About Electronics - BD FACSCelesta Flow Cytometer User Manual

112 BD FACSCelesta Flow Cytometer User's Guide

About electronics

Introduction
Pulse
This topic describes the electronics in the BD FACSCelesta flow
cytometer
As cells or other particles pass through a focused laser beam, they
scatter the laser light and can emit fluorescence. Because the laser
beam is focused on a small spot and particles move rapidly through
the flow cell, the scatter or fluorescence emission signal has a very
brief duration—only a few microseconds. This brief flash of light is
converted into an electrical signal by the detectors. The electrical
signal is called a pulse. The following figures illustrate the anatomy
of a pulse.
1. A pulse begins when a particle enters the laser beam. At this
point, both the beam intensity and signal intensity are low.
2. The pulse reaches a maximum intensity or height when the
particle reaches the middle of the beam, where the beam and
signal intensity are the brightest. The peak intensity, or height
of the pulse, is measured at this point.
Time
Time