Coherent Raman scattering imaging with a near-infrared achromatic metalens

Achromatic and Coma-Corrected Hybrid Meta-Optics for High-Performance Thermal Imaging

Long-wave infrared (LWIR) imaging, or thermal imaging, is widely applied in night vision and security monitoring. However, the widespread use of LWIR imagers is impeded by their bulky size, considerable weight, and high cost. While flat meta-optics present a potential solution to these limitations, existing pure LWIR meta-optics face constraints such as severe chromatic or coma aberrations. Here, we introduce an approach utilizing large-scale hybrid meta-optics to address these challenges and demonstrate the achromatic, coma-corrected, and polarization-insensitive thermal imaging. The hybrid metalens doublet is composed of a metasurface corrector and a refractive lens, featuring a full field-of-view angle surpassing 20° within the 8-12 μm wavelength range. Employing this hybrid metalens doublet, we showcase high-performance thermal imaging capabilities both indoors and outdoors, effectively capturing ambient thermal radiation. The proposed hybrid metalens doublet holds considerable promise for advancing miniaturized, lightweight, and cost-effective LWIR optical imaging systems.

Full-space wavefront control enabled by a bilayer metasurface sandwiching 1D photonic crystal

Metasurfaces, composed of sub-wavelength structures, have a powerful capability to manipulate light propagations. However, metasurfaces usually work either in pure reflection mode or pure transmission mode. Achieving full-space manipulation of light at will in the optical region is still challenging. Here we propose a design method of full-space meta-device containing a bilayer metasurface sandwiching 1D photonic crystal to manipulate the transmitted and reflected wave independently. To provide a proof-of-concept demonstration, a device is proposed to show the light focusing in transmission and a vortex beam in reflection. Meanwhile, a device focusing the reflected light with oblique 45° incidence and the transmitted light with normal incidence is designed to indicate its application potential in augmented reality (AR) application. Our design provides a promising way to enrich the multifunctional meta-devices for potential applications.

Miniature Two-Photon Microscopic Imaging Using Dielectric Metalens

Miniature two-photon microscopy has emerged as a powerful technique for investigating brain activity in freely moving animals. Ongoing research objectives include reducing probe weight and minimizing animal behavior constraints caused by probe attachment. Employing dielectric metalenses, which enable the use of sizable optical components in flat device structures while maintaining imaging resolution, is a promising solution for addressing these challenges. In this study, we designed and fabricated a titanium dioxide metalens with a wavelength of 920 nm and a high aspect ratio. Furthermore, a meta-optic two-photon microscope weighing 1.36 g was developed. This meta-optic probe has a lateral resolution of 0.92 μm and an axial resolution of 18.08 μm. Experimentally, two-photon imaging of mouse brain structures in vivo was also demonstrated. The flat dielectric metalens technique holds promising opportunities for high-performance integrated miniature nonlinear microscopy and endomicroscopy platforms in the biomedical field.

High-power laser beam shaping using a metasurface for shock excitation and focusing at the microscale

Achieving high repeatability and efficiency in laser-induced strong shock wave excitation remains a significant technical challenge, as evidenced by the extensive efforts undertaken at large-scale national laboratories to optimize the compression of light element pellets. In this study, we propose and model a novel optical design for generating strong shocks at a tabletop scale. Our approach leverages the spatial and temporal shaping of multiple laser pulses to form concentric laser rings on condensed matter samples. Each laser ring initiates a two-dimensional focusing shock wave that overlaps and converges with preceding shock waves at a central point within the ring. We present preliminary experimental results for a single ring configuration. To enable high-power laser focusing at the micron scale, we demonstrate experimentally the feasibility of employing dielectric metasurfaces with exceptional damage threshold, experimentally determined to be 1.1 J/cm2, as replacements for conventional optics. These metasurfaces enable the creation of pristine, high-fluence laser rings essential for launching stable shock waves in materials. Herein, we showcase results obtained using a water sample, achieving shock pressures in the gigapascal (GPa) range. Our findings provide a promising pathway towards the application of laser-induced strong shock compression in condensed matter at the microscale.

Design of achromatic hybrid metalens with secondary spectrum correction

Metasurface can be used in combination with singlet refractive lens to eliminate chromaticity, in which the metasurface usually works as a dispersion compensator. Such a kind of hybrid lens, however, usually has residual dispersion due to the limit of meta unit library. Here, we demonstrate a design method that considers the refraction element and metasurface together as a whole to achieve large scale achromatic hybrid lens with no residual dispersion. The tradeoff between the meta-unit library and the characteristics of resulting hybrid lenses is also discussed in detail. As a proof of concept, a centimeter scale achromatic hybrid lens is realized, which shows significant advantages over refractive lenses and hybrid lenses designed by previous methods. Our strategy would provide guidance for designing high-performance macroscopic achromatic metalenses.

Mid-infrared biomimetic moth-eye-shaped polarization-maintaining and angle-insensitive metalens

Metalenses can potentially reduce the size and complexity of existing cameras, displays, and other optical devices, owing to their capability of flexible manipulation of the polarization, amplitude, and phase of light. However, metalenses capable of maintaining polarization and broadband wavefront shaping under arbitrarily polarized excitation have not been studied. In this study, we present the first demonstration of a biomimetic moth-eye-shaped metalens for polarization-maintaining, broadband and angle-insensitive focusing under an arbitrarily polarized excitation in the mid-infrared waveband (3.1-8.0 µm). Modulation and focusing efficiencies of 92% and 90%, respectively, were achieved. Moreover, a bifocal moth-eye-shaped metalens operating at normal and oblique incidences was realized. Compared to previously reported metalenses, the one proposed in this study exhibited a better focusing under oblique incidence, ensuring light transmission as effectively as a traditional lens. This study paves the way for the development of polarization-maintaining, broadband, and angle-insensitive microscale optical devices and imaging systems.