Ludmila Nikolova

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POLARIZATION HOLOGRAPHY AND LIGHT INDUCED
STRUCTURES IN PHOTOANISOTROPIC MATERIALS
Ludmila Nikolova Central Laboratory of Optical
Storage and Processing of Information Bulgarian
Academy of Sciences
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What is polarization holography?
The polarization of the interference field is
modulated
The intensity is constant
Photoanisotropic materials
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Photoanisotropic materials

• INORGANIC
• - AgCl emulsions
• - Alkali halide crystals
• - Chalcogenide layers
• - Photochromic glasses

• ORGANIC
• - Thriphenylmethane,
• xanthene, etc. dyes in
• solid matrices
• - Azobenzene polymers
• - bacteriorhodopsin

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Azobenzene polymers
izomerization
reorientation
amorphous
Photoinduced effects
liquid-crystalline

• - Linear anisotropy
• - Circular anisotropy
• Surface relief

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Photoinduced processes in azobenzene polymers
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Stability of the photoinduced dichroism
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Application of polarization holography for novel
optical elements
- polarization holographic gratings
The polarization pattern
The properties of the grating
I1 I-1 const.
Measuring the S3 parameter
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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
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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)) ?n
?d/2pd d arctg (S3 /S2)
The changes in the optical constants of a film
of fluorescein in a solid matrix
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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
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Observation of photoinduced circular anisotropy
in liquid - crystalline azopolymers
( holographic method )
The polarization pattern
Dependence of the diffraction efficiency on the
probe beam azimuth
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Observation of photoinduced circular anisotropy
in liquid - crystalline azopolymers
( polarimetric method )
The optical set-up
The photoinduced optical rotation
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Light-induced polarization rotation in
previously ordered amorphous azopolymers
The optical set-up
The induced polarization rotation
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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
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Understanding the phenomenon
?
Rotation of the polarization ellipse in
anisotropic media
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Photoinduced chirality in amorphous azopolymers
Gradually rotation of the optical axis
One macroscopic chiral structure
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Light propagation through photoinduced chiral
structures
- The eigenmodes are elliptical
Output azimuth
Output ellipticity
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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