Laser-absorber modes naturally occur in parity-time ($\mathcal{PT}$)-symmetric systems, where a pole and a zero of the scattering matrix coincide, enabling the system to operate simultaneously as a laser oscillator (or amplifier) and a coherent perfect absorber. Here, by leveraging the effective $\mathcal{PT}$ symmetry that emerges under evanescent-wave excitation, we realize the analog of laser-absorber modes for evanescent waves in anti-$\mathcal{PT}$-symmetric photonic heterostructures, characterized by complex permittivity and permeability satisfying $\varepsilon \left(-\mathrm{z}\right)=-{\varepsilon }^{*}\left(\mathrm{z}\right)$ and $\mu \left(-\mathrm{z}\right)=-{\mu }^{*}\left(\mathrm{z}\right)$, respectively. Building on this mode, we show that such anti-$\mathcal{PT}$-symmetric systems can strongly amplify evanescent waves incident from either side, while completely absorbing coherently incident evanescent waves with appropriate amplitudes and phases. Furthermore, together with the excitation-frequency tuning, this functionality enables extreme tunability of the energy transport carried by interfering evanescent waves between the excitation and the anti-$\mathcal{PT}$-symmetric structure in the presence of realistic material dispersion. This mode has also been extended to exhibit a unidirectional spectral singularity, producing infinite reflection of evanescent waves from one side and zero reflection from the other, while maintaining a reciprocal finite transmission. Our approach reveals a strategy to manipulate evanescent waves for extreme light-matter interactions grounded in non-Hermitian physics, with implications for functional devices and applications in sensing and communication.

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• Evanescent waves
• Wave scattering
• Non-Hermitian systems
• PT-symmetry