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Optical method for measuring thermal accommodation coefficients using a whispering-gallery microresonator
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10.1063/1.3631342
/content/aip/journal/jcp/135/8/10.1063/1.3631342
http://aip.metastore.ingenta.com/content/aip/journal/jcp/135/8/10.1063/1.3631342

Figures

Image of FIG. 1.
FIG. 1.

Experimental setup. A fused-silica microsphere is mounted inside a vacuum chamber in which the ambient gas and pressure are controlled. After the microsphere is heated by a diode-pumped solid state (DPSS) laser, its WGM frequency spectrum is probed by light from a frequency-scanned cw diode laser that is launched into a bi-tapered fiber to excite TE or TM modes. A polarizing beamsplitter (PBS) separates throughput of the two polarizations.

Image of FIG. 2.
FIG. 2.

Thermal conductivity of air vs. pressure, measured using two bare single-stem microspheres of different effective radii a and different stem diameters. The lines are the fitted Eq. (10); the fit gives α = 0.770 ± 0.012 for the larger sphere (a = 179 ± 1μm, red, upper curve) and α = 0.997 ± 0.012 for the smaller sphere (a = 78 ± 1μm, blue, lower curve).

Image of FIG. 3.
FIG. 3.

Photograph of a bare fused-silica microsphere with two thin stems. This one has an effective radius in air, as defined in the text, of 290 ± 1 μm.

Image of FIG. 4.
FIG. 4.

Thermal conductivity of air vs. pressure, measured using a bare microsphere. The line is the fitted Eq. (10); the fit gives effective radius a = 290 ± 1 μm, and thermal accommodation coefficient α = 0.745 ± 0.006.

Image of FIG. 5.
FIG. 5.

Thermal conductivity of air vs. pressure, measured using a PDDA-coated microsphere. The line is the fitted Eq. (10); the fit gives effective radius a = 391 ± 1 μm, and thermal accommodation coefficient α = 0.802 ± 0.011.

Image of FIG. 6.
FIG. 6.

Thermal conductivity of air vs. pressure, measured using a microsphere silanized with aminosilane. The line is the fitted Eq. (10); the fit gives effective radius a = 344 ± 1 μm, and thermal accommodation coefficient α = 0.767 ± 0.008.

Image of FIG. 7.
FIG. 7.

Thermal conductivity of helium vs. pressure, measured using a bare microsphere. The line is the fitted Eq. (10); the fit gives effective radius a = 299 ± 1 μm, and thermal accommodation coefficient α = 0.394 ± 0.003.

Tables

Generic image for table
Table I.

Properties of the various ambient gases used in this work.

Generic image for table
Table II.

Summary of measurements of thermal accommodation coefficient α, of various gases on different surfaces, using a fused-silica microsphere of effective radius a as the substrate.

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/content/aip/journal/jcp/135/8/10.1063/1.3631342
2011-08-30
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Optical method for measuring thermal accommodation coefficients using a whispering-gallery microresonator
http://aip.metastore.ingenta.com/content/aip/journal/jcp/135/8/10.1063/1.3631342
10.1063/1.3631342
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