Charge-coupled device spatial resolution

Alongside improvements in synchrotron sources, X-ray detectors have improved enormously. Up to the early 1990s X-ray film was the detector of choice at synchrotrons because of its high spatial resolution, despite its poor efficiency and low dynamic range. Imaging plate and charge coupled device (CCD) detectors swept film aside in the early-to-mid 1990s. 

One disadvantage of photomultipliers is that they do not have spatial resolution, so the spectrum must be scanned to measure light intensity at each wavelength in turn. This can be overcome using diode array or charge-coupled devices (CCDs) in which the intensity distribution across the entire wavelength field of the spectrometer may be captured simultaneously. 

Charge coupled devices are silicon chips containing a matrix of potential wells that can trap electrons released by radiation. Since the size of the potential wells is only a few micrometers, they have good spatial resolution, a useful feature for electronic imaging (p. 1684). 

Commonly, Raman scattering is observed using charge-coupled device (CCD) detectors upon exposure of the sample to monochromatic visible laser light The spatial resolution of measurements can be optimized (down to 1 pm) by coupling an optical microscope to a Raman spectrometer. A schematic layout of a Raman microscope system is shown in Figure 3.16, where the laser beam passes through the microscope and is focused onto the sample. 

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