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Outline

The measurement of the pollen density is based on the measurement of the settling velocities of pollens in two different fluids. The settling velocities of individual corn pollens were measured using an In-line Digital Holography system. The system consisted of a HeNe laser (632.8 nm), optics, a settling chamber and a Kodak ES4 CCD camera (2kx2k) with a maximum frame rate of 15 fps. A neutral density filter was used to attenuate the laser beam intensity after which the beam was expanded and spatially filtered. The spatially filtered beam was then collimated and sent through the volume of interest (VOI) in the settling chamber. The interference between the reference and the object beam created a diffraction pattern that was recorded by the CCD camera without a lens. The settling chamber consisted of a square Acrylic chamber with a height of 45 cm and an inside channel width of 5 cm.

Digital Holography setup

The recorded holograms were reconstructed in two different ways. First in order to speed up the data analysis time, a recorded hologram was reconstructed digitally by collapsing all the different planes into one one image (collapsed reconstruction). Second, in order to know the shape of the particle, in-focus reconstruction was performed. In this case multiple planes are reconstructed and the in-focus plane is found.

van Hout, R., Katz, J., 2004. A method for measuring the density of irregularly shaped biological aerosols such as pollen. Journal of Aerosol Science 35, 1369-1384.

van Hout, R., Katz, J., 2003. A method for measuring the density of irregularly shaped particles such as pollen. AGU 2003 Fall meeting, 8-12 December, Moscone Center West, San Francisco
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Department of Mechanical Engineering, The Johns Hopkins University
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