  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 PT-symmetric loss-gain bilayer. For high
enough gain, powerful quasilasing pulses are observed at later times
symmetrically (single amplifying layer) or symmetrically (PT-symmetric
structure) generated in both propagation directions.
