EMCCDs

An Electron Multiplying CCD (EMCCD) uses the latest technology to enhance the signal to noise (S/N) ratio in measurements where extremely low signal levels are present.

In low light regimes the electron multiplication process can provide a good S/N ratio, unlike the conventional CCD where only a few of the stronger features can be just observed above the noise. The benefits of EM gain are clearly obvious in fast Raman imaging, where the necessary short integration times can often result in signals which are barely visible above the noise when measured with a conventional CCD.

SWIFT ultra-fast Raman image of carbon nanotubes
SWIFT™ ultra-fast Raman image of carbon nanotubes acquired with standard CCD detector (left) and EMCCD (right).

How does it work

The EMCCD has two readout registers on the chip – a conventional register and an EM register. In the EM register, the clocking voltages used are higher than for conventional clocking, causing the electrons to acquire sufficient energy that impact ionization can occur.  At this point, extra electrons are produced and stored in the next pixel. There is only a small probability of electrons acquiring sufficient energy for impact ionisation to occur (thus creating additional electrons) but since the readout register has many elements within it, significant gain factors are possible (up to ~1000x). The key benefit of an EMCCD is that the amplification occurs before readout of the signal, which means that the signal is not readout noise limited. In other words, through amplification the signal is raised well above the noise floor which is largely determined by the noise of the readout electronics (pre-amplifier and A/D convertor).

EMCCD - How does it work?