Spin‐Selective Second‐Harmonic Vortex Beam Generation with Babinet‐Inverted Plasmonic Metasurfaces

Abstract

in plasmonic metasurfaces. [24] Compared to the conventional quadratic nonlinear optical materials such as ferroelectric crystals, nonlinear plasmonic metasurfaces can continuously control the local phase shift of effective nonlinear polarizability in the entire 2π range with subwavelength resolution for nonlinear wavefront shaping. [14] Among various applications of metasurfaces, the generation of optical vortex beam with helical wavefront carrying orbital angular momentum (OAM) has attracted great interests. [8,11,[25][26][27][28][29] Compared to the conventional bulky optical components used for generating vortex beams, such as spatial light modulator and spiral phase plate, metasurfaces provide a compact and high-resolution approach, which open new avenues for optical particle trapping, [30,31] precision photolithography, [32,33] and remote optical communication. [34,35] Furthermore, the generation of secondharmonic (SH) vortex beams have been recently achieved with both the fork-type and rotation plasmonic metasurfaces, [19,21] but the formed SH vortex beams can only carry OAM of one absolute value and the vortex mode purity is still limited. Besides, the fork-type metasurface demonstrates no spin control over the created SH vortex pair, [19] while the rotation metasurface can only generate one vortex beam with the opposite spin at one time. [21] Moreover, most of the existing nonlinear plasmonic metasurfaces employ metallic nanoantennas as their constitutional meta-atoms, which suffer from strong background transmission, undesired optical scattering, and low laser damage threshold. As a solution, Babinet-inverted plasmonic metasurfaces based on nanoapertures in metallic film as nonlinear meta-atoms have their unique advantages, where the transmission of background illumination and undesired optical scattering can be efficiently suppressed, resulting in a significantly improved signal-to-noise ratio for the nonlinear beam conversion. [36] Meanwhile, the generated Joule heat in Babinetinverted plasmonic metasurfaces under the femtosecond laser illumination can diffuse rapidly across the continuous metallic film with high thermal conductivity, leading to a high laser damage threshold. [37,38] In this work, we present Babinet-inverted plasmonic metasurfaces based on C-shaped nanoapertures for achieving strong SH emission with large nonlinear conversion efficiency and generating spin-selective SH vortex beams with high mode purity. The geometrical parameters of C-shaped nanoapertures, Metasurfaces have drawn considerable attentions for their revolutionary capability of tailoring the amplitude, phase, and polarization of light. By integrating the nonlinear optical processes into metasurfaces, new wavelengths are introduced as an extra degree of freedom for further advancing the device performance. However, most of the existing nonlinear plasmonic metasurfaces are based on metallic nanoantennas as meta-atoms, suffering from strong background transmission, low laser damage threshold and small nonlinear conversion e...

Dielectric Chiral Metasurfaces for Second‐Harmonic Generation with Strong Circular Dichroism

“…The above SHG-CD is similar to the maximum achieved values [46] and the SHG efficiency which we obtained is 10 4 -10 6 times higher compared with the preceding results obtained in the nonlinear chiral metasurfaces (see, e.g., refs. [47][48][49] ). Highly efficient SHG with strong CD shown in this paper can find important applications for biosensing and imaging.…”

Structuring Nonlinear Wavefront Emitted from Monolayer Transition-Metal Dichalcogenides

“…These materials show promising applications in nanoprobing [1], imaging [2,3], and crystalline detection [4][5][6]. Compared with the control of linear optical signals with a metasurface [7][8][9][10][11][12][13][14], the wavefront engineering and control of generated nonlinear signals are the most challenging task to realizing integrated, ultrathin, and efficient nonlinear optical devices, ranging from nonlinear beam steering [15,16], nonlinear metalenses [17,18], nonlinear holography [19,20], optical image encoding [21], and the generation of a nonlinear optical vortex beam [22][23][24]. There have been several pioneering works on nonlinear phase control based on plasmonic metasurfaces, most of which focus on SHG manipulation [17,[20][21][22][23][24][25][26][27].…”

Spin-controlled wavefront shaping with plasmonic chiral geometric metasurfaces

“…Metasurfaces composed of ultrathin metallic or dielectric nanostructures with subwavelength size and spacing 1 – 4 that are able to fully control the electromagnetic wavefront have recently been developed for many applications, such as flat optical elements 5 – 9 , holograms 10 – 14 , and vortex beam generation 15 – 19 . Among the various types of metasurfaces, geometric metasurfaces have drawn the greatest attention for their superior capability in optical phase manipulation 20 , 21 .…”