In Chapter 4 we discussed briefly the optical resonator, which consists of a pair of mirrors facing each other in between which is placed the active laser medium which provides for optical amplification. As we discussed, the mirrors provide optical feedback and the system then acts as an oscillator generating light rather than just amplifying. In this chapter we give a more detailed account of optical resonators. In Section 7.2 we will discuss the modes of a rectangular cavity and show that there exist an extremely large number of modes of oscillation under the linewidth of the active medium in a closed cavity of practical dimensions (which are large compared to the wavelength of light). Section 7.3 discusses the important concept of the quality factor of an optical resonator. In this section we obtain the linewidth corresponding to the passive cavity in terms of the parameters of the resonator.
KeywordsSpontaneous Emission Round Trip Transverse Mode Saturable Absorber Population Inversion
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