Infrared imaging is a crucial technique in a multitude of applications, including night vision, autonomous vehicle navigation, optical tomography, and food quality control. Conventional infrared imaging technologies, however, require the use of materials such as narrow bandgap semiconductors, which are sensitive to thermal noise and often require cryogenic cooling. We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas, using a nonlinear wave-mixing process. We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation. In this process, an infrared image of a target is mixed inside the metasurface with a strong pump beam, translating the image from the infrared to the visible in a nanoscale ultrathin imaging device. Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.
Dielectric metasurfaces have recently shown to be an excellent candidate for efficient frequency mixing at the nanoscale due to the excitation of Mie resonances. Among various dielectric materials, GaAs-based nanostructures have been reported to have high-efficiency of second-order nonlinear processes due to their high quadratic nonlinear susceptibility. Efficient frequency up-conversion can thereby be realised in GaAs-based metasurfaces through the process of sum-frequency generation (SFG), thereby opening new opportunities for nonlinear imaging and infrared vision not possible before. Here we demonstrate for the first time, infrared imaging based on nonlinear mixing of an infrared image with a pump beam in a GaAs resonant metasurface. The nonlinear mixing process generates visible images (Fig. 1a), which can be time resolved with femtosecond resolution and can be observed on a conventional CMOS sensor. Our results open new opportunities for the development of compact night-vision devices operating at room temperature and have multiple applications in defense and life sciences.
Here we will present a reliable (experimentally and numerically proved) technique for multi-spot pattern formation in the focus of a lens (i.e. in the artificial far field). This was done using large square-shaped and/or hexagonal optical vortex (OV) lattices generated by spatial light modulators. Experimental and numerical results showing a controllable far-field beam reshaping when such lattices are generated in the Fourier plane will be discussed. Even more interesting bright structures can be obtained by combining OV lattices (of any type) with different node spacings. We show that the small-scale structure of the observed patterns results from the OV lattice with the larger array node spacing, whereas the large-scale structure stems from the OV lattice with the smaller array node spacing. The orientation of the mixed far-field structures is proven to rotate by 180° when all TCs are inverted.
Optical vortices (OVs) are the only known truly two-dimensional phase dislocations. Because of their spiral phase fronts, the OV interaction results, in the simplest case (when two OVs are presented), in vortex mutual attraction/repulsion or in OV pair rotation. In this work we provide experimental evidences that a stable elementary cell forming the base for a large optical vortex lattice can be created by situating equally and singly charged OVs in the apices of a triangle and square and by nesting an additional control OV with an opposite unit charge in the center of the structure. Experimental data for the rotation of these triangular and quadratic elementary cells vs. OV-to-OV separation as well as the rotation of the same structures vs. propagation distance are presented. Generation and stable propagation of large rigid square-shaped and hexagonal OV lattices is demonstrated.
In this work we study the influence of the additional second-order dispersion introduced in sub-45 femtosecond laser pulses by intentional misaligning a folded 4-f otherwise dispersionless system. The theoretically calculated pulse durations are found to be in a good agreement with the respective experimental data from frequency-resolved optical gating measurements.
We study by computer simulations the initial stage of bright background beam self-focusing initiated by the energy density redistribution due to the presence of optical vortex and/or ring dark wave. Local self-focusing Kerr nonlinear medium is considered. When a single ring dark wave is nested on the background, ring radius-to-width ratio Δ=2 promises up to 4 times peak intensity increase at a propagation distance of 2 dark beam diffraction lengths. Δ=6 seems adequate when flat-toped super-Gaussian beam is desired. Self-focusing in bright rings of different radii and even in two coaxial rings (at Δ=3) is observed when initially optical vortex and ring dark wave are simultaneously nested on the background. The detailed numerical analysis of the evolution of azimuthal perturbations confirmed the physical intuition that self-focusing rings of small radii suffer much less (when at all) from ring filamentation, because the spatial frequency of the perturbations on the inner rings appear higher than the critical one.
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