Detector

Detectors are transducers that transform the analog output of the spectrometer into an electrical signal that can be viewed and analyzed using a computer. There are two types: photon detectors and thermal detectors.

• Photon detectors work generally by either causing electrons to be emitted or development of current when photons strike the detector surface. Examples include photovoltaic cells, phototubes, and charge-transfer transducers. Photovoltaic cells generate electrical current on a semiconductor material when photons in the visible region are absorbed. Phototubes, however, emit electrons from a photon-sensitive material. Charge-transfer transducers (such as photodiodes) develop a charge from visible region photon-induced electron transfer reactions within a silicon material. In each case, it is the current, the number of electrons, or the charge that is actually detected (not the photons themselves) and is then related to the energy/quantity of photons that caused the change in the material.
• Thermal detectors detect a temperature change in a material due to photon absorption. Thermocouples work by measuring the difference in temperature between a pair of junctions (usually the reference against the sample) and are generally used for the infrared wavelengths. The temperature difference is related to a potential difference, which is the output signal. Pyroelectric transducers are used in infrared region and utilize a dielectric material that produces a current when its temperature is changed by radiation absorption.