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 = 104 - 107 Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.

Choosing a PMT Average anodic current Single photon counting Hamamatsu Catalog

Modes of Operations Average anodic current Single photon counting Hamamatsu Catalog

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

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

Thermionic Emission is Dependent on Bias Voltage Hamamatsu Catalogue

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

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

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

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.

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

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

Avalanche Photodiode Hamamatsu Catalog http://micro.magnet.fsu.edu/primer/java/digitalimaging/avalanche/index.html

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.

Charge Coupled Device (CCD) Ingle and Crouch, Spectrochemical Analysis www.piacton.com

CCD Architecture Image Area Top View SiO2 backing Pixel Array insulating oxide Image Area Top View serial register amplifier http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/ccdanatomy.html and Bryce Marquis (Haynes Lab)

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)

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

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

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 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

+5V 0V -5V 2 +5V 0V -5V 1 +5V 0V -5V 3 1 2 3 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

+5V 0V -5V 2 +5V 0V -5V 1 +5V 0V -5V 3 1 2 3 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

+5V 0V -5V 2 +5V 0V -5V 1 +5V 0V -5V 3 1 2 3 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

+5V 0V -5V 2 +5V 0V -5V 1 +5V 0V -5V 3 1 2 3 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

+5V 0V -5V 2 +5V 0V -5V 1 +5V 0V -5V 3 1 2 3 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

+5V 0V -5V 2 +5V 0V -5V 1 +5V 0V -5V 3 1 2 3 http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

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.

Quantum Efficiency www.piacton.com

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

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.

Other Issues: Blooming

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

Other Issues: Etaloning www.piacton.com

Other Features: Binning On Chip Pixel Binning Increases S/N Shot noise decrease Increased speed Less storage space needed Decreases resolution http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/binning.html

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