RESONANT MODES OF OPTICAL CAVITIES

The optical cavities of many gas lasers must necessarily be rather long in order that amplification in a low-gain medium can offset the unavoidable cavity losses which can seldom be reduced below 1-2 per cent. It is not immediately obvious then that such open-walled structures will indeed possess a set of low-loss modes. The cavity will certainly have very substantial losses for any radiation which propagates in a direction making a large angle with the cavity axis. 

Therefore, in order that such a resonator should possess low-loss, high-Q modes, two criteria must be satisfied  

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The experimental setup is shown in Fig. 1.18. The laser pulses are coupled into the resonator by carefully designed mode-matching optics, which ensure that only the TEMoo modes of the cavity are excited. Diffraction losses are minimized by spherical mirrors, which also form the end windows of the absorption cell. If the absorbing species are in a molecular beam inside the cavity, the mirrors form the windows of the vacuum chamber. For a sufficiently short input pulse (Tp < 7r), the output consists of a sequence of pulses with a time separation Tr and with exponentially decreasing intensities, which are detected with a boxcar integrator. For longer pulses (Tp > 7r), these pulses overlap in time and one observes a quasi-continuous exponential decay of the transmitted intensity. Instead of input pulses, the resonator can also be illuminated with cw radiation, which is suddenly switched off at f = 0. 

This problem demonstrates the link between the widths of the cavity response and the transmission peaks of this well-known interferometer. However, the fringe pattern observed with a Fabry-Perot etalon should not be confused with the mode pattern of a laser having a plane-parallel resonator. The Fabry-Perot etalon is normally used with the plates so close together that all the transverse modes of the corresponding optical cavity are virtually degenerate in frequency. The plane wavefronts assumed in the discussion of the theory of the etalon are composed of an infinite sum over the transverse modes of the cavity. 

Photons in quantum optical cavities also constitute excellent qubit candidates [52]. Resonant coupling of atoms with a single mode of the radiation field was experimentally achieved 25 years ago [53], and eventually the coherent coupling of quantum optical cavities with atoms or (simple) molecules was suggested as a means to achieve stable quantum memories in a hybrid quantum processor [54]. There might be a role to play for molecular spin qubits in this kind of hybrid quantum devices that combine solid-state with flying qubits. 

Abstract The self-organized and molecularly smooth surface on liquid microdroplets makes them attractive as optical cavities with very high quality factors. This chapter describes the basic theory of optical modes in spherical droplets. The mechanical properties including vibrational excitation are also described, and their implications for microdroplet resonator technology are discussed. Optofluidic implementations of microdroplet resonators are reviewed with emphasis on the basic optomechanical properties. 

The top-emitting OLED with a bilayer anode of Ag/CFX and an ultrathin Ag layer used in the upper semitransparent cathode forms an optical microcavity, which can tailor the spectral characteristics of the emitters therein by allowing maximum light emission near the resonance wavelengths of an organic microcavity [80,81], When the mode wavelength of the cavity is fixed at 550 nm, the thickness of the Ph-PPV layer is determined to be about 110 nm [81]. 

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