ABSTRACT
The scope widened with the advent of instrumentation to emit and detect: photons corresponding to wide region of the electromagnetic spectrum apart from the visible radiation, electrons and ions. Discharge lamps are the most common photon sources. An ideal photon detector should have high sensitivity, high signal to noise ratio, constant response over range of wavelengths, fast response time, and zero output signal in dark. Photons incident on the photocathode emit cascade of electrons due to the photoelectric effect. Flux of photons is reconverted into flux of electrons which can be reconverted into flux of photons to reproduce image with the help of image intensifier. Photon detectors, are semiconductors having forbidden gap corresponding to the infra-red region. The cross section of electron-matter interaction is much larger compared to photon-matter interaction. Advantage of using a beam of photons for exploring material properties is that most of the experiments can be carried out in air.
