Scientists from Siberian Federal University (SFU) and the L. V. Kirensky Institute of Physics (SB RAS) carried out theoretical studies of hybrid Tamm plasmons. With the help of numerical calculations, they succeeded in predicting the structure in which it is possible to control the wavelength of these quasiparticles through means of heating or through an external electric field. The study is featured in the Journal of the Optical Society of America B.
"Cats-quasiparticles" - color transferred position of cats in the electromagnetic spectrum. (Image credit: Pavel Pankin)
School physics teaches that the foundation of an ordinary mirror is a thin silver or aluminum foil. Glass, which is actually a large transparent piece of ordinary silica sand, does not permit the foil to bend and rust. However, glass also reflects light, hence a dozen layers of ordinary glass and flint glass (a special type of high-reflective glass) is a high-quality and more expensive analogue of a metal mirror. Such a structure is also known as a one-dimensional photonic crystal. This means that the refractive index varies periodically in one direction, in this case perpendicular to the layers.
What would happen if such a multilayered mirror is covered with silver? It appears like a Napoleon cake, where instead of cake – flintglass and glass. Instead of top-cream, silver. The thickness of this cake is slightly more than a micron. In such a device, it is possible for light to be locked between two mirrors – multilayer and metal. The energy of light accumulates on the boundary between the multilayer and metallic mirrors and starts to leak via the multilayer mirror. Hence, a double mirror can indeed pass, and not reflect light. In such a scenario, a special quasiparticle of light is developed between the mirrors - not a photon, but a Tamm plasmon.
The appearance of such a quasiparticle is possible only when the metal is coated with a multilayer mirror. In this case, it is possible to obtain a light trapped between mirrors, and one of the reflecting surfaces must necessarily be metallic. Unlike the ordinary plasmon, which is a traveling wave, Tamm plasmon represents a standing wave, that is, it does not lead to energy transfer.
Pavel Pankin, First Author
For a number of practical applications, it is extremely vital to control the wavelength of a Tamm plasmon and it's color. For instance, this permits users to make a laser with a tunable frequency of radiation, instead of using a fixed frequency. For this purpose, Russian physicists suggested to connect the plasmon with a microcavity. This was attained by integrating a layer of a liquid crystal in a multilayer mirror in the model. Due to this, light started to accumulate on the border of two mirrors and also in this layer - the hybrid structure was thus attained. Earlier, scientists had to produce a new structure in order to change the color of a Tamm plasmon. Now it is just enough to electrify or heat the liquid crystal and the connection will allow Tamm plasmon to change color.
The Tamm plasmon permits creating lasers, single photon sources, optical filters, absorbers and thermal emitters of a new type. The authors believe that their work will expand the variety of possible applications.