Revealing invisible scattering poles with complex-frequency signals

Complex-frequency signals have been employed to increase light capture, improve the sensitivity of optical detection systems, and reduce losses in superresolution imaging setups. In this work, we present an approach that uses complex-frequency excitations to expose previously undetectable hidden or invisible poles, which feature predominantly imaginary components. By tailoring poles and zeros in the complex-frequency plane, it is shown that these otherwise invisible poles can strongly influence the scattering effects when they couple to visible poles. The efficient transformation of non-oscillating fields into oscillating ones is demonstrated. This phenomenon is confirmed in both radio frequency and optical domains, specifically within the C-band infrared range crucial for communication technologies. The findings deepen the theoretical understanding of wave interactions in photonic platforms and offer promising directions for designing advanced photonic devices.