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8THz-O-5
Reconfigurable terahertz optics made of thin films with phase transition
P. Solyankin1, A. Shkurinov2, B. Knyazev3, O. Kameshkov3
1ILIT RAS - Branch of the FSRC «Crystallography and Photonics» RAS, -, Shatura, Russian Federation
2Lomonosov Moscow State University, Faculty of Physics and International Laser Center, Moscow, Russian Federation
3Budker Institute of Nuclear Physics of the Siberian Branch of RAS, n/a, Novosibirsk, Russian Federation
Recent progress in terahertz (THz) sources development, such as quantum cascade lasers (QCL), significantly increases the availability of the THz photonics for practical applications. To minimize the cost and the size of optical components for such systems one can utilize diffractive optics. Moreover, such components can be made reconfigurable, that is hard to achieve with usual optics.
In this work we present two types of optical components for 3.1 and 3.7 THz QCL radiation: switching focusers based on Fresnel zone plates and beamsplitters based on gratings. These structures were made by etching of thin (100-450 nm) films of vanadium dioxide (VO2) on sapphire substrates. Due to the phase transition, VO2 film can significantly change its transparency for the THz radiation under heating above 68°C or under optical irradiation [1]. In low-temperature transparent state film does not affect on incident THz beam, while in opaque high-temperature state Fresnel lenses or gratings are formed.
We made switching focusers with F = 50 mm and 100 mm, each structure contained 7 rings (see Fig. 1). With the help of microbolometer camera we were able to measure intensity distributions near the focal point of our structures and compare it with numerical simulations. We
achieved up to 38 times contrast in the focal spot between two states of the film. Power efficiency and focal spot size at different frequencies were measured. 3-way beamsplitter with 1:6:1 ratio was demonstrated, intensity contrast in 1-st order maximum between two phase states was as high as 68. For more details, one can see our work [2]. This work was partially supported by the Russian Foundation for Basic Research under project no. 16-29-11800 ofi-m. Work was partially supported by the Ministry of Science and Higher Education within the Sate assignment of the FSRC "Crystallography and Photonics" RAS.
References
[1] Cocker, T. L., Titova, L. V., Fourmaux, S., Holloway, G., Bandulet, H. C., Brassard, D., Kieffer, J-C., El Khakani, M. A., Hegmann, F. A. Phase diagram of the ultrafast photoinduced insulator-metal transition in vanadium dioxide // Physical Review B 2012, V. 85 No. 15, P. 155120.
[2] Solyankin, P. M., Esaulkov, M. N., Chernykh, I. A., Kulikov, I. V., Zanaveskin, M. L., Kaul, A. R., Makarevich, A.M., Sharovarov, D.I., Kameshkov, O.E., Knyazev, B.A., Shkurinov, A. P. (2018). Terahertz Switching Focuser Based on Thin Film Vanadium Dioxide Zone Plate. Journal of Infrared, Millimeter, and Terahertz Waves, 39(12), 1203-1210.
Fig.1. Example of the fabricated device.
