Graphene and Thin Graphite Films Achieve 141 Fs Temporal Resolution at 1GHz for Ultrafast Optical Kerr Gating

Detecting incredibly fast events in the realm of light, those occurring in picoseconds or even femtoseconds, presents a significant challenge for researchers in quantum science, nonlinear optics and ultrafast spectroscopy. Now, Amr Farrag, Assegid M. Flatae, and Mario Agio, alongside their colleagues, have developed a new ultrafast detection method utilising graphene and thin graphite films. This innovative approach overcomes limitations in existing techniques by harnessing the exceptional nonlinear optical properties of these materials, achieving 141 femtosecond temporal resolution at a 1GHz repetition rate. The team’s work demonstrates that graphene and thin graphite films offer a compact and practical platform for nano-optical and on-chip ultrafast Kerr gating, promising substantial improvements in detection efficiency and simplified integration with existing technologies.

This innovative approach achieves a temporal resolution of 141 femtoseconds, operating at a 1 gigahertz repetition rate with remarkably low pulse energies. The enhanced performance stems from the materials’ extraordinarily high nonlinear refractive index, surpassing that of conventional materials used in Kerr gating. This compact and versatile technique, facilitated by the atomic-scale thickness of graphene and graphite, allows for seamless integration with existing microscopy setups, optical fibers, and on-chip photonic circuits. This integration unlocks opportunities for investigating ultrafast photophysical processes at the single-emitter level and promises advancements in areas such as ultrafast single-photon detection, quantum photonics, high-speed optical switching, and time-resolved spectroscopy in both nanophotonic and biological systems.

Ultrafast Detection via Graphite Nonlinearity Demonstrated

Scientists have demonstrated an ultrafast detection scheme leveraging the third-order nonlinearity of graphite films, achieving a temporal resolution of 141 femtoseconds with 1 gigahertz repetition rate pulses possessing sub-nanojoule energies. The team achieved this performance using thin graphite films, capitalizing on their exceptionally large nonlinear refractive index, which surpasses that of conventional Kerr media by several orders of magnitude. This enhanced nonlinearity enables efficient detection at reduced thicknesses and supports broadband operation, crucial for high-speed optical measurements. Experiments revealed that laser-induced damage to graphite films begins at a fluence of approximately 0.

31 mJ/cm2, delivered by a 100 femtosecond laser at 820nm with 1 gigahertz repetition rate and 1 Watt average power. Optical microscopy and Raman spectroscopy were employed to characterize the damage threshold in thin graphite films containing 7-8 layers of graphene, and samples generally remained intact after one hour of laser exposure, though some developed cracks. Investigations into the damage mechanisms showed that laser irradiation induces structural changes in graphene, beginning with the removal of adsorbed dopants like water and oxygen after approximately two hours of 1mW laser power. Prolonged exposure, lasting several to ten hours, leads to the breaking of sp2 carbon-carbon bonds, resulting in the disassembly of single-crystal graphene into interconnected nanocrystallines approximately 10 nanometers in size. These changes are accompanied by a strong growth of the D peak in Raman spectra, a blueshift from phonon confinement, and a reduction in the 2D peak intensity. The team observed that increasing the number of graphene layers substantially weakens these effects, and bulk highly oriented pyrolytic graphite does not exhibit similar behavior even at higher laser powers.