Chapter 2: Introduction 29
• Bandpass filters (BPs). Pass a narrow spectral band of light.
When dichroic filters are used as steering optics to direct different
color light signals to different detectors, they are called dichroic
mirrors. Longpass dichroic mirrors transmit longer wavelengths to
one detector while reflecting shorter wavelengths to a different
detector.
The BD FACSCelesta flow cytometer polygon detector arrays use
dichroic longpass mirrors on the inside, and bandpass filters on the
outside of the filter holders.
Signal detectors Light signals are generated as particles pass through the laser beam
in a fluid stream. When these optical signals reach a detector,
electrical pulses are created that are then processed by the
electronics system.
There are two types of signal detectors in the BD FACSCelesta
flow cytometer:
• Photomultiplier tubes (PMTs). Used to detect the weaker
signals generated by side scatter and all fluorescence channels.
These signals are amplified by applying a voltage to the PMTs.
Longpass dichroic mirrors
Bandpass filters
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