Near-simultaneous measurements at forward and back scatter angles in light scattering photometers

摘要

A light scattering photometer including a rotating segmented mirror intercepting light from a laser source and alternately directing the light into a sample zone along an optical axis in first and second opposite directions. A mask annulus coaxial with the optical axis intercepts light scattered from the sample in an incremental angle &Dgr; &thgr; at a selected angle &thgr; with respect to the axis. As the direction of sample illumination alternates, the annulus alternately intercepts forward scatter and back scatter of light from the sample at angles &thgr; and 180°-&thgr;, respectively, and passes the forward and back scatter in alternate succession to a detector. The detector output signal is demodulated to derive near-simultaneous forward and back scatter measurements from the sample. The photometer permits measurement at small values of &thgr; approaching 0° and hence permits near- simultaneous scatter measurements at forward and back scatter angles spaced by an angle approaching 180°.