We have investigated the effect of co-doping Yb –Tm on the cooling parameters : and EQE. We have studied six different samples, three single doped with 5% and 10% Yb3+ and three co-doped with Tm3+: 16 ppm, 40 ppm and 80 ppm, respectively.
The samples have been cut and optically polished for cooling investigation. We obtained for a three co-doped samples an interesting effect on cooling parameters: the decrease of the , the increase of EQE and the red shift of the peak wavelength. To understand these effects it has been studied the absorption and emission spectroscopy. In particular we studied the emission of the manifolds of Tm3+ (1G4 and 3H4) and the energy transfer mechanisms between Yb-Tm to investigate the variation of cooling parameters. This study continued in-depth both with dynamic spectroscopic of Yb 3+ and Tm3+ levels in single and co-doped samples to put in evidence the cross-relaxation effect on the levels and possible effects caused by impurities transitions metals.
In laser cooling of crystals in solid-state physics, it is really important to obtain crystals with a large size at a relatively fast growth rate and high-optical quality that is defect-free. To get that, one of the methods to grow crystals is the Czochralski technique. The Czochralski technique will be presented and, in particular, the furnaces in New Materials for Laser Applications Laboratories of Pisa for this application will be discussed. Afterward the parameters for the growth of crystal fluorides are depicted and it is shown how these parameters lead to build samples suitable for optical cooling. All processes that are necessary to avoid contamination inside crystals like OH− ion and how to avoid reduction of Yb3+ to Yb2+ will be given. Spectroscopy of all samples will be treated in order to obtain the cooling parameters λf and αb for each sample. Afterward, an efficiency model will be discussed and the data efficiency of cooling obtained by a sample’s own crystals will be shown.
Optical cooling of solids, relying on annihilation of lattice phonons via anti-Stokes fluorescence, is an emerging technology that is rapidly advancing. The development of high-quality Yb-doped fluoride single crystals definitely led to cryogenic and sub-100-K operations, and the potential for further improvements has not been exhausted by far. Among fluorides, so far the best results have been achieved with Yb-doped LiYF4 (YLF) single crystals, with a record cooling to 91 K of a stand-alone YLF:10%Yb. We report on preliminary investigation of optical cooling of an LiLuF4 (LLF) single crystal, an isomorph of YLF where yttrium is replaced by lutetium. Different samples of 5% Yb-doped LLF single crystals have been grown and optically characterized. Optical cooling was observed by exciting the Yb transition in single-pass at 1025 nm and the cooling efficiency curve has been measured detecting the heating/cooling temperature change as a function of pumping laser frequency.
We present a characterization of the optical refrigeration properties of two 5% Ytterbium-doped YLF crystals. Measurements showed different cooling efficiencies for the samples, despite the same concentration of dopant. We carried out a spectroscopic study on the crystals devoted to the identification of foreign contaminants inside them. These searches determined the presence of Erbium and Holmium impurities in both the cooling samples. We attributed the reduction of the cooling efficiency in one of the crystals to an increased amount of these contaminants.
We have achieved cryogenic optical refrigeration with a record low temperature in optical refrigeration by cooling 5% wt.Yb:YLF crystal to 119K ±1K (~-154 C) at 1=1020 nm corresponding to its E4-E5 Stark manifold resonance with an estimated cooling power of 18 mW. This demonstration confirms the predicted minimum achievable temperature (MAT). Further cooling is achievable as shown by measurements of a doping study where a 10% wt. Yb:YLF crystal with reduced parasitic heating has predicted cooling below 100K (~-173K).
Since recent demonstration of cryogenic optical refrigeration, a need for reliable
characterization tools of cooling performance of different materials is in high demand. We present
our experimental apparatus that allows for temperature and wavelength dependent characterization
of the materials' cooling efficiency and is based on highly sensitive spectral differencing technique
or two-band differential spectral metrology (2B-DSM). First characterization of a 5% w.t.
ytterbium-doped YLF crystal showed quantitative agreement with the current laser cooling model,
as well as measured a minimum achievable temperature (MAT) at 110 K. Other materials and ion
concentrations are also investigated and reported here.
We report on the first observation of intracavity laser cooling inside of a vertical external-cavity surface-emitting laser
(VECSEL). A Yb:YLF crystal is placed under Brewster angle inside the cavity of an InGaAs quantum well VECSEL
emitting around 1030 nm. With the crystal in air, we observed cooling by about 0.5 degrees. By placing the sample and
cavity end mirror inside a vacuum chamber, with the window also at Brewster angle to the laser mode, cooling by 20
degrees has been realized. Furthermore, the development of a compact and efficient integrated cryocooler device is
We utilize highly sensitive spectroscopic local temperature probe to ascertain cooling performance of Yb:YLF
crystal as a function of wavelength and temperature. A minimum achievable temperature of 120 K is measured
at pump wavelength corresponding to E4-E5 Stark manifold transition. Results verify current model for laser
cooling cycle as well as demonstrate the lowest temperature achievable by means of optical refrigeration to date.
We demonstrate cooling of a 2 micron thick GaAs/InGaP double-heterostructure to 165 K from ambient using
an all-solid-state optical refrigerator. Cooler is comprised of Yb<sup>3+</sup>-doped YLF crystal, pumped by 9 Watt near
E4-E5 Stark manifold transition.
Spectroscopic characterization of YLF crystal doped with Yb reveals the performance potential of this material in laser
cooling applications. Temperature-dependent spectra allow us to estimate the minimum achievable temperature and the
parasitic background absorption.
We demonstrate first cryogenic operation in a Ytterbium doped YLF crystal by means of an optical refrigeration.
We have achieved cooling to 155 Kelvin absolute temperature with heat lift of 90 mW, exceeding performance of
multi-stack thermo-electric coolers. This progress was possible by pumping the system near the Stark-manifold
resonance of highly pure Yb:YLF crystal and careful thermal management in the cooling experiment. Detailed
spectroscopic analysis demonstrated that cooling to 110 Kelvin is currently possible if pumped exactly on that
We report the successful growth and the laser cooling results of Yb<sup>3+</sup>-doped single fluoride crystals. By investigating
the mechanical and thermal properties of Yb-doped BaY<sub>2</sub>F<sub>8</sub> and LiYF<sub>4</sub> 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:LiYF<sub>4</sub> and Yb:BaY<sub>2</sub>F<sub>8</sub> 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
We describe the development of Nd:YVO<sub>4</sub> lasers with continuous wave emission at 1.342 μm; theycon tain either
one or two crystals which are longitudinally pumped by fiber-coupled diode laser arrays. The two systems deliver respectively 7.3 and 12.1 W of output power. The best slope efficiency is 40% and the output beam divergence is about two times the diffraction limit. The influence of the Nd concentration, of the pump spot-size, and of the resonator configuration on the lasing performances have been experimentally studied. We also present and discuss data on spectroscopic properties of the crystals and on the thermally induced lens.