G. Alombert-Goget

Multilayered YAG-Yb:YAG ceramics: manufacture and laser performance

Thermal effects in transparent laser crystals and ceramics are generally an unwanted consequence of the pumping process: temperature gradients give rise to an unevenly distributed refractive index variation and a distortion of the optical surfaces crossed by the laser beam (thermal lens); birefringence due to thermomechanical stress can cause depolarization losses; and absorption from the ground level usually increases with temperature in quasi-three-level systems. All these effects can seriously impair laser performance, especially in high-power devices. Layered structures with a tailored modulation of the doping level can be used to reduce the peak temperature, the temperature gradients and also the thermally induced deformation of the laser material, thus mitigating the overall thermal effects. In the present work, structures comprising two and three layers of different compositions (pure YAG/10 at% Yb:YAG and pure YAG/10 at% Yb:YAG/pure YAG) were designed with a view to control deformation and stresses, and to reduce the thermal lensing effect. The multilayered samples were assembled by linear and cold isostatic pressing, and co-sintered under a high vacuum in a clean-atmosphere furnace. The microstructure of the layered samples obtained was characterized by FEG SEM, ESEM and TEM. The Yb diffusion profile across the doped/undoped interface was identified and related to the lasers output power. An internal optical transmittance up to 96% was obtained. A laser output power up to 5 W, with a slope efficiency as high as 74.3%, was also achieved.

Conjugation of TEM-EDX and optical spectroscopy tools for the localization of Yb3+, Er3+ and Co2+ dopants in laser glass ceramics composed of MgAl2O4 spinel nano-crystals embedded in SiO2 glass

The main goal of this work is to conjugate two independent techniques of TEM-EDX and optical spectroscopy, which is rare, for the localization of Yb3+ and Er3+ rare earth ions and Co2+ transition metal ions as dopants in a compact self-Q-switched microchip laser glass ceramic composed of MgAl2O4 spinel nano-crystals of 10–20 nm size embedded in SiO2 glass. The use of the TEM-EDX technique associated with both the elemental mapping of each dopant and the direct visualization of the heavier rare earth ions has led to the result that Er3+ and Yb3+ rare earth ions are preferentially located in the spinel nano-crystals. Regarding the low Co2+ concentration this technique was not accurate enough for characterization and finally we have used absorption spectroscopy to probe the main presence of Co2+ ions in the spinel nano-crystals. The use of Yb3+ ions as structural probes allows the identification of the 0-phonon broad line at 977 nm as both that of the disordered glass and that of the spinel inverted phases. A new Yb3+ radiationless center has been pointed out by the presence of a strong absorption line at 970 nm which has been assigned to the strongly perturbed area of the spinel nano-crystallite surface. This dopant characterization is worthwhile to be shown as a special case where characterization of rare earth and transition metal ions needs the use of both TEM and spectroscopic techniques.

Thermally driven dual-frequency Q-switching of Nd:YGd2Sc2Al2GaO12 ceramic laser.

Multi-wavelength operation of Q-switched Nd-doped YGd(2)Sc(2)Al(2)GaO(12) garnet ceramic lasers has been investigated. Dual-wavelength emission around ~1.06 µm has been demonstrated both in the actively and passively Q-switched configurations. The ratio of output energy between the two laser wavelengths was driven by the temperature elevation caused by pumping. Passively Q-switched operation yields dual-frequency emission of two unsynchronized laser pulses carried by distinct transverse modes whereas active Q-switched configuration offers the possibility of synchronizing emission at the two wavelengths.

Laser Properties of the Nd:YGd2 Sc2 Al2Ga O12 Garnet Ceramic

CW lasing at 1058.6 and 1061.3 nm was demonstrated with 45% slope efficiency from the Nd:YGd2Sc2Al2GaO12 ceramic. From passive Q-switching, 2 ns pulses with 6.2 µJ energy are obtained at 7.3 kHz repetition rate.