Theoretical strategy for coherent perfect absorption based on photonic time crystals: Interference and energy control

Photonic time crystals (PTCs) are artificial materials whose electromagnetic (EM) properties vary with time, enabling the realization of physical phenomena and energy conversion devices through the utilization of the time dimension. A theoretical strategy based on the PTCs for achieving coherent perfect absorption (CPA) is introduced in this Letter, enabling controllable switching between energy amplification (EA) and CPA. A single EM wave propagating within the PTC momentum bandgap absorbs pump energy and grows exponentially, thereby generating EA. Signal wave and control one generate coherent interference within the PTCs, enabling CPA by controlling the phase difference and intensity of the two waves. Further research reveals that increasing the PTCs' period effectively enhances performance of CPA, while altering the control wave's phase and intensity facilitate mutual switching between CPA and EA. The study employs theoretical calculations using the transfer matrix method to establish a PTC-based CPA strategy, while analyzing the generation processes of EA and CPA within the PTCs via the finite-difference time-domain method. This research expands the field of PTC studies, achieves controllable switching between PTC-based EA and CPA, and demonstrates the physical mechanism based on energy control, conversion, and EM wave interference within the PTCs.