No abstract

Nanograting-based plasmonic sensors are capable of real-time and label-free detection for biomedical applications. Simple and low-cost manufacturing methods of high-quality sensors are always demanding. In this study, we report on a one-step etch-free method achieved by directly patterning a photoresist on a copper substrate using laser interference lithography. Large area uniform gratings with a period of 600 nm were fabricated on the copper film, and its refractive index sensing performance was tested using glucose as analyte. By replacing the metallic grating ridges with photoresist ridges, the Ohmic absorption and radiative scattering losses of surface plasmons were greatly reduced. As a result, a much sharper resonance linewidth (∼ 10 nm) was experimentally obtained. Compared with pure metallic gratings, the reported structure is characterized by sharper resonance and a much easier fabrication process, making it a cost-effective plasmonic sensor with high quality.

Nanograting-based plasmonic sensors are widely regarded as promising platforms due to their real-time label-free detection and ease of integration. However, many reported grating structures are too complicated to fabricate, which limits their application. We propose a 1D bilayer metallic grating with trapezoidal profile as a near-infrared plasmonic sensor in the spectral interrogation. Trapezoidal gratings tend to perform better than rectangular gratings as sensors, particularly as they can detect at oblique incidence to obtain higher performance. Furthermore, we have successfully fabricated such a grating with a period of 633 nm over a 2.25 cm2 area using a two-step approach based on laser interference lithography. Glucose detection has been conducted to experimentally validate the sensing performance of the as-prepared grating. The measured sensitivity and figure-of-merit can reach up to 786 nm/RIU and 30, respectively. Our research sheds new light on the development of cost-effective sensing devices.

Non-invasive imaging beyond the diffraction limit and free from fluorescent labels in the visible is highly desired for microscopy. It remains a challenge to obtain such super-resolution focusing along with multiwavelength achromatic performance in the far field using an integratable and easily designed system. In this work, we demonstrate a straightforward metasurface-based method to realize multiwavelength achromatic generation and focusing of cylindrically polarized vortex beams (CPVBs). Attributed to the extra degrees of freedom of CPVBs and multi-section design, we have realized multiwavelength achromatic super-resolution focusing in the air with focal size tighter than that of normally used schemes like immersion metalenses or focused radially polarized beams. It is expected that this metasurface-empowered ultra-compact design will benefit potential applications which call for high resolution, like optical microscopy, laser processing, etc.