Radiometric Imaging In The Ultraviolet

Abstract

There are now available a wide variety of electronic imaging techniques for producing images and spatially-resolved spectra in the far- and middle-ultraviolet wavelength ranges below 300 nm. These are basically similar to techniques used in the near-UV and visible. They include devices with electronic readout, and those whose final images are produced on film. Radiometric imaging, however, requires special consideration of the photometric qualities of the sensor and means for calibrating the images- that is, correlating some measure of image intensity to the intensity or integrated flux of input radiation. As is true in most other wavelength ranges, calibration techniques can be based on (a) standard light sources, whose intensities vs. wavelength are known, or (b) standard comparison detectors, whose detection efficiencies vs. wavelength are known. Our group at NRL has been developing ultraviolet cameras and spectrographs, for space science and for DoD applications, primarily for the far-ultraviolet (below 200 nm) range. These record images electrographically (on electron-sensitive film) or electronically (using electron-bombarded CCD arrays). Our calibration techniques are primarily based on standard detectors, including calibrated photodiodes and windowless gas photoionization chambers, although we have occasionally used the SURF facility at NBS as a standard light source.