A new platform for guiding compressed light waves in very thin van der Waals crystals has been demonstrated by researchers at the Korea Advanced Institute of Science and Technology. Their method to guide the mid-infrared light with minimal loss will provide a breakthrough for the practical applications of ultra-thin dielectric crystals in next- generation optoelectronic devices.
Phonon-polaritons are a type of collective oscillations of ion in polar dielectrics combined with the waves of light. When thin van der Waals crystals are placed on top of a highlyconductive metal, they can be compressed further. A new type of polariton waves called the image phonon-polaritons can be created by reflecting charges in the polaritonic crystal. Strong light-matter interactions are provided by highly compressed image modes, but they are very sensitive to the surface of the object.
Four research groups tried to develop an experimental platform using advanced fabrication and measurement methods. Their findings were published in a journal.
A research team led by Professor Min Seok Jang from the School of Electrical Engineering used a scanning near-field optical microscope to measure the optical fields of the hyperbolic image.
Professor Jang and a research professor in his group detected a signal from the ultra-compressed high-order HIP in a regular h-BN crystal for the first time. They showed that the Van der Waals crystals can be more compressed.
Due to the atomically smooth surfaces of the home-grown gold crystals, this was possible. The low-loss environment for the propagation of the HIP is provided by zero surface scattering and extremely small losses in gold. The researchers found that the HIP mode was more compressed and had a similar lifetime compared to the phonon-polaritons.
The gold used in the experiment was grown at the University of Southern Danes.
Many important organic absorption molecules have lines in the mid-infrared, so it's important for sense applications. The detection limit down to a single molecule can be improved by using the ultra-compressed phonon-polariton fields instead of the conventional detection methods. The detection performance will be improved by the long lifetime of the HIP.
The team conducted a study that showed the similarity between the HIP and the image Graphene plasmons. The longer polariton wavelength doesn't affect the lifetime of both image modes. This observation gives a broader perspective on image polaritons in general, and highlights their superiority in terms of the light waveguiding compared to the low-dimensional polaritons in van der Waals crystals.
The research showed the advantages of image polaritons. In the future optoelectronic devices, both the low-loss propagation and strong light-matter interaction are needed. I hope that our results will lead to the realization of more efficient devices such as metasurfaces, optical frequencies, sensors, and other applications.
More information: Sergey G. Menabde et al, Near-field probing of image phonon-polaritons in hexagonal boron nitride on gold crystals, Science Advances (2022). DOI: 10.1126/sciadv.abn0627. www.science.org/doi/10.1126/sciadv.abn0627 Journal information: Science Advances
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