Principles of Raman lasers and parametric amplifiers

Abstract

With the advent of powerful lasers at selected frequencies, it has now become possible to generate new frequencies by stimulating Raman scattered waves of these light sources. In a medium with high second-order non-linear optical susceptibility, new frequencies are also generated by parametric conversion. Principles of stimulated Raman scattering and the three-wave parametric interaction in a non-linear medium are presented and compared with the physical process involved in the operation of a conventional laser. As two recent examples of tunable devices based on these principles, the case of lithium niobate (LiNbO₃), where a polariton mode is excited, and the case of n-type InSb in a magnetic field, where an electron is excited to an empty spin-level, are discussed. The device using LiNbOs crystal is capable of generating tunable infra-red sources from 50 fl to 250 µ whereas lnSb device can generate tunable sources in the range 6-13 µ.