The interaction between light and the time-varying medium
exhibits
non-Hermitian characteristics, leading to intriguing phenomena, such
as parametric amplification, momentum gaps, and temporal refraction.
In this study, we introduce the concept of the conformally evolved
spatiotemporal modulation, where the space- and time-dependent permittivity
function ε (x,t) undergoes
rescaling over time, i.e., ε (x,t + Δt) = ε (sx,st). In such systems, spatiotemporal interfaces are no longer
modulated at a uniform speed, enabling us to generate a special type
of geometric optical comb with exponentially distributed frequency
spacing under monochromatic incidence. Compared with traditional linear
frequency combs, these optical combs exhibit several distinct properties.
First, the excitation of geometric harmonics can drastically amplify
the output signal through cascade field enhancement with the appropriate
modulation speeds. Second, the designed geometric comb showcases a
significant reduction of ambiguous peaks in the autocorrelation, resulting
in suppression of reverberation and resolution enhancement for radar
detections.