6 research outputs found
Hidden Gratings in Holographic Liquid Crystal Polymer-Dispersed Liquid Crystal Films
Dynamic
diffraction gratings that are hidden in the field-off state
are fabricated utilizing a room-temperature photocurable liquid crystal
(LC) monomer and nematic LC (NLC) using holographic photopolymerization
techniques. These holographic LC polymer-dispersed LCs (HLCPDLCs)
are hidden because of the refractive index matching between the LC
polymer and the NLC regions in the as-formed state (no E-field applied).
Application of a moderate E-field (5 V/μm) generates a refractive
index mismatch because of the NLC reorientation (along the E-field)
generating high-diffraction efficiency transmission gratings. These
dynamic gratings are characterized by morphological, optical, and
electrooptical techniques. They exhibit a morphology made of oriented
LC polymer regions (containing residual NLC) alternating with a two-phase
region of an NLC and LC polymer. Unlike classic holographic polymer-dispersed
LC gratings formed with a nonmesogenic monomer, there is index matching
between the as-formed alternating regions of the grating. These HLCPDLCs
exhibit broad band and high diffraction efficiency (≈90%) at
the Bragg angle, are transparent to white light across the visible
range because of the refractive index matching, and exhibit fast response
times (1 ms). The ability of HLCPDLCs not to consume electrical power
in the off state opens new possibilities for the realization of energy-efficient
switchable photonic devices
Hidden Gratings in Holographic Liquid Crystal Polymer-Dispersed Liquid Crystal Films
Dynamic
diffraction gratings that are hidden in the field-off state
are fabricated utilizing a room-temperature photocurable liquid crystal
(LC) monomer and nematic LC (NLC) using holographic photopolymerization
techniques. These holographic LC polymer-dispersed LCs (HLCPDLCs)
are hidden because of the refractive index matching between the LC
polymer and the NLC regions in the as-formed state (no E-field applied).
Application of a moderate E-field (5 V/μm) generates a refractive
index mismatch because of the NLC reorientation (along the E-field)
generating high-diffraction efficiency transmission gratings. These
dynamic gratings are characterized by morphological, optical, and
electrooptical techniques. They exhibit a morphology made of oriented
LC polymer regions (containing residual NLC) alternating with a two-phase
region of an NLC and LC polymer. Unlike classic holographic polymer-dispersed
LC gratings formed with a nonmesogenic monomer, there is index matching
between the as-formed alternating regions of the grating. These HLCPDLCs
exhibit broad band and high diffraction efficiency (≈90%) at
the Bragg angle, are transparent to white light across the visible
range because of the refractive index matching, and exhibit fast response
times (1 ms). The ability of HLCPDLCs not to consume electrical power
in the off state opens new possibilities for the realization of energy-efficient
switchable photonic devices
Soft Periodic Microstructures Containing Liquid Crystals
An empty polymeric structure has been realized by combining
a high
precision level optical holographic setup and a selective microfluidic
etching process. The distinctive features of the realized periodic
microstructure enabled aligning several kinds of liquid crystal (LC)
compounds, without the need of any kind of surface chemistry or functionalization.
In particular, it has been possible to exploit light sensitive LCs
for the fabrication of all-optical devices, cholesteric and ferroelectric
LCs for ultrafast electro-optical switches, and a common LC for a
two-dimensional periodic structure with high anisotropy. All-optical
and electro-optical experiments, performed for investigating the samples
in terms of switching voltages and response times, confirm good performances
of the realized devices
Directed Organization of DNA Filaments in a Soft Matter Template
We have developed a noninvasive,
all-optical, holographic technique
for permanently aligning liquid crystalline DNA filaments in a microperiodic
template realized in soft-composite (polymeric) materials. By combining
optical intensity holography with a selective microfluidic etching
process, a channelled microstructure has been realized which enables
self-assembly of DNA. The striking chemicophysical properties of the
structure immobilize the DNA filaments within the microchannels without
the need of any kind of surface chemistry or functionalization. Polarized
optical, confocal, and electronic microscopies have been used for
characterizing the DNA geometry inside the microchannels in terms
of birefringence, fluorescence, and nanoscale organization properties.
In particular, observation of a far-field diffraction pattern confirms
a periodic organization of the DNA filaments inside the polymeric
template
Visualization 1: Digital polarization holography advancing geometrical phase optics
Polarized image of an “invisible” cat revealed by inserting and removing a polarizer. Originally published in Optics Express on 08 August 2016 (oe-24-16-18297
Visualization 3: Digital polarization holography advancing geometrical phase optics
Sample with the invisible photo of George Washington (the background is The New York Times homepage) Originally published in Optics Express on 08 August 2016 (oe-24-16-18297