TABLE OF CONTENTS A detector is a characteristic component in an archetypal electro-optical system. For imaging systems, they are most useful as a dense two-dimensional array called a focal plane array (FPA). Traditionally, detector arrays have held the dubious position of being the system sensitivity limiter, resolution limiter, and cost driver. However, advances in the technology are making the FPA less of a performance and cost concern. A million-dollar FLIR may contain a FPA that costs $20,000 or less.
This chapter includes rules relating to detector performance, manufacture, and applications. For the most part, the material in this chapter is based on physics and concentrates on exotic detector materials and nonvisible portions. Many additional rules and information concerning visible CCDs, CMOS, and active pixel cameras and detectors can be found in Chap. 18, "Visible and TV Sensors".
Generally, detectors are categorized by nature, depending on their chemical constituents and/or wavelength response. Table 6.1 summarizes the typical wavelengths of commonly used detector materials. The conversion from light to electricity can occur through several mechanisms. The most popular for present devices are as follows:
A thermal effect, whereby the light raises the temperature of some material (such as bulk germanium or coatings of vanadium oxide or amorphous silicon as used in silicon microbolometer arrays). This is also called a bolometric effect.
The photoconductive effect, whereby the resistance is changed so that the conductance of a material is altered with the level of irradiance. This requires a bias voltage and circuit to read the...
