Nonlinear Optics & Multi-photon Processes.  Electro-optics & Photonics   

Persons in charge:    Georgi HADJICHRISTOV       (Prof., Dr., Dipl. Eng.-Phys.)                georgibh@issp.bas.bg

Spectroscopic methods and activity :
  • Nonlinear optics and laser spectroscopy: multi-photon, coherent and stimulated optical processes in condensed media :
    – Optical wave-mixing and optical harmonics spectroscopy (optical parametric processes);
    – Nonlinear Raman spectroscopy (Coherent Raman scattering/Stimulated Raman scattering);
    – Optical limiting / Nonlinear refraction & Nonlinear optical transmission;
    – Multi-photon absorption / Multi-photon emission;
    – Raman and photoluminescence spectroscopy for structural characterization of solid and soft condensed media
  • Quantum-mechanical calculations of nonlinear optical susceptibilities
  • Dielectro-optical spectroscopy, optics and electro-optics of liquid-crystalline materials
  • Complex electrical impedance spectroscopy & dielectric spectroscopy
  • Elastic incoherent neutron scattering for the study of the structure and molecular dynamics in anisotropic systems
  • Photo-induced, photo-stimulated and photo-controllable effects in solid and soft condensed media
Equipment
Experimental system (Fig. 1) for the optical four-wave mixing (FWM) and Coherent anti-Stokes Raman  Scattering (CARS) (Fig. 2e). We employ this set-up for x(3)- (as well as x(2)-) spectroscopy for measurement of the third-order nonlinear optical (NLO) susceptibility x(3) and photonic properties of solid and soft condensed media (bulk or layers/films) by means the above spectroscopic methods and techniques (e.g., optical second-harmonic (Fig. 2b) or third-harmonic generation, two-photon resonance FWM (Fig. 2c), two-photon non-resonant FWM (Fig. 2d) or degenerate FWM, as well as for characterization of emissive samples (Figs. 2 and 2a,b). The experimental system enables narrow-band as well as broadband (multiplex) CARS measurements. Narrowband and broadband laser sources are used for spectra excitation, and the resulting optical signal is registered with optical multi-channel analyzer (PARC OMA) (Fig. 1). Figs. 3 and 4 represent two examples for evaluation of x(3) of bulk polymers by CARS spectroscopy.
Materials
The materials of interest (liquid, soft & solid condensed media): organic polymers, dyes, dye-doped polymers, organic molecular crystals, inorganic crystals, liquid crystals, polymer-dispersed liquid crystals (PDLCs), organo-metallic complexes,  ion-implanted polymers, polar media, fluorescent materials, photoactive media, nanostructured materials, composites & nanocomposites based on liquid crystals or/and polymers.
Examples

 

 

 Fig. 3. Optical four-wave mixing spectra of bulk polymer
poly-(vinyl toluol), 8 mm-thick sample. Instrumental resolution 5 cm-1.
The nonresonant (electronic) cubic NLO susceptibility is measured to be
x(3) = 3.4 x 10-14 esu.
Fig. 4. Broadband nonresonance CARS spectra of 2mm-thick sample of
poly[3-(bromocarbazol-9-yl)propyl]methylsiloxane dissolved in trichlorethylene. This electro-conducting and photochromic liquid polymer is of interest for organic photonics and optoelectronics.
The phase match for the optical four-wave mixing and multiplex CARS  is optimized for ωas = 1500 cm-1 (a);  and ωas = 1600 cm-1 (b).
The arrows indicate the analyzed Raman line shapes at 1486 cm-1 for the polymer and 1586 cm-1 for the solvent. The measured electronic cubic susceptibility of the polymer:  x(3)  = 7.5 x 10-11 esu.
Selected Publications
  1. N. Kirov, G.B. Hadjichristov: "Nonlinear optics in materials: integral transformation of optical four-wave mixing spectra",
    J. Mater. Sci. - Materials in Electronics 14(10-12) (2003) 725-728.
  2. N. Kirov, G.B. Hadjichristov, M.P. Fontana: "Vibrational spectroscopy of solid polymorphic modifications formed by thermotropic liquid crystals",
    J. Molec. Struct. 706(1-3) (2004) 65-73.
  3. N. Kirov, I. Dozov, J. Jordanova, M.P. Fontana, G.B. Hadjichristov: "Elastic incoherent neutron scattering of rotational and translational dynamics in liquid crystals",
    J. Molec. Struct. 788(1-3) (2006) 7-15.
  4. N. Kirov, I. Dozov, J. Jordanova, G.B. Hadjichristov, M.P. Fontana: "Uncorrelated jumps model for molecular orientational relaxation in liquid crystals",
    J. Molec. Struct. 839(1-3) (2007) 84-89.
  5. S. Stanimirov, G.B. Hadjichristov, I.K. Petkov: "Emission efficiency of diamine derivatives of tris [4,4,4-trifluoro-1-(2-thienyl)-1,3-butanediono]europium",
    Spectrochim. Acta A: Mol. Biomolec. Spectrosc. 67(5) (2007) 1326-1332.
  6. G.B. Hadjichristov, S.S. Stanimirov, I.L. Stefanov, I.K. Petkov: "The luminescence response of diamine-liganded europium complexes upon resonant and pre-resonant excitation",
    Spectrochim. Acta A: Mol. Biomolec. Spectrosc. 69(2) (2008) 443-448.
  7. G.B. Hadjichristov, V. Ivanov, E. Faulques: "Reflectivity modification of polymethylmethacrylate by silicon ion implantation",
    Appl. Surf. Sci. 254(15) (2008) 4820-4827.
  8. G.B. Hadjichristov, V.K. Gueorguiev, Tz.E. Ivanov, Y.G. Marinov, V.G. Ivanov, E. Faulques: “Silicon ion implanted PMMA for soft electronics",
    Org. Electron.: Mater. Phys. Chem. Appl. 9(6) (2008) 1051-1060.
  9. G.B. Hadjichristov, Y.G. Marinov, A.G. Petrov: "Linear size gradient single layers of polymer-dispersed liquid crystal micrometer-sized droplets for diffractive optics”,
    Opt. Mater. 31(11) (2009) 1578-1585.
  10. Y.G. Marinov, G.B. Hadjichristov, A.G. Petrov: “Single-layered microscale linear-gradient PDLC material for electro-optics”,
    Cryst. Res. Technol. 44(8) (2009) 870-878.
  11. V.G. Ivanov, G. Hadjichristov, E. Faulques: “Characterization of chemical bonding in ion-implanted polymers by means of mid-infrared reflectivity”,
    Appl. Spectrosc. 63(9) (2009) 1022-1026.
  12. G.B. Hadjichristov, I.L. Stefanov, B.I. Florian, G.D. Blaskova, V.G. Ivanov, E. Faulques: "Optical reflectivity study of silicon ion implanted poly(methyl methacrylate)”,
    Appl. Surf. Sci. 256(3) (2009) 779-786.
  13. G.B. Hadjichristov, I.L. Stefanov, S.S. Stanimirov, I.K. Petkov: “The luminescence response of Eu(III)-thenoyltrifluoroacetonate complexes upon preresonant excitation with femtosecond laser pulses”,
    Spectrochim. Acta A: Mol. Biomol. Spectrosc. 75(1) (2010) 448-452.
  14. G.B. Hadjichristov, Y. Marinov, A.G. Petrov: “Single-layered PDLC for diffractive optics”,
    Mol. Cryst. Liq. Cryst. 525(1) (2010) 128-139.
  15. G.B. Hadjichristov, I.L. Stefanov: "Ion-implanted polymethyl methacrylate beam splitter/coupler for 1.55 μm applications",
    Appl. Opt. 49(10) (2010) 1876-1879.
  16. Y.G. Marinov, G.B. Hadjichristov, A.G. Petrov: "Single-layered PDLC films for electrically variable laser light reflection application",
    Opt. Las. Eng. 48(12) (2010) 1161-1165.
  17. A.G. Petrov, Y.G. Marinov, G.B. Hadjichristov, S. Sridevi, U.S. Hiremath, C.V. Yelamaggad, S.K. Prasad: "New photoactive guest-host nematics showing photoflexoelectricity",
    Mol. Cryst. Liq. Cryst 544(1) (2011) 3/[991]-13/[1001].
  18. V.G. Ivanov, G.B. Hadjichristov: “Orientation of sp2 carbon nanoclusters in ion-implanted polymethylmethacrylate as revealed by polarized Raman spectroscopy”,
    J. Raman Spectrosc. 42(6) (2011) 1340-1343.
  19. G.B. Hadjichristov, Y.G. Marinov, A.G. Petrov: "Gradient polymer-disposed liquid crystal single layer of large nematic droplets for modulation of laser light",
    Appl. Opt. 50(16)(2011) 2326-2333.
  20. S. Sridevi, U.S. Hiremath, C.V. Yelamaggad, S.K. Prasad, Y.G. Marinov, G.B. Hadjichristov, A.G. Petrov: “Behaviour of photosensitive soft materials: Thermo-optical, dielectric and elastic constant studies on azo-dye doped nematic liquid crystals”,
    Mater. Chem. Phys.130(3) (2011) 1329-1335.
  21. I.L. Stefanov, G.B. Hadjichristov: "Interferometric pump-probe characterization of the nonlocal response of optically transparent ion implanted polymers",
    Appl. Surf. Sci. 258(10) (2012) 4770-4776.
  22. H.Y. Stoyanov, I.L. Stefanov, G.G. Tsutsumanova, S.C. Russev, G.B. Hadjichristov: “Depth-profiled characterization of complex refractive index of ion implanted optically transparent polymers using multilayer calculations and reflectance data”,
    Vacuum 86(12) (2012) 1822-1827.
  23. Y.G. Marinov, G.B. Hadjichristov, A.G. Petrov, S. Marino, C. Versace, N. Scaramuzza: “Electro-optical response of PDLC single layers of large nematic droplets oriented by rubbed teflon nanolayers”,
    J. Appl. Phys. 113(6) (2013) 064301 (1-11).
  24. S.C. Russev, G.G. Tsutsumanova, I.L. Stefanov, G.B. Hadjichristov: “Ellipsometrical characterization of complex refractive index depth profile of 50 keV silicon ion implanted PMMA”,
    Vaccum 94 (2013) 19-25.
  25. G.B. Hadjichristov, Y.G. Marinov, A.G. Petrov, E. Bruno, L. Marino, N. Scaramuzza: "Electro-optically responsive composites of gold nanospheres in 5CB liquid crystal under direct current and alternating current joint action",
    J. Appl. Phys. 115(8) (2014) 083107 (1-14).
  26. G.B. Hadjichristov, Y.G. Marinov, A.G. Petrov, E. Bruno, L. Marino, N. Scaramuzza: "Electro-optics of nematic/gold nanoparticles composites: the effect from dopants",
    Mol. Cryst. Liq. Cryst. 610(1) (2015) 135-148.
  27. Y.G. Marinov, G.B. Hadjichristov,  A.G. Petrov, S. Krishna Prasad: "Electro-optic modulation by silica-nanostructured nematic system (aerosil/7CB nanocomposite)”,
    Composites Part B: Engineering 90 (2016) 471-477.
  28. G.B. Hadjichristov, Y.G. Marinov: "Optical diffraction by using electrically-controlled spatially patterned nematic pentylcyanobiphenyl films under static electric field”,
    Mol. Cryst. Liq. Cryst. 632(1) (2016) 9-20.
  29. A A. Ayriyan, E.A. Ayrjan, A.A. Egorov, G.B. Hadjichristov, Y.G. Marinov, I.A. Maslyanitsyn, A.G.Petrov, J. Pribis, L. Popova, V.D. Shigorin, A. Strigazzi, S.I. Torgova: "Some features of second harmonic generation in the nematic liquid crystal 5CB in the pulsed-periodic electric field",
    Phys. Wave Phenomena 24(4) (2016) 1-9.
  30. H.K. Koduru, L. Marino, F. Scarpelli, A.G. Petrov, Y.G. Marinov, G.B. Hadjichristov, M.T. Iliev, N. Scaramuzza: "Structural and dielectric properties of NaIO4-complexed PEO/PVP blended solid polymer electrolytes",
    Curr. Appl. Phys. 17(11) (2017) 1518-1531.
  31. G.B. Hadjichristov, Y.G. Marinov, A.G. Petrov, S.K. Prasad: "Light-stimulated electro-optics by azo-doped aerosil/7CB nanocomposites",
    Opto-Electronics Review 26(2) (2018) 172-182.
  32. H.K.Koduru, Y.G.Marinov, G.B.Hadjichristov, A.G.Petrov, N.Godbert, N.Scaramuzza: "Polyethylene oxide (PEO) – Liquid crystal (E8) composite electrolyte membranes: Microstructural, electrical conductivity and dielectric studies",
    J. Noncryst. Solids 499(1 Nov) (2018) 107-116.
  33. H.K. Koduru, F. Scarpelli, Y.G. Marinov, G.B. Hadjichristov, P.M. Rafailov, I.K. Miloushev, A.G. Petrov, N. Godbert, L. Bruno, N. Scaramuzza: "Characterization of PEO/PVP/GO nanocomposite solid polymer electrolyte membranes: microstructural, thermo-mechanical, and conductivity properties", 
    Ionics 24(11) (2018) 3459–3473.
  34. G.B. Hadjichristov, Tz.E. Ivanov, Y.G. Marinov, H.K. Koduru, N. Scaramuzza: "PEO-PVP-NaIO4 ion-conducting polymer electrolyte: Inspection for ionic space charge polarization and charge trapping", 
    Physica Status Solidi (A): Applications and Materials Science 216(13) (2019) 1800739 (1-11).
  35. H.K. Koduru, Y.G. Marinov, G.B. Hadjichristov, N. Scaramuzza:"Characterization of polymer/liquid crystal composite based electrolyte membranes for sodium ion battery applications", 
    Solid State Ionics 335(July 2019) 86-96.
  36. H.K.Koduru, L. Bruno, Y.G. Marinov, G.B. Hadjichristov, N. Scaramuzza: ”Mechanical and sodium ion conductivity properties of graphene oxide–incorporated nanocomposite polymer electrolyte membranes”, 
    J. Solid State Electrochem. 23(9) (2019) 2707–2722.
  37. Y.G. Marinov, G.B. Hadjichristov, T.E. Vlakhov, H.K. Koduru, N. Scaramuzza: "Electrochemical impedance and dielectric spectroscopy study of TiO2-nanofilled PEO/PVP/NaIO4 ionic polymer electrolytes", 
    Bulg. Chem. Commun. 52(E) (2020) 57-61.
  38. G.B. Hadjichristov, Y.G. Marinov, Tz.E. Ivanov, H.K. Koduru, N. Scaramuzza: "PEO/E8 Polymer-Liquid Crystal Flexible Complex Blend Electrolyte System for Na Ions",
    In: Liquid and Single Crystals: Properties, Manufacturing and Uses, Editor: Jai Goosen, Nova Science Publ., Series: Chemistry Research and Applications, 2020, New York, 
    ISBN: 978-1-53616-541-8, 
    Chapter 1, pp. 1-64.
  39. Y.G. Marinov, G.B. Hadjichristov: “Electro-optical characteristics of thin films of aerosil-7CB nematic gel nanocomposites doped with photoresponsive liquid crystalline azo-compounds”, 
    Compt. Rend. Acad. Bulg. Sci. 73(10) (2020) 1368-1375.
  40. M. Dencheva-Zarkova, G.B. Hadjichristov, Y.G. Marinov, I.A. Maslyanitsyn, A.G. Petrov, L. Popova, V.D. Shigorin, S.I. Torgova: “Effect of inhomogeneous electric field in a cell with side electrodes: Nematic liquid crystal 5CB”, 
    Phys. Wave Phenomena 28(3) (2020) 250-254.
  41. H.K. Koduru, Y.G. Marinov, S. Kaleemulla, P.M. Rafailov, G.B. Hadjichristov, N. Scaramuzza: "Fabrication and characterization of magnesium-ion-conducting flexible polymer electrolyte membranes based on a nanocomposite of poly(ethylene oxide) and potato starch nanocrystals", 
    J. Solid State Electrochem. 25(8-9) (2021) 2409-2428.
  42. G.B. Hadjichristov, T.E. Vlakhov, Y.G. Marinov, N. Scaramuzza:"Ion-Conducting Flexible Thin Films of Composites from Poly(ethylene oxide) and Nematic Liquid Crystals E8 - Characterization by Impedance and Dielectric Relaxation Spectroscopy", 
    Polymers 13(24) (2021) art. no 4465 (1-27).
  43. G.B. Hadjichristov, Tz.E. Ivanov: "Near-surface nanostructuring of polymethylmethacrylate by silicon ion implantation", 
    J. NanoRes. 72 (2022) 95-112.
  44. G.B. Hadjichristov: "Ion-Conducting Composites of Polymers and Nematic Liquid Crystals", 
    ACS Omega 8(11) (2023) 9684-9701.
  45. G.B. Hadjichristov, Y.G. Marinov: "Photoluminescent Thin Films of Room-Temperature Glassy Tris(keto-hydrozone) Discotic Liquid Crystals and Their Nanocomposites with Single-Walled Carbon Nanotubes for Optoelectronics", 
    ACS Omega 8(30) (2023) 27102-27116..
  46. G. B. Hadjichristov: "Control of coherent light through microperiodic director modulation in nematic films under low-voltage DC electric field",
    Materials 16(17) (2023) 6014 (1-29).
  47. G.B. Hadjichristov, D.G. Kovacheva, Y.G. Marinov, D.B. Karashanova, T.E. Vlakhov, N. Scaramuzza: "Dielectric spectroscopy characterization of Na+ ion-conducting polymer nanocomposite system PEO-PVP-NaIO4-TiO2", 
    J. Adv. Dielectr. 14(1) (2024) 2350021 (1-15).
  48. S. Minkovska, G.B. Hadjichristov, A. Neacsu, V. Chihaia, Y.V. Fedorov: "Photoswitchable Photochromic Chelating Spironaphthoxazines: Synthesis, Photophysical Properties, Quantum-Chemical Calculations, and Complexation Ability",
    ACS Omega 9(4) (2024) 4144-4161.
  49. Georgi B. Hadjichristov, Stela Minkovska: "Spirooxazine-based optical sensing of metal ions using laser beam",
    OPTIK 299 (2024) 171546 (1-8).
  50. G.B. Hadjichristov: "Coherent Raman Scattering Spectral Shapes in a Strong Excitation Regime (Model Calculations)",
    Photonics 11(4) (2024) 384 (1-19).
  51. Ivanov, G.R.; Venelinov, T.; Marinov, Y.G.; Hadjichristov, G.B.; Terfort, A.; David, M.; Florescu, M.; Karakuş, S.: "First Direct Gravimetric Detection of Perfluorooctane Sulfonic Acid (PFOS) Water Contaminants, Combination with Electrical Measurements on the Same Device - Proof of Concepts",
    Chemosensors 12(7) (2024) 116 (1-20). 
  52. G.B. Hadjichristov, B.P. Katranchev: "Numerical modeling of partially coherent anti-Stokes Raman scattering (pCARS) in transparent molecular liquids",
    J. Molec. Liq. 413 (2024) 125977 (1-11). 
  53. G.B. Hadjichristov, I.L. Stefanov: "Evaluating the single-shot photodegradation of optically-transparent bulk polymers under two-photon Raman-resonant laser irradiation in nanosecond regime (multiplex CARS test)",
    Polymer Testing 133(Apr) (2024) 108401 (1-10).

  

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          Updated page 2 Dec 2024