Giant Three‐Photon Absorption in Monolayer MoS2 and Its Application in Near‐Infrared Photodetection

For decades, there has been extensive research on exploring fundamental physical mechanisms for strong and fast optical nonlinearities. One of the important nonlinear‐optical mechanisms is multiphoton absorption which has a wide range of photonic applications. Herein, a theoretical model is proposed for three‐photon absorption (3PA) in monolayer MoS₂. The model shows that the 3PA coefficients are on the order of 0.1 cm³/GW². As compared to bulk semiconductors, these coefficients are enhanced by several orders of magnitude due to excitonic effects. Such exciton‐enhanced 3PA is validated by light‐intensity‐dependent photocurrent measurements on a monolayer MoS₂ photodetector with femtosecond laser pulses. These results lay both theoretical and experimental foundation for developing sensitive near‐infrared MoS₂‐based three‐photon detectors.