Two-photon absorption under few-photon irradiation for optical nanoprinting

Two-photon absorption (TPA) has been widely applied for 3D imaging and nanoprinting; however, the efficiency of TPA imaging and nanoprinting using laser scanning techniques is extremely low due to the trade-off shackle between resolution and efficiency. In this work, we unveil a novel concept, few-photon irradiated TPA ( fp TPA), supported by a spatiotemporal model that describes the precise time-dependent mechanism of TPA under ultralow photon irradiance with a tightly focused femtosecond laser pulse. We demonstrate that a feature size of 26 nm (1/20 λ) and a pattern period of 0.41 λ with a laser wavelength of 517 nm can be achieved by performing two-photon digital optical projection nanolithography (TPDOPL) under few-photon irradiation using the in-situ digital multiple exposure ( i DME) technique, improving printing efficiency by 5 orders of magnitude. Our work offers deeper insights into the TPA mechanism and encourages the exploration of new potential applications for TPA in nanoprinting and nanoimaging.