Patent ID: 8241914

Claim:
An apparatus for sorting stained particles in a fluid stream according to one or more characteristics of the particles, said apparatus comprising: a. a fluid delivery system for delivering a fluid stream containing the particles to a first location; b. a pulsed laser for delivering a pulsed beam of electromagnetic radiation to the first location for exciting particles in the fluid stream to produce fluorescence emissions, wherein the pulsed laser is position to deliver the pulsed beam of electromagnetic radiation at an angle which is not perpendicular to the fluid stream; c. an epi-illumination optics system including a focusing lens, the optics system being operable to direct the pulsed beam of electromagnetic radiation through the focusing lens in a forward direction along a beam axis intersecting particles in the fluid stream at said first location so that said particles pass through the pulsed beam, resulting in the fluorescence emissions from the particles being directed along said beam axis in a rearward direction; d. a photodetector positioned on the beam axis for detecting fluorescence emissions from the excited particles directed along said beam axis in the rearward direction; and e. a processor in communication with the photodetector to classify the particles according to the one or more characteristics based upon the fluorescence emissions of the particles and to sort the particles according to the classification of particles.