procedure, 80 holograms were recorded on polymer blends (Hackel et al. 2007).
Researchers are exploring the possibility for making still higher number of holograms.
Combination of angular multiplicity with the polarization direction is being
explored. After recording the hologram with s-polarized beams, the other hologram
can be recorded with p-polarized beams in the same spot as well as same incident
angle of the writing beams. Further, the hologram recorded with s-polarized writing
beams is read only by using s-polarized probe beam.
Chiral Photoactive Liquid Crystalline Polymer
This type of polymer exhibits simultaneously the liquid crystalline, chiral, and
photochromic properties. The molecular architecture can be built up by attaching
all three component separately as side group in ternary copolymer, or as copolymer
with various combinations, or attaching chiral moiety to mesogen or chromophore in
a copolymer or similar compositions or various types polymer or polymer/molecule
blend, etc. Thus there are numerous possibilities.
The principle of photoinduced control of the optical properties of such copolymers is the photoisomerization of chiral-photochromic fragments, which in turn
changes their anisometry and helix twisting power. The change of the helical
twisting power of the chiral fragments is associated with sharp changes in the
supramolecular helical structure as well and also the optical properties of polymer
film (Shibaev et al. 2003). This type of dual photochromism helps in recording
optical information of two types on one sample: the first one is by varying the helix
pitch and the second one by using polarized light of the visible range of the
spectrum, taking the advantage of photoinduced birefringence,. Thus the controlled
local optical properties, such as birefringence, refractive index, selective light
reflection, color characteristics, etc., are possible. This phenomenon indicates possibilities toward making various commercial optical products.
Mechanical Motion in LC/Azo Polymers
Photo-induced changes in LC order of chromophores in azo-polymers generate internal
stress in the material, which relaxes via flow or deformation of the sample. The polymer
molecular architecture decides the exact microscopic mechanism. In more detail, the
orientation of azo LC moieties and related polymer network perpendicular to the laser
beam polarization provides a clear picture of the photomechanical effect.
• Orientation shrinks the volume of the polymer along the polarization direction
and, on the other hand, expands along the perpendicular direction. In other way, it
can be said that the compression force acts along the polarization direction.
• The areas close to beam input surface undergo maximum changes in sizes.
• The areas closer to the beam exit surface are not affected much due to strong
attenuation of light caused by absorption and scattering. Further, after
14 Photoactive Liquid Crystalline Polymers
403
Researchers are exploring the possibility for making still higher number of holograms.
Combination of angular multiplicity with the polarization direction is being
explored. After recording the hologram with s-polarized beams, the other hologram
can be recorded with p-polarized beams in the same spot as well as same incident
angle of the writing beams. Further, the hologram recorded with s-polarized writing
beams is read only by using s-polarized probe beam.
Chiral Photoactive Liquid Crystalline Polymer
This type of polymer exhibits simultaneously the liquid crystalline, chiral, and
photochromic properties. The molecular architecture can be built up by attaching
all three component separately as side group in ternary copolymer, or as copolymer
with various combinations, or attaching chiral moiety to mesogen or chromophore in
a copolymer or similar compositions or various types polymer or polymer/molecule
blend, etc. Thus there are numerous possibilities.
The principle of photoinduced control of the optical properties of such copolymers is the photoisomerization of chiral-photochromic fragments, which in turn
changes their anisometry and helix twisting power. The change of the helical
twisting power of the chiral fragments is associated with sharp changes in the
supramolecular helical structure as well and also the optical properties of polymer
film (Shibaev et al. 2003). This type of dual photochromism helps in recording
optical information of two types on one sample: the first one is by varying the helix
pitch and the second one by using polarized light of the visible range of the
spectrum, taking the advantage of photoinduced birefringence,. Thus the controlled
local optical properties, such as birefringence, refractive index, selective light
reflection, color characteristics, etc., are possible. This phenomenon indicates possibilities toward making various commercial optical products.
Mechanical Motion in LC/Azo Polymers
Photo-induced changes in LC order of chromophores in azo-polymers generate internal
stress in the material, which relaxes via flow or deformation of the sample. The polymer
molecular architecture decides the exact microscopic mechanism. In more detail, the
orientation of azo LC moieties and related polymer network perpendicular to the laser
beam polarization provides a clear picture of the photomechanical effect.
• Orientation shrinks the volume of the polymer along the polarization direction
and, on the other hand, expands along the perpendicular direction. In other way, it
can be said that the compression force acts along the polarization direction.
• The areas close to beam input surface undergo maximum changes in sizes.
• The areas closer to the beam exit surface are not affected much due to strong
attenuation of light caused by absorption and scattering. Further, after
14 Photoactive Liquid Crystalline Polymers
403