Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence

Choudhury, Bikash Dev; Sahoo, Pankaj K.; Sanatinia, Reza; Andler, G.; Anand, Srinivasan; Świłło, Marcin

doi:10.1364/ol.40.002072

Cited by 9 publications

(7 citation statements)

References 21 publications

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“…Moreover, the gradual shift of the azimuthal angle from the HRTEM measurements in Figure 4d suggested that the screw structure should be a twisted structure, rather than the reported thermodynamically stable stacking structure, 38 which is further affirmed by the polarization test. The broken symmetry along the [0001] direction from the twisted structures is believed to lead to their accumulated SHG effect with increasing layer number, rather than other effects, such as surface-enhanced SHG 47 or plasmonic-enhanced SHG. 48 Finally, the effective second-order nonlinear susceptibility of this spiral WS 2 nanosheet was roughly estimated, using a commercial BBO crystal as a reference sample.…”

Section: Resultsmentioning

confidence: 99%

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS₂ Nanosheets

et al. 2017

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Transition metal dichalcogenides (TMDs) have provided a fundamental stage to study light-matter interactions and optical applications at the atomic scale due to their ultrathin thickness and their appropriate band gap in the visible region. Here, we report the strong nonlinear optical effects, including second-harmonic generation (SHG) and third-harmonic generation (THG) in spiral WS structures. SHG intensity quadratically increases with layer numbers, other than diminishing the oscillation of 2H stacking TMDs. The contrary SHG behavior is attributed to the broken symmetry from twisted screw structures, revealed by aberration-corrected transmission electronic microscope observation. Furthermore, the twist angle of the screw structure (5 degrees) was obtained by high-resolution transmission microscope measurements and confirmed by polarization tests of SHG output. Moreover, we roughly estimate the effective second-order nonlinear susceptibility. The discovery and understanding of the accumulation of nonlinear susceptibility of spiral structures with increasing thickness will extend the nonlinear applications of TMDs.

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Section: Resultsmentioning

confidence: 99%

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS₂ Nanosheets

et al. 2017

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“…Similar to THG, peaks in the SHG spectrum are observed at 2ω frequencies correlated with the ω fundamental frequencies of the quasi -BICs. Because bulk Si is centrosymmetric, SHG is expected to arise from the breaking of symmetry at the NW surface and from field gradients due to resonant modes or tightly focused beams. ,,− As shown in Figure B and Figure D, the field enhancements at the NW surface are apparent from the top view and cross-sectional | E ω | field profiles of the m = 0 and m = 1 quasi -BICs, respectively, and enhancement of SHG signals would thus be expected to occur as a result of enhanced fields close to the NW surface. Although enhancement of SHG from centrosymmetric nanostructures is often expected to occur as a result of enhanced fields components normal ( E ⊥ ) to the surface, contributions from tangential fields ( E ∥ ) at the surface as well as from strong field gradients ([ E ·∇] E ) in the Si NW have to be considered when under optical resonance conditions .…”

Section: Resultsmentioning

confidence: 99%

Optical Nonlinearity in Silicon Nanowires Enabled by Bound States in the Continuum

Park

Kim

et al. 2023

ACS Nano

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Intense electromagnetic fields localized within resonant photonic nanostructures provide versatile opportunities for engineering nonlinear optical effects on a subwavelength scale. For dielectric structures, optical bound states in the continuum (BICs, resonant nonradiative modes that exist within the radiation continuum) are an emerging strategy to localize and intensify fields. Here, we report efficient second and third harmonic generation from Si nanowires (NWs) encoded with BIC and quasi-BIC resonances. In situ dopant modulation during vapor−liquid−solid NW growth was followed by wet-chemical etching to periodically modulate the diameter of the Si NWs and create cylindrically symmetric geometric superlattices (GSLs) with precisely defined axial and radial dimensions. By variation of the GSL structure, BIC and quasi-BIC resonant conditions were created to span visible and near-infrared optical frequencies. To probe the optical nonlinearity of these structures, we collected linear extinction spectra and nonlinear spectra from single-NW GSLs, demonstrating that quasi-BIC spectral positions at the fundamental frequency are directly correlated with enhanced harmonic generation at second and third harmonic frequencies. Interestingly, we find that deliberate geometric detuning from the BIC condition leads to a quasi-BIC resonance with maximal harmonic generation efficiency by providing a balance between the capacity to trap light and the capacity to couple to the external radiation continuum. Moreover, under focused illumination, as few as 30 geometric unit cells are required to achieve more than 90% of the approximate maximum theoretical efficiency of an infinite structure, indicating that nanostructures with projected areas smaller than ∼10 μm 2 can support quasi-BICs for efficient harmonic generation. The results represent an important step toward the design of efficient harmonic generation at the nanoscale and further highlight the photonic utility of BICs at optical frequencies in ultracompact one-dimensional nanostructures.

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“…Due to the inversion symmetry of the bulk silicon, only third-harmonic generation is possible in the dipole approximation, and one could not consider using bulk silicon for obtaining second-harmonic generation. By breaking this inversion symmetry, the surfaces of silicon appear as an interesting choice for obtaining SHG in nano-manufactured all-Silicon devices, where the surface-to-volume ratio increases [122]. In this chapter, I will briefly review some fundamental properties of silicon and present some applications of its surfaces in the context of second-harmonic generation.…”

Section: Silicon and Its (001) Surfacementioning

confidence: 99%

“…Therefore, the surfaces of Si appear as an crucial key for handling the silicon photonics, and in particular for the SHG on Sibased devices. Among the ways proposed in the literature for obtaining a SHG from silicon, we find nano-particles [142], micro-cavities [143], nano-pillars [122] or more recently strained silicon wave-guides [13]. In those nano-objects, the surface properties can become relatively important with respect the bulk properties, making the understanding of Si surfaces of major importance.…”

Section: The Role Of Silicon Surfaces In Novel Applicationsmentioning

confidence: 99%

Ab initiodescription of second-harmonic generation from crystal surfaces

2016

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When applying an external electric field to a dielectric material, electric dipoles are created at a microscopic level. These dipoles are responsible for the apparition, inside the material, of an induced field. The fluctuations of the electric field at a microscopic level, the density fluctuations or any kind of microscopic inhomogeneities must be taken into account when describing the optical properties of a system. These effects are often referred as "local-field effects". These local-field effects have been widely studied in the past and in particular their effects on the optical properties of bulk materials are now well established. In the case of surfaces, the theoretical description and the numerical simulations are more intricate than for bulk materials. The abrupt change in the electronic density leads to a huge variation of the electric field at the interface with vacuum. As a result, strong effects of the local-field are expected, in particular in the direction perpendicular to the plane of the surface. The goal of this thesis is to quantify how important these effects are for the linear and second-order optical properties of surfaces. This thesis is organised in four parts. The Part I focuses on the theoretical background, necessary to understand the development reported in this thesis. Part II presents the first theoretical results of this thesis, improving the microscopic description of second-harmonic generation at crystal surfaces. A macroscopic theory of second-harmonic generav Contents tion from crystal surfaces is developed in Part III, in order to account for local-field effects. The last part of this thesis, Part IV, is dedicated to the application of the theory developed to silicon surfaces. The numerical simulations have been focused on the Si(001) surface, and the macroscopic formalism developed during this thesis has been applied to three surface reconstructions, namely the clean Si(001)2×1, the monohydride Si(001)2×1:H and the dihydride Si(001)1×1:2H surfaces. Comparison with available experimental results is also reported.

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Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence

Cited by 9 publications

References 21 publications

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS₂ Nanosheets

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS₂ Nanosheets

Optical Nonlinearity in Silicon Nanowires Enabled by Bound States in the Continuum

Ab initiodescription of second-harmonic generation from crystal surfaces

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Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence

Cited by 9 publications

References 21 publications

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS2 Nanosheets

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS2 Nanosheets

Optical Nonlinearity in Silicon Nanowires Enabled by Bound States in the Continuum

Ab initiodescription of second-harmonic generation from crystal surfaces

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Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS₂ Nanosheets

Broken Symmetry Induced Strong Nonlinear Optical Effects in Spiral WS₂ Nanosheets