The preparation and study of the optical absorption edge of thin films of gallium arsenide

Abstract

This chapter describes the various aspects of the microwave spectrometers. Reflex klystrons remain as the most widely used oscillators for microwave spectroscopy. It often tends to be extremely sensitive to thermal changes and mechanical vibrations. Significant improvements, in both source stability and noise, can be achieved with any reflex klystron by providing a firm mount and adequate cooling. Bolometers have also been used to detect microwave radiation, and offer an entirely different set of characteristics from diode detectors. A possibility for increasing sensitivity in recovering very weak signals is to amplify the signal at the microwave frequency before it is detected. Several types of low noise amplifiers are used in spectrometers operating with radio telescopes. Stark-effect modulation has been, by far, the most popular technique, and has been used on the most sensitive spectrometers. The Stark effect depends on the fact that the relative positions of the energy levels in polar molecules can be shifted by applying an external electric field. It is suggested that both the specificity and sensitivity of microwave methods can offer significant advantages in applications where specific molecules must be monitored.