A 255-slot Hadamard-transform spectrometer is described which has experimentally verified the multiplex advantage in signal-to-noise ratio previously predicted for this class of spectrometer.

Experimental Realization of the Multiplex Advantage with a Hadamard-Transform Spectrometer

Critical comparison of photon counting and direct current measurement techniques for quantitative spectrometric methods

In order to be able to compare light intensity measurements derived from the anode current of a photomultiplier with measurements derived from photoelectron pulse counting, a systematic investigation of the properties of some photomultiplier tubes has been made. This has led to a correlation of the properties of a photomultiplier based on an over-all quantum efficiency ηF, the gain G, a photoelectron noise factor S, and an effective dark rate D. In terms of these quantities the signal-to-noise ratio of an experimental measurement can be calculated, given the light flux and measurement technique. It is shown that the noise power spectral density is constant for a photomultiplier, down to about 10−2 Hz, and that pulse counting and current measurement will give similar signal-to-noise ratios under most experimental conditions.

Noise in the Measurement of Light with Photomultipliers

Structure of deoxyribonucleoproteins. III. Spectroscopic characterization of the ethidium bromide binding sites

The effect of gain variation on the integrated output-charge distribution of a photomultiplier tube is investigated experimentally and shown to be a predictable function of the multiplier single-electron response. Standardized or nonstandardized pulses recorded using either capacitive or digital storage are considered. Theoretical values for the moment-generating functions and variances (noise powers) of the charge distributions obtained in these four cases are given, and the role of these various distributions in determining the length of time required to achieve a given accuracy in a light-flux measurement is discussed. The experimental measurements adequately confirm the theoretical predictions. The work includes a critical discussion of the field of theoretical and experimental noise investigations in photomultiplier tubes with regard to their relevance in the present state of technology.

Experimental and theoretical comparison of photon-counting and current measurements of light intensity.

The experimental value of the signal-to-noise ratio (S/N) was used as a criterion for comparing different photomultiplier tubes and for assessing the relative merits of pulse-counting and dc measurement. For tubes with S-11 and S-20 photocathodes at room temperature, no significant difference was found between pulse-counting and dc methods. When different tubes were compared, other factors being equal, those with smaller cathodes gave higher S/N values. A comparison was also made between a cooled S-1 cathode photomultiplier tube and a p-i-n photodiode at room temperature. The photomultiplier tube was found to have a S/N many times higher than the photodiode.

S. E. Moore

Papers

The efficient use of photomultiplier tubes for recording spectra.