Romain Gaume

Determination of laser parameters of ytterbium-doped oxide crystalline materials

Spectroscopic and laser properties at ∼1 µm of seven new ytterbium-doped crystalline materials—silicates Y2SiO5,Ca2Al2SiO7,SrY4(SiO4)3O, borates Ca3Y2(BO3)4,Ca3Gd2(BO3)4,Sr3Y(BO3)3, and Ba3Lu(BO3)3— are investigated. Absorption and emission cross sections are strongly dependent on the crystalline host. Good agreement is obtained between emission cross sections calculated by the reciprocity method and by the Fuchtbauer–Ladenburg method. The wavelength dependence of the gain cross sections are also determined. Except for Ba3Lu(BO3)3, which is of poor crystalline quality, laser oscillations in a plano-concave cavity are obtained for all the presented hosts. From optical spectroscopy and laser results, large tunability of the emission is expected for these materials. Slope efficiencies are in the range 40%–60% with very low threshold values.

Spectroscopic and crystal-field analysis of new Yb-doped laser materials

Crystal-field effects are very important as far as laser performances of Yb-doped materials are concerned. In order to simplify the interpretation of low-temperature spectra, two tools derived from a careful examination of crystal-field interaction are presented. Both approaches are successfully applied in the case of new Yb-doped materials, namely Ca3Y2(BO3)4 (CYB), Ca3Gd2(BO3)4 (CaGB), Sr3Y(BO3)3 (SrYBO), Ba3Lu(BO3)3 (BLuB), Y2SiO5 (YSO), Ca2Al2SiO7 (CAS) and SrY4(SiO4)3O (SYS). The 2F7/2 splitting is particularly large in these materials and favourable to a quasi-three-level laser operating scheme. Calculations performed using the point charge electrostatic model for these compounds and using a consistent set of effective atomic charges confirm the experimental results. This should permit to use this model in a predictive approach.

Yb3+-doped laser materials for high-power or ultrafast applications

The emergence of new laser crystals has allowed crucial progress in the ultrashort-pulsed laser technology. Recently extensive researches on new Yb3+ doped crystals permit the development of all-solid-state femtosecond lasers. In the Yb3+ solid state lasers, thermo-mechanical properties plays a key role. Thermo-mechanical parameters are gathered and analyzed in the framework of simple theoretical models. Consequently, structural properties relationships could be expressed. The review of the state of the art on the Yb doped laser material for high power and ultrafast pulses generation are presented.

Thermal lensing measurements in diode-pumped Yb-doped materials

A Shack-Hartmann wavefront sensor was used to measure thermal lensing in diode-pumped Yb-doped YCOB and YSO, under lasing or non-lasing conditions. Reduction of thermal effects in composite crystals is observed, as well as a dependance of thermal lensing with the emission wavelength.

Laser characterization of the Yb3+:Y2SiO5 (Yb:YOS)

The spectroscopic properties of Yb3+:Y2SiO5 (Yb:YOS) and its laser potential for 1 micrometers emission are investigated. Crystals containing 5% of Yb3+ ions (9.2 X 1020 ions/cm3) with very good optical quality have been grown by the Czochralski process. An energy-level diagram for Yb3+ in this host is proposed, taking into account electron-phonon coupling phenomena. A broad emission, from 0.98 micrometers to 1.1 micrometers , with a lifetime of 1.5 ms have been measured and the laser parameters indicate that this host could be well adapted for high power lasers. In good agreement with the spectroscopic predictions, laser oscillation under Ti:sapphire laser pumping was observed for the first time, on uncoated crystals in a plano-concave cavity. A slope efficiency of 44% and a laser threshold around 160 mW have been obtained. This laser material appears very attractive for the development of new Yb3+ sources.

135-fs Diode-Pumped Laser with 1-W Average Power Based on a YAG//Yb:SYS Hetero-Bonded Crystal

We present the first demonstration in femtosecond regime of a Yb-doped hetero-bonding crystal: YAG//Yb:SYS. Pulses of 135 fs with an average power of 1 W have been produced.

Diode pumped femtosecond oscillators based on new ytterbium doped borates crystals

We demonstrate for the first time the use of a new borate crystals: Yb:GdCOB and Yb:BOYS in femtosecond mode-locked oscillators. Pulses as short as 69 fs for the Yb:BOYS and 89 fs for the Yb:GdCOB have been obtained near 1 µm.

CW Yb:YSO diode pumped laser emitting at 1003.4 nm for the realization of a stable frequency standard

Laser emission at 1003.4 nm with an ytterbium doped crystal (Yb:YSO) is reported for the first time by using a new diode pumping scheme. A power of 170 mW at 1003.4 nm was obtained.

69-fs and broadly-tunable diode-pumped Yb:BOYS laser

Summary from only given. We present the first diode pumped femtosecond Yb:Sr/sub 3/Y(BO/sub 3/)/sub 3/ (also called Yb:BOYS) laser. Laser materials suitable for efficient, simple and compact ultrafast laser sources should provide a broad emission bandwidth, should exhibit favorable thermal properties, and should offer the possibility to be directly diode-pumped.

Evidence of nonradiative processes in Yb-doped oxoborate crystals by thermal lensing measurements

Summary from only given. Since they exhibit a low heat generation, ytterbium-doped materials turned out to be serious competitors of neodymium-doped materials for high power diode-pumped lasers. Because there is no excited-state absorption and upconversion processes, the only heat source is commonly admitted to be the quantum defect. As a consequence, thermal lensing is not expected to be different under lasing or non lasing conditions, provided the lasing wavelength is close to the average fluorescence wavelength. We herein relate thermal lensing measurements in diode-pumped Yb-doped oxoborate crystals: we observed strong differences between lasing and nonlasing conditions, proving that the quantum defect is not the only heat generating process.