THE PHOTOELASTICITY OF RHOMBIC SYNGONY CRYSTALS

Vasyl Stadnyk, I. Matviishyn, N. Ftomyn, V. Vyshnevskyi, V. Baliga, O. Shtuka

Abstract


The Rb2SO4 crystals were synthesized by slow evaporation of room-temperature aqueous solution of pure rubidium sulfate salts that had been recrystallized many times. The solution temperature was 310 K, controlled by a thermostat with an accuracy of 0.5 K.

The dispersion dependences of the birefringence Δni of a mechanically free and uniaxially clamped Rb2SO4 crystal at room temperature were studied. It was found that the crystal has a small normal dispersion d(Δnx)/dλ = -1.2…1.8∙10-6; uniaxial compressions σm do not change the character, but only the magnitude of the slope of the Δnі(λ) curves. Thus, uniaxial compression σz leads to a decrease in the Δnх value on the average of δ(Δnх) ⁓ 0.89·10-4, while uniaxial compression σy to an increase in Δnх on the average of δ(Δnх) ⁓ 1.01·10-4. This behavior of baric-induced changes in Δnі confirmed the previously discovered regularity for crystals of the A2BX4 group: uniaxial compressions along mutually perpendicular directions lead to changes in birefringence of different magnitudes and signs. Since uniaxial loads along the Y- and Z-axes shift the Δnх(λ) curves towards larger and smaller wavelength values, the position of the optical isotropic point in the spectrum changes accordingly. Since the following relations Δny = nх – nz, and Δnz = nх – ny hold for the RS crystal, this will mean the equality of the refractive indices nz = ny, which corresponds to the emergence of a new “pseudoisotropic” point. That is, in the case of simultaneous application of a uniaxial load along the crystal-physical Y- and Z-directions, we can obtain a new optical isotropic point at room temperature, which was previously discovered in a number of isomorphic crystals of this group (e.g. K2SO4 and (NH4)2SO4). Since the values dΔnz = dΔny and nz = ny in the vicinity of this “pseudoisotropic” point, we obtain the following combination between the absolute piezo-coefficients and refractive indices in the vicinity of the optical isotropic point n3yπ22–n3xπ12 ⁓ n3zπ33–n3yπ13.

Using the obtained spectral-baric dependences of Δni, Δnyx(λ), Δnzx(λ), Δnxy(λ), Δnzy(λ), Δnyz(λ), Δnxz(λ), for 9 different experimental geometries, as well as Δnzxy(λ), Δnyxz(λ), Δnxzy(λ), the spectral dependences of the combined piezo-coefficients were calculated. A feature of the behavior of Rb2SO4 crystals is their insignificant dispersion dependence, while the nature of the dispersion π0lm/dλ < 0 corresponds to the dispersion of the refractive indices dnі/dλ < 0. The most spectrally dependent is the constant π012 (dπ012/dλ = 2.2∙102∙Br/nm), while π021 changes very weakly in the studied spectral range (0.5∙10-2∙Br/nm). Different signs and spectral changes of π0lm indicate that the influence of uniaxial mechanical pressure along the crystallographic axes X, Z, and Y leads to different nature of the change in the induced birefringence of the Rb2SO4 crystal. It was found that at a light wavelength λ = 490 nm π031 ⁓ │π021│ ⁓ 1.67∙10-11 N/m2. That is, in the vicinity of the optical isotropic point, not only an increase in the symmetry of the optical indicatrix, but also increase of the tensor of piezo-optical coefficients take place.

Keywords:  crystal, birefringence, dispersion, photoelasticity, piezooptic coefficients, optic isotropic point.


References


  1. Романюк М.О. Кристалооптика: навч. посібник / М.О. Романюк. – (2-е видання, випр. і доповн. – Львів: ЛНУ імені Івана Франка, 2017. – 456 с.
  2. Мицик Б.Г. Фотопружність аніотропних матеріалів: наук. видання / Б.Г. Мицик. – Львів: Ліга-Прес, 2012. – 400 с.
  3. Стадник В.Й. Електронна поляризовність фероїків: монографія / В.Й. Стадник, М.О. Романюк, Р.С. Брезвін. – Львів: ЛНУ імені Івана Франка, 2014. – 306 с.
  4. Erba A. Photoelasticity of crystals from theoretical simulations. / A. Erba, R. Dovesi // Phys. Rev. B – 2013. – V. 88, https://doi.org/10.1103/PhysRevB.88.045121, 045121/1–8.
  5. Natali P.P. Theoretical and experimental evaluation of piezo-optic parameters and photoelastic constant in tetragonal PWO / P.P. Natali, L. Montalto, F. Davi, P. Mengucci, A. Ciriaco, N. Paone, D. Rinaldi // Appl. Opt. – 2018. – V. 57 – P. 730–737, https:// doi.org/10.1364/AO.57.000730.
  6. Mytsyk B.G. Characterization of photoelastic materials by combined Mach-Zehnder and conoscopic interferometry: application to tetragonal lithium tetraborate crystals / B.G. Mytsyk, A.S. Andrushchak, D.M. Vynnyk, N.M. Demyanyshyn, Ya P. Kost, A. V. Kityk // Opt Laser. Eng. – 2020. – V. 127, https://doi.org/10.1016/j. optlaseng.2019.105991, 105991/1–8.
  7. Dixon R.W. A new technique for measuring magnitudes of photoelastic tensors and its application to lithium niobite / R.W. Dixon, M.G. Cohen // Appl. Phys. Lett. – 1966. – V.8. – P. 205–207, https://doi.org/10.1063/1.1754556.
  8. Coquin G.A. Physical properties of lead molybdate relevant to acousto-optic device applications / G.A. Coquin, D.A. Pinnow, A.W. Warner // J. Appl. Phys. – 1971. – V. 42 – P. 2162–2168, https://doi.org/10.1063/1.1660520.
  9. Narasimhamurty T.S. Photoelastic and Electro-Optic Properties of Crystals / T.S. Narasimhamurty // Springer, 1981, https://doi.org/10.1007/978-1-4757-0025-1
  10. Gaba V.M. Temperature-and-Spectral Deformations of the Optical Indicatrix of Rubidium Sulphate Single Crystal / V.M. Gaba // Acta Physica Polonica A – 2010. – Vol. 117, No. 1. – P. 129-132.
  11. Rudysh M. Ya. Optical and electronic parameters of Rb2SO4 crystals / M. Ya Rudysh, I.A. Pryshko, P.A. Shchepanskyi, V. Yo Stadnyk, R.S. Brezvin, Z.O. Kogut // Optik. 2022. – – V. 269. 69875. DOI 10.1016/j.ijleo.2022.169875
  12. Onodera A. The crystal structure of paraelectric ammonium fluoroberyllate at room temperature / А. Onodera, Y. Shiozaki // Ferroelectrics. – 1981. – V.31, № 1-2. – P.27-36.
  13. Stadnyk V.Y. Piezooptic properties of (NH4)2BeF4 crystals / V.Y. Stadnyk, М.О. Romanjuk // Phys. status solidi (a). – 1996. – V.158. – Р.289-296.
  14. Rudysh M.Ya. Ionicity and birefringence of α-LiNH4SO4 crystals: ab initio DFT study, X-ray spectroscopy measurements / M. Ya. Rudysh, M. G. Brik, O. Y. Khyzhun, A. O. Fedorchuk, I. V. Kityk, P. A. Shchepanskyi, V. Yo Stadnyk, G. Lakshminarayana, R. S. Brezvin, Z. Bak and M. Piasecki // RSC Adv. –2017. V. 7. P.6889–6901.
  15. Rudysh М. Ya. Energy Band Structure of LiNH4SO4 Crystals / М. Ya. Rudysh, V. Yo. Stadnyk, R. S. Brezvin, P. A. Shchepanskii // Condensed Metter Physics –2015. –V. 57. –P.50–55.
  16. Shchepanskyi P. A. Structure and optical anisotropy of K1.75(NH4)0.25SO4 solid solution / Р. А. Shchepanskyi, O. S. Kushnir, V. Yo. Stadnyk, A. O. Fedorchuk, M. Ya. Rudysh, R. S. Brezvin // Ukr. Jour. Phys. Opt. – 2017. – V. 18, № 4. – Р.187-196.




DOI: http://dx.doi.org/10.30970/eli.28.13

Refbacks

  • There are currently no refbacks.