Sub-nanojoule ultrafast optical Kerr gating at 1 GHz repetition rates using multilayer graphene and thin graphite films

Resolving ultrafast dynamics of weak optical signals is crucial for progress in quantum science, nonlinear optics, and ultrafast spectroscopy. However, conventional optical Kerr gating (OKG) is bottlenecked by the weak nonlinear response of standard media, necessitating high-energy pulses from complex amplified lasers that restrict operation to low repetition rates. Moreover, the application of OKG is generally limited to fluorescent ensemble measurements, making ultrafast detection in nano-optics challenging. Here, we demonstrate an ultrafast OKG platform operating with pulse energies below 0.3 nJ—a reduction of over six orders of magnitude compared to traditional setups. By utilizing the giant third-order nonlinearity of multilayer graphene and thin graphite films under focusing, we consistently achieve sub-ps resolution (spanning 110–372 fs for the probed samples) at a 1 GHz repetition rate. This lowering of the nonlinear threshold—enabled by a nonlinear refractive index orders of magnitude higher than bulk media—enhances the detection efficiency within an atomic-scale footprint and minimizes dispersion. By bridging the gap between ultrafast gating and low power, high-repetition-rate operation, our platform provides a scalable framework for characterizing hybrid quantum systems and on-chip integration.