Radiation Hardness of High-Q Silicon Nitride Microresonators for Space Compatible Integrated Optics

Integrated optics has distinct advantages for applications in space because it integrates many elements onto a monolithic, robust chip. As the development of different building blocks for integrated optics advances, it is of interest to answer the important question of their resistance with respect to ionizing radiation. Here we investigate effects of proton radiation on high-Q silicon nitride microresonators formed by a waveguide ring. We show that the irradiation with high-energy protons has no lasting effect on the linear optical losses of the microresonators

Warped Brane worlds in Critical Gravity

We investigate the brane models in arbitrary dimensional critical gravity presented in [Phys. Rev. Lett. 106, 181302 (2011)]. For the model of the thin branes with codimension one, the Gibbons-Hawking surface term and the junction conditions are derived, with which the analytical solutions for the flat, AdS, and dS branes are obtained at the critical point of the critical gravity. It is found that all these branes are embedded in an AdS$_{n}$ spacetime, but, in general, the effective cosmological constant $\Lambda$ of the AdS$_{n}$ spacetime is not equal to the naked one $\Lambda_0$ in the critical gravity, which can be positive, zero, and negative. Another interesting result is that the brane tension can also be positive, zero, or negative, depending on the symmetry of the thin brane and the values of the parameters of the theory, which is very different from the case in general relativity. It is shown that the mass hierarchy problem can be solved in the braneworld model in the higher-derivative critical gravity. We also study the thick brane model and find analytical and numerical solutions of the flat, AdS, and dS branes. It is find that some branes will have inner structure when some parameters of the theory are larger than their critical values, which may result in resonant KK modes for some bulk matter fields. The flat branes with positive energy density and AdS branes with negative energy density are embedded in an $n$-dimensional AdS spacetime, while the dS branes with positive energy density are embedded in an $n$-dimensional Minkowski one.Comment: 14 pages, 7 figures, updated version, accepted by EPJ

Thermal noise of whispering gallery resonators

By direct application of the fluctuation-dissipation theorem, we numerically calculate the fundamental dimensional fluctuations of crystalline CaF2 whispering gallery resonators in the case of structural damping, and the limit that this noise imposes on the frequency stability of such resonators at both room and cryogenic temperatures. We analyze elasto-optic noise - the effect of Brownian dimensional fluctuation on frequency via the strain-dependence of the refractive index - a noise term that has so far not been considered for whispering-gallery resonators. We find that dimensional fluctuation sets a lower limit of 1E-16 to the Allan deviation for a 10-millimeter-radius sphere at 5 K, predominantly via induced fluctuation of the refractive index.Comment: 7 pages, 3 figure

Extraction-condition Optimization of Baicalein and Schisandrin from Hu-gan-kang-yuan Formula Using Orthogonal Array Design

Purpose: To optimize the extraction conditions for Hu-gan-kang-yuan Formula based on extraction rates of baicalein and schisandrin using an orthogonal array design.Methods: Ethanol concentration (50 - 70 %), ratio of solvent to raw material (8 - 12 mL/g), and extraction time (1 - 3 h) were examined with a three-factor and three-level L9(3)3 orthogonal array design. In addition, analysis of variance (ANOVA) was used to evaluate the statistical significance of the effects of individual factors on extraction rates of baicalein and schisandrin determined by high performance liquid chromatography (HPLC). The number of extractions was further investigated to confirm the extraction rate of target compounds based on the optimized conditions.Results: The optimized conditions were an ethanol concentration of 70 %; ratio of solvent to raw material, 12:1 mL/g; and extraction time of 60 min. Ethanol concentration and ratio of solvent to raw material showed significant effects on the extraction of the two compounds (p < 0.05). The number of extraction steps, two, was reasonable. The final optimum extraction conditions resulted in 79.48 ± 1.40 and 88.55 ± 1.85 % of extraction for baicalein and schisandrin, respectively.Conclusion: The optimized extraction conditions for baicalein and schisandrin are practicable and repeatable, and can be upgraded for pilot-scale production of Hu-gan-kang-yuan preparations.Keywords: Hu-gan-kang-yuan Formula, Extract-condition optimization, Orthogonal array design, Baicalein, Schisandri

A silicon single-crystal cryogenic optical resonator

We report on the demonstration and characterization of a silicon optical resonator for laser frequency stabilization, operating in the deep cryogenic regime at temperatures as low as 1.5 K. Robust operation was achieved, with absolute frequency drift less than 20 Hz over 1 hour. This stability allowed sensitive measurements of the resonator thermal expansion coefficient ($\alpha$). We found $\alpha=4.6\times10^{-13}$ ${\rm K^{-1}}$ at 1.6 K. At 16.8 K $\alpha$ vanishes, with a derivative equal to $-6\times10^{-10}$ ${\rm K}^{-2}$. The temperature of the resonator was stabilized to a level below 10 $\mu$K for averaging times longer than 20 s. The sensitivity of the resonator frequency to a variation of the laser power was also studied. The corresponding sensitivities and the expected Brownian noise indicate that this system should enable frequency stabilization of lasers at the low-$10^{-17}$ level.Comment: 5 pages, 5 figure

Bis[(diphenyl­phosphanylmeth­yl)diphenyl­phosphane sulfide-κ2 P,S]copper(I) hexa­fluoridophosphate

In the title compound, [Cu(C25H22P2S)2]PF6, the CuI atom, lying on a twofold rotation axis, adopts a distorted tetra­hedral geometry. The (diphenyl­phosphanylmeth­yl)diphenyl­phos­phane sulfide ligand coordinates to the CuI atom through one S and one P atom, forming a stable five-membered chelate ring. The P atom of the PF6 − anion also lies on a twofold rotation axis