On thermal effects in solid state lasers: the case of ytterbium-doped materials

A review of theoretical and experimental studies of thermal effects in solid-state lasers is presented, with a special focus on diode-pumped ytterbium-doped materials. A large part of this review provides however general information applicable to any kind of solid-state laser. Our aim here is not to make a list of the techniques that have been used to minimize thermal effects, but instead to give an overview of the theoretical aspects underneath, and give a state-of-the-art of the tools at the disposal of the laser scientist to measure thermal effects. After a presentation of some general properties of Yb-doped materials, we address the issue of evaluating the temperature map in Yb-doped laser crystals, both theoretically and experimentally. This is the first step before studying the complex problem of thermal lensing (part III). We will focus on some newly discussed aspects, like the definition of the thermo-optic coefficient: we will highlight some misleading interpretations of thermal lensing experiments due to the use of the dn/dT parameter in a context where it is not relevant. Part IV will be devoted to a state-of-the-art of experimental techniques used to measure thermal lensing. Eventually, in part V, we will give some concrete examples in Yb-doped materials, where their peculiarities will be pointed out

Nonlinear properties of RTP for second harmonic generation at 1030nm (orale)

International audienceWe demonstrate that around 1030 nm, RbTiOPO4 (RTP) realizes the second harmonic generation of Yb-doped lasers in non-critically phase-matched configuration at ambient temperature, with efficiencies comparable to LBO and wide thermal acceptanc

Amplificateurs laser à cristaux massifs pompés par diode (fibres cristallines Yb)

Un grand nombre d applications réclament des sources laser en régime impulsionnel toujours plus puissantes et énergétiques. Les progrès continus des technologies laser permettent non seulement d améliorer les performances de l outil laser mais aussi d ouvrir la voie à de nouvelles applications. Cependant, l'augmentation de la puissance des sources laser est aussi accompagnée par une complexification des systèmes. Cette thèse porte sur l étude d amplificateurs laser de puissances qui se distinguent par la simplicité de leurs architectures : avec un ou deux passages dans le milieu laser. Dans la première partie, nous étudions le potentiel de la fibre cristalline Yb: YAG pompée par diode en tant qu amplificateur. Les effets de confinement de l intensité de pompe au centre de la fibre cristalline par guidage sont étudies théoriquement et expérimentalement. Deux expériences démontrent ensuite l intérêt de la fibre cristalline Yb:YAG en tant qu amplificateur de puissance de sources laser à fibres, l une en régime femtoseconde et l autre avec un laser mono-fréquence. Par ailleurs, nous explorons le potentiel de notre concept en régime de forte puissance. Une puissance de 250 W en oscillateur et une extraction de 100 W en amplificateur ont été obtenues avec une diode de pompe de 600 W. La deuxième partie traite de l étude d amplificateurs à base de cristaux de Nd:YVO4. Le dimensionnement de notre système est réalisé en s appuyant sur une étude des propriétés du Nd:YVO4. L amplificateur ainsi obtenu affiche des performances inédites qui se caractérisent par un très fort gain optique (40-60 dB) couplé à une forte extraction de puissance moyenne (10 à 15 W).A wide range of scientific and industrial applications require pulsed laser sources delivering increasing amount of powers and pulse energies. Continuous progresses in the field of laser technology do not only bring significant process efficiency improvements but also allow developing new applications. However, the complexity of laser sources has significantly increased over the years together with their performance. In contrast, this work focuses on power amplifier architectures which are particularly simple (with one or two passes). In the first part, we study the potential of Yb:YAG single crystal fibers. Pump intensity confinement by the pump beam guiding is studied in details both theoretically and experimentally. Two experiments demonstrate the interest of Yb:YAG single crystal fibers as a power amplifier for fiber based laser sources, one in femtosecond regime and the other one with a single frequency laser. Furthermore, the potential of our architecture is also explored in high power regime. An output power of 250 W for the oscillator and 100 W power extraction with the amplifier were obtained with a 600 W pump diode. The second part describes the study of laser amplifiers using longitudinally pumped Nd:YVO4 bulk crystals. We study the effect of temperature increase in the laser crystal and evaluate the influence of the doping concentration and excited state population on the heat load. Guided by the conclusion of our study, we design a high gain amplifier characterized by very high optical gain (40-60 dB) coupled to a high average power extraction (10 to 15 W)PARIS11-Inst. Optique (914712302) / SudocSudocFranceF

Passively mode-locked diode-pumped Nd:YVO4 oscillator operating at ultra-low repetition rate

We demonstrate the operation of an ultra low repetition rate, high peak power, picosecond diode pumped Nd:YVO4 passively mode locked laser oscillator. Repetition rates even below 1 MHz were achieved with the use of a new design multiple-pass cavity and a semiconductor saturable absorber. Long term stable operation at 1.2 MHz, pulse duration of 16.3 ps and average output power of 470 mW corresponding to 24 KW peak power pulses is reported. This is, to our knowledge, the lowest repetition rate high peak power pulses ever generated directly from a picosecond laser resonator without cavity dumping

Thermal behaviour of ytterbium-doped fluorite crystals under high power pumping

International audienceWe report an in situ thermal study of Yb-doped fluorite crystals Yb:CaF2 and Yb:SrF2 under high power pumping, with or without laser operation. The experiment combines simultaneously thermography and measurement of the thermal aberrations. This setup allows us to measure temperature gradients, thermal lens, and absorption coefficients. From these measurements, we evaluate the thermal conductivity, fractional thermal load, and thermo-optic coefficient. Great differences are observed between the lasing and non lasing regimes. Our measured thermal lenses are greater than what are expected from the thermo-optic parameters found in previous work. Based on this thermal study, we design a laser cavity operating with large output power and TEM00, leading to better performances for Yb:CaF2 than Yb:SrF2

Practical Single Microwave Photon Counter with 10−2210^\mathrm{-22} W/Hz\mathrm{W/\sqrt{Hz}} sensitivity

Single photon detection played an important role in the development of quantum optics. Its implementation in the microwave domain is challenging because the photon energy is 5 orders of magnitude smaller. In recent years, significant progress has been made in developing single microwave photon detectors (SMPDs) based on superconducting quantum bits or bolometers. In this paper we present a new practical SMPD based on the irreversible transfer of an incoming photon to the excited state of a transmon qubit by a four-wave mixing process. This device achieves a detection efficiency $\eta = 0.43$ and an operational dark count rate $\alpha = 85$ $\mathrm{s^{-1}}$, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is $\mathcal{S} = 10^{-22}$ $\mathrm{W/\sqrt{Hz}}$, one order of magnitude lower than the state of the art. The detector operates continuously over hour timescales with a duty cycle $\eta_\mathrm{D}=0.84$, and offers frequency tunability of $\sim 400$ MHz around 7 GHz