Detector Dark Counts Research Articles

Photometric Characteristics of Data from the Hubble Space Telescope Goddard-High Resolution Spectrograph

The G-HRS is one of four axial scientific instruments which will fly aboard the Hubble Space Telescope (ref 1,2). It will produce spectroscopic observations in the 1050 A ≤ λ ≤ 3300 A region with greater spectral, spatial and temporal resolution than has been possible with previous space-based instruments. Five first order diffraction gratings and one Echelle provide three modes of spectroscopic operation with resolving powers of R = λ/ΔΔ = 2000, 20000 and 90000. Two magnetically focused, pulse-counting digicon detectors, which differ only in the nature of their photocathodes, produce data whose photometric quality is usually determined by statistical noise in the signal (ref 3). Under ideal circumstances the signal to noise ratio increases as the square root of the exposure time. For some observations detector dark count, instrumental scattered light or granularity in the pixel to pixel sensitivity will cause additional noise. The signal to noise ratio of the net spectrum will then depend on several parameters, and will increase more slowly with exposure time. We have analyzed data from the ground based calibration programs, and have developed a theoretical model of the HRS performance (ref 4). Our results allow observing and data reduction strategies to be optimized when factors other than photon statistics influence the photometric quality of the data.

Raman spectroscopy applications of an imaging photomultiplier tube

A Raman spectroscopy system having an unprecedented combination of high sensitivity and low noise has been built incorporating an imaging (2-D) photomultiplier tube. The number of photons detected for a vibrational band approaches the theoretical limit set by the Raman cross section and experimental configuration. A detector dark count of 10(-4) counts/s/pixel is the major electronic source of noise. The spectrum of air reveals low concentration gas components, specifically (16)O(18)O and CO(2). Vibrational Raman spectra are obtained from solid samples as thin as 20 nm with low laser powers, e.g., 6.5 mW. The imaging photomultiplier yields 1-D (along the focused laser beam) Raman images of interfaces or concentration gradients.

Space–time photon correlation using a 2-D photon event detector

A 2-D photon event detector, consisting of a microchannel plate coupled to a resistive anode for position readout, has been used to measure the spatiotemporal correlation of dynamic speckle. In this paper we discuss the implementation of this detector for these measurements and the effect of detector dark count, dead time, spatiotemporal integration, and other inherent biases. Initial results on dynamic speckle produced by a rotating diffuser are presented, and these agree well with theoretical predictions.