Response of graphene to femtosecond high-intensity laser irradiation (1105.1193v1)

Abstract: We study the response of graphene to high-intensity 10^11-10^12 Wcm^-2, 50-femtosecond laser pulse excitation. We establish that graphene has a fairly high (~3\times10^12Wcm^-2) single-shot damage threshold. Above this threshold, a single laser pulse cleanly ablates graphene, leaving microscopically defined edges. Below this threshold, we observe laser-induced defect formation that leads to degradation of the lattice over multiple exposures. We identify the lattice modification processes through in-situ Raman microscopy. The effective lifetime of CVD graphene under femtosecond near-IR irradiation and its dependence on laser intensity is determined. These results also define the limits of non-linear applications of graphene in femtosecond high-intensity regime.

Response of Graphene to Femtosecond High-Intensity Laser Irradiation

The paper "Response of graphene to femtosecond high-intensity laser irradiation" presents a detailed examination of the interaction between graphene, a two-dimensional carbon structure, and femtosecond laser pulses. The investigation sheds light on the damage threshold and modifications induced in graphene when exposed to varying intensities of laser irradiation. This paper is pivotal for understanding the boundary conditions for non-linear graphene applications under high-intensity femtosecond laser regimes.

Key Findings

1. Single-Shot Damage Threshold: The research identifies a distinct threshold for single-shot laser damage in graphene surfaces, observed at a peak intensity of approximately $3 \times 10^{12}$ W/cm² with a 50-fs laser pulse. This is notably higher than the modification threshold under continuous-wave laser irradiation, emphasizing the significantly resilient nature of graphene against impulsive laser excitation.
2. Raman Spectroscopy Analysis: The researchers employed in-situ Raman spectroscopy to discern lattice modifications at microscopic scales. Raman spectral analysis provides insight into defect formations and lattice structures, with particular emphasis on the D, G, and 2D vibrational line strengths which are indicative of structural integrity and presence of defects.
3. Defect Accumulation: The paper finds that cumulatively, laser exposures below the damage threshold cause defect formations leading to lattice degradation. The defect density was monitored through variations in the D line strength, initially increasing until saturation, followed by degradation.
4. Lifetime and Degradation: The effective lifetime of graphene under sub-threshold femtosecond irradiation was characterized. The relationship between the decay lifetime of the 2D Raman signal and laser intensity was established, demonstrating an inverse dependency on intensity. This facilitates predictions of graphene's longevity in high-intensity ultrafast applications.
5. Unexpected Raman Signal Enhancements: With progressive laser exposures, the paper observed unexpected increases in the G line strength of Raman spectra. This peculiar response ties back to heavy p-type doping from atmospheric contaminants bonding to carbon defects. Such shifts indicate notable alterations in electronic properties under high defect densities.

Implications and Future Work

This research delineates the operational limits for graphene in high-intensity femtosecond applications, which may encompass photonics, optoelectronics, and materials processing domains. The observation of clean ablation suggests potential for precise micro-machining applications in fabricating graphene patterns using femtosecond lasers.

The paper's insights into defect-induced electronic modifications due to doping also raise intriguing questions regarding tunable electronic and optical properties in heavily processed graphene, unlocking further investigation avenues.

Future developments could explore the influence of substrate effects on damage thresholds and defect dynamics. Comparisons between CVD and exfoliated graphene emphasize the need for advancements in fabrication techniques that may enhance stability and application lifetimes.

Understanding graphene's behavior under extreme conditions remains crucial for harnessing its capabilities in next-generation technology, as well as for refining materials engineering processes that exploit its unique non-linear optical features.