The configuration of a typical pyroelectric sensor and its operational output can be seen in the above Figure. A pyroelectric material, which is usually crystalline, possesses an electric polarization, even in the absence of an applied voltage. An incident laser pulse heats the crystal, which causes the material to expand and produce a change in the polarization. Charge builds up on opposite surfaces of the crystal which generates a current flow that charges a capacitor. This charged capacitor induces a voltage whose amplitude change is proportional to the original laser pulse energy. Since it is the change in temperature that produces the current, pyroelectric detectors respond only to pulsed or modulated radiation. They respond much more rapidly to variations in radiation than thermopiles and are unaffected by steady background radiation. Please see our Pyroelectric Sensor Physics technical note for additional information.