Simple optical devices called "scattering reticles" have been invented for calibrating Phase Doppler Particle Analyzers (PDPAs), which are optical instruments that analyze scattered light to determine the sizes and velocities of droplets. A scattering reticle comprises a polymeric plano-convex microlens, typically with a diameter of about 60 μm, on a glass substrate about 4 mm thick. In operation, a three-axis positioning stage is used to hold the substrate and move the microlens into the intersection of laser beams that defines the probe volume of a PDPA. The PDPA collects and analyzes the light scattered from the microlens.
Heretofore, PDPAs have been calibrated by use of droplet generators, which are difficult to use, are unreliable, and do not give repeatable results. Scattering reticles are easy to use, are small and inexpensive in comparison with droplet generators, and exhibit a high degree of repeatability.
To be useful for calibrating a PDPA, an optical device must scatter light in a manner similar to that of the droplets to be observed by the PDPA.
Ideally, the microlens on a scattering reticle should be hemispherical, but small deviations from hemisphericity are permissible.
Typically, a PDPA responds to light scattered by a microlens in the same way as to light scattered by droplets with a monodisperse size distribution. Scattering reticles with microlenses have been tested on two PDPAs, yielding results that were in agreement.
This work was done by Edward A. Hovenac of NYMA, Inc., and Steven James Bever of Wabash College for Lewis Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Physical Sciences category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Lewis Research Center
Commercial Technology Office
Attn: Tech Brief Patent Status
Mail Stop 7 - 3
21000 Brookpark Road
Refer to LEW-16350.