are shown as u201c u201d signs and the detectors are shown at boxes in the embodiment shown the array of light sources is provided adjacent one side of the flow stream 50 and the array of light detectors is provided adjacent the opposite side of the flow stream each of the light detectors is preferably aligned with a corresponding one of the light sources the array of light sources and the array of light detectors are shown arranged along a light source axis 200 that is slightly rotated relative to the axis 202 of the flow stream 50 the array of light sources is preferably an array of lasers such as vertical cavity surface emitting lasers vcsel fabricated on a common substrate because of their vertical emission vcsels are ideally suited for packaging in compact instruments such as a portable cytometer preferably the vcsels are u201c red u201d vcsels that operate at wavelengths that are less than the conventional 850 nm and more preferably in the 670 nm to 780 nm range red vcsels may have a wavelength power and polarization characteristic that is ideally suited for scatter measurements some prior art cytometer bench models use a single 9 mw edge emitting laser with a wavelength of 650 nm the beam is focussed to a 10 u00d7 100 micron elongated shape to cover the uncertainty in particle position due to misalignment and width of the core stream in contrast the output power of the red vcsels of the present invention operating at 670 nm is typically around 1 mw for a 10 u00d7 10 micron emitter and 100 micron spacing thus the total intensity of the light from a linear.