近日，德国慕尼黑路德维希马克西米利安大学Andreas Tittl团队研究了全光介电常数-连续介质中的非对称准束缚态。这一研究成果于2025年5月7日发表在《光：科学与应用》杂志上。

共振通常与有限系统有关——吉他中固定弦的振动或由镜子限定的腔中的光学模式。在光学中，谐振可以通过其光学性质的周期性调制在无限连续介质中引起。研究组证明了无特征薄膜介电常数的周期性调制也可以作为对称破缺机制，允许在连续体（qBIC）中激发光子准束缚态。通过在无界薄膜中干涉两个超短激光脉冲，可以通过泵浦光束的不同参数来定制瞬态共振。 

研究组表明，该系统提供了波长和品质因数可调的谐振，以及三次谐波产生的光谱选择性增强。由于介电常数不对称性的快速衰减，观察到了超快动力学，实现了皮秒精度的时间选择性近场增强。光学诱导的介电常数不对称可以在无光刻超表面中按需弱到超强光物质相互作用机制和动态选择波长的光操纵中加以利用。

附：英文原文

Title: All-optical permittivity-asymmetric quasi-bound states in the continuum

Author: Bert, Rodrigo, Possmayer, Thomas, Tittl, Andreas, Menezes, Leonardo de S., Maier, Stefan A.

Issue&Volume: 2025-05-07

Abstract: Resonances are usually associated with finite systems—the vibrations of clamped strings in a guitar or the optical modes in a cavity defined by mirrors. In optics, resonances may be induced in infinite continuous media via periodic modulations of their optical properties. Here we demonstrate that periodic modulations of the permittivity of a featureless thin film can also act as a symmetry-breaking mechanism, allowing the excitation of photonic quasi-bound states in the continuum (qBICs). By interfering two ultrashort laser pulses in the unbounded film, transient resonances can be tailored through different parameters of the pump beams. We show that the system offers resonances tunable in wavelength and quality-factor, and spectrally selective enhancement of third-harmonic generation. Due to a fast decay of the permittivity asymmetry, we observe ultrafast dynamics, enabling time-selective near-field enhancement with picosecond precision. Optically induced permittivity asymmetries may be exploited in on-demand weak to ultrastrong light-matter interaction regimes and light manipulation at dynamically chosen wavelengths in lithography-free metasurfaces.

DOI: 10.1038/s41377-025-01843-9

Source: https://www.nature.com/articles/s41377-025-01843-9