Emissivity measurements of single levitated microparticles

Dee William Pack; Anthony Pluchino; Donald E. Masturzo

doi:10.1117/12.145695

24 May 1993 Emissivity measurements of single levitated microparticles

Dee William Pack, Anthony Pluchino, Donald E. Masturzo

Proceedings Volume 1862, Laser Applications in Combustion and Combustion Diagnostics; (1993) https://doi.org/10.1117/12.145695
Event: OE/LASE'93: Optics, Electro-Optics, and Laser Applications in Scienceand Engineering, 1993, Los Angeles, CA, United States

Abstract

Single micron-sized spherical particles of carbon and aluminum oxide are suspended in an electrodynamic levitator equipped with a high vacuum system. A CO₂ laser is used to heat the particles while their infrared emission signals are monitored from 1.3 - 5.5 micrometers . At atmospheric pressure, particle cooling from air conduction is quite rapid, and the IR signal from a particle follows the 5 millisecond laser pulse. When the levitator is evacuated to pressures ranging from 1 X 10^-4 to 1 X 10^-5 torr, the efficiency of molecular impact cooling is greatly reduced, and radiative cooling becomes dominant. Under these conditions the particle temperature and emissivity can be found by theoretical fits of the radiative decay curves. For the carbon samples, our analysis has yielded emissivity values in good agreement with those calculated from Mie theory. One interesting feature of this agreement is the determination of emissivities greater than one for the smaller carbon particles. The emissivities found from the thermal decays of Al₂O₃ micro- particles are much larger than those predicted using Mie theory with bulk optical constants. These anomalously high emissivities for the alumina particles may be caused by surface contaminants.

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Dee William Pack, Anthony Pluchino, and Donald E. Masturzo "Emissivity measurements of single levitated microparticles", Proc. SPIE 1862, Laser Applications in Combustion and Combustion Diagnostics, (24 May 1993); https://doi.org/10.1117/12.145695

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