Book contents
- Frontmatter
- Contents
- Acknowledgements
- 1 Introduction
- 2 Fluid flow dynamics
- 3 Light and optics
- 4 Electronics
- 5 Computing
- 6 Cell sorting
- 7 Preparation and staining
- 8 Miscellaneous techniques
- 9 Instrument performance
- 10 Light scatter applications
- 11 Nucleic acid analysis
- 12 Nucleic acids and protein
- 13 Chromosomes
- 14 Dynamic cellular events
- 15 Applications in oncology
- 16 Epilogue
- References
- Index
4 - Electronics
Published online by Cambridge University Press: 27 October 2009
- Frontmatter
- Contents
- Acknowledgements
- 1 Introduction
- 2 Fluid flow dynamics
- 3 Light and optics
- 4 Electronics
- 5 Computing
- 6 Cell sorting
- 7 Preparation and staining
- 8 Miscellaneous techniques
- 9 Instrument performance
- 10 Light scatter applications
- 11 Nucleic acid analysis
- 12 Nucleic acids and protein
- 13 Chromosomes
- 14 Dynamic cellular events
- 15 Applications in oncology
- 16 Epilogue
- References
- Index
Summary
Photodetectors
Photodetectors are light-sensitive devices which proportionally convert light energy (photons) into electrical energy and they fall into two categories.
Photomultipliers
In photomultipliers the incident photons strike the photocathode which then emits electrons in direct proportion to the number of photons striking the cathode. This is the point at which the light flux is transduced (changed) into the electronic signal. The electron flux emitted from the photocathode is then amplified through a dynode chain within the photomultiplier to produce a current.
There are now literally hundreds of different varieties of photomultiplier tubes. They vary in their photocathode material and construction, their ‘windows’ through which the light passes before striking the photocathode and in their dynode chain construction. Different photocathode materials and construction have different sensitivities to light of different wavelengths. Typically, the S11 and bialkali tubes are relatively more sensitive in the high UV, violet, indigo, blue and through to the green. The S20 tubes are relatively more sensitive to the lower energy wavelengths, namely the yellows, oranges and reds. In order to obtain the greatest efficiency for the conversion of light into electrons the photomultiplier should be chosen to be maximally sensitive to the particular wavelength band that is to be measured with that particular photomultiplier tube. For example, it makes no sense to use an S20 tube with an extended red response to measure violet and blue light, and equally, it makes no sense to use an S11 tube to measure red light. Quartz transmits UV light much more efficiently than optical crown glass and photomultipliers which are required to quantitate UV and violet light should be equipped with quartz windows.
- Type
- Chapter
- Information
- Introduction to Flow Cytometry , pp. 65 - 73Publisher: Cambridge University PressPrint publication year: 1991