High-harmonic generation at the nanoscale boosted by bound states in the continuum

Carletti, Luca; Kruk, Sergey; Bogdanov, Andrey; Angelis, Costantino De; Kivshar, Yuri S.

doi:10.1103/physrevresearch.1.023016

Cited by 128 publications

(85 citation statements)

References 47 publications

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“…Induced energy leakage can be compensated by inserting a reflective layer of metal of epsilon-near-zero material inside the substrate at the optimal distance. [34] The thickness adjustment of the spacer between the resonator and the reflective layer allows for control of the phase of reflection and even increase of the Q factor with respect to a free-standing resonator up to several times. [10] To determine the performance of supercavity modes, we compare the Q factor of supercavities with the Q factor of the fundamental dipole mode Q md of the cylindrical resonator (Table 1).…”

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confidence: 99%

Observation of Supercavity Modes in Subwavelength Dielectric Resonators

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Observation of Supercavity Modes in Subwavelength Dielectric Resonators

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“…A similar study showed similar findings with a 600-fold enhancement of third-harmonic generation from silicon arrays compared to bare films. [70] The experimental verification of [81] has been carried our recently confirming an enhanced second-harmonic generation from individual AlGaAs nanoscale resonators. [56] Using a combination of quasi-BIC on an ENZ substrate enabled a relatively high-Q factor in the telecommunication regime.…”

Section: Bics For Harmonic Generationmentioning

confidence: 97%

Photonic Bound States in the Continuum: From Basics to Applications

Azzam

Kildishev

2020

Advanced Optical Materials

363

141

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In theory, BICs are dark states with infinite radiative lifetime and generally require at least one dimension of the structure extending to infinity. [6] Similar conditions can also be obtained in localized systems of finite extent when the permittivity approaches zero. [5,11] However, in practice, due to the finite extent of structures, material absorption, and other external perturbations, BICs collapse to a Fano resonance with a limited radiative Q factor. Such resonances are known as quasi-BIC and they have been used to obtain very high Q resonances in numerous photonic systems to date. [6,8,12] Even though practical implementations of BICs are limited to quasi-BIC, in the literature, as well as in this review, quasi-BIC are commonly referred to as BICs. Another type of high-Q resonances called near-BIC is obtained in the vicinity of the BIC through detuning the system from the BIC regime. [9,13,14] Near-BICs can be explained by the Theory of Resonance Reactions by Fonda [13,14] as a bound state can exist in the continuum at an energy where some channels are open even when the open and closed channels are strongly coupled. If the Hamiltonian of the system differs slightly from the one that can produce such a bound state, a sharp resonance appears in all scattering and reaction cross-sections. Near-BIC resonances can be obtained over an interval of values of a specific parameter of the system, unlike BICs that are generally achieved at a single value of the parameter. [9,15] This is of importance for practical systems as it provides stability to fabrication errors and other imperfections. [12] It is also worth mentioning that the total Q factor (Q t) realizable through BICs is generally limited by the material loss. While the radiative Q-factor (Q r) at BICs can diverge, the non-radiative Q-factor (Q nr) is limited by material absorption and its inhomogeneous broadening, scattering from the structural disorder, and in-plane lateral leakage. It is therefore, important to have an accurate distinction between Q r and Q nr and account for non-radiative processes as generally the main contributors to the total Q." 1.2. BIC Types and Formation Mechanisms Since the time of initial prediction of BICs in photonics, they have been realized in numerous geometrical systems, including gratings, waveguides, metasurfaces, and photonic crystals. [4,7,9,16-24] Such a broad diversity of photonic systems supports different types of BICs that originate from various physical mechanisms. We will briefly highlight the different The introduction of bound states in the continuum (BICs) to photonics has revolutionized the way cavity design and light-matter interactions are thought about in general. BICs can have very high quality factors, even in open structures where access to radiation is permissible. Now, BICs found applications in a large class of areas, including nonlinear enhancement, coherent light generation, sensors, filters, integrated circuits, and many others. In this review, the different types of BICs in photonic systems,...

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“…The BIC, in the case of a PhC slab, corresponds to the mode that lies inside the light cone but is nevertheless nonradiative, either because of symmetry protection or because of destructive interference between different radiation channels [33][34][35]. BICs have been theoretically proposed and experimentally implemented to enhance nonlinear generation in singly resonant regime [36][37][38]. The doubly resonant PhC cavity design [32] abandoned the commonly held notion of engineering photonic bandgaps at both FH and SH frequencies.…”

Section: Introductionmentioning

confidence: 99%

Doubly resonant second-harmonic generation of a vortex beam from a bound state in the continuum

Wang

Clementi

Minkov

et al. 2020

Optica

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Second-harmonic generation in nonlinear materials can be greatly enhanced by realizing doubly resonant cavities with high quality factors. However, fulfilling such doubly resonant condition in photonic crystal (PhC) slab cavities is a long-standing challenge, because of the difficulty in engineering photonic bandgaps around both frequencies. Here, by implementing a second-harmonic bound state in the continuum (BIC) and confining it with a heterostructure design, we show the first doubly resonant PhC slab cavity with 2.4 × 10 −2 W −1 intrinsic conversion efficiency under continuouswave excitation. We also report the confirmation of highly normal-direction concentrated far-field emission pattern with radial polarization at the second harmonic frequency. These results represent a solid verification of previous theoretical predictions and a cornerstone achievement, not only for nonlinear frequency conversion but also for vortex beam generation and prospective nonclassical sources of radiation.

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High-harmonic generation at the nanoscale boosted by bound states in the continuum

Cited by 128 publications

References 47 publications

Observation of Supercavity Modes in Subwavelength Dielectric Resonators

Observation of Supercavity Modes in Subwavelength Dielectric Resonators

Photonic Bound States in the Continuum: From Basics to Applications

Doubly resonant second-harmonic generation of a vortex beam from a bound state in the continuum

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