A sealed, compact mercury atomic-absorption resonance ionization imaging detector has been developed and evaluated. The sensitivity of the detector as well as its ability to form two-dimensional images has been demonstrated. Images of faint light (1000 photons) have been recorded by image summation. It is shown that one can obtain high-quality images with a spatial resolution of at least 130 mum by detecting the ionic component of the imaging signal. Distortion, more noise, and poorer spatial resolution were observed when the electron component of the signal was detected. We studied the influence of voltage on the cell electrodes to find the conditions for optimum signal-to-noise ratio.
The recently developed mercury resonance ionization imaging detector (RIID) has many potential applications in the field of imaging science. We have demonstrated that useful information can be obtained from the time-resolved ionization signal detected along with the image of the object. Clearly distinguishable time-resolved signals from resonance ionization of mercury atoms and photoelectrons created within the channels of a microchannel plate by a UV signal transition of Hg at 253.7 nm were observed. Also, a new source of noise has been identified as low-mass ion desorption by 253.7 nm radiation from the inner parts of the Hg RIID. The time-resolved signal detection allowed temporal correction for the additional noises caused by nonresonant ionization processes inside the RIID, such as photoelectric effect and low-mass ion desorption. The temporal resolution of the RIID could be used for frequency shifted radiation detection and imaging.
A novel method of ultrahigh-resolution, frequency-resolved imaging using atomic vapor cells is proposed. The method is based on the accurate measurement of the fluorescence signal intensity distribution along the absorption path length when the signal frequency is tuned to a wing of the atomic absorption line. Two-step resonance fluorescence of Hg202 vapor was used for one-dimensional imaging of the Hg resonance radiation at 253.7 nm. An imaging signal with a frequency difference of 500 MHz could be easily distinguished visually and even a frequency difference of 80 MHz could be detected after appropriate processing of the fluorescence imaging signal. Several other novel methods of one- and two-dimensional multifrequency imaging are discussed.
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