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Ludmila Nikolova Central Laboratory of Optical Storage and Processing of Information Bulgarian Academy of Sciences

POLARIZATION HOLOGRAPHY AND LIGHT INDUCED STRUCTURES IN PHOTOANISOTROPIC MATERIALS. Ludmila Nikolova Central Laboratory of Optical Storage and Processing of Information Bulgarian Academy of Sciences. What is polarization holography?.

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Ludmila Nikolova Central Laboratory of Optical Storage and Processing of Information Bulgarian Academy of Sciences

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  1. POLARIZATION HOLOGRAPHY AND LIGHT INDUCED STRUCTURES IN PHOTOANISOTROPICMATERIALS Ludmila Nikolova Central Laboratory of Optical Storage and Processing of Information Bulgarian Academy of Sciences

  2. What is polarization holography? The polarization of the interference field is modulated The intensity is constant Photoanisotropic materials

  3. INORGANIC -AgCl emulsions - Alkali halide crystals - Chalcogenide layers - Photochromic glasses ORGANIC -Thriphenylmethane, xanthene, etc. dyes in solid matrices -Azobenzene polymers - bacteriorhodopsin Photoanisotropic materials

  4. Azobenzene polymers izomerization reorientation amorphous Photoinduced effects liquid-crystalline • -Linear anisotropy • - Circular anisotropy • Surface relief

  5. Photoinduced processes in azobenzene polymers

  6. Stability of the photoinduced dichroism

  7. Application of polarization holography for novel optical elements - polarization holographic gratings The polarization pattern The properties of the grating I+1 + I-1 = const. Measuring the S3 parameter

  8. A spectrophotopolarimetric scheme The optical scheme The instrument matrix PHG - polarization diffraction grating DG – conventional diffraction grating LDS – linear diode sensors K1 = I0/I1; k2 = I0/2I2;; K3 = I0/2k3; k4 = I0/Ik4

  9. Photopolarimeter for one wavelength Measurement of the photoinduced anisotropy of fluorescein in a solid matrix F PP Ar 00 He-Ne 450 , The optical set-up , The changes in the Stokes parameters D par = lg(-(S0 + S2)) D ort = lg(-(S0 - S1)) Δn = λδ/2πd δ= arctg (S3 /S2) , The changes in the optical constants of a film of fluorescein in a solid matrix

  10. A first version of the spectral device Spectral range: 500 – 1500 nm, determined by the polarization grating Polarization selectivity of the grating The diffraction efficiency of the polarization grating Photoinduced dichroism and birefringence in MR/PMMA

  11. Observation of photoinduced circular anisotropy in liquid - crystalline azopolymers ( holographic method ) The polarization pattern Dependence of the diffraction efficiency on the probe beam azimuth

  12. Observation of photoinduced circular anisotropy in liquid - crystalline azopolymers ( polarimetric method ) The optical set-up The photoinduced optical rotation

  13. Light-induced polarization rotation in previously ordered amorphous azopolymers The optical set-up The induced polarization rotation

  14. Self-induced rotation of the polarization ellipse The rotation of the azimuth in amorphous samples The optical scheme The rotation of the azimuth in liquid-crystalline samples Output/input ellipticity

  15. θ Understanding the phenomenon Ө Rotation of the polarization ellipse in anisotropic media

  16. Photoinduced chirality in amorphous azopolymers Gradually rotation of the optical axis One macroscopic chiral structure

  17. Light propagation through photoinduced chiral structures - The eigenmodes are elliptical Output azimuth Output ellipticity

  18. Photoinduced chirality in liquid-crystalline azopolymers The initial structure of the polymer – many domains with different axes The photoinduced effect – many microscopic chiral structures Photoinduced optical activity Light controlled polarization rotators

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