More description of this probe is on this EOL web page, and on the NCAR U: drive (U:\EOL\EOL Users\dcrogers\UHSAS).
A description by the current manufacturer is available at this DMT web site. This description is a little out-of-date because it doesn't take into account a recent change, as described in the next item:
Cai, Y., D.C. Montague, W. Mooiweer-Bryan, T. Deshler, 2008: Performance characteristics of the ultra high sensitivity aerosol spectrometer for particles between 55 and 800 nm: Laboratory and field studies. J. Aerosol Sci.,39, 759--769.