Fresnel zone plate sculptured out of diamond by femtosecond laser for harsh environments.

With the rapid development of micro-optical applications, there is an increasing demand for micro-optical elements that can be made with minimal processing steps. Current research focuses on practical functionalities of optical performance, lightweight, miniaturization, and easy integration. As an important planar diffractive optical element, the Fresnel zone plate (FZP) provides a compact solution for focusing and imaging. However, the fabrication of FZPs with high quality out of hard and brittle materials remains challenging. Here, we report on the fabrication of diamond FZP by femtosecond laser direct writing. FZPs with the same outer diameter and different focal lengths of 250-1000 µm were made via ablation. The fabricated FZPs possess well-defined geometry and excellent focusing and imaging ability in the visible spectral range. Arrays of FZPs with different focal lengths were made for potential applications in imaging, sensing, and integrated optical systems.

Highly Sensitive and Selective Dopamine Determination in Real Samples Using Au Nanoparticles Decorated Marimo-like Graphene Microbead-Based Electrochemical Sensors.

A sensitive and selective electrochemical dopamine (DA) sensor has been developed using gold nanoparticles decorated marimo-like graphene (Au NP/MG) as a modifier of the glassy carbon electrode (GCE). Marimo-like graphene (MG) was prepared by partial exfoliation on the mesocarbon microbeads (MCMB) through molten KOH intercalation. Characterization via transmission electron microscopy confirmed that the surface of MG is composed of multi-layer graphene nanowalls. The graphene nanowalls structure of MG provided abundant surface area and electroactive sites. Electrochemical properties of Au NP/MG/GCE electrode were investigated by cyclic voltammetry and differential pulse voltammetry techniques. The electrode exhibited high electrochemical activity towards DA oxidation. The oxidation peak current increased linearly in proportion to the DA concentration in a range from 0.02 to 10 µM with a detection limit of 0.016 µM. The detection selectivity was carried out with the presence of 20 µM uric acid in goat serum real samples. This study demonstrated a promising method to fabricate DA sensor-based on MCMB derivatives as electrochemical modifiers.

Graphite Equivalent Evaluation of Anthracite-Associated Graphite by Raman Spectroscopy.

Anthracite-associated graphite is an important graphite resource with a wide range of applications besides being used as a fuel. This paper introduces a method for evaluating the graphite equivalent evaluation of anthracite-associated graphite. A series of graphite-anthracite standard samples with known graphite content were prepared, and their Raman spectra were obtained using a Raman spectrometer. By employing peak-fitting analysis to decipher the peak spectrum information of the D peak and G peak, trends in the peak position, peak intensity ratio, half-width, and peak area of the D peak and G peak in standard samples with different graphite contents were obtained. Subsequently, a standard curve and fitting equation were established using the peak area data. The goodness of fit for the equation (R2) was 0.9984. Then the equation was used to evaluate 100 natural anthracite-associated graphite samples with unknown graphite content, obtaining a corresponding graphite equivalent evaluation.