Investigation of Yb-doped LiLuF4 single crystals for optical cooling

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

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Fluoride Laser Crystals-Old And New

The development of oxide and fluoride materials as gain materials of choice for solid state lasers ranges from early materials such as Calcium Fluoride and Calcium Tungstate crystals to the now ubiquitous Nd hosts YLF, YAG and Vanadate. Among Tunable laser materials, MgF 2 - an early favorite, gave way to superior oxides such as Alexandrite and Ti:Sapphire only to be followed by development of still newer tunable fluoride media, notably, fluoride colquiriites such as Cr-doped LiSAF and LiCaF. Newer fluoride crystals, such as Barium Yttrium Fluoride BaY 2 F 8 (BYF), KY 3F 10 (KYF) and the tunable Cr doped LiCaGaF 6 are attractive laser materials, but their growth has not been optimized. Key advantages of two of these new crystals are discussed. Crystal growth results for BYF and Cr:LiCaGaF 6 as well as some material characterization are presented

Fluorescence Quantum Efficiency Measurements In The Presence Of Auger Upconversion By The Thermal Lens Method

Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAlF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upcon-version rate that is proportional to the excited-state population, Wup = γN6, the theoretical model developed fits the experimental data well. The ETU parameters (γ) were determined with unprecedented accuracy for low Cr concentrations. Thermo-optical parameters (K, ds/dT) were also obtained. © 2003 Optical Society of America

Volumetric Three-Dimensional Up-Conversion Display Medium

Several rare-earth-doped fluoride crystals that are excited to emit visible light by sequential two-photon absorption have been investigated as display-medium candidates for static volumetric three-dimensional displays. Dispersion of powders of these materials in a refractive-index-matched polymer is reported because such a medium may result in a scalable display. The scattering problem in such a medium is greatly reduced by index-matching the polymer to the crystalline particles. An index-matching condition that optimizes the performance is identified. © Copyright 2007 Society for Information Display

Distinguished Student Paper: Development Of A Scalable Volumetric Three-Dimensional Up-Conversion Display Medium

Several rare-earth doped fluorides that are excited to emit visible light by sequential two photon absorption have been investigated for use in volumetric three dimensional displays. Dispersion of powders of these materials in a refractive index matched polymer is reported since such a medium may result in a scalable display. © 2007 SID

Discrimination Between Thermal Quenching Of The Fluorescence And Auger Upconversion Processes Using Thermal Lens Technique

In this work we used the Thermal Lens (TL) technique to discriminate two important processes responsible to reduce the upper-state population and fluorescence quantum efficiency (η) in Cr3+ doped colquiriite crystals: the thermal quenching of the fluorescence (TQF) and the Auger upconversion (ETU). We observed a nonlinear increase of the TL signal with laser power due to the decrease of η by ETU and/or TQF. The analysis of these curves allowed the determination of the thermal load, the increase of the crystal temperature as a function of the pump excitation and the discrimination between ETU and TQF processes. © 2006 Elsevier B.V. All rights reserved

High Pulse Energy 3.9 Μm Lasers In Ho:Byf

Experimental results describing pulsed lasers operating near 3.9 μm on the Ho 3+ ( 5I 5- 5I 6) transition in highly-doped (\u3e 10 at. %) barium yttrium fluoride (BaY 2F 8 or BYF) will be presented. The 5I 5 manifolds in Ho:BYF were pumped using a flashlamp excited, free-running Cr:LiSAF laser tuned to the Ho 3+ absorption peak near 889nm. Ho 3+ concentrations of 10%, 20%, 30% and 40% in BYF were lased in a simple end-pumped resonator. Some similar data was also obtained in 10% and 20% Ho: YLF. The highest 3.9 μm pulse energy obtained in the comparative study was 55 mJ (at ∼10% optical-to-optical efficiency) using the 30% Ho:BYF crystal. A dual end-pumped laser in 30% Ho:BYF was also demonstrated, providing a pulse energy of 90 mJ in a near diffraction limited beam (M 2 ∼ 1.2). Emission decay data was taken to shed light on the observed dependence of laser efficiency on holmium concentration and excitation density. The lifetimes of both lasing levels ( 5I 5 and 5I 6) deviate rather significantly from their low-concentration values. Plausible energy transfer processes that may be responsible for the observed trends in the laser and emission data will also be discussed

Temperature-dependent stimulated emission cross section in Nd(3+) : YVO(4) crystals

Spectroscopic properties of neodymium-doped yttrium orthovanadate crystals were measured in the temperature range between 5 and 350 K. Crystals fabricated by different suppliers, with 0.3 and 1 at% Nd(3+), were compared. For each temperature, the stimulated emission cross sections of the Nd(3+) (4)F(3/2) decay to the (4)I(9/2), (4)I(1/2), and (4)I(13/2) states were obtained using the Fuchtbauer-Ladenburg and the reciprocity techniques. Nd:YVO(4) shows higher absorption at room temperature and higher stimulated emission cross section with similar variation with temperature when compared with Nd:YAG. The anomalous dependence on temperature of the Nd(3+) (4)F(3/2) excited-state lifetime is discussed and an explanation is suggested. (C) 2009 Optical Society of Americ