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Copyright (2023) Society of Photo‑Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited., Vertical-cavity semiconductor lasers as well as single units or arrays of Edge Emitting Lasers suffer from dynamical spatiotemporal instabilities leading to temporally unstable and low spatial beam quality. We propose a feasible stabilization mechanism for microlasers based on periodic non-Hermitian potentials, i.e. simultaneous modulations of refractive index and gain-loss. The proposed spatiotemporal modulations can be introduced by a potential directly acting on the field or by carrier modulations. The stabilization effect is based either on the suppression of the modulation instability or on asymmetric couplings in the transverse direction to localize and stabilize the field., Postprint (published version)

Current and future gravitational wave detectors (GWDs) require high power and low noise laser systems at a wavelength of 1064nm in the continuous wave regime, with excellent spatial beam quality. These systems are highly complex and not commercially available. Hence, this thesis is dedicated to the development of a laser system, to be used in current GWDs, and of different concepts for laser systems, suitable to provide even laser powers of ∼400W or larger for future detectors. It also presents a promising solution to transport the generated high power laser beams via a hollow-core fiber from the laser table into the GWD’s isolated in-vacuum environment. First, investigations on a sequential installation of solid-state laser amplifiers are presented. They confirm the suitability of these amplifiers for the generation of laser powers up to 195W, and uncover limitations of them. These results built the basis for the laser system that the advanced Laser Interferometer Gravitational- Wave Observatorys (aLIGOs) will use in their fourth science run, a prototype of which was tested successfully at the aLIGO Livingston site within this thesis. In sequence, three different configurations for the coherent combination of two laser beams are reported as possibility to increase the laser power above the level available from sequential amplifier chains. They were investigated under the different aspects important for GWD laser systems. The first configuration is a pre-stabilized laser system (PSL) based on the coherent combination of two laser beams from the same seed laser source amplified by solid-state laser amplifiers, that allowed for the generation of a 100W laser beam, with beam quality and noise characteristics similar or better as for current GWD systems. The second configuration is a coherent combination of two laser beams from the same seed source amplified by fiber laser amplifiers, which generated a total output power of 398W with beam quality and free-running noise

presented by Alex Steiner, Zusammenfassung in deutscher Sprache, Kumulative Masterarbeit aus einem Artikel, Masterarbeit University of Innsbruck 2023

The most precise measurement tools of humankind are equipped with ultra-stable lasers. State-of-the-art laser stabilization techniques are based on external cavities, that are limited by noise originated in the coatings of the cavity mirrors. Microstructured mirror coatings (so-called meta-mirrors) are a promising technology to overcome the limitations of coating noise and therewith pave the way towards next-generation ultra-stable lasers. We present experimental realization of a 12,000-finesse optical cavity based on one low-noise meta-mirror. The use of the mirrors studied here in cryogenic silicon cavities represents an order of magnitude reduction in the current limiting mirror noise, such that the stability limit due to fundamental noise can be reduced to 5 × 10−18.

presented by Alex Steiner, Zusammenfassung in deutscher Sprache, Kumulative Masterarbeit aus einem Artikel, Masterarbeit University of Innsbruck 2023

A high-stability compact optical system is proposed for integrating sphere cold atom clock. Both an extended cavity diode laser with linewidth of about 50 kHz and a distribution feedback Bragg laser are applied as laser sources. The frequency of the former is locked with high frequency stability of the 10-13 level between 1~104s averaging time. A new scheme of laser frequency stabilization and shift is realized and the laser power is stabilized to the 10-5 level between 1~104s averaging time. The reasonable arrangement of the optical paths enables a compact system with a total size of 500mm×500mm×200mm. © 2022 IEEE.

We demonstrate the construction of the optical system in the atomic clock-beyond atomic fountain based on Rb-87 atom. The optical system includes a high-stability laser system and an optical lattice. The high-stability laser system with the new scheme of frequency locking and shift is introduced in detail, which is an important laser source for laser cooling. The optimized frequency and intensity stability are achieved to 4 x 10(-14) tau - 1 / 2 ( tau is the averaging time) and 4 x 10(-5) tau - 1 / 2 , respectively, which are highly stable. On the basis of the conventional atomic fountain clock, the optical lattice is specially investigated along the direction of gravity and its characteristics are studied systematically. For the optimized and novel exploration, we predict the achievable stability of 3.6 x 10 - 14 tau - 1 / 2 and it has the potential to be improved to 3.6 x 10 - 15 tau - 1 / 2 . The realizability of the construction due to the stabilized laser and optical lattice makes the beyond fountain promising candidate for the next-generation high performance microwave atomic clock.

Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus, both in position and angle, is critical to many laser applications such as optical guiding, laser-plasma acceleration, and laser-produced secondary radiation. We present an online, non-destructive laser diagnostic, capable of measuring the transverse position and pointing angle at focus. The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line, producing a witness beam highly correlated with the main beam. By propagating low-power kilohertz pulses to focus, we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz. The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train, opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.

Controlling the delivery of multi-terawatt and petawatt laser pulses to final focus, both in position and angle, is critical to many laser applications such as optical guiding, laser-plasma acceleration, and laser-produced secondary radiation. We present an online, non-destructive laser diagnostic, capable of measuring the transverse position and pointing angle at focus. The diagnostic is based on a unique double-surface-coated wedged-mirror design for the final steering optic in the laser line, producing a witness beam highly correlated with the main beam. By propagating low-power kilohertz pulses to focus, we observed spectra of focus position and pointing angle fluctuations dominated by frequencies below 70 Hz. The setup was also used to characterize the excellent position and pointing angle correlation of the 1 Hz high-power laser pulses to this low-power kilohertz pulse train, opening a promising path to fast non-perturbative feedback concepts even on few-hertz-class high-power laser systems.

Many atomic sensors depend on using a laser with a precisely defined frequency. Unfortunately, most lasers suffer from perturbations in their effective cavity length (which determines the operating frequency of the laser) and active stabilization is required. The atomic interferometry lab at NPS currently uses a laser locking system that has two major problems: The method to determine the desired frequency is not only frequency-sensitive but also intensity-sensitive and the bandwidth of the feedback is too low. The first step in controlling the laser frequency is to find the desired frequency. This value is usually found by taking the midpoint of a transmission peak that is obtained from a doppler-free absorption spectrometer. Currently, this value is the reference frequency for the control system. The current method to determine this reference creates the drawbacks outlined above. To alter the transmission spectrum in a way that eliminates these errors, it is possible to modulate the laser frequency while slowly sweeping across an atomic absorption spectrum. By modulating the signal, the frequency band of the error signal increases which eliminates low frequency noise and thereby improves the accuracy. The modulated signal can then be used to create a new error signal that is used in a feedback system. Once the error signal is defined, it is then used to create a higher speed feedback loop which became limited to 1kHz., Ensign, United States Navy, Approved for public release. Distribution is unlimited.

We present the frequency stabilization of a monolithically integrated extended cavity single mode InP diode laser using the Pound-Drever-Hall (PDH) frequency locking technique. The laser is a multi-section distributed Bragg reflector (DBR) laser with an intra-cavity ring resonator, fabricated using an InP active-passive integration technology. The laser is locked to a 700 kHz wide resonance of a Fabry-Perot etalon. The single electrical feedback is applied on the reverse biased rear DBR section of the laser, used to tune the lasing mode. This is the first time to our knowledge that the feedback is applied on a reverse biased, voltage controlled section of an integrated laser cavity. In our implementation the tuning is based on electro-optic effects avoiding significant thermal effects in the tuning element. We demonstrate a linewidth reduction down to 5 kHz and frequency noise suppression of about 30 dB at 10 Hz offset frequency. The bandwidth of the control loop is about 500 kHz, limited by the phase delay of components in our loop.

Residual amplitude modulation of the phase modulator deployed in Pound-Drever-Hall frequency stabilization is an effect known to cause instabilities to the absolute wavelength of the stabilized laser. We present measurements and analysis of the residual amplitude modulation in an InP-based waveguide electro-optic phase modulator. The modulator is monolithically integrated in the output waveguide of a tuneable laser. The effects on the frequency stabilization of such a laser system to a reference etalon using a Pound-Drever-Hall frequency stabilization scheme are quantified. Frequency offset values in the stabilization point from the reference Fabry-Perot etalon resonance caused by the amplitude modulation are predicted and optimum operating points to minimize residual amplitude modulation are discussed. By operating an electro-refractive phase modulator at the proper bias point we show that frequency offsets corresponding to less than 3×10 ^{-3}$ of the reference cavity full-width half-maximum can be achieved.

We present the frequency stabilization of a monolithically integrated extended cavity single mode InP diode laser using the Pound-Drever-Hall (PDH) frequency locking technique. The laser is a multi-section distributed Bragg reflector (DBR) laser with an intra-cavity ring resonator, fabricated using an InP active-passive integration technology. The laser is locked to a 700 kHz wide resonance of a Fabry-Perot etalon. The single electrical feedback is applied on the reverse biased rear DBR section of the laser, used to tune the lasing mode. This is the first time to our knowledge that the feedback is applied on a reverse biased, voltage controlled section of an integrated laser cavity. In our implementation the tuning is based on electro-optic effects avoiding significant thermal effects in the tuning element. We demonstrate a linewidth reduction down to 5 kHz and frequency noise suppression of about 30 dB at 10 Hz offset frequency. The bandwidth of the control loop is about 500 kHz, limited by the phase delay of components in our loop.

Residual amplitude modulation of the phase modulator deployed in Pound-Drever-Hall frequency stabilization is an effect known to cause instabilities to the absolute wavelength of the stabilized laser. We present measurements and analysis of the residual amplitude modulation in an InP-based waveguide electro-optic phase modulator. The modulator is monolithically integrated in the output waveguide of a tuneable laser. The effects on the frequency stabilization of such a laser system to a reference etalon using a Pound-Drever-Hall frequency stabilization scheme are quantified. Frequency offset values in the stabilization point from the reference Fabry-Perot etalon resonance caused by the amplitude modulation are predicted and optimum operating points to minimize residual amplitude modulation are discussed. By operating an electro-refractive phase modulator at the proper bias point we show that frequency offsets corresponding to less than 3×10 ^{-3}$ of the reference cavity full-width half-maximum can be achieved.

Using laser and arc power in equal parts, laser-arc hybrid welding processes are successfully adapted by the industry. This paper shows the stabilizing effects of diode lasers on short arc GMAW (gas metal arc welding) which deliver just a fraction of the supplied arc power. In a comprehensive comparison the stabilized and the sole GMAW processes are confronted and differences regarding process behavior and weld bead properties are pointed out. The tests were carried out with DC01 (1.0330) plates of 1 mm thickness deploying lasers using a mean laser intensity of 1,1 x104 W/cm2. Adding this low amount of intensity provides stability to the weld process and results in weld beads of higher homogeneity. The process behavior is characterized by the transient current and voltage curves which are analyzed in regards to consistency and uniformity. Metallographic analysis is employed to compare the weld bead dimensions at different energy ratios.

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Frequenzen sind die am präzisesten messbaren physikalischen Größen. Viele Messprinzipien und Geräte basieren daher primär auf der Bestimmung der Phase und Frequenz eines genauen und stabilen Oszillators. Die präzise Bestimmung der Zeitintervalle verbessert sich mit der Erhöhung der Frequenz des periodischen Signals des Frequenzstandards. Optische Frequenzen sind gegenüber den MikrowellenAtomuhren, die aktuell noch die SI-Sekunde defnieren, um etwa vier bis fünf Größenordnungen höher und können potentiell um diesen Faktor genauer sein. Die Entwicklung des optischen Frequenzkammgenerators im Jahr 1998 von der Gruppe um Theodor W. Hänsch [1, 2], welche 2005 mit dem Physik-Nobelpreis gewürdigt wurde, hat dabei den Fortschritt der Atomuhren im optischen Bereich stark beschleunigt. Die derzeit präzisesten optischen Atomuhren erreichen inzwischen Instabilitäten und Ungenauigkeiten in der Größenordnung von 10^{−18} [3], was einem Gangunterschied von weniger als einer Sekunde in einem Zeitraum entsprechend dem Alter des Universums entspricht. Um die bestmögliche Präzision bereits in kurzen Zeitskalen zu erreichen wird ein hochstabiler Lokaloszillator benötigt, welcher die atomare Referenzfrequenz anregen und mit einer entsprechenden Stabilität zwischen den jeweiligen Messzyklen halten kann. Inzwischen liegt die erreichbare Genauigkeit atomarer Referenzen deutlich über der Stabilität der Oszillatoren. Eine Verbesserung der Stabilität von Lokaloszillatoren ist daher ein wichtiger Forschungsschwerpunkt innerhalb des Bereichs der optischen Atomuhren [4]. In dieser Arbeit zeige ich die Methode einer Stabilisierung eines Lokaloszillators, wie er für die Abfrage des in Entwicklung befndlichen Frequenzstandards basierend auf atomaren neutralem Magnesium-24 eingesetzt wird, bis zum Limit des berechneten thermischen Rauschens. Es werden Instabilitäten von 4 · 10^{−16} in 1 Sekunde erreicht mit Spitzenwerten von 2 · 10^{−16} für längere Mittelungszeiten, was unter dem berechneten therm, Frequencies are the physical values which can be measured most precisely. Many measurement principles and devices are therefore based on the determinination of the phase and frequency of an accurate and stable oscillator. The precise determination of time intervals improves with increasing frequency of the periodic signal explicited as frequency standard.Optical frequencies are about four to fve orders of magnitudes larger compared to current microwave frequency standards, which still defne the SI-second, and have therefore a larger potential. The development of the frequency comb in the year 1998 increased the advance in optical clock technologies. Due to their importance in frequency measurements its development was awarded with the Nobel Prize in 2005. An atomic reference defnes the accuracy of such a frequency. For that purpose it needs to be well isolated from environmental disturbances. Current most precise optical clocks achieve instabilities and accuracies in the order of 10^{−18} [3]. This would correspond to an accuracy of one second compared to the age of the universe. To achieve such a precision in short time scales an ultrastable local oscillator is necessary, which is capable of adressing the ultranarrow atomic transition and stays that stable in between the measurement cycle time. The achievable accuracy of these atomic references exceed the instabilites of the oscillators and therefore those became a limiting factor. So currently the improvement in the stability of these local oscillators is an important feld of research [4]. In this work I show how to stabilize a laser to its fundamental limit, which is the brownian thermal noise and therefore to push the limits for future setups. Instabilities in the order of 4 · 10^{−16} in 1 second are achieved with best values of 2 · 10^{−16} for integration times of a few ten seconds, which is even below the calculated thermal noise floor, but still as part of the statistical error. Additionally the long term pe

An electromagnetic wave propagating through an optical fiber is sensitive to external disturbances, such as mechanical vibrations and temperature and pressure fluctuations, which add phase noise onto the wave. For high-precision frequency-based applications this phase noise has to be removed. By partially reflecting light from the remote end of the fiber back through the fiber, and comparing it to light that has not passed through the fiber, their beat note can be phase locked to a stable reference, using an acousto-optic modulator for phase noise compensation. This effectively cancels the phase noise at the remote end of the fiber. In this project, two such fiber noise cancellation systems have been successfully assembled. The fiber noise cancellation systems will be used for laser locking to a slow light crystal cavity. Using spectral hole burning, a very low group velocity can be obtained in rare-earth-ion-doped crystals. By depositing mirrors on such a crystal, it could act as a reference cavity with a very long effective length, but without the increased difficulty of isolating the cavity from mechanical vibrations associated with a physically long cavity. By locking a laser to a slow light crystal cavity, an improved stability could potentially be achieved. A possible setup for slow light crystal cavity laser locking experiments, where the fiber noise cancellation systems have been integrated, is also presented in this thesis., Atomur som är baserade på en optisk frekvens är under utveckling. Dessa optiska klockor är i dagsläget så exakta att om de startades vid big bang, så skulle de bara visa en sekund fel idag. Nästa generations kommunikation- och navigeringssystem kommer att dra nytta av noggrannare tidsmätning. I detta examensarbete behandlas två saker som är viktiga för den fortsatta utvecklingen av optiska klockor: laserstabilisering och eliminering av fasbrus i optiska fiber. Optiska klockor tar för tillfället upp hela labb och är alltså inte lätta att transportera. Det behövs därför ett sätt att noggrant kunna jämföra klockorna över långa avstånd. Detta kommer troligtvis göras med ett nätverk av optiska fiber. När laserljus färdas genom ett optiskt fiber påverkas det av yttre störningar som vibrationer och förändringar i temperatur och tryck, vilket får längden på fibern att ändras. Detta leder till att ljuset blir brusigt, och ljus som var väldigt enfärgat innan fibern, kommer då bestå av ett bredare spektrum av färger efter fibern. För applikationer som till exempel optiska klockor, där det är önskvärt att kunna överföra väldigt enfärgat ljus med optiska fiber, så behövs detta fiberbrus kompenseras bort. En metod för att göra detta, är att man skickar tillbaka en liten del av ljuset som har färdats genom fibern, och jämför det med ljus direkt från lasern. På detta sätt kan man mäta hur mycket brus som fibern adderar till laserljuset. Det är då möjligt att kompensera för bruset redan innan fibern, så att ljuset ut ur fibern blir brusfritt. I detta examensarbete har två system som gör just detta byggts. Dessa systemen kommer inte att användas för att jämföra klockor, utan för framtida experiment om laserstabilisering till en långsamtljus-kavitet, där det också är viktigt att kunna transportera brusfritt ljus i optiska fiber. I optiska klockor jämför man frekvensen på en laser med oscillationsfrekvensen för en specifik atom. Genom att hålla laserns frekvens så nära atomens frekvens

An electromagnetic wave propagating through an optical fiber is sensitive to external disturbances, such as mechanical vibrations and temperature and pressure fluctuations, which add phase noise onto the wave. For high-precision frequency-based applications this phase noise has to be removed. By partially reflecting light from the remote end of the fiber back through the fiber, and comparing it to light that has not passed through the fiber, their beat note can be phase locked to a stable reference, using an acousto-optic modulator for phase noise compensation. This effectively cancels the phase noise at the remote end of the fiber. In this project, two such fiber noise cancellation systems have been successfully assembled. The fiber noise cancellation systems will be used for laser locking to a slow light crystal cavity. Using spectral hole burning, a very low group velocity can be obtained in rare-earth-ion-doped crystals. By depositing mirrors on such a crystal, it could act as a reference cavity with a very long effective length, but without the increased difficulty of isolating the cavity from mechanical vibrations associated with a physically long cavity. By locking a laser to a slow light crystal cavity, an improved stability could potentially be achieved. A possible setup for slow light crystal cavity laser locking experiments, where the fiber noise cancellation systems have been integrated, is also presented in this thesis., Atomur som är baserade på en optisk frekvens är under utveckling. Dessa optiska klockor är i dagsläget så exakta att om de startades vid big bang, så skulle de bara visa en sekund fel idag. Nästa generations kommunikation- och navigeringssystem kommer att dra nytta av noggrannare tidsmätning. I detta examensarbete behandlas två saker som är viktiga för den fortsatta utvecklingen av optiska klockor: laserstabilisering och eliminering av fasbrus i optiska fiber. Optiska klockor tar för tillfället upp hela labb och är alltså inte lätta att transportera. Det behövs därför ett sätt att noggrant kunna jämföra klockorna över långa avstånd. Detta kommer troligtvis göras med ett nätverk av optiska fiber. När laserljus färdas genom ett optiskt fiber påverkas det av yttre störningar som vibrationer och förändringar i temperatur och tryck, vilket får längden på fibern att ändras. Detta leder till att ljuset blir brusigt, och ljus som var väldigt enfärgat innan fibern, kommer då bestå av ett bredare spektrum av färger efter fibern. För applikationer som till exempel optiska klockor, där det är önskvärt att kunna överföra väldigt enfärgat ljus med optiska fiber, så behövs detta fiberbrus kompenseras bort. En metod för att göra detta, är att man skickar tillbaka en liten del av ljuset som har färdats genom fibern, och jämför det med ljus direkt från lasern. På detta sätt kan man mäta hur mycket brus som fibern adderar till laserljuset. Det är då möjligt att kompensera för bruset redan innan fibern, så att ljuset ut ur fibern blir brusfritt. I detta examensarbete har två system som gör just detta byggts. Dessa systemen kommer inte att användas för att jämföra klockor, utan för framtida experiment om laserstabilisering till en långsamtljus-kavitet, där det också är viktigt att kunna transportera brusfritt ljus i optiska fiber. I optiska klockor jämför man frekvensen på en laser med oscillationsfrekvensen för en specifik atom. Genom att hålla laserns frekvens så nära atomens frekvens

[no abstract]

[no abstract]

[ANGLÈS] Rydberg atoms with principal quantum number n>>1 have extraordinary atomic properties including tunable long range dipole-dipole interactions that lead to the so called Rydberg blockade. Atoms excited to these particular levels have been shown to be excellent candidates to implement several quantum information tasks, from two-qubit gates to single photon sources. In this work, we demonstrate Electromagnetic Induced Transparency (EIT) using Rydberg levels in a hot gas of rubidium atoms. We then use the EIT window as a reference to stabilize the frequency of the coupling laser., [CASTELLÀ] Los átomos excitados a estados de Rydberg con número cuántico principal n >> 1 tienen propiedades atómicas exageradas, como por ejemplo interacciones de largo alcance sintonizables que dan lugar al conocido efecto de "blockade". Se ha demostrado que los átomos excitados a estos particulares niveles son excelentes candidatos para implementar tareas de computación cuántica. En este trabajo mostramos el fenómeno conocido como "Electromagnetically induced Transparency" (EIT) utilizando un gas de rubidio y átomos excitados a niveles de Rydberg. En particular se muestra cómo usar la ventana de EIT como referencia para estabilizar en frecuencia un láser de acoplamiento., [CATALÀ] Els àtoms excitats a estats de Rydberg amb número quàntic principal n>>1 tenen propietats atòmiques exagerades, com per exemple interaccions de llarg abast sintonitzables que donen lloc al conegut efecte de "blockade". S'ha demostrat que els àtoms excitats fins aquests particulars nivells són excel·lents candidats per implementar tasques de computació quàntica. En aquest treball mostrem el fenòmen conegut com "Electromagnetically Induced Transparency" (EIT) utilitzant un gas de rubidi i àtoms excitats a nivells de Rydberg. En particular es mostra com utilizar la finestra d'EIT com a referència per estabilitzar en frequència un làser d'acoblament.

This thesis work is optical metrology techniques to determine material stability. In addition to displacement interferometry, topics such as periodic nonlinearity, Fabry-Perot interferometry, refractometry, and laser stabilization are covered., Precision and Microsystems Engineering, Mechanical, Maritime and Materials Engineering

This thesis work is optical metrology techniques to determine material stability. In addition to displacement interferometry, topics such as periodic nonlinearity, Fabry-Perot interferometry, refractometry, and laser stabilization are covered., Precision and Microsystems Engineering, Mechanical, Maritime and Materials Engineering

A self-starting, passively stabilized, monolithic all polarizationmaintaining femtosecond Yb-fiber master oscillator / power amplifier with very high operational and environmental stability is demonstrated. The system is based on the use of two different photonic crystal fibers. One is used in the oscillator cavity for dispersion balancing and nonlinear optical limiting, and another one is used for low nonlinearity final pulse recompression. The chirped-pulse amplification and recompression of the 232-fs, 45-pJ/pulse oscillator output yields a final direct fiber-end delivery of 7.3-nJ energy pulses of around 297 fs duration. Our laser shows exceptional stability. No Q-switched modelocking events were detected during 4-days long observation. An average fluctuation of only 7.85 · 10−4 over the mean output power was determined as a result of more than 6-hours long measurement. The laser is stable towards mechanical disturbances, and maintains stable modelocking in the temperature range of at least 10 – 40 0C.

A self-starting, passively stabilized, monolithic all polarizationmaintaining femtosecond Yb-fiber master oscillator / power amplifier with very high operational and environmental stability is demonstrated. The system is based on the use of two different photonic crystal fibers. One is used in the oscillator cavity for dispersion balancing and nonlinear optical limiting, and another one is used for low nonlinearity final pulse recompression. The chirped-pulse amplification and recompression of the 232-fs, 45-pJ/pulse oscillator output yields a final direct fiber-end delivery of 7.3-nJ energy pulses of around 297 fs duration. Our laser shows exceptional stability. No Q-switched modelocking events were detected during 4-days long observation. An average fluctuation of only 7.85 · 10−4 over the mean output power was determined as a result of more than 6-hours long measurement. The laser is stable towards mechanical disturbances, and maintains stable modelocking in the temperature range of at least 10 – 40 0C.

Accurate and traceable length metrology is employed by laser frequency stabilization. This paper describes a laser frequency stabilzation technique as a secondary standard with a fractional frequency stability of 5.2×10?10 with 2 mW of power, suitable for practical applications. The feedback stabilization is driven by an intrinsic mixed mode signal, caused by nonlinear optical phenomena with adjacent modes. The mixed mode signals are described theoretically and experimentally verified., Precision and Microsystems Engineering, Mechanical, Maritime and Materials Engineering

This thesis describes a number of coherent processes, such as quantum information processing, superradiance and electromagnetically induced transparency, which have been experimentally implemented using rare-earth-ion-doped crystals. The rare-earths are a class of elements that have in common, an atomic structure that allows for very long lifetimes as well as coherence times, both on optical transitions and on spin transitions. These ions can be naturally trapped inside host crystals, and with the phonon vibrations removed by cooling down to cryogenic temperatures (< 4 K), they can be used for a number of different quantum information processes. Most experiments were carried out using PrYSO, but also other crystal types were investigated, such as Nd:YVO4, and La2(WO4)3. The characterization of the ions were done with a variety of methods, including among others, photon echo techniques and electromagnetically induced transparency. Quantum computing is a rapidly growing field and there are still many potential candidates for its implementation. In our work we have utilized the spin states of the Pr rare-earth ion as a qubit, and demonstrated arbitrary single qubit gates, which are important pieces towards a quantum computing realization in these systems. Most of the experimental work done for the thesis was carried out using an ensemble approach, that has the advantage of giving a strong readout signal, but for future scaling to multiple qubits, single instances are more promising, which is discussed. Quantum memories are crucial components in applications such as quantum networks and long distance quantum communication. In this thesis, work has been done to investigate how quantum memories can be implemented in rare-earth crystals. In particular, there are two protocols, CRIB and AFC, which were suggested with rare-earth crystals directly in mind, and both of these require high optical depth, for maximum recall efficiency. In this thesis, implications of being in the

not available, Applied Sciences

not available, Applied Sciences

The main aim of this work, was to lay the foundations for the experimental realisation of a quantum mechanical controlled NOT gate in rare-earth-metal-ion-doped crystals. Small amounts of rare-earth elements, added during the growth of some inorganic crystals, will become substituted into the crystal lattice as trivalent ions. The trivalent rare-earth-metal ions between cerium, with atomic number 58, and ytterbium, with atomic number 70, have a partly filled 4f shell, which does not extend spatially outside the full 5s and 5p shells. The 4f vacancies make electronic inner shell transitions possible between spectroscopic 4f terms. Some of these optical transitions have coherence times of the order of milliseconds, when the crystals are cooled down to ~ 4 K. There are several reasons for these extraordinary coherence times, which are approximately 8 orders of magnitude greater than those typical for electronic transitions in solids. The most important one is the cage-like shield which the outer 5s and 5p shells provide for the 4f electrons. Furthermore, since these ions are naturally trapped inside the crystal lattice there is no Doppler broadening of the line-width. The coherence properties of these optical transitions is one of the features that makes these materials attractive for use as a solid-state platform for quantum computing, using these ions as qubits. Another appealing characteristic is the fact that different ions have different optical resonance frequencies, which means that ions belonging to different qubits, which only have nm separation, can still be addressed separately by using different laser frequencies. Since the inter-ion spacing is so small, it is possible to make two ions interact strongly, although they are well shielded, through a permanent dipole-dipole interaction. This interaction can be turned on and off by switching between two different ways of encoding the qubit, a most useful feature. When the qubit is represented as a superposition

Future space missions, among which the Darwin Space Interferometer, will consist of several free flying satellites. A complex metrology system is required to have all the components fly accurately in formation and have it operate as a single instrument. Our work focuses on a possible implementation of the sub-system that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy is on the order of 70 micrometer over a distance of 250 meter. We are exploring a technique called frequency sweeping interferometry, which involves interferometrically measuring a phase difference while sweeping the wavelength of a tunable laser. This phase difference is directly proportional to the absolute distance. A very high finesse Fabry-P´erot cavity is used as a reference standard, to which the laser is locked end-points of the sweep. We will discuss the control system that drives the setup and show some first experimental results., Optics Research Groep, Applied Sciences

Future space missions, among which the Darwin Space Interferometer, will consist of several free flying satellites. A complex metrology system is required to have all the components fly accurately in formation and have it operate as a single instrument. Our work focuses on a possible implementation of the sub-system that measures the absolute distance between two satellites with high accuracy. For Darwin the required accuracy is on the order of 70 micrometer over a distance of 250 meter. We are exploring a technique called frequency sweeping interferometry, which involves interferometrically measuring a phase difference while sweeping the wavelength of a tunable laser. This phase difference is directly proportional to the absolute distance. A very high finesse Fabry-P´erot cavity is used as a reference standard, to which the laser is locked end-points of the sweep. We will discuss the control system that drives the setup and show some first experimental results., Optics Research Groep, Applied Sciences