Ultra Start KE-6 Specifications download pdf (Page 103)

Version 1.1 rev Jan 2013

Page 103

iXon Ultra

Appendix

A.1.16 - Scans (Keep Clean and Acquired)

The EMCCD is continually being “scanned” to prevent its becoming saturated with dark current (see Appendix A.1.8 on

page 99).

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

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.

A.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 EMCCD-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 EMCCD-chip.

A.1.18 - Signal To Noise Ratio

The Signal to Noise Ratio (commonly abbreviated as S/N or SNR) is the ratio between a given signal and the noise

associated with that signal. Noise has a xed component and a variable component (shot noise), which is the square

root of the signal. Thus, the S/N usually increases (improves) as the signal increases.

The maximum S/N is the ratio between the maximum signal (i.e. the saturation level) and the noise associated with that

signal. At near saturation levels the dominant source of noise is the shot noise of the signal.

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Ultra Start KE-6 Specifications Page 103