1. Photomultiplier Tube m = k 8–19 dynodes (9-10 is most common).
Gain (m) is # e- emitted per incident e- () to the power of the # of dynodes (k).
m = k
E.g., 5 e- emitted / incident e-, 10 dynodes.
m = k = 510  1 x 107
Typical Gain =
Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.

2. Choosing a PMT Average anodic current Single photon counting
Hamamatsu Catalog

3. Modes of Operations Average anodic current Single photon counting
Hamamatsu Catalog

4. Single Photon Counting
Single photons give bursts of e-
The rise time of PMTs depends on the spread in the transit time of e- during the multiplication process.
FWHM: Full Width at Half of Maximum
Hamamatsu Catalogue

5. Single Photon Counting
Improved S/N at low p
Hamamatsu Catalogue

6. Thermionic Emission is Dependent on Bias Voltage
Hamamatsu Catalogue

7. Sources of Dark Current: Glass Scintillation
Brief flash of light when an e- strikes the glass envelope.
Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.
Ingle and Crouch, Spectrochemical Analysis

8. Sources of Dark Current: Thermionic Emission
Thermal energy releases e- from the cathode.
Reduced by cooling
Hamamatsu Catalogue

9. Photodiodes Photons incident on the depletion layer induce a current.
In most cases, best response in the NIR.
Response is linear over 6 – 7 orders of incident radiant power
Ingle and Crouch, Spectrochemical Analysis

10. Semiconductors Silicon or Germanium are common.
n-type: Si (or Ge) doped with group V element (As, Sb) to add electrons.
p-type: Doped with group III element (In, Ga) to add holes.
J. Michael Hollas, Modern Spectroscopy, John Wiley & Sons, New York, 1992.

11. Diode (pn – Junction)
Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.

12. Spectral Response of Photodiodes
Shinya Inoue and Kenneth Spring, Video Microscopy, Plenum Press, New York, 1997.

13. Avalanche Photodiode Hamamatsu Catalog

14. Photodiode Arrays (PDA or DAD)
Simultaneous  detection in a spectrophotometer.
Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.

15. Charge Coupled Device (CCD)
Ingle and Crouch, Spectrochemical Analysis

16. CCD Architecture Image Area Top View SiO2 backing Pixel Array
insulating oxide
Image Area
Top View
serial register
amplifier
and Bryce Marquis (Haynes Lab)

17. Bryce Marquis (Haynes Lab)
CCD Architecture
“Channel Stops” form horizontal pixel boundaries
Top View
3 electrodes
form vertical
pixel boundaries
One pixel
Electrode
Insulating oxide
n-type silicon
p-type silicon
Cross section
Bryce Marquis (Haynes Lab)

18. Charge Generation/Collection-V +V -V -V +V -V
N-type
P-type
Incident photons excite electron-hole pairs,
electrons gather in potential wells in each pixel

19. CCD Rain Bucket Analogy
1. Generation
2. Collection
3. Transfer
4. Measurement
Shinya Inoue and Kenneth Spring, Video Microscopy, Plenum Press, New York, 1997.

20. Charge Transfer Every third electrode is 2 coupled, charge packets
are walked towards
serial registry 2
+5V 0V
-5V 1
+5V 0V
-5V 3
to serial registry 1 2 3
Time-slice shown in diagram

21. +5V 0V
-5V 2
+5V 0V
-5V 1
+5V 0V
-5V 3 1 2 3

22. +5V 0V
-5V 2
+5V 0V
-5V 1
+5V 0V
-5V 3 1 2 3

23. +5V 0V
-5V 2
+5V 0V
-5V 1
+5V 0V
-5V 3 1 2 3

24. +5V 0V
-5V 2
+5V 0V
-5V 1
+5V 0V
-5V 3 1 2 3

25. +5V 0V
-5V 2
+5V 0V
-5V 1
+5V 0V
-5V 3 1 2 3

26. +5V 0V
-5V 2
+5V 0V
-5V 1
+5V 0V
-5V 3 1 2 3

27. Charge Transportation
amplifier
Pixels at end of the array dump charge into serial register
Serial register walks charge packets to amplifier, where it is measured.

28. Quantum Efficiency

29. Noise Sources in CCD Shot Noise Dark Signal Noise Readout Noise
Statistical variation of signal over time
Increases with the square of the intensity
Dark Signal Noise
Caused by thermal liberation of electrons
Strongly coupled to temperature
Readout Noise
Summation of noise associated with amplification of signal, and conversion from analogue to digital
Increases with the processing speed

30. Other Issues: Bad Pixels
Increasing hot pixels
Hot Pixels
Increased charge accumulation due to variations in chip surface.
Dead Pixels
Defective pixels that do not respond.

31. Other Issues: Blooming

32. Other Issues: Cosmic Rays
Noise From Outer Space!!!
* indicates cosmic rays

33. Other Issues: Etaloning

34. Other Features: Binning
On Chip Pixel Binning
Increases S/N
Shot noise decrease
Increased speed
Less storage space needed
Decreases resolution

35. Are you getting the concept?
List the advantages and disadvantages of using each of the discussed detectors to achieve single molecule detection.