Abstract: Various optical apparatus, in particular embodiments, may provide a source of parallel light (7, 75). The parallel light (7, 75) may be generally achieved by directing an incident beam at the apex of a prism (1, 22, 24, 26, 28). The prism may have varying configurations. One configuration has a forward conical face (24). Another configuration has a pyramidal forward end (22). Other configurations are also disclosed. Various optical methods and methods for flow cytometry are also disclosed.

Abstract: Various optical apparatus provide a source of parallel light (7, 75). The parallel light (7, 75) is generally achieved by directing an incident beam at the apex of a prism (1, 22, 24, 26, 28). The prism may have varying configurations. One configuration has a forward conical face (24). Another configuration has a pyramidal forward end (22). Other configurations are also disclosed. The application also discloses the use of reflectors (20, 78, 216, 316, 400) having internal reflective surfaces shaped as three-dimensional figures of revolution, for example paraboloid or ellipsoid. The reflectors (20, 78, 216, 316) focus light incident onto the reflectors at one or more foci (F, 220, 320, 420). The reflectors may be used in combination with the optical apparatus including the prisms (1, 22, 24, 26, 28). The reflectors (20, 78, 216,316) may be used in flow cytometers for focusing light at a sample stream (237, 337) passing through the focus (F, 220, 320, 420) of the reflector (20, 78, 216, 316).