Abstract: A method and apparatus for identifying individual particles or cells which have been labeled with different fluorochromes, on the basis of the lifetime of their fluorescence, or based on different decay times for a fluorochrome in different cells.

Abstract: A flow cytometer measures phase fluorescence lifetimes by the phase shift of a reference signal and an emission from a particle or cell in a flow chamber. An acoustic optic modulator modulates laser light with a sinusoidal wave of a predetermined frequency to excite particles or cells. Detectors respond to emissions of individual particles or cells in the form of an output signal pulse at the predetermined frequency. The output signal pulse is divided into equal pulses with each at the modulation frequency, the same amplitude and fidelity and amplitude. One part of the divided pulse is stripped of its envelope to pass the width thereof and out of band components are rejected. A variable amplifier passes a portion of the pulse above a present level. A delay line sets a central part of the signal at a predetermined point in time. A circuit limits the attenuated one part. A double balance mixer multiplies and the relates the limited signal with a reference signal to determine the phase shift.

Abstract: A flow cytometer measures fluorescence lifetimes by the phase shift of a reference signal and an emission from a fluorescent particle or cell in a flow chamber in order to identify the particle or cell. An acoustic optic modulator modulates laser light with a sinusoidal wave of a predetermined frequency to excite particles or cells. Detectors respond to emissions of individual particles or cells in the form of an output signal pulse at the predetermined frequency. Signals representative of fluorescence emitted and reference beam signals is measured. The particle is identified by the phase shift.