Modification of reduced graphene oxide in a controllable manner provides a promising material platform for producing graphene based devices. Its fusion with direct laser writing methods has enabled cost-effective and scalable production for advanced applications based on tailored optical and electronic properties in the conductivity, the fluorescence and the refractive index during the reduction process. This mini-review summarizes the state-of-the-art status of the mechanisms of reduction of graphene oxides by direct laser writing techniques as well as appealing optical diffractive applications including planar lenses, information storage and holographic displays. Owing to its versatility and up-scalability, the laser reduction method holds enormous potentials for graphene based diffractive photonic devices with diverse functionalities.

Noble metal nanoparticles (NPs), owing to their unique optical and physicochemical properties, are routinely used for optical imaging and labeling of biological specimens. Even though they can provide vital information for studying multiple cellular events and their interplays at the same time, optically multiplexing and resolving specific NPs within a diffraction‐limited region labeled in complex biological specimens remains a fundamental challenge. By introducing and manipulating plasmonic resonance assisted saturable scattering effects, multiplexed fluorescence‐free super‐resolution imaging of gold NPs in tumor cells with remarkable subdiffraction resolution is demonstrated. The saturable scattering allows fluorescence‐free resolving single plasmonic nanoprobes with significantly improved resolution down to ≈100 nm. The revealed plasmonic resonance assisted saturation effect as well as the associated spectral flexibility to variant sizes provides access to multiplexing capability in complex bioenvironments. The demonstrated feasibility of two‐color super‐resolution cellular imaging is achieved at ultralow suppression powers ≈0.28 MW cm−2, corresponding to a two‐order of magnitude improvement compared to the state‐of‐the‐art of stimulated emission depletion (STED) nanoscopy.

Stimulated emission depletion nanoscopy and its derivatives based on saturation induced competition effects have become an indispensable tool for studying cellular events and their dynamics in living conditions. The successful implementation of these techniques heavily relies on the competition between excitation induced spontaneous emission and stimulated emission from fluorescent dyes. The use of two laser beams at different wavelengths perplexes the optical system and the high intensity saturation beam inevitably introduces detrimental photobleaching effects. Harnessing the emerging saturation scattering of plasmonic nanoparticles, here, we demonstrate a novel fluorescence-free single-wavelength super-resolution imaging technique using gold nanoparticles. A lateral resolution of 101.2 nm (<λ/5) is achieved through introducing saturation scattering competition (SSC) of 60 nm gold nanospheres between dual beams at the same wavelength. In addition, the SSC drastically reduces the saturation intensity by three orders of magnitude than the conventional stimulated emission depletion process at comparable resolutions. As a proof of concept, we realized robust single-wavelength super-resolved imaging in dMG-63 cells with a simplified system. The current technique provides a new modality of biosample-friendly technology for optical super-resolution imaging.

A passively Q-switched Nd:YAG/Cr⁴⁺:YAG microchip laser operating at 1112 nm is demonstrated. Under a pump power of 5.5 W, a maximum average output power of 623 mW was obtained with T=6% output coupler, corresponding to an optical-to-optical conversion efficiency of 11.3% and a slope efficiency of 19.5%. The minimum pulse width was 2.8 ns, the pulse energy and peak power were 39.3 μJ and 14 kW, respectively. Additionally, based on the 1112 nm laser, a 230 mW 556 nm green-yellow laser was achieved within an LBO crystal.

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