The Electron-Multiplying Charge-Coupled Device (EM-CCD) shares a similar structure to the CCD except for the
inclusion of a gain register that multiplies signal before the addition of read-noise, offering sub-electron effective readnoise
at high frame-rates.
EM-CCDs were proposed for the dispersive spectrometer on the International X-ray Observatory (IXO) to bring
sub-300 eV X-rays above the noise, increasing the science yield. The high-speed, low-noise performance of the EMCCD
brought added advantages of reduced dark current and stray-light per frame, reducing cooling and filtering
requirements. To increase grating efficiency, several diffracted spectral orders were co-located so the inherent energy
resolution of the detector was required for order separation. Although the spectral resolution of the EM-CCD is
degraded by the gain process, it was shown that the EM-CCD could achieve the required separation.
The RIXS spectrometer at the Advanced Resonant Spectroscopy beamline (ADRESS) of the Swiss Light Source (SLS)
at the Paul Scherrer Institute currently uses a CCD, with charge spreading between pixels limiting the spatial resolution
to 24 μm (FWHM). Through improving the spatial resolution below 5 μm alongside upgrading the grating, a factor of
two energy resolution improvement could theoretically be made. With the high-speed, low-noise performance of the
EM-CCD, photon-counting modes could allow the use of centroiding techniques to improve the resolution. Using
various centroiding techniques, a spatial resolution of 2 μm (FWHM) has been achieved experimentally, demonstrating
the benefits of this detector technology for soft X-ray spectrometry.
This paper summarises the use of EM-CCDs from our first investigations for IXO through to our latest developments in
ground-based testing for synchrotron-research and looks beyond to future possibilities.