Cubic Nonlinearity of Graphene-Oxide Monolayer

Area of Science:

• Nonlinear Optics
• Materials Science
• Condensed Matter Physics

Background:

• Graphene oxide (GO) is a promising material with unique electronic and optical properties.
• Understanding its nonlinear optical (NLO) behavior is crucial for applications in photonics and optoelectronics.
• Characterizing cubic nonlinearity is essential for predicting material response under intense light.

Purpose of the Study:

• To quantitatively characterize the cubic nonlinearity of a graphene oxide monolayer.
• To investigate the interplay between nonlinear absorption and nonlinear refraction in GO.
• To determine the nonlinear absorption and nonlinear refraction coefficients of GO.

Main Methods:

• Utilized open and closed z-scan experiments.
• Employed a nanosecond pulsed laser with a Gaussian beam profile.
• Analyzed absorption and refraction changes under laser excitation.

Main Results:

• Observed reverse saturable absorption (RSA) in open z-scan, indicating a positive nonlinear absorption coefficient (β ≈ 2.62 × 10⁻⁸ m/W).
• Detected valley-peak traces in closed z-scan, signifying positive nonlinear refraction (n₂ ≈ 3.9 × 10⁻¹⁵ m²/W).
• Attributed RSA and positive n₂ to two-photon or two-step absorption processes, suggesting a higher excited-state absorption cross-section than ground-state absorption.

Conclusions:

• Graphene oxide exhibits significant positive cubic nonlinearity.
• The observed nonlinear optical effects are consistent with two-photon or two-step excitation mechanisms.
• The quantified NLO coefficients provide essential data for designing GO-based photonic devices.