Abstract
An analysis of the frequency distribution of noise of two synchrotrons (CHESS and SSRL) indicates significant increases of noise at frequencies below 10 Hz. Noise energy distributions above 10 Hz and extending through 200 Hz indicate significant regions of noise distributions relatively independent of frequency, presumably ‘‘white noise.’’ We report tests of two carrier modulation systems in which the ratio (or difference) of a reference signal and measure signal is computed. In one case, the reference and measure sample are alternated at equal intervals, for example, where difference spectroscopy is required. In another version, the measure signal is periodically interrupted by the reference signal at a duty ratio of 10%–15%, thereby maintaining high efficiency of measure signal detection. When using a 10-Hz oscillator for reference and measure samples, the improvement as observed on beam line A-3 at CHESS over the ‘‘single-ended’’ signal is 10- to 20-fold in the nonscanning mode. In the case of a vibrating reed modulator, the signal-to-noise ratio at a count rate of 6×105 per s is equal to the statistical limit to within the error of calculation. The improvement over a conventional fluorescence signal to ionization chamber output ratio F/I0 is over tenfold. Application of these modulation techniques to a variety of detectors is included.
Published Version
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