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Nanophysics: a question of resonance
24 Jun 2025
A team led by LMU physicist Andreas Tittl presents a novel method that could make manufacturing processes for semiconductor components easier and cheaper.
Physicist Andreas Tittl at the LMU Nanoinstitute | © LMU
Resonances are usually associated with finite systems – the vibrations of clamped strings in a guitar, for example, 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. In a study published in the journal Light: Science & Applications, a team led by LMU nanophysicist Andreas Tittl has demonstrated that periodic modulations of the permittivity in 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.
New applications possible
The manipulation of matter on scales comparable to the wavelength of light has opened the door to a plethora of new functionalities. It is expected that components thus manufactured will play a key role in fields as diverse as clean energy production, sensor technology, and photonic data processing – indeed some are already doing so. Despite optimizations, however, the manufacturing methods remain time-consuming and expensive.
Optical control
One problem is that as soon as you define the size of the components (e.g. through lithography), this also fixes the interaction with the electromagnetic spectrum. “We’ve demonstrated how to dynamically create strong, precisely tailored optical resonances in a thin silicon film – the important, initially blank starting element in the semiconductor industry,” says Rodrigo Berté, lead author of the study.
The researchers achieved this all-optically through an asymmetry in the permittivity of the film. “In principle, it’s possible to induce strong reactions even with negligible asymmetries,” notes Berté. “Using our optical control over the symmetries, we can circumvent some of the costly manufacturing processes and their bandwidth limitations.”
Rodrigo Berté, Andreas Tittl et al.: All-optical permittivity-asymmetric quasi-bound states in the continuum, Light: Science & Applications, 2025.