Calibration of the Forward-scattering Spectrometer Probe: Modeling Scattering from a Multimode Laser Beam

Edward A. Hovenac Sverdrup Technology, Inc., NASA/Lewis Research Center Group, Cleveland, Ohio

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James A. Lock Department of Physics, Cleveland State University, Cleveland, Ohio

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Abstract

Scattering calculations using a more detailed model of the multimode laser beam in the forward-scattering spectrometer probe (FSSP) were carried out by using a recently developed extension to Mie scattering theory. From this model, new calibration curves for the FSSP were calculated. The difference between the old calibration curves and the new ones is small for droplet diameters less than 10 µm, but the difference increases to approximately 10% at diameters of 50 µm. When using glass beads to calibrate the FSSP, calibration errors can be minimized, by using glass beads of many different diameters, over the entire range of the FSSP. If the FSSF is calibrated using one-diameter glass beads, then the new formalism is necessary to extrapolate the calibration over the entire range.

Abstract

Scattering calculations using a more detailed model of the multimode laser beam in the forward-scattering spectrometer probe (FSSP) were carried out by using a recently developed extension to Mie scattering theory. From this model, new calibration curves for the FSSP were calculated. The difference between the old calibration curves and the new ones is small for droplet diameters less than 10 µm, but the difference increases to approximately 10% at diameters of 50 µm. When using glass beads to calibrate the FSSP, calibration errors can be minimized, by using glass beads of many different diameters, over the entire range of the FSSP. If the FSSF is calibrated using one-diameter glass beads, then the new formalism is necessary to extrapolate the calibration over the entire range.

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