Virtual perfect absorption in resonant media and their <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="script">PT</mml:mi></mml:math>-symmetric generalizations

Virtual perfect absorption (VPA) is an effect simulating real absorption of light by using excitation at a complex frequency corresponding to a scattering zero. We theoretically study VPA in resonantly absorbing and amplifying media irradiated by two counterpropagating waves with exponentially growing amplitudes. We show that VPA critically depends on the medium density (i.e., level of loss or gain) deteriorating in the high-density limit. In contrast, almost ideal VPA persists in the $\mathcal{P}T$-symmetric loss-gain bilayer. For high enough gain, powerful quasilasing pulses are observed at later times symmetrically (single amplifying layer) or asymmetrically ($\mathcal{P}T$-symmetric structure) generated in both propagation directions.

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