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Abstract

A light scatter detector assembly for an analytical instrument, such as a laser flow cytometer or clinical hematology instrument having at least two angles of scatter. A high numerical aperture lens system is used, preferably a system using only two lenses to collect light after interacting with suspended particles passing through a flow cell into a collimated beam. A dark stop having apertures in different locations is interposed in the collimated beam light detected to produce therefrom two optical beams, respectively corresponding to the two scatter signals, e.g., high angle scatter and low angle scatter. The apertures are preferably radial sectors. The two scatter beams are passed to a beam separating element and through a collimating lens onto respective photodetectors. The beam separating element may be a split mirror having two mirrors mounted at an angle to each other, e.g., less than 15.degree., preferably 51/2.degree., to direct the beams in different directions to the two photodetectors. Alternatively, the beam separating element may be a multifaceted prism having at least two refracting portions to direct the two beam outputs to different photodetectors. The same lens may be used to pass the beams directed in different directions by the beam separating element to the two different photodetectors. The two photodetectors are preferably mounted on a single printed circuit board (pcb) in a prealigned manner using conventional pcb component mounting technology.

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