How these images are made (short version, assuming some knowledge of CL basics)
All images were made using an Oxford Instruments cathodoluminescence detector attached to a JEOL JSM T-330A scanning electron microscope. Signal is processed by an Oxford Instruments PA-1 amplifier (I wish it was a PA-2) passed to the Spectral Engine II interface from 4pi which routes it to a PowerMacintosh 7300 using a plug-in for Adobe Photoshop. Color images were obtained by filtering panchromatic CL images through red, green, and blue filters (a monochromator) and assembling the grayscale images as a color representation in Adobe Photoshop. The monochromator was constructed in the Scientific Instrument Shop here at the U.T. Department of Geological Sciences. Filters are Kodak Wratten gelatin filters.
Once in Photoshop the images are typically processed further. In particular, red, green, and blue channels are adjusted separately for contrast and brightness to bring out the maximum possible detail from each channel. This process will produce a color image that is slightly different in color than might be obtained from a standard cathodoluminescence device. However, the Kodak filters have distinctly less transmissivity in the blue and green wavelengths, so adjusting intensity either with the amplifier or with Photoshop is necessary. Adjusting the contrast and brightness of the individual channels typically restores detail lost versus the panchromatic image.
Samples are typically polished carbon-coated thin sections, although polished rock chips and polished grain mounts can be used. Samples can also be gold coated.
Robert M. Reed
Department
of Geological Sciences
University of Texas at Austin
rmr@uts.cc.utexas.edu