A. Toncelli

Single fluoride crystals as materials for laser cooling applications

We report the successful growth and the laser cooling results of Yb3+-doped single fluoride crystals. By investigating the mechanical and thermal properties of Yb-doped BaY2F8 and LiYF4 crystals and using the spectroscopic data we collected from our samples, the theoretical and experimental cooling efficiency of fluoride crystals are evaluated and compared with respect to those of ZBLAN. Two different methods, a thermal camera and a fluorescence intensity ratio technique, have been used to monitor the temperature change of the samples. The temperature change is clearly exponential, as expected from theory, and the temperature drops are 6.3 K and 4 K for Yb:LiYF4 and Yb:BaY2F8 respectively in single-pass configuration, corresponding to a cooling efficiency of about 2% and 3%. This last value is slightly larger than that observed in Yb-ZBLAN in similar experimental condition.

Effect of Tm concentration on the tunability of the YLF laser in the 1.9 µm region

We describe the continuous-wave (cw) operation of a LiYF4 laser based on crystals doped with different concentrations of Tm3+. We observed the fluorescence spectra from the upper laser level when the crystal is placed inside the laser resonator, in the same optical environment of the coherent emission. We measured the laser intensity as a function of pump power and obtained a 24% slope efficiency by selecting a suitable orientation of the crystal. Using all this information, we were able to demonstrate laser tunability at 1.9 µm in a 50 cm−1 wide interval.

Time-resolved pump-probe measurements of UV material cerium-doped BYF

We present the results of an investigation of the spectroscopic properties of Ce3+:BaY2F8 (BYF), which is a potential laser material with an emission wavelength range from 320 nm to 360 nm. We have employed a time-resolved pump-probe technique to investigate the polarization-dependent absorption and emission properties, and the dynamic color centre formation process. We observe strong absorption from colour centres with millisecond and second lifetimes that will certainly prevent laser action with the crystals used here. Evidence suggests that there may be potential gain in this crystal if long-lived colour centres can be reduced.

Laser Cooling in Rare Earth Doped BaY2F8 Crystals

Laser cooling in thulium- and ytterbium-doped BaY2F8 crystals is observed. We investigate the potential of this crystalline host for all-solid-state cryocooler applications as compared to those based on rare-earth doped ZBLANP systems.

Widely tunable Tm-Ho:KYF4 laser around 2 µm

The development of room-temperature diode-pumped 2 µm Tm-Ho:KYF4 laser is reported for the first time. 268 mW output power, 33% efficiency and 100 nm tunability are demonstrated. Single-mode operation is selected using an intracavity etalon.

High-power Diffraction-limited Diode-pumped Nd:YVO4 cw Laser at 1.34 µm

A Nd:YVO4 laser, end-pumped by a fiber-coupled diode laser, provides 40% slope efficiency, a nearly diffraction-limited beam and 6.5 W of output power at 1.34 |im, the highest so far reported for this host. The use of crystals with a very low Nd concentration is a key element for performance improvement.

Frequency analysis of nonlinear energy transfer

We study the behavior of the Er3+:4S3/2 green fluorescence of three different Er3+-doped crystals, from both a theoretical and an experimental point of view and develop a new frequency analysis method to measure the upconversion parameter based on rate equation formalism. This formalism is then corrected taking into account the migration process. Theoretical and experimental results show a qualitatively good agreement.

Nonlinear process analysis in Er3+:Ca3Sc2Ge3O12

In this paper we report two different approaches to study the energy transfer mechanisms inside laser crystals under steady-state and dynamical conditions. The first method is based on the fluorescence Fourier analysis and is able to identify from which multiplets and through which processes the observed multiplet is populated. With the second method we analyse the decay kinetics of the fluorescences by numerical integration of a rate equation model. This analysis permits to evaluate the rate of the energy transfer mechanisms.