Micro/nanoprocessing of graphene surfaces has attracted significant interest for both science and applications due to its effective modulation of material properties, which, however, is usually restricted by the disadvantages of the current fabrication methods. Here, by exploiting cylindrical focusing of a femtosecond laser on graphene oxide (GO) films, we successfully produce uniform subwavelength grating structures at high speed along with a simultaneous in situ photoreduction process. Strikingly, the well-defined structures feature orientations parallel to the laser polarization and significant robustness against distinct perturbations. The proposed model and simulations reveal that the structure formation is based on the transverse electric (TE) surface plasmons triggered by the gradient reduction of the GO film from its surface to the interior, which eventually results in interference intensity fringes and spatially periodic interactions. Further experiments prove that such a regular structured surface can cause enhanced optical absorption (>20%) and an anisotropic photoresponse (~0.46 ratio) for the reduced GO film. Our work not only provides new insights into understanding the laser-GO interaction but also lays a solid foundation for practical usage of femtosecond laser plasmonic lithography, with the prospect of expansion to other two-dimensional materials for novel device applications.

Advances in femtosecond laser‐material interaction facilitate the extension of maskless optical processing to the high efficiency and deep‐subwavelength scale. Here, a hybrid plasmon lithography technique has been demonstrated by irradiating near‐infrared femtosecond laser pulses onto the Si material coated with thin Cr films in a vacuum chamber, and superior nanograting structures are found to deeply penetrate through the thin Cr film into the underlying Si substrate. In stark contrast to the common ripple structures formed on the Si surface, the Cr‐layer mediated Si nanograting structures not only exhibit the spatially super‐regular arrangements with a deep‐subwavelength period of 355 nm but also present the nonsinusoidal sharp‐edged groove geometry with a large depth‐to‐width aspect ratio of 2.1. Theoretical analyses and calculations reveal that the anomalous structure characterizations are physically ascribed to the excitation of dual‐interface coupled plasmons in the thin metal layer, which possess the squeezed spatial wavelength and the periodic columnar intensity distributions. Moreover, the further deepening of periodic nanostructures into the Si substrate is also elucidated by the simulation of electric field enhancements at the bottom of shallow grooves under irradiation of subsequent laser pulses. In combination with a wet etching process, the Si nanograting structures can be modified into the smooth and narrow‐mouthed V ‐profiles, whose optical measurements show a near omnidirectional antireflection especially in the visible range of 565–750 nm, which is expected for the design of advanced photonic devices.

In-plane birefringent materials present an effective modulation of the optical properties and more degrees of freedom for the signal detection in low dimension, and thus remain a hot topic in realizing the integrated, miniature, and flexible devices for multiple applications. Here, the artificial in-plane birefringence properties have been successfully achieved on a graphene oxide film by a novel femtosecond laser lithography method, which provides a high-speed, large-area, and regular subwavelength gratings (∼ 380 nm) fabrication and photoreduction. The obtained sample manifests an evident optical birefringence (∼ 0.18) and anisotropic photoresponse (∼ 1.21) in the visible range, both of which can be significantly modulated by either the structural morphology or the degree of oxide reduction. Based on the analysis of effective-medium theory and measurements of angle-resolved polarized Raman spectroscopy, the artificial in-plane birefringence is originated from various optical responses of the periodic subwavelength structures for the incident light with different polarization states. This technique shows great advantages for the fabrication of integrated in-plane polarization-dependent devices, which is expected to solve the problems in this field, such as the deficient selection of materials, complex design of micro/nanostructure, and inflexible processing technology.