Resonant photonic devices are governed by poles and zeros that often lie off the real-frequency axis. As a result, steady-state measurements don’t always reveal the full response landscape. Complex-­frequency excitations (CFE) offer a practical workaround: time-­domain waveforms engineered to include controlled exponential growth or decay on top of an oscillation. By shaping the drive rather than redesigning the device, researchers can access and exploit that “hidden” complex-frequency structure without redesigning the hardware.