F. Auge

Theoretical and experimental investigations of a diode-pumped quasi-three-level laser: the Yb/sup 3+/-doped Ca/sub 4/GdO(BO/sub 3/)/sub 3/ (Yb:GdCOB) laser

We present a theoretical and experimental analysis of a diode-pumped Yb/sup 3+/-doped Ca/sub 4/GdO(BO/sub 3/)/sub 3/ (Yb:GdCOB) laser. A new model for a diode-pumped quasi-three-level laser is described. The effects of absorption saturation, temperature profile, and the beam quality M/sup 2/ factor of the pump diode have been taken into account, for the first time to our knowledge. We have obtained a good agreement between experimental measurements and theoretical calculations with two different pump wavelengths, 902 and 976 nm. Our model has given good predictions of the laser performances for different crystal temperatures and different M/sup 2/ factors of the pump beam. As much as 440 mW of output power (at 1082 nm) have been achieved for 640 mW of absorbed pump power at 976 nm, corresponding to one of the highest slope efficiencies (81%) ever obtained with Yb-doped lasers.

Enhancement of high-order harmonic generation at tuned wavelengths through adaptive control

An adaptive learning loop enhances the efficiency and tuning of high-order harmonic generation. In comparison with simple chirp tuning, we observe a broader tuning range and a twofold to threefold enhancement in integrated photon flux in the cutoff region. The driving pulse temporal phase varies significantly for different tunings and is more complicated than a simple chirp. We compare our experimental results with a one-dimensional, time-dependent model that incorporates the intrinsic atomic response, the experimental pulse temporal phase, ionization effects, and transverse coherence of the spatial mode of the laser. The model agrees with our experimental results and indicates that a specific quantum path coupled with ionization effects determines the optimized harmonic spectrum.

Diode-pumped self-frequency-doubling Nd:GdCa 4 O(BO 3 ) 3 lasers: toward green microchip lasers

An output power of 115 mW at 545 nm has been obtained from a diode-pumped self-frequency doubling Nd:GdCa4O(BO3)3 laser in a stable cavity. The infrared emission of the laser was found to be 1091 nm, not the 1060 nm that was expected when the highest line of the fluorescence spectrum was considered. We have demonstrated that the emission at 1091 nm was caused by the temperature increase at the focus of the pump beam. We demonstrated also, for what we believe was the first time, lasing operation of Nd:GdCOB in a plano–plano cavity and obtained an output power of 22 mW at 545 nm. To our knowledge, this is the highest output power ever reported with a self-frequency-doubling crystal in a plano–plano cavity.

Imaging and quality assessment of high-harmonic focal spots

We present a direct method of studying the focusability of an intense, short-pulse extreme-ultraviolet (XUV) beam obtained by high-harmonic generation. We perform near-field imaging of the focal spot of five high-harmonic orders strongly focused by a broadband toroidal mirror. To visualize the focal spot directly, we image the fluorescence induced by an XUV beam on a cerium-doped YAG crystal on a visible CCD camera. We can thus measure the harmonic spot size on a single image, together with the Strehl ratio, to evaluate the quality of focusing. Such techniques should become instrumental in optimizing the focusing conditions and reaching intensities required for exploring attosecond nonlinear optics in the XUV range.

High-power diode-pumped Yb:GdCOB laser: from continuous-wave to femtosecond regime

Abstract We present an efficient tunable continuous-wave diode-pumped Yb 3+ :Ca 4 GdO(BO 3 ) 3 (Yb:GdCOB) laser producing at room temperature up to 3.2 W average power with a slope efficiency of 80% when pumped with a 10 W laser diode. A large tunability from 1017 to 1086 nm is obtained. The broad emission spectrum has been used to develop a diode-pumped Yb:GdCOB femtosecond laser. The laser generated 90 fs pulses, at a center wavelength of 1045 nm. By using a semiconductor saturable absorber mirror (SESAM) for the mode locking, the average power was 40 mW and the repetition rate of 100 MHz.

New efficient self-frequency doubling Nd-doped crystal for diode-pumped green laser

Neodymium-doped gadolinium calcium oxoborate, Ca/sub 4/Gd/sub 1-x/Nd/sub x/O(BO/sub 3/)/sub 3/ (Nd:GdCOB) is an ideal self-frequency doubling crystal available in a very large size and high quality and has a nonlinear coefficient of /spl sim/1 pm/V, comparable with that of LBO crystal. Nd:GdCOB is a monoclinic biaxial crystal that has a high damage threshold (>1 GW/cm at 1061 nm, 6 ns). The Czochralski pulling method was employed to grow large single crystals. In this paper, we present a work on self-frequency doubling Nd:GdCOB crystal under cw Ti:sapphire and laser diode pumping. we succeeded in the realization of an efficient diode-pumped Nd:GdCOB laser producing 21 mW cw output of green radiation for 820 mW absorbed pump power.

Code for simulation of the spatial and temporal transformation of femtosecond laser pulses induced by optical systems

Summary form only given. One of the important issue in high intensity CPA chains, is the determination of the output pulse duration. The seed pulse is modified through the CPA amplification by different processes (dispersion through amplifying materials, spatial and temporal transformation through lenses or other optical components...) and it is often difficult to predict the pulse duration after compression. This duration can be measured with techniques such as spider or autocorrelators, but to design such complex systems, it is of crucial importance to be able to foresee what the pulse duration should be. Moreover spatio-temporal effects are often neglected for ultrashort pulses and however strongly modify the temporal characteristics of the laser pulse on interaction targets. We present a set of simulations of stretchers-compressors systems including dispersive beam expanders and show for pulses shorter than 30 femtoseconds how crucial are these spatio-temporal coupling effects.

Towards visible microchip lasers based on Nd:Ca/sub 4/GdO(BO/sub 3/)/sub 3/

Summary form only given.Summary from only given. Crystals combining laser and nonlinear properties for self-frequency conversion of the fundamental laser wavelength are very promising materials to develop diode-pumped visible microchip lasers. The Nd/sup 3+/:Ca/sub 4/GdO(BO/sub 3/)/sub 3/ crystal (Nd:GdCOB) has been demonstrated to be efficient for self-frequency doubling. It has also very good physical properties for crystalline growth and cutting. We report on the performances of diode-pumped Nd:GdCOB crystals put in a short plano-plano cavity, which represents a step toward microchip lasers.

3-W, diode-pumped, tunable, CW Yb:GdCOB laser

Summary form only given. We present diode-pumped Yb:GdCOB laser producing 3.2 W CW at 1043 nm with a slope efficiency of 68% and an optical-to-optical conversion efficiency of 36%.

77-%-slope-efficiency, 800-mW-average-power, diode-pumped at 976-nm Yb/sup 3+/:Ca/sub 4/GdO(BO/sub 3/)/sub 3/ laser

Summary form only given. The recently-developed Yb/sup 3+/ doped Ga/sub 4/LnO(BO/sub 3/)/sub 3/ (Ln=Y, Gd) crystals (Yb: LnCOB) have been shown to be promising for efficient all-solid-state lasers. These crystals exhibit many advantages such as simple quasi-three-level laser structure and absence of parasitic levels for the Yb/sup 3+/ ions. We present the results obtained from an Yb:GdCOB laser operating in the cw regime at room temperature pumped by 976-nm laser-diodes. Subsequently we will describe the results obtained in the Q-switch regime.