Particle detection system implemented with an immersed optical system

In a particle detection system for detecting particles entrained in a fluid stream that flows along a flow axis, the particle detection system having a view volume in which a light beam propagating along a light propagation path transversely intersects the fluid stream such that entrained particles upon which the light beam is incident cause portions of the light beam to scatter from the view volume as scattered light components, at least some of the scattered light components propagating through a light collection lens system that has a light collection lens system axis and being incident on a light detector that produces a signal representing the intensity of the scattered light components propagating through the collection lens system and incident on the light detector, the improvement comprising:

• a flow-though cell including first and second body sections coupled to form a unitary article, the first and second body sections associated with respective first and second optical elements;
• each of the first and second body sections having opposed interior surface portions configured to form opposed walls of a flow channel through which the fluid stream flows;
• and
• the unitary flow-through cell sized for insertion into the particle detection system in an orientation that positions the first and second optical elements along the light collection lens system axis.