Applications define detector requirements

Designers of optoelectronic systems or experiments in which light is to be measured may find it difficult to choose the appropriate detection technique. Knowing the signal wavelength is of first importance. Next come more-demanding specifications: will the signal be strong, faint, or time-dependent? What are the voltage requirements and the packaging constraints? Will the system be installed in the laboratory, in the field, or in space? This handbook attempts to present solutions to the problem of defining detector requirements.

Our eyes are excellent visible-light detectors, but the characteristics of human eyes are difficult to reproduce in an optoelectronic component. Simple and rugged photodiodes can be used in visible-light detection systems when there is ample signal available or when cost is a primary consideration. Photomultiplier tubes have long been useful detectors for very-low-light situations. Avalanche photodiodes bridge these two components—they are sensitive to low light levels but are packaged more like photodiodes. Earl Hergert explains how to choose between these solutions.

Infrared detectors basically respond to heat, so these devices need to be in a stable temperature environment to pick out a desired signal against a thermal background. Cooling infrared detectors improves their sensitivity, and traditionally, cryogenic cooling systems have been used. Andrew Allen discusses how and why thermoelectric cooling is now viable for cooling a wide variety of infrared-sensitive materials.

Imaging PMTs present a novel solution to spatially resolving low-light signals. These devices can map a two-dimensional area from which faint light emanates. Applications described by Michael Mellon include luminescence in semiconductor structures, time-resolved fluorescence from biological compounds, and localization of "hot spots" in operating integrated circuits.

A discussion of detector solutions is not complete without considering charge-coupled-device (CCD) cameras. High resolution is important in many scientific and industrial applications—a requirement often met with large-area (1024 × 1024 pixels or more) sensing chips. If, however, the signals striking these million or so pixels need to be read out at a high rate, compromises must be made. George Williams, Serge Ioffa, and Jim Janesick describe an approach to designing CCD cameras that preserves the high sensitivity of large sensors while handling a large volume of high-speed signals.

To complement these discussions, we have included a listing of literature available from numerous manufacturers offering further information on detector solutions.