas une exigence fondamentale.Dans sa dernière partie, la thèse montre la mise en œuvre de la technique "Shifted Wave Interference Fourier Transform Spectroscopy" (SWIFTS), utilisée selon deux configurations différentes, pour reconstruire le profil d'intensité temporel du laser à des échelles de temps ultrarapides. Cela démontre la nature des OFC générés dans ces ICL. L'ICL fonctionne en régime de modulation de fréquence (FM) lorsqu'il est en fonctionnement libre et transite vers un régime de modulation d'amplitude (AM) lorsqu'il est en régime AML en par injection RF. L'étude montre également que les ICL peuvent générer des impulsions courtes de ∼6.7 ps en fonctionnement libre, malgré leur caractère FM, et met en évidence le contrôle de la largeur d'impulsion et de l'intensité maximale via l'injection RF. Cela permet de compresser d'un facteur de 2.3 les impulsions libres pour obtenir des impulsions inférieures à 3 ps.Ces travaux constituent une étape importante dans la réalisation et le contrôle des OFC dans la région MWIR. Les perspectives sont d'élargir la bande passante spectrale des ICL et de générer des impulsions ultracourtes de haute puissance dans le MWIR et au-delà<br>Optical frequency combs (OFCs) are coherent light sources that emit a broad spectrum of discrete, perfectly spaced modes, each with an absolute frequency measurable with the precision of an atomic clock.OFCs in the mid-infrared (MIR 3-12 μm) have recently become of great interest to molecular spectroscopy by the presence of strong absorption of molecular vibration and rotation modes in the spectroscopic "fingerprint" region. Nevertheless, the operation of the OFC in the crucial mid-infrared region (MWIR 3-6 μm) remains significantly underdeveloped compared to other parts of the MIR.In this work, we present an in-depth experimental study of a new generation of interband cascade laser (ICL) and their potential for OFCs in MWIR. The thesis provides proof of the OFC regime both by high-frequency beatnote spectroscopy (BN), and by the new technique of temporal reconstruction of the ultrafast dynamics of these lasers, this making it possible to "visualize" the control of the type of operation of the OFC in ICL. In particular, was carried out the optoelectrical characterization of a set of ICLs with a range of geometries, with the aim of studying low group delay dispersion (GDD) ICLs at longer wavelengths than those previously studied: an ICL operating at 3.8 μm with a 2-section architecture, ICLs operating at 4.1 μm, and another generation of ICL operating at a wavelength of 4.2 μm designed with a wide spectral gain. OFC regime formation and GDD are linked and important for understanding the fundamental mechanisms of OFC formation. ICLs were studied using optical and electrical BN spectroscopy. Passive mode locking (PML) (or free running) and active mode locking (AML) were demonstrated. For 2-section ICLs, where the ICL is divided into a long part and a short part for a single cavity, the exact effect of the small section on the BN has been explained: allows to (a) control very finely the intracavity GDD, (b) introducing losses and showing that we converge towards PML behavior.This work then feeds into the case of ICLs operating at longer wavelengths in a single section cavity and where the GDD is expected to be less. In the particular case of the ICLs operating at 4.1 μm, we demonstrate a strong optical BN, which can be injection locked by radio frequency (RF) injection at the round trip frequency of the ICL, showing the first-steps of active modelocking. This injection locking was achieved using a simple single-section laser architecture with very low waveguide dispersion, and showing that adapting the ICL waveguide for RF operation is not a fundamental requirement. In the final part of the thesis, we show the implementation of the "Shifted Wave Interference Fourier Transform Spectroscopy" (SWIFTS) technique, used in two different configurations, to reconstruct the laser's temporal intensity profile at ultrafast timescales. This permits to demonstrate the nature of OFC generated in these ICLs. Indeed, we show that the ICL operates in the frequency modulation (FM) regime when free-running and transits towards an amplitude modulation (AM) regime when actively modelocked. Interestingly, we also show that ICLs can generate short pulses of ~6.7 ps in free-running operation, despite FM operation, and highlight the control of the pulse width and peak intensity via RF injection. This permits to compress the free-running pulses by a factor of 2.3 to obtain sub-3 ps pulses.This work constitutes an important step in the creation and control of OFCs in the MWIR region. The prospects are to broaden the spectral bandwidth of ICLs and generate high-power ultrashort pulses in the MWIR and beyond

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.<br>Includes bibliographical references.<br>This thesis addresses issues of the design and modeling of the Bipolar Cascade Laser (BCL), a new type of quantum well laser. BCLs consist of multiple single stage lasers electrically coupled via tunnel junctions. The BCL ideally operates by having each injected electron participate in a recombination event in the topmost active region, then tunnel from the valence band of the first active region into the conduction band of the next active region, participate in another recombination event, and so on through each stage of the cascade. As each electron may produce more than one photon the quantum efficiency of the device can, in theory, exceed 100%. This work resulted in the first room temperature, continuous-wave operation of a BCL, with a record 99.3% differential slope efficiency. The device was fully characterized and modeled to include light output and voltage versus current bias, modulation response and thermal properties. A new singlemode bipolar cascade laser, the bipolar cascade antiresonant reflecting optical waveguide laser, was proposed and modeled.<br>by Steven G. Patterson.<br>Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.<br>Includes bibliographical references (p. 297-310).<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>The development of the terahertz frequency range has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) that operate in the terahertz with photon energies below the semiconductor Reststrahlen band. Photons are emitted via electronic intersubband transitions that take place entirely within the conduction band, where the wavelength is chosen by engineering the well and barrier widths in multiple-quantum-well heterostructures. Fabrication of such long wavelength lasers has traditionally been challenging, since it is difficult to obtain a population inversion between such closely spaced energy levels, and because traditional dielectric waveguides become extremely lossy due to free carrier absorption. This thesis reports the development of terahertz QCLs in which the lower radiative state is depopulated via resonant longitudinal-optical phonon scattering. This mechanism is efficient and temperature insensitive, and provides protection from thermal backfilling due to the large energy separation between the lower radiative state and the injector. Both properties are important in allowing higher temperature operation at longer wavelengths. Lasers using a surface plasmon based waveguide grown on a semi-insulating (SI) GaAs substrate were demonstrated at 3.4 THz in pulsed mode up to 87 K, with peak collected powers of 14 mW at 5 K, and 4 mW at 77 K.<br>Additionally, the first terahertz QCLs have been demonstrated that use metalmetal waveguides, where the mode is confined between metal layers placed immediately above and below the active region. These devices have confinement factors close to unity, and are expected to be advantageous over SI-surface-plasmon waveguides, especially at long wavelengths. Such a waveguide was used to obtain lasing at 3.8 THz in pulsed mode up to a record high temperature of 137 K, whereas similar devices fabricated in SI-surface-plasmon waveguides had lower maximum lasing temperatures due to the higher losses and lower confinement factors. This thesis describes the theory, design, fabrication, and testing of terahertz quantum cascade laser devices. A summary of theory relevant to design is presented, including intersubband radiative transitions and gain, intersubband scattering, and coherent resonant tunneling transport using a tight-binding density matrix model. Analysis of the effects of the complex heterostructure phonon spectra on terahertz QCL design are considered. Calculations of the properties of various terahertz waveguides are presented and compared with experimental results. Various fabrication methods have been developed, including a robust metallic wafer bonding technique used to fabricate metal-metal waveguides. A wide variety of quantum cascade structures, both lasing and non-lasing, have been experimentally characterized, which yield valuable information about the transport and optical properties of terahertz devices. Finally, prospects for higher temperature operation of terahertz QCLs are considered.<br>by Benjamin S. Williams.<br>Ph.D.