Calcium difluoride (CaF2) is an industrially important material for high power optical devices due to its high melting point, stoichiometric composition, low background absorption coefficient, and large optical transparency window. Solid state laser refrigeration has recently been reported with single crystals of cubic CaF2 (fluorite crystal structure, space group Fm-3m) doped with trivalent ytterbium ions. In this presentation we present the recent design, hydrothermal synthesis, and characterization of ytterbium-doped CaF2 microspheres with diameters ranging from 500 nm to 4 micrometers. Raman spectroscopy reveals the presence of point defects that compensate for trivalent ytterbium ions that reside at divalent calcium ion sites in the crystal lattice. Near-infrared optical luminescence spectroscopy is used to demonstrate that CaF2 microspheres undergo solid state laser refrigeration under ambient conditions. These materials are anticipated to have significant applications in experimental single molecule biophysics, radiation-balanced microlasing, and the future development of optomechanical quantum sensors.
We present the hydrothermal synthesis of highly porous α-NaYF nanocubes with edge lengths on the order of 150 nm using sodium dodecyl sulfate (SDS) as a ligand. The surface area is increased by a factor of four compared to hypothetical ideal cubes of the same size. Furthermore, the surface-to-volume ratio of these particles is higher than that of 50 nm spherical α-NaYF particles commonly obtained with EDTA under similar conditions, resulting in the highest surface-to-volume particles obtained with hydrothermal synthesis. Laser cooling at ambient pressure and laser heating of the same particles in vacuum is demonstrated. The implications of our results for payload cooling of optically levitated nanoscale sensors are discussed.
Hexagonal microcavities have been proposed for a wide range of applications including microlasers, levitated optomechanics, quantum information science, and biosensors that make use of both Fabry-Perot and whispering gallery mode cavity resonances. Photothermal heating impacts a number of optical and mechanical properties of hexagonal microcavities based on the temperature dependence of quantities such as radiative lifetime, Young’s modulus, optical index of refraction, and the corresponding wavelength of cavity mode resonances. This talk will present recent results in both analytical and numerical modeling of photothermal heating in hexagonal cavities inspired by recent optomechanical levitation experiments in both aqueous and high-vacuum environments.
Recent advances in the synthesis of inorganic materials have enabled a wide range of control of particle size, composition, phase, and morphology that can be tuned in the design of future levitated optomechanical sensors. This talk will describe recent results in the hydrothermal synthesis and characterization of two-dimensional microprisms of hexagonal sodium yttrium fluoride crystals based on novel molecular ligands. Hexagonal cavities with high aspect with high aspect ratios of ~50 are observed with potential applications in the detection of high frequency gravitational waves, radiation balanced microlasers, and the solid-state laser cooling of quantum sensors.
Negatively charged nitrogen-vacancy (NV-) centers in diamond have a plethora of potential applications in quantum systems, including sensing and computing1-3. Photothermal heating can limit the utility of NV- center nanodiamonds, especially under high laser irradiances4-6. A composite of nanodiamonds with NV- defects and ytterbium-doped cubic sodium yttrium fluoride (Yb:α-NaYF4 or NaYF) could offset the photothermal heating of nanodiamonds by the anti-Stokes fluorescence cooling of Yb3+ ions7. We present a novel preparation method for generating a NV- diamond NaYF composite material based on a hydrothermal synthesis approach. Particle size was determined to be 230 ± 90 nm by SEM, and DLS data show a permanent connection between nanodiamonds and NaYF. Nanodiamonds are observed on the surfaces of NaYF materials. Nanodiamonds may also be incorporated within the body of individual NaYF grains, however the question of whether nanodiamonds are fully incorporated into the host NaYF material remains to be answered. The temperatures of host material and NV- defects are accessed using mean fluorescence wavelength shifts and Debye-Waller factor thermometry respectively. The obtained temperature changes with increasing 1020 nm irradiance show good agreement. Two data sets showed photothermal heating of around 10 and 13 K at 6.3 MW/cm2. Increased particle smoothness and sizes could lead to coolable composite materials.
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