Specifications

Version 1.1 rev Jan 2013
Page 60
iXon Ultra
, Features and Functionality
3.4.2.1 - Points to note about using an FT EMCCD as a standard EMCCD
• Theexposuretime,accumulationcycletimeandthekineticcycletimeareindependent.
• Theminimumexposuretimeisnotrelatedtothetimetakentoreadouttheimage.
• AsthecapturedimageisquicklyshiftedintotheStoragearea,eveninNFTmode,thesystemcanstillbeused
without a mechanical shutter.
• Forshortexposuretimes,theimagemayappearstreakedasthetimetakentoshifttheImageareaintothe
Storage area and the exposure time may be of similar magnitude, but much less than a non-frame transfer.
• InconditionswherelightlevelfallingontothepixelsintheImageareaexceedsthepixelwelldepthofthose
pixels during the readout of the Storage area image charge blooming can occur vertically along the column
contaminating the image being readout.
Example:
During a 100μs exposure enough light has fallen on a pixel to register 10000 counts, or 100,000 electrons assuming
10e/count. The image is then shifted into the Storage area. To read out the image, assuming 1,000 x 1,000 pixels,
it would take approximately 100ms at 10MHz readout rate. This means that during the reading out of the image
10 million counts (10,000 * 1,000) will have been acquired into the pixel described above. As a pixel saturates at
approximately 160,000 electrons this means that the pixel will be over saturated by 60 times. All the excess charge
has to go somewhere, and spreads vertically along the EMCCD column. As the clocks in the Image area are
not actively shifting the charge, the mobility of the charge will be low and you may not see any effect. However,
when you consider that more than one pixel in any given column could be exposed to 10,000 counts per 100μs,
the chance of corrupting data is correspondingly increased. Reducing the amount of light falling on the EMCCD
outside of the exposure period and increasing the exposure time accordingly will reduce the possibility of data
corruption.