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"Investigation of photorefractive effect in LiNbO3 crystals"
(Supervisor: Ivan Turek)



    The photorefractive effect, early referred to as the “optical damage” [1, 2], is the process of the refractive index inhomogeneities creation due to irradiation of the crystal by (laser) light with the proper wavelength. Depending on the intensity of the illumination used one has to distinguish between the photorefractive effect and the so-called „optical breakdown“. In the first case mentioned there is the change of refractive index created due to illumination, which disappears (the crystal “turns” back to the “initial” state) if the specific treatment is used. In the latter case, the crystal becomes permanently damaged due to laser irradiation. As early, as the reference to photoinduced refractive index changes occurred for the first time in 1966, several models trying to explain (qualitatively and/or quantitatively) the origin of the effect were introduced [e.g. 1-6]. Although the models differ in details, they have the common core: they all consider the photoexcitation of charge carriers from the further unspecified donors or impurities that produce the localised states in the band gap. Moreover, the level is considered deep enough not to allow the excitation of the carriers by room temperature but by light with the proper wavelength only. Next, the models assume an inhomogeneous illumination due to diffusion causes the redistribution of the charge carriers (modulation of the photoexcited charge carrier density), which consequently forms the internal electric field. This field then induces the refractive index change via linear electrooptic effect. Today, such a refractive index inhomogeneity is referred to as the optical record (or just record) because the region with changed refractive index carries the information about optical wave that have induced the change.

   Although there are many different kinds of photorefractive materials existing today, probably the most often material used is the crystal of   lithium niobate – LiNbO3 . It belongs to the oldest photorefractive materials known and its advantages are good photorefractive sensitivity, enabling the temporary permanent records and relatively low price.

   The properties of LiNbO3 are relatively strong dependent on crystal purity and doping by proper dopants can influence the properties of the crystal in crucial way. It is very important for optical data storage, for example. As the LiNbO3 doped with Fe shows considerably strong photorefractivity, the most of our experiments were performed with that crystal when investigating the photorefractive effect.

   There are several methods available to investigate the photorefractive effect [7-9]: the so-called convention optical polarisation method using compensators [e.g. 2, 4], diffraction or holographic method [e.g. 3, 6] and, the method which is based on interference imaging of the photorefractive record [e.g. 8]. The first method mentioned is based on measuring the birefringence of the crystal before and after its irradiation by laser light, which induces the change of refractive index of the crystal. The second method is called holographic one because the arrangement of the experimental set-up corresponds to that one usually used at hologram recording when the sample is put into the place of interference field of two coherent laser beams. It is used for creation of the periodic field record. At the same time, these two beams are diffracted by the record during its formation and consequently the intensity of those beams provides the information about the record that is just being created. However, sometimes the optical field, which is to be recorded, can be created by help of the screen with the proper dependence of the transmittance with respect to coordinate. In general, both cases can be referred to as the diffraction investigation.

   The experimental set-up used in our investigation comes out from the holographic arrangement but record is illuminated by an extra beam of another (He-Ne) laser and the diffraction of that beam is monitored (Fig. 1.).


Fig. 1. The experimental set-up used for the recording.


   The record of the interference field behaves as the phase diffraction grating. This information is of cardinal importance from point of view of studying the photorefractive process itself. According to monitoring and investigation of diffraction of light incident upon the grating, it is possible to conclude what mechanisms are responsible for changing of the crystal properties. It is so, because the intensity of diffracted beam depends on amplitude of the record – the intensity “carries” the information about the record [10]. Moreover, it seems the monitoring of the intensity of diffracted beams can give some interesting information about actual sample of the crystal under the investigation [e.g. 11].

   For illustration, Fig. 2. shows the time dependence of the diffraction efficiency of the three diffraction maxima measured on the left (Fig. 2a) and on the right (Fig. 2b) side of the zeroth order.

                                                                  a)                                                                     b)
Fig. 2. Diffraction efficiencies of the first (red), the second (blue) and the third (green) diffraction maximum. Part a) - situation on the left of the zeroth order, part b) - on the right of the zeroth diffraction order.







References:
  1. A. Ashkin, G. D. Boyd, J. M. Dziedzic, R. G. Smith, A. A. Ballman, J. J. Levinstein, K. Nassau, „Optically – induced refractive index inhomogeneities in LiNbO3 and LiTaO3“, Appl. Phys. Lett. Vol. 9, 72 (1966)
  2. Y. Ohmori, Y. Yasojima, Y. Inuishi, „Photoconduction, Thermally Stimulated Luminescence, and Optical Damage in Single Crystal of LiNbO3“, Japan. J. Appl. Phys. Vol. 14, No.9 (1975)
  3. F. S. Chen, J. T. LaMacchia, D. B. Fraser, „Holographic storage in lithium niobate“, Appl. Phys. Lett. Vol. 13, No.7 (1968)
  4. F. S. Chen, „Optically Induced Change of Refractive Indices in LiNbO3 and LiTaO3“, J. Appl. Phys. Vol. 40, No.8 (1969)
  5. W. D. Johnston, Jr., „Optical Index Damage in LiNbO3 and Other Pyroelectric Insulators“, J. Appl. Phys. Vol. 41, No.8 (1970)
  6. V. M. Fridkin, „Fotosegnetoelektriki“ Moscow, 1979
  7. G. T. Avanesyan, E. S. Vartanyan, R. S. Mikaelyan, R. K. Hovsepyan, A. R. Pogosyan, „Mechanisms of Photochromic and Photorefractive Effects in Doubly Doped Lithium Niobate Crystals“, Phys. Stat. Sol. (a) 126, 245 (1995)
  8. I. Turek, N. Tarjányi, „Interference imaging of photorefractive record in thin sample of LiNbO3 crystal“, Proc. of SPIE Vol. 5945, 59450J-1 (2005)
  9. I. Turek, N. Tarjányi, „Complex imaging of photorefractive records“, 11th International Workshop on Applied Physics of Condensed Matter, Malá Lučivná, Slovak Republic, June 15-17, 2005
  10. N. Tarjányi, „Štúdium fotorefraktívneho javu a jeho využitie pre záznam optických polí“, Department of Physics, FEE Univ. of Zilina, (2000)
  11. N. Tarjányi, I. Turek, „The Photorefractive Effect In LiNbO3 Crystals With Various Dopants“, Acta Physica Slovaca 54, 433 (2004)







Publications:


    ~2014~

  1. N. Tarjányi, I. Turek, I. Martinček, "Effect of mechanical stress on optical properties of polydimethylsiloxane II - Birefringence" , Optical Materials, Vol. 37, 798–803 (2014), doi: http://dx.doi.org/10.1016/j.optmat.2014.09.010 .

  2. I. Martinček, I. Turek, N. Tarjányi, "Effect of boundary on refractive index of PDMS" , Optical Materials Express, Vol. 4, Issue 10, 1997-2005 (2014); DOI:10.1364/OME.4.001997.

  3. N. Tarjányi, "Specially shaped negative lens produced in a lithium niobate crystal" , Opt. Eng., Vol. 53, Issue 5, 057104 (2014); doi:10.1117/1.OE.53.5.057104.

  4. I. Turek, N. Tarjányi, I. Martinček, D. Káčik, "Effect of mechanical stress on optical properties of polydimethylsiloxane" , Optical Materials, Vol. 36 (5), 965–970 (2014), doi: http://dx.doi.org/10.1016/j.optmat.2013.12.049 .

    5. ~2013~

  5. N. Tarjányi, "The photorefractive response of LiNbO3:Fe:Mn crystal depending on electrical properties of its surroundings", Acta Electrotechnica et Informatica, Vol. 13, Issue 1, 37–40 (2013), ISSN (Online) 1338-3957, ISSN (Print) 1335-8243, DOI: 10.2478/aeei-2013-0007.

    6. ~2012~

  6. N. Tarjányi, I. Turek, "Influence of surroundings on photorefractive effect in lithium niobate crystals" , Physica B: Condensed Matter, Vol. 407, Issue 21, 4347–4353 (2012); doi:10.1016/j.physb.2012.07.031.

    7. ~2010~

  7. N. Tarjányi, "Real-time imaging of grating formation in LiNbO3:Fe using Mach–Zehnder interferometer" , Opt. Eng., Vol. 49, Issue 8, 085602 (2010); doi:10.1117/1.3481117.

  8. D. Káčik, N. Tarjányi, I. Turek, "Low-coherence interferometry for measurement of properties of optical components", Communications - scientific letters of the University of Žilina, 12 (2) (2010), pp. 14-18.

    9. ~2009~

  9. I. Turek, N. Tarjányi, Investigation of nonlinearity of photorefractive effect in LiNbO3 , Optica Applicata 39 (3) (2009), pp. 587-599.

  10. D. Pudiš, J. Škriniarová, I. Martinček, J. Kováč Jr., N. Tarjányi, Š. Haščík, Periodic structures patterned on metal and III-V compound surfaces using two-beam interference method , in Journal of Electrical Engineering 60 (3) (2009), pp. 166 - 169.

    11. ~2008~

  11. D. Káčik, I. Martinček, D. Pudiš, N. Tarjányi, I. Turek, Photonic crystals - optical structures for advanced tehcnology, Communications - scientific letters of the University of Žilina, 10 (2) (2008), pp. 25 - 29.

    12. ~2007~

  12. N. Tarjányi, D. Káčik, G. Tarjányiová, Light-induced microstructure fabrication , in SPIE Newsroom, Micro/Nanolithography & Fabrication, (2007), doi: 10.1117/2.1200708.0818.

  13. I. Turek, N. Tarjányi, Investigation of symmetry of photorefractive effect in LiNbO3 , Opt. Express 15 (17) (2007), pp. 10782 - 10788.

  14. J. Škriniarová, D. Pudiš, I. Martinček, J. Kováč, N. Tarjányi, M. Veselý, I. Turek, Periodic structures prepared by two-beam interference method , Microel. Journal 38 (2007), pp. 746-749.

    15. ~2005~

  15. I. Turek, N. Tarjányi, Complex imaging of photorefractive records, AEEE 4 (2005) 87-92.

    16. ~2004~

  16. I. Turek, N. Tarjányi, Interference imaging of photorefractive record in thin sample of LiNbO3 crystal, "Jemná mechanika a optika / Fine Mechanics and Optics", 49 (2004) 339, Institute of Physics of Czech Academy of Sciences and SPIE/CZ, Prague.

  17. N. Tarjányi, I. Turek, The Photorefractive Effect In LiNbO3 Crystals With Various Dopants , Acta Physica Slovaca 54 (2004), pp. 433 - 445.

  18. I. Turek, N. Tarjányi, Interference imaging of refractive index distribution in thin samples, AEEE 3 (2004) 257.

  19. N. Tarjányi, I. Turek, The generation of higher order diffraction beams by photorefractive record of harmonic optical field, AEEE 3 (2004) 253.

    20. ~2002~

  20. N. Tarjányi, I. Turek, An estimation of donor concentration in LiNbO3 using the photorefraction phenomenon, AEEE 1 (2002) 48.

    21. ~2000~

  21. I. Turek, N. Tarjányi, On photorefractive effect in LiNbO3, "Jemná mechanika a optika / Fine Mechanics and Optics", 45 (2000) 205 (in Slovak) Institute of Physics of Czech Academy of Sciences and SPIE/CZ, Prague.


Conferences:
    ~2014~

  1. N. Tarjányi, Analysis of interferograms of refractive index inhomogeneities produced in optical materials , In: 19th Polish-Slovak-Czech Optical Conference on Wave and Quantum Aspects of Contemporary Optics, Proc. SPIE Vol. 9441, p. 944116, 2014.

  2. N. Tarjányi, D. Sabol, Holographic optical element recorded in a photopolymer based medium , In: Advances in Electronic and Photonic Technologies : proceedings of the scientific conference ADEPT, High Tatras, Tatranská Lomnica, Slovak Republic, June 1-4, 2014, pp. 39-42, ISBN 978-80-554-0881-1.

    3. ~2013~

  3. N. Tarjányi, Lensing properties of a refractive index inhomogeneity induced in lithium niobate crystal , In: Advances in Electronic and Photonic Technologies : proceedings of the scientific conference ADEPT, High Tatras, Spa Novy Smokovec, Slovak Republic, June 2-5, 2013, pp. 287-290, ISBN 978-80-554-0689-3.

    4. ~2012~

  4. N. Tarjányi, Influence of the environment on temporal behaviour of the photorefractive inhomogeneity in LiNbO3 crystal , In: Physics of materials 2012 : proceedings of the scientific conference, Košice: Technical University, Slovak Republic, October 17-19, 2012, pp. 139-144, ISBN 978-80-553-1175-3.

  5. N. Tarjányi, G. Tarjányiová, KRAJINA VĹN – Expozícia interaktívnych demonštrácií vlnových procesov, 19th Conference of Slovak physicists, University of Prešov, Prešov, Slovak Republic, September 3-6, 2012, pp.

    6. ~2011~

  6. N. Tarjányi, D. Káčik, Fabrication and evaluation of photorefractive waveguide in LiNbO3:Fe , in Integrated Photonics: Materials, Devices, and Applications, Proc. SPIE Vol. 8069, 80690B, 2011.

  7. N. Tarjányi, D. Káčik, Light-guiding structure prepared in LiNbO3:Fe:Mn crystal utilizing the photorefractive effect, 17th International conference on Applied Physics of Condensed Matter, Nový Smokovec, High Tatras, Slovak Republic, June 22-24, 2011, pp.106-109.

    8. ~2009~

  8. N. Tarjányi, D. Sabol, J.T. Sheridan, Imaging of the grating recorded in photopolymer material, inPhotonics Ireland 2009, Kinsale, Ireland, September 14-16, pp. A58

  9. N. Tarjányi, I. Martinček, M. Koneracká, M. Timko, P. Kopčanský, The external magnetic field-induced partial preservation of the diffraction grating formed in magnetic fluid, 15th International conference on Applied Physics of Condensed Matter, Bystrá, Slovak Republic, June 24-26, 2009, pp.80-83.

  10. N. Tarjányi, D. Káčik, D. Sabol, J.T. Sheridan, Low spatial frequency grating recorded in photopolymer material , in Holography: Advances and Modern Trends, Proc. SPIE Vol. 7358, 73581I-1, 2009.

    11. ~2008~

  11. D. Pudiš, J. Škriniarová, I. Martinček, J. Kováč jr., N. Tarjányi, S. Haščík, Periodic structures patterned on metal and III-V compound surfaces using two-beam interference method, 34th International Conference on Micro and Nano Engineering 2008, Athens, Greece, September 15-18, 2008.

  12. D. Pudiš, I. Martinček, N. Tarjányi, I. Turek, D. Káčik, Photonic crystals – advanced structures for new optic and optoelectronic devices, Škola vákuovej techniky, Štrbské Pleso, 2008, pp. 88-93.

  13. D. Káčik, I.Turek, N.Tarjányi, Measurement of modal dispersion by low coherence interferometer , 16th Polish-Slovak-Czech Optical Conference on Wave and Quantum Aspects of Contemporary Optics, Proc. SPIE Vol. 7141, 71411K, 2008. DOI:10.1117/12.822401.

  14. I. Turek, N. Tarjányi, D. Káčik, Refractive index determination using a low coherence interferometry, 14th International conference on Applied Physics of Condensed Matter, Bystrá, Slovak Republic, June 25-27, 2008.

    15. ~2007~

  15. N. Tarjányi, D. Káčik, G. Tarjányiová, Ligth-induced microstructures in Fe doped LiNbO3 crystal , in Photonic Crystal Fibers, Proc. SPIE Vol. 6588, 658812, 2007.

  16. I. Turek, N. Tarjányi, The photorefractive effect in LiNbO3 crystals , 15th Czech-Polish-Slovak Conference on wave and Quantum Aspects of Contemporary Optics, Proc. SPIE Vol. 6609, 660906, 2007.

  17. N. Tarjányi, J. Vlk, J. Škriniarová, G. Tarjányiová, The possibility of studying the photochemical processes through grating recording in photoresist layer,13th International conference on Applied Physics of Condensed Matter, Bystrá, Slovak Republic, June 27-29, 2007.

    18. ~2006~

  18. I. Turek, N. Tarjányi, Interference imaging of photorefractive record in thin sample of LiNbO3 crystal , 14th Slovak-Czech-Polish Optical Conference on Wave and Quantum Aspects of Contemporary Optics Proc. of SPIE Vol.5945 ,59450J, 2006.

  19. J. Škriniarová, D. Pudiš, I. Martinček, J. Kováč, N. Tarjányi, Photonic Structures Prepared by Two-Beam Interference Method, 11th Joint Vacuum Conference and Inelastic Mean Free Path Worshop, Praha 2006.

  20. I. Turek, N. Tarjányi, J. Škriniarová, D. Pudiš, M. Dúbravka, Interference imaging of the photoresist layers, 12th International conference on Applied Physics of Condensed Matter, Malá Lučivná, Slovak Republic, June 21-23, 2006.

  21. D. Pudiš, J. Škriniarová, I. Martinček, N. Tarjányi, J. Kováč, M. Dúbravka, Photonic structures prepared by two-beam interference, 12th International conference on Applied Physics of Condensed Matter, Malá Lučivná, Slovak Republic, June 21-23, 2006.

    22. ~2005~

  22. I. Turek, N. Tarjányi, Complex imaging of photorefractive records, 11th International Workshop on Applied Physics of Condensed Matter, Malá Lučivná, Slovak Republic, June 15-17, 2005.

    23. ~2003~

  23. I. Turek, N. Tarjányi, The photorefractive effect and LiNbO3 band structure, 9th International Workshop on Applied Physics of Condensed Matter, Malá Lučivná, Slovak Republic, June 11-13, 2003.

    24. ~2002~

  24. N. Tarjányi, I. Turek, A study of photerefractive record of an optical field in LiNbO3:Fe, 14th Conference of Czech and Slovak Physicists (in Slovak), Plzeň, Czech Republic, September 2002.



A library-source list of publications can be found here



Grants:

  1. APVT-20-013504 Investigation of photorefractive records and their relationship to photonic crystals

Patents, designs and utility models:

  • Inventors: I. Turek, N. Tarjányi, M. Dúbravka

    Owner: University of Žilina

    Title: "Method for creating system of dioptric elements"

    Application number: 156-2006

    Status: Granted

    Publication Date of Published Application: 5.9.2008

    Date from which patent has effect: 7.5.2010



  • Inventors: I. Turek, N. Tarjányi, M. Dúbravka

    Owner: University of Žilina

    Title: "Sústavy dioptrických prvkov z fotorefraktívneho materiálu"

    Status: Registered

    Document No.: 4988

    Effective from: 19.12.2007