Active absorption of electromagnetic pulses in a cavity

  • S A R Horsley, R N Foster, T Tyc, T G Philbin
  • New Journal of Physics, May 2015, Institute of Physics Publishing
  • DOI: 10.1088/1367-2630/17/5/053050

What is it about?

There are limits to how much energy can be absorbed within a given region of space, but these limits do not apply to absorbers that include a second source of energy. This paper demonstrates that a pulse of energy sent into a cavity can be completely withdrawn by sending a second pulse into the cavity. Although this may sound counter-intuitive, this result is shown theoretically and experimentally.

Why is it important?

Active absorption of pulses has been addressed using time-reversal techniques. Here, we have shown a different method that relies on the geometry of the cavity and shape (modulation) of the pulse, but is not time-reversal.


Dr Robert N Foster
University of Birmingham

Although it may seem counter-intuitive that you can pump more energy into a box to retrieve the energy within it, that is what this work shows! It depends on the resonances within the cavity and the location of the "ports", of course: you either have to use the same port for input and output, or they must be symmetrically positioned, so that the ports couple to the same modes in the cavity.

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