Generation of high-uniformity and high-resolution Bessel beam arrays through all-dielectric metasurfaces

Bessel beam arrays are progressively attracting attention in recent years due to their remarkable non-diffracting nature and parallel manipulation capabilities in diverse applications. However, the poor phase discretization of conventional approaches such as spatial light modulators leads to low numerical aperture (NA) beam arrays due to the limitation imposed by the Nyquist sampling theorem and poor uniformity of the beam intensity. The key contribution of this study is to experimentally demonstrate the generation of high-uniformity and high-resolution Bessel beam arrays by utilizing all-dielectric metasurfaces. This is attained by optimizing the design of the supercell of a Dammann grating, particularly decreasing each supercell of the grating to a proper size. We demonstrate a 4 × 4 array of Bessel beams with a subwavelength transverse dimension (570 nm, ∼0.9λ) and a large NA of 0.4 for each beam in the array, while maintaining a relatively high uniformity intensity (52.40%) for the array. Additionally, the Bessel beam arrays are generated in a broadband range through the proposed all-dielectric metasurfaces. Our results are of great significance and particularly useful for applications of metasurface-based Bessel beam arrays in multidisciplinary fields such as laser fabrication, biomedical imaging, data storage, and multi-particle trapping.

Optogenetic Manipulation of Cell Migration with High Spatiotemporal Resolution Using Lattice Lightsheet Microscopy

Lattice lightsheet microscopy (LLSM) is modified with the aim of manipulating cellular behavior with subcellular resolution through three-dimensional (3D) optogenetic activation. In this study, we report a straightforward implementation of the activation source in LLSM in which the stimulating light can be generated by changing the spatial light modulator (SLM) patterns and the annual masks. As a result, a Bessel beam as a stimulation source is integrated into the LLSM without changing the optical configuration, achieving high spatiotemporal activation. We show that the energy power required for optogenetic reactions is lower than 1 nW (24 mW/cm2) and membrane ruffling can be activated at different locations within a cell with subcellular resolution. We also demonstrate guided cell migration using optogenetic stimulation for up to 6 h with 463 volume imaging without noticeable damage to cells.

Deep Learning-powered Bessel-beam Multi-parametric Photoacoustic Microscopy

Enabling simultaneous and high resolution quantification of the total concentration of hemoglobin (CHb), oxygen saturation of hemoglobin (sO2), and cerebral blood flow (CBF), multi parametric photoacoustic microscopy (PAM) has emerged as a promising tool for functional and metabolic imaging of the live mouse brain. However, due to the limited depth of focus imposed by the Gaussian beam excitation, the quantitative measurements become inaccurate when the imaging object is out of focus. To address this problem, we have developed a hardware-software combined approach by integrating Bessel beam excitation and conditional generative adversarial network (cGAN) based deep learning. Side by side comparison of the new cGAN powered Bessel-beam multi parametric PAM against the conventional Gaussian beam multi parametric PAM shows that the new system enables high resolution, quantitative imaging of CHb, sO2, and CBF over a depth range of ~600 μm in the live mouse brain, with errors 13 to 58 times lower than those of the conventional system. Better fulfilling the rigid requirement of light focusing for accurate hemodynamic measurements, the deep learning powered Bessel beam multi parametric PAM may find applications in large field functional recording across the uneven brain surface and beyond (e.g., tumor imaging).

Laser Fabrication of Nanoholes on Silica through Surface Window Assisted Nano-Drilling (SWAN)

Nano-structures have significant applications in many fields such as chip fabrications, nanorobotics, and solar cells. However, realizing nanoscale structures on hard and brittle materials is still challenging. In this paper, when processing the silica surface with a tightly focused Bessel beam, the smallest nanohole with ~20 nm diameter has been realized by precisely controlling the interior and superficial interaction of the silica material. An effective surface window assisted nano-drilling (SWAN) mechanism is proposed to explain the generation of such a deep subwavelength structure, which is supported by the simulation results of energy depositions.