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iXon 3

Appendix

A1.1.13 - Quantum Efciency/Spectral Response

Theglossaryreferstosignalsasanumberofelectrons.Morestrictlyspeakingtheseare“photoelectrons”,created

when a photon is absorbed. When a UV or visible photon is absorbed by the detector it can at best produce only

one photoelectron. Photons of different wavelengths have different probabilities of producing a photoelectron and this

probability is usually expressed as Quantum Efciency (QE) or Spectral Response.

QE is a percentage measure of the probability of a single photon producing a photoelectron, while spectral response

is the number of electrons that will be produced per unit photon energy. Many factors contribute to the QE of a CCD,

but the most signicant factor is the absorption coefcient of the silicon that serves as the bulk material of the device.

A1.1.14 - Readout

Readout is the process by which data are taken from the pixels of the CCD and stored in computer memory. The pixels,

which are arranged in a single row, are read out individually in sequence. Readout involves amplifying the charge on

each pixel into a voltage, performing an analog to digital conversion then storing the data in computer memory. The time

takentoperformthisoperationisknownasthe“readtime”.

A1.1.15 - Saturation

Saturation is the largest signal the CCD can measure. A signal is measured in terms of the amount of charge that has

built up in the individual pixels on the CCD-chip. A number of factors determine the maximum amount

of charge that the CCD can handle

A1.1.16 - Scans (Keep Clean & Acquired)

TheCCDiscontinuallybeing“scanned”topreventitsbecomingsaturatedwithdarkcurrent(seeDark Signal on page 80).

• IftheScanisbeingusedsimplyto“clean”theCCD(i.e.itisakeep-cleanscan),thechargefromtheCCDis

discarded.

• Inanacquiredscanhowever,thechargeundergoesanalogtodigitalconversionandisacquired

intocomputermemorysothatitcanbeusedforsubsequentprocessinganddisplay:itis“readout”(see

Readout above).

Unlessthecontextspecicallyindicatesotherwise,“scan”inthisUserGuidegenerallyreferstoanacquired

scan.

A1.1.17 - Shift Register

The Shift Register usually consists of a single row of elements (or pixels) running parallel to and below the

bottom row of light-gathering pixels (the image area) on the CCD-chip. The shift register is protected from light by an

aluminiummask.Theelementsintheshiftregisterhaveagreatercapacitytostorecharge(i.e.agreater“welldepth”)

than the other pixels on the CCD-chip

Andor Technology iXon3 Series User Manual

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