Electric currents -- Measurement, Charge coupled devices, Image processing -- Digital techniques, Electrooptics
The spatial resolution of an optical device is generally characterized by either the Point Spread Function (PSF) or the Modulation Transfer Function (MTF). To directly obtain the PSF one needs to measure the response of an optical system to a point light source. We present data that show the response of a back-illuminated CCD to light emitted from a sub-micron diameter glass fiber tip. The potential well in back-illuminated CCD"s does not reach all the way to the back surface. Hence, light that is absorbed in the field-free region generates electrons that can diffuse into other pixels. We analyzed the diffusion of electrons into neighboring pixels for different wavelengths of light ranging from blue to near infrared. To find out how the charge spreading into other pixels depends on the location of the light spot, the fiber tip could be moved with a piezo-electric translation stage. The experimental data are compared to Monte Carlo simulations and an analytical model of electron diffusion in the field-free region.
Ralf Widenhorn ; Alexander Weber ; Morley M. Blouke ; Albert J. Bae and Erik Bodegom, "PSF measurements on back-illuminated CCDs", Proc. SPIE 5017, Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications IV, 176 (May 14, 2003); doi:10.1117/12.482797