Detection of optical radiation
The birth of photodetectors can be dated back to 1873 when Smith discovered photoconductivity in selenium. There are two general types of photon detectors without internal gain: photoconductive and junction devices. The majority of optical detectors can be classified in two broad categories: photon detectors and thermal detectors. The practical operating limit for most IR detectors is the background fluctuation limit also known as the background limited infrared photodetector (BLIP) limit. A common problem of any type of photon detector is how to terminate the photodetector with a suitable load resistor and to trade off the performance between bandwidth and signal-to-noise ratio (SNR). A lock-in amplifier uses phase-sensitive detection to improve the SNR in continuous wave (cw) experiments. In energy spectroscopy, the integration of detector current pulses is performed using preamplifier based on charge-sensitive amplifier (CSA).