https://doi.org/10.15407/iopt.2019.54.079
Optoelectron. Semicond. Tech. 54, 79-87 (2019)
I. Z. Indutnyi, V. I. Mynko, M. V. Sopinskyy, K. V. Svezhentsova
Plasmon-stimulated polarization conversion on diffraction gratings with different spatial frequencies
Experimental study of plasmon-stimulated polarization conversion on diffraction gratings with different spatial frequency 1/d, as well as different depth of modulation h/d (the λ/d ratio varied from 0,7 to 1,9 and h/d ratio from 0,01 to 0,25) was carried out. Gratings with sinusoidal groove’s profile were formed on the films of vacuum chalcogenide photoresists using interference lithography and covered with Au film. The geometric parameters of the obtained gratings were determined using an atomic force microscopy. Polarization conversion of incident light was studied by measuring the angular dependences of the specular reflection of linearly p-polarized monochromatic radiation of He-Ne laser with λ = 632,8 nm. The variation range of the incidence angle of the light beam on the sample was 2–80 °, the range of variation of the azimuth angle (the angle between the inverse vector of the grating and the projection of the wave vector of radiation to the sample surface) was 0–90°. Both non-converted Rpp and converted Rps components were registered. It was found that for low-frequency gratings with a period which is longer than the wavelength and also for gratings with an intermediate frequency (the grating period is somewhat less than the wavelength), the maximum conversion value is reached at an azimuth value of about 45° and is determined by the depth of modulation. For such gratings, there are two extremums of reflections corresponding to two branches of plasmon-polaritons excitation. But for high-frequency gratings, for which the ratio of wavelength to period is close to 2 and surface plasmon-polaritons are excited at large angles of incidence, the conversion is an order of magnitude smaller than the corresponding values for lower-frequency gratings. Thus, not only the parameter h/d (as was shown earlier) but also the λ/d parameter is essential parameter that determines the maximum achievable values of the effect of plasmon-stimulated polarization conversion.
Keywords: surface plasmon-polaritons, polarization conversion, metal diffraction gratings, conical diffraction, interference lithography, chalcogenide photoresists.