Optical coherence effects introduction

Stimulated Raman spectroscopy is a useful introduction to coherent effects in optical spectroscopy. A discussion of coherent excitation can be used to make the connection between optical spectroscopy and nuclear magnetic resonance spectroscopy clear. The relation of the stimulated Raman effect to gain in lasers provides a hook to another important topic. 

It can be shown that the microwave and optical probe fields propagate simultaneously and are spatially coherent, in the sense that their amplitudes add - the polariton effects alluded to in the Introduction. We are presently exploring the implications of this fact, especially the possibility of phase matching the two signals in the cavity. 

A good introduction to electro- and magneto-optical effects can be found in the book by Harvey on Coherent Light [158]. The main effects and the relationship between them are indicated in table 4.1. Many atoms are readily produced as vapour columns, using standard laboratory methods [159]. The natural mode in which to conduct experiments on unperturbed free atoms is therefore in transmission. As table 4.1 emphasises (the reason is given below), the Faraday effect contains equivalent information to the Zeeman effect in transmission. Actually, what Harvey calls the Zeeman effect in transmission is usually referred to as the inverse Zeeman effect [160], to distinguish it from the Zeeman effect observed in emission.5... 

In the introduction to this chapter we gave an intuitive explanation of the origin of nonlinear optical effects and stressed the key role played by high power lasers and coherent light beams. These two concepts are defined here. We will describe one specific characteristic of laser light, namely the absorption saturation, and finally we will discuss susceptibility and frequency conversion of light. 

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