RESONATORS

onance can be enormous, actually approaching a singularity.1

Any resonance arises from a delicate balance of phase and amplitude of the waves in a system. One can engineer either the phase or the amplitude by adjusting the materials and dimensions, but causality requires that both can never occur together for a mechanically static system.

At the heart of this resonance is the concept of a negative-fre- quency photonic mode. This is an intriguing phenomenon that occurs in moving media due to extreme Doppler shifts. For observers in relative motion, frequencies of light are shifted depending on the velocity. If the

FIGURE 1. Singular Fabry–Perot (FP) resonance of evanescent waves can be achieved by setting the FP plates in relative motion. Plate 1 is stationary while plate 2 is moving at a constant velocity ν along the

x direction. The reflection coefficients and the distance for the moving case can lead to a perfect balance of both phase and amplitude, which cannot occur for stationary plates. (Courtesy: University of Alberta)

metal, or about one hundredth of the speed of light.

As a result, we are thinking of innovative approaches using sound waves and water waves to observe this resonance, which is a kinematic phenomenon related to waves in general. This resonance also offers intriguing possibilities for cooling and stopping moving media by sudden emission of large amounts of electromagnetic energy.

REFERENCES

1.Y. Guo and Z. Jacob, Opt. Express 22, 21 (2014); doi:10.1364/OE.22.026193

2.A.J. Hoffman et al., Nat. Mater. 6, 946 (2007).

3.A.I. Volokitin and B.N. J. Persson, Phys. Rev. Lett. 106, 094502 (2011).

Zubin Jacob is an associate professor of electrical and computer engineering at the University of Alberta, Edmonton, AB, Canada; e-mail: zjacob@ualberta.ca; www.ece.ualberta.ca/~zjacob.

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