ABSTRACT
This chapter outlines the noise source on the basis of a quantum theory. A quantum theory is, however, needed for a rigorous analysis of the spontaneous parametric scattering process and a clear understanding of the spontaneous parametric process is important for a number of reasons. First, since the frequency and phase-matching conditions for the spontaneous emission are the same as those for the corresponding stimulated parametric process, the tuning characteristics of optical parametric oscillators and amplifiers can be determined from the spontaneous parametric emission prior to the construction of an actual oscillator or amplifier. It is, however, far from clear whether such an amplifier can be made practical, although there are interesting fundamental issues related to squeezing in optical parametric processes that have attracted a great deal of attention. For optical parametric processes, one is usually interested in the transparent region of the optical media.
