22 Cooperative Molecular Alignment Process Enabled by Scanning …
383
Here, we propose the single-step fabrication of CDWs and q-plates over large
areas by means of SWaP [34, 67–70]. As described above, SWaP has a principal
advantage unlike conventional photoalignment methods. Thus, SWaP allows one to
generate arbitrary 2D orientation patterns (various DWs) over large areas in a singlestep only by scanning spatiotemporal patterned light during photopolymerization. As
a first step, cycloidal molecular alignment was fabricated by SWaP using 1D scanning
with periodically arranged rod-shaped pattern for less than 3 min (Fig. 22.4a). The
resultant polymer film showed a cycloid pattern of ∼30 μm pitch over an area.
Detailed investigation with a probe laser beam at 633 nm elucidated that the resultant
film successfully acts as a CDW with a diffractive efficiency of 50% (Fig. 22.4b).
SWaP could precisely and briefly control the complex molecular orientation pattern
by scanning the rod-shaped pattern light in one direction. This process can be easily
applied to large-area production, and the fabrication of films with precise molecular
orientation can be greatly expected.
Next, molecular pattern I acts a waveplate with a specific optical function to
convert a phase polarization state of a laser beam into optical axis symmetry, which
is now one of the most desired and useful devices [71, 72]. Q-Plates function as optical
devices with a passive optical element that is capable to manipulate the spatial distribution of the polarization of a homogenous polarized beam (e.g. a simple Gaussian
laser beam). A q-plate can be fabricated simply as a birefringent waveplate with a
2D patterned distribution of the optical axis in the cross section. “Q” indicates a
semi-integer topological charge defined as the degree of optical axis distribution.
For example, it is known that a film having a π rotated optical axis of the retardation
rotated on a laser optical axis works as a q = 1 q-plate. As a result, a radial vector
beam or an optical vortex were obtained when linearly polarized light or circularly
polarized light is introduced to the film, respectively. We confirmed that radial molecular alignment pattern achieved by SWaP successfully acts as a q-plate that converts
a linearly polarized beams into a vector beam [70].
22.5 Conclusion
We have demonstrated that arbitrary 2D alignment patterns over large areas is
readily achieved by SWaP without any surface treatment, electrodes, or polarized
light sources. SWaP offers great potentials for the fabrication of a variety of highperformance LC devices because 2D patterns with complex and high resolution are
inscribed, which is challenging or even impossible to achieve with conventional
photoalignment techniques. Moreover, SWaP has great economic advantages for
enabling to introduce it in existing photoproduction facilities. We believe that SWaP
provides a new and powerful pathway for the direct design of highly functional
organic materials with arbitrary, fine molecular alignment patterns over large areas.
383
Here, we propose the single-step fabrication of CDWs and q-plates over large
areas by means of SWaP [34, 67–70]. As described above, SWaP has a principal
advantage unlike conventional photoalignment methods. Thus, SWaP allows one to
generate arbitrary 2D orientation patterns (various DWs) over large areas in a singlestep only by scanning spatiotemporal patterned light during photopolymerization. As
a first step, cycloidal molecular alignment was fabricated by SWaP using 1D scanning
with periodically arranged rod-shaped pattern for less than 3 min (Fig. 22.4a). The
resultant polymer film showed a cycloid pattern of ∼30 μm pitch over an area.
Detailed investigation with a probe laser beam at 633 nm elucidated that the resultant
film successfully acts as a CDW with a diffractive efficiency of 50% (Fig. 22.4b).
SWaP could precisely and briefly control the complex molecular orientation pattern
by scanning the rod-shaped pattern light in one direction. This process can be easily
applied to large-area production, and the fabrication of films with precise molecular
orientation can be greatly expected.
Next, molecular pattern I acts a waveplate with a specific optical function to
convert a phase polarization state of a laser beam into optical axis symmetry, which
is now one of the most desired and useful devices [71, 72]. Q-Plates function as optical
devices with a passive optical element that is capable to manipulate the spatial distribution of the polarization of a homogenous polarized beam (e.g. a simple Gaussian
laser beam). A q-plate can be fabricated simply as a birefringent waveplate with a
2D patterned distribution of the optical axis in the cross section. “Q” indicates a
semi-integer topological charge defined as the degree of optical axis distribution.
For example, it is known that a film having a π rotated optical axis of the retardation
rotated on a laser optical axis works as a q = 1 q-plate. As a result, a radial vector
beam or an optical vortex were obtained when linearly polarized light or circularly
polarized light is introduced to the film, respectively. We confirmed that radial molecular alignment pattern achieved by SWaP successfully acts as a q-plate that converts
a linearly polarized beams into a vector beam [70].
22.5 Conclusion
We have demonstrated that arbitrary 2D alignment patterns over large areas is
readily achieved by SWaP without any surface treatment, electrodes, or polarized
light sources. SWaP offers great potentials for the fabrication of a variety of highperformance LC devices because 2D patterns with complex and high resolution are
inscribed, which is challenging or even impossible to achieve with conventional
photoalignment techniques. Moreover, SWaP has great economic advantages for
enabling to introduce it in existing photoproduction facilities. We believe that SWaP
provides a new and powerful pathway for the direct design of highly functional
organic materials with arbitrary, fine molecular alignment patterns over large areas.