Options
Südmeyer, Thomas
Nom
Südmeyer, Thomas
Affiliation principale
Fonction
Directeur
Email
thomas.sudmeyer@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 10 sur 10
- PublicationAccès libreNovel laser sources for metrology and spectroscopy(2017)
La première partie de ce travail est consacrée à un peigne de fréquences optique généré par un laser titane:saphir. Les solutions habituelles de pompage dans le bleu-vert pour les lasers titane:saphir sont volumineuses, coûteuses, peu efficaces et contraignantes en termes de maintenance. De plus, leur puissance optique ne peut généralement pas être directement modulée, ce qui empêche de mettre en œuvre la méthode la plus simple pour l'auto-référencement d'un peigne, c'est-à-dire la stabilisation du décalage de phase entre la porteuse et l'enveloppe des impulsions (carrier-envelope offset en anglais, CEO). Dans cette thèse, l'utilisation de nouvelles diodes lasers émettant dans le vert comme sources de pompage est démontrée. Ce travail a donné lieu à des rendements optiques records pour les lasers titane:saphir pompés par diode. Un rendement de plus de 20% a ainsi été obtenu en régime continu avec une puissance de sortie de 650 mW, et supérieur à 15% en fonctionnement en verrouillage de mode, avec une puissance optique moyenne de 450 mW. Les diodes de pompe vertes présentent de moins bonnes caractéristiques spectrales et spatiales par rapport aux autres sources de pompage utilisées habituellement dans les peignes de fréquence titane:saphir. Dans ce travail, ce défi a pu être surmonté, menant à la première détection et stabilisation de la fréquence CEO d'un laser titane:saphir pompé par diode. Ce travail démontre le haut potentiel du pompage direct par diodes qui peut mener à une nouvelle génération de lasers titane:saphir économiques et compacts.
Dans la deuxième partie de ce travail, une nouvelle méthode de stabilisation est démontrée pour les peignes de fréquence générés par des lasers à fibre. De nos jours, les lasers à fibre représentent la majorité des peignes de fréquence commerciaux, car ils sont compacts, faciles à utiliser et polyvalents. Cependant, la méthode traditionnelle de stabilisation de la fréquence CEO par modulation du laser de pompe est fortement limitée dans sa bande passante par la longue durée de vie de l’état excité du gain. Par conséquent, des modulateurs supplémentaires sont nécessaires pour réaliser des peignes à faible bruit. Ici, la première stabilisation de la fréquence CEO d'un laser à fibre est démontrée par modulation opto-optique d'un composant semiconducteur. Par rapport à la modulation standard du courant du laser de pompe, la bande passante de modulation est améliorée d'un facteur supérieur à 60, ce qui permet d'atteindre un régime à bas bruit pour les peignes de fréquence basés sur des lasers à fibre.
Dans l'étude finale de cette thèse, une nouvelle génération de QCLs est évaluée, qui présente des propriétés d'accordabilité en fréquence améliorées. Les mécanismes existants de balayage en longueur d'onde utilisent d'une part la température du laser et d'autre part le courant d'injection. Le réglage par la température est lent, tandis que celui par le courant d'injection influence aussi la puissance optique du laser. Ici les propriétés d'accord de fréquence et de modulation d'un QCL par l’intermédiaire d'un élément résistif intégré à proximité de la zone active du laser sont étudiées. Ce nouvel élément permet un contrôle rapide de la fréquence du laser avec des effets minimaux sur sa puissance de sortie. Dans une expérience de spectroscopie simple, le bénéfice de ce nouvel actuateur est démontré. Abstract: Lasers have revolutionized the photonics field as a coherent intense light source, capable of performing many tasks. They are widely used in industrial and medical applications, as well as for scientific research. Two important areas of applications are frequency metrology and spectroscopy. Quantum cascade lasers (QCL) cover a wide spectral region in the mid-infrared where most molecules exhibit strong characteristic absorption lines, the so-called molecular fingerprint. QCLs are highly suited for precise molecular spectroscopy, but in their standard configuration, their tuning range is limited. Better frequency tuning mechanisms are required, which can improve many applications. Frequency combs from mode-locked lasers cover a large optical bandwidth and are proven to be ideal tools for frequency metrology. However, many commonly used comb sources have strong drawbacks, in particular with respect to complexity, cost and size. This thesis presents novel directions to improve both QCLs and frequency combs for spectroscopy and metrology.
In the first part of this work, I focus on simple frequency combs generated by Ti:Sapphire lasers. The standard blue-green pumping solutions for Ti:Sapphire lasers are bulky, expensive, have low efficiency, and require a high degree of maintance. Moreover, they usually lack direct power modulation, which is an advantage for simple implementation of carrier-envelope offset (CEO) stabilization. In this thesis, I investigated the suitability of newly-emerged green laser diodes as pump sources. This work resulted in record-high optical-to-optical efficiencies for diode-pumped Ti:Sapphire lasers. More than 20% with 650 mW of output power for continuous wave, and 15% with 450 mW of output power for mode-locked operation of the laser have been obtained. Green pump diodes exhibit poor spectral and spatial properties compared to other previously used pump sources for Ti:Sapphire frequency combs. In this work, I showed that this challenge can be overcome and demonstrated the first CEO frequency detection and stabilization of a diode-pumped mode-locked Ti:Sapphire laser. Our work indicates the high potential of direct diode-pumping, and might lead to a new generation of cost-efficient and compact Ti:Sapphire lasers.
In the second part of this work, I investigate a novel comb stabilization method for fiber lasers. Today, fiber lasers constitute the majority of commercial frequency combs, because they are compact, easy-to-use and versatile. However, the traditional method of pump modulation is severely limited in feedback bandwidth due to the long gain lifetime, and low-noise sources require additional modulators. Here I demonstrate the first CEO frequency stabilization of an ultrafast fiber laser using opto-optical modulation of a semiconductor chip. Compared to standard pump modulation, the modulation bandwidth is improved by at least a factor of 60, enabling low-noise operation of the fiber laser frequency comb.
In the final study of this thesis, I evaluate a new generation of QCLs with improved frequency tuning properties. Existing frequency tuning mechanisms involve laser mount temperature and laser injection current tuning. Temperature tuning suffers from lack of speed and injection current tuning affects the optical output power due to the cross-talk. Here, I study the frequency tuning and modulation properties of a QCL with an integrated resistive heater placed in close proximity to the active region of the laser. This new heater enables fast actuation of the laser frequency with minimal effects on the laser output power. In a simple spectroscopy experiment, I clearly show that this new technique is a highly promising frequency actuator. - PublicationAccès libreCarrier envelope offset frequency detection and stabilization of a diode-pumped mode-locked Ti:sapphire laser
; ; ; We demonstrate the first diode-pumped Ti:sapphire laser frequency comb. It is pumped by two green laser diodes with a total pump power of 3 W. The Ti:sapphire laser generates 250 mW of average output power in 61-fs pulses at a repetition rate of 216 MHz. We generated an octave-spanning supercontinuum spectrum in a photonic-crystal fiber and detected the carrier envelope offset (CEO) frequency in a standard ƒ-to-2ƒ interferometer setup. We stabilized the CEO-frequency through direct current modulation of one of the green pump diodes with a feedback bandwidth of 55 kHz limited by the pump diode driver used in this experiment. We achieved a reduction of the CEO phase noise power spectral density by 140 dB at 1 Hz offset frequency. An advantage of diode pumping is the ability for high-bandwidth modulation of the pump power via direct current modulation. After this experiment, we studied the modulation capabilities and noise properties of green pump laser diodes with improved driver electronics. The current-to-output-power modulation transfer function shows a bandwidth larger than 1 MHz, which should be sufficient to fully exploit the modulation bandwidth of the Ti:sapphire gain for CEO stabilization in future experiments. - PublicationAccès libreCarrier-Envelope Offset Frequency Stabilization of a Fiber Laser by Cross Gain Modulation
; We present the first carrier-envelope offset (CEO) frequency stabilization of a fiber laser by cross gain modulation. The Yb-doped fiber laser is mode-locked by nonlinear polarization evolution and emits 32-nm wide dissipative solitons at a repetition rate of 125 MHz with 150 mW of average output power. A continuous wave laser signal at a wavelength of 1025 nm is used as an intracavity power modulator. A low power of only 200 μW of modulator signal is coupled into the fiber laser and amplified in the gain segment. This signal cross modulates the laser gain, achieving 40 times larger modulation bandwidth of the intracavity laser power than with standard pump-current control. A tight CEO lock is demonstrated with 361 mrad of residual integrated phase noise (from 1 Hz to 1 MHz). The method allows easy implementation in many existing fiber laser frequency combs based on various saturable absorbers and fiber configurations. - PublicationAccès libreFull stabilization and characterization of an optical frequency comb from a diode-pumped solid-state laser with GHz repetition rate
; ; ; ; - PublicationAccès libreCarrier-envelope offset frequency stabilization of a thin-disk laser oscillator operating in the strongly self-phase modulation broadened regime
; ; ; ; ; ; We demonstrate the carrier-envelope offset (CEO) frequency stabilization of a Kerr lens mode-locked Yb:Lu2O3 thin-disk laser oscillator operating in the strongly self-phase modulation (SPM) broadened regime. This novel approach allows overcoming the intrinsic gain bandwidth limit and is suited to support frequency combs from sub-100-fs pulse trains with very high output power. In this work, strong intra-oscillator SPM in the Kerr medium enables the optical spectrum of the oscillating pulse to exceed the bandwidth of the gain material Yb: Lu2O3 by a factor of two. This results in the direct generation of 50-fs pulses without the need for external pulse compression. The oscillator delivers an average power of 4.4 W at a repetition rate of 61 MHz. We investigated the cavity dynamics in this regime by characterizing the transfer function of the laser output power for pump power modulation, both in continuous-wave and mode-locked operations. The cavity dynamics in mode-locked operation limit the CEO modulation bandwidth to ~10 kHz. This value is sufficient to achieve a tight phase-lock of the CEO beat via active feedback to the pump current and yields a residual in-loop integrated CEO phase noise of 197 mrad integrated from 1 Hz to 1 MHz. - PublicationAccès libreFrequency Comb Stabilization of Ultrafast Lasers by Opto-Optical Modulation of Semiconductors
; ; In this paper, we review the current state and discuss new developments in opto-optical modulation (OOM) of semiconductor elements for frequency comb self-referenced stabilization of ultrafast lasers. This method has been successfully used for carrier-envelope offset (CEO) frequency stabilization of diodepumped solid-state lasers operating in 1-μm and 1.5-μm regimes, providing high feedback bandwidth and resulting in low noise performance. We compare the achieved results for Er- and Yb-based laser materials and in different regimes of repetition rates up to 1 GHz. In addition, we present the first semiconductor OOM for CEO stabilization in an ultrafast fiber laser. Moreover, we discuss requirements and design guidelines for OOM chips. In most demonstrations, semiconductor saturable absorber mirrors have been used for OOM, which in parallel were also responsible for pulse formation. By separating the OOM functionality from the pulse formation, we expect that it will enable low-noise CEO stabilization in other types of ultrafast lasers, such as, for example, high-power Kerr-lens mode-locked thin disk lasers. - PublicationAccès libreCarrier-envelope offset stabilization of a GHz repetition rate femtosecond laser using opto-optical modulation of a SESAM
; ; ; We demonstrate, to the best of our knowledge, the first carrier-envelope offset (CEO) frequency stabilization of a GHz femtosecond laser based on opto-optical modulation (OOM) of a semiconductor saturable absorber mirror (SESAM). The 1.05-GHz laser is based on a Yb:CALGO gain crystal and emits sub-100-fs pulses with 2.1-W average power at a center wavelength of 1055 nm. The SESAM plays two key roles: it starts and stabilizes the mode-locking operation and is simultaneously used as an actuator to control the CEO frequency. This second functionality is implemented by pumping the SESAM with a continuous-wave 980-nm laser diode in order to slightly modify its nonlinear reflectivity. We use the standard ƒ-to-2ƒ method for detection of the CEO frequency, which is stabilized by applying a feedback signal to the current of the SESAM pump diode. We compare the SESAM-OOM stabilization with the traditional method of gain modulation via control of the pump power of the Yb:CALGO gain crystal. While the bandwidth for gain modulation is intrinsically limited to ∼250 kHz by the laser cavity dynamics, we show that the OOM provides a feedback bandwidth above 500 kHz. Hence, we were able to obtain a residual integrated phase noise of 430 mrad for the stabilized CEO beat, which represents an improvement of more than 30% compared to gain modulation stabilization. - PublicationAccès libreCarrier-envelope offset frequency stabilization of a gigahertz semiconductor disk laser
; ; ; ; ; - PublicationAccès libreFrequency Tuning and Modulation of a Quantum Cascade Laser with an Integrated Resistive Heater
; - PublicationAccès libreGreen-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average power
; ; ; ; We investigate power-scaling of green-diode-pumped Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation. In a first configuration with a total pump power of up to 2 W incident onto the crystal, we achieved a CW power of up to 440 mW and self-starting mode-locking with up to 200 mW average power in 68-fs pulses using semiconductor saturable absorber mirror (SESAM) as saturable absorber. In a second configuration with up to 3 W of pump power incident onto the crystal, we achieved up to 650 mW in CW operation and up to 450 mW in 58-fs pulses using Kerr-lens mode-locking (KLM). The shortest pulse duration was 39 fs, which was achieved at 350 mW average power using KLM. The mode-locked laser generates a pulse train at repetition rates around 400 MHz. No complex cooling system is required: neither the SESAM nor the Ti:Sapphire crystal is actively cooled, only air cooling is applied to the pump diodes using a small fan. Because of mass production for laser displays, we expect that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers. This will be highly attractive for potential mass applications such as biomedical imaging and sensing.