Spontaneous emission cavity effects

In these equations and hereafter we use simplified symbols for quantities referring to the P-branch line v, 7—l- c—I, /. Namely, Xvy instead of Xu,y-i etc. The second term in (2) represents the rate of spontaneous emission into the oscillating cavity modes. 1 is approximately the effective solid angle subtended by the mirrors after several reflections. (Alternatively, e is the fraction of stable transverse modes.) After threshold eS j is negligible, eS j- Xvj- i i i " i important only before threshold —as a source of noise photons to trigger-on the lasing process. The spontaneous emission terms in (1) are given by =A j+iN y, A j is the Einstein coefficient. In infrared lasers where typically A ) 10s. S, ... 

If the cavity may be regarded as linear (i.e., the peak intensity within the cavity is insufiicient for the Kerr effect to be significant), and the fi equency shift per round trip is not harmonically related to the cavity fundamental fi equency, then the laser will generate a broadband output with low coherence, seeded by the amplifier s spontaneous emission noise. 

A superfluorescent source is effectively an open-loop laser cavity, i.e., with no feedback. A typical example of a double-pass backward-pumped source is shown schematically in Fig. 15. The output consists of spontaneous emission noise which has been increased in power by passage through the amplifying fiber once or twice, ideally converting the input pump power to a broadband output with... 

Both regimes (i) and (ii) have been recently investigated the enhanced spontaneous emission effect which requires cavities of relatively moderate Q (y 10 ) has been observed by Goy et al. in 1983 . The oscillatory exchange of photon between the atom and the cavity requires larger Q s (y 10 ) and is just now in the process of being directly observed by Walther and Rempe . 

The second phenomenon is of a much more fundamental nature. As we have discussed above, spontaneous emission can be seen to be caused by a coupling to the vacuum state of the electromagnetic field. It has recently been shown [4.15,16] that it is possible to manipulate this fundamental interaction by enclosing the atom in a cavity. If the cavity is so small that the modes of the vacuum field at the transition frequency cannot be supported by the cavity (dimensions smaller than the transition wavelength) the lifetime is prolonged. If, on the other hand, a cavity is tuned to resonance with a transition the spontaneous emission is enhanced. Clearly, the Lamb shift, which is a pure quantum electro-dynamical effect is also influenced by a cavity. 

Gould, P. I., Ruff, G.A., and Pritchard, D. E. (1986). Diffraction of atoms by light the near-resonant Kapitza-Dirac effect. Physical Review Letters, 56, 827-830. Goy, P., Raimond, J. M., Gross, M., and Haroche, S. (1983). Observation of cavity-enhanced single-atom spontaneous emission. Physical Review Letters, 50, 1903-1906. 

Abstract Rapid advances in quantum technology have made possible the control of quantum states of elementary material quantum systems, such as atoms or molecules, and of the electromagnetic radiation field resulting from spontaneous photon emission of their unstable excited states to such a level of precision that subtle quantum electrodynamical phenomena have become observable experimentally. Recent developments in the area of quantum information processing demonstrate that characteristic quantum electrodynamical effects can even be exploited for practical purposes provided the relevant electromagnetic field modes are controlled by appropriate cavities. A central problem in this context is the realization of an ideal transfer of quantum information between a state of a material quantum system and a quantum... 

It turns out that the spontaneous lifetime of the Rydberg levels is shortened if the cavity is tuned into resonance with the frequency a>o of the atomic transition n) n — 1). liis prolonged if no cavity mode matches coq [1297]. This effect, which had been predicted by quantum electrodynamics, can intuitively be understood as follows in the resonant case, that part of the thermal radiation field that is in the resonant cavity mode can contribute to stimulated emission in the transition n) n — 1), resulting in a shortening of the lifetime (Sect. 6.3). For the... 

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