Daniela Parisi

Anti-Stokes luminescence cooling of Tm3+ doped BaY2F8.

We report laser-induced cooling with thulium-doped BaY2F8 single crystals grown using the Czochralski technique. The spectroscopic characterization of the crystals has been used to evaluate the laser cooling performance of the samples. Cooling by 3 degrees below ambient temperature is obtained in a single-pass geometry with 4.4 Watts of pump laser power at lambda = 1855 nm.

Yellow solid state laser for metrological applications

We present laser results obtained from a Dy³⁺-Tb³⁺ co-doped LiLuF₄ crystal, pumped by a blue emitting InGaN laser diode, aiming for generation of a compact 578 nm source. We exploit the yellow Dy³⁺ transition ⁴F(9/2)⇒⁶H(13/2) to generate yellow laser emission. The lifetime of the lower laser level is quenched, via energy transfer, to co-doped Tb³⁺ ions in the fluoride crystal. We report the growth technique, spectroscopic study, and room temperature continuous wave laser results in a hemispherical cavity at 574 nm, and with a highly reflective output coupler at 578 nm. A yellow laser at 578 nm is very relevant for metrological applications, in particular for pumping of the forbidden ¹S₀-³P₀ ytterbium clock transition, which is recommended as a secondary representation of the second in the international system of units.We present a blue diode pumped solid-state laser results of Dy3+-Tb3+ co-doped in LiLuF4 host crystal. We exploit the yellow Dy3+ transition between 4F9/2 ??? 6H13/2 energy levels, pumping with an InGaN laser diode. The lifetime of lower laser level is quenched via energy migrations, co-doping the fluoride crystal with Tb3+ ions. We also report the growth technique and the room temperature continuous wave (CW) laser results in a two mirrors cavity. This yellow laser at 578 nm is very relevant for metrological applications.y, in particular it corresponds to the forbidden 1S0->3P0 Ytterbium clock transition which will be used in the next generation optical clocks developed at INRiM, the Italian institute for metrology.

Diode-pumped Pr:BaY2F8 cw orange laser

We report the realization of the continuous wave laser emission in the orange at 607 nm from a Pr:BaY(2)F(8) (Pr:BYF) crystal pumped by a blue GaN laser diode. A maximal output power of 78 mW is obtained in a quasi-single transverse mode beam. The effect of reabsorption losses at the laser wavelength is also evidenced.

Spectroscopy and Diode-Pumped Laser Experiments of LiLuF

In this work we report on the 2-mum laser emission of LiLuF4 crystals doped with thulium trivalent ions (Tm:LLF) at different doping density up to 16%. We will present our results regarding growth, absorption and emission spectroscopy, Judd-Ofelt analysis and room temperature diode pumping laser experiments as a function of the dopant density. The best result is 56% of slope efficiency, with a maximum output power of 280 mW. The emission wavelength ranges between 1985 and 2038 nm, exploiting the vibronic emission of Tm in LLF.

_{\bf 4}

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.

:Tm

A maximum laser power of 2.4 W was obtained at a wavelength of ~ 2040 nm for 23 W of absorbed pump power with a slope efficiency of 21.6 % with respect to absorbed power.

^{{\bf 3}+}

We report continuous-wave and repetitively Q-switched operation of a resonantly pumped Ho3+:KY3F10 laser at room temperature. End pumped by a Tm3+-doped silica fiber laser operating at 1938 nm, a maximum laser power of 7.8 W was obtained at a wavelength of ∼2041  nm for 21 W of absorbed pump power, corresponding to a slope efficiency of 60.7% with respect to absorbed power. At a repetition rate of 10 kHz up to 0.78 mJ, energy per pulse was demonstrated with pulse widths of 100 ns. The beam propagation factor (M2) was measured to be <1.26 at the maximum output power.

Crystals

We report on the first laser emission of (Lu x Gd(1−x))3 Ga5O12 doped with Tm3+ ions obtaining a slope efficiency of 20% and a maximum output power of 170 mW centered at 2013 nm. Evidences of a multiline emission are shown. Moreover a spectroscopic investigation on six samples of (Lu x Gd(1−x))3 Ga5O12:Tm3+ having different Lu concentrations is presented. In particular the stark sublevels energy of 3H6 and 3F4 manifolds have been determined. Spectroscopic data have been utilized to calculate absorption and emission cross sections and gain curves.

Single fluoride crystals as materials for laser cooling applications

A novel laser material BaYLuF8 (BYLF), doped with 12?at% of Tm3+, has been grown and optically investigated, in order to evaluate its potential performances as a 2??m laser. The BYLF crystal is interesting mainly because indications are that the mixed crystal would be sturdier than BaY2F8 (BYF). The addition of lutetium would improve the thermo-mechanical properties of the host. Absorption, fluorescence and lifetime measurements have been performed in the temperature range 10?300?K focusing on the 3H4 and 3F4 manifolds, those involved in the laser scheme at 2??m. The Stark sublevels structure of Tm3+ up to the 1D2 manifold has been figured out. Diode-pumped CW laser emission at 2??m has been achieved obtaining a slope efficiency of about 28% with respect to the absorbed power, by pumping along the Z-axis. A maximum output power of 240?mW was achieved by pumping along the favourable Y-axis, with an incident power of about 800?mW.

In-band pumped Ho 3+ :KY 3 F 10 2 μm laser

We demonstrate passive Q-switching (PQS) of the Tm-doped BaY2F8 (Tm:BYF) laser for the first time. The Tm:BYF laser is diode-pumped using an L-shaped hemispherical resonator. In the cw regime, the maximum output power with an 18% Tm-doped BYF crystal reached 1.12 W at ~1920 nm for an absorbed pump power of 3.06 W. In the PQS regime, maximum pulse energy (720 μJ) and peak power (17.1 kW) were obtained with an 8% Tm-doped BYF crystal and a Cr:ZnS saturable absorber with 92% low-signal transmission, again near 1920 nm, for a pulse width of ~40 ns and a repetition rate of 50 Hz.