Ultra Start KE-6 Specifications download pdf (Page 89)

Version 1.1 rev Jan 2013

Page 89

iXon Ultra

Hardware

4.2 - EMCCD SENSOR

The EMCCD sensor is the core enabling technology of the system. Everything else in the camera has been designed to

extract the absolute best operational performance from this sensor. All EMCCD sensors in the iXon Ultra range have a

frame transfer architecture. The frame-transfer EMCCD uses a two-part sensor in which one-half of the array is used as

a storage region and is protected from light by a light-tight mask. Incoming photons are allowed to fall on the uncovered

portion of the array and the accumulated charge is then rapidly shifted into the masked storage region for transfer to the

serial output register. While the signal is being integrated on the light-sensitive portion of the sensor, the stored charge

is read out. Frame transfer devices have typically faster frame rates than full frame devices, and have the advantage of a

high duty cycle i.e. the sensor is always collecting light.

A potential disadvantage of this architecture is the charge smearing during the transfer from the light-sensitive to

the masked regions of the EMCCD (although they are signicantly better than full frame devices).The smearing is

more prevalent when exposure times are closer to the time taken to shift the charge under the mask (in the order of

milliseconds).

The Andor iXon Ultra is the best camera on the market for minimizing such smear, as the vertical clock speeds can

be tuned via the software to deliver the fastest parallel shifts in the industry, which has the further advantage of faster

overall frame rates (especially when using sub-array and/or pixel binning readout options).

The EMCCD sensor is capable of detecting single photon events without an image intensier, achievable by way of a

unique electron multiplying structure built into the chip. Traditional CCD cameras offered high sensitivity, with readout

noises in single gure < 10e

but at the expense of slow readout. Hence they were often referred to as ‘slow scan’

cameras. The fundamental constraint came from the CCD charge amplier. To have high speed operation the bandwidth

of the charge amplier needs to be as wide as possible. However, it is a fundamental principle that the noise scales with

the bandwidth of the amplier, hence higher speed ampliers have higher noise.

Slow scan CCD’s have relatively low bandwidth and hence can only be read out at modest speeds, typically less than

1MHz. EMCCD cameras avoid this constraint by amplifying the charge signal before the charge amplier and hence

maintain unprecedented sensitivity at high speeds. By amplifying the signal the readout noise is effectively by-passed

and, as such, EMCCD readout noise is no longer a limit on sensitivity (and can often be considered negligible).

Please see pages 87- 88 for further details on EMCCD technology and sensor architecture.

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Ultra Start KE-6 Specifications Page 89