We have investigated defect mode lasing when a cell containing a dye solution is sandwiched between two cholesteric
liquid crystal cells. When the cholesteric pitch of both cells is equal, the dye emission generates the typical multi-mode
lasing peaks inside the photonic stop band. We prepared two cholesteric mixtures whose pitches were shifted one respect
to the other in such a way that only the edges of band gaps of the cholesteric liquid crystals layers overlapped. Using
these mixtures we have observed single mode lasing. Moreover the divergence of the laser beam spot is considerably
lower than the one observed in dye doped cholesteric liquid crystal lasers.
The Erythemal Response Spectrum is a scientific expression that describes the sensitivity of the skin to the ultraviolet radiation. The skin sensitivity strongly depends on the UV wavelength: a long exposition to UV radiation causes erythema once a threshold dose has been exceeded. In the past years several devices have been developed in order to monitor the UV exposure, most of them are based on inorganic materials that are able to mimic the human skin behaviour under UV radiation.
We present a new device based on liquid crystals technology. The sensor is based on a liquid crystalline mixture that absorbs photons at UV wavelength and emits them at a longer one. This system presents several innovative features: the absorption range of the mixture can be varied to be sensitive to different wavelengths, the luminescence intensity can be tuned, the system can be implemented on flexible devices.
Electro-optical effects in room temperature blue phases (BP) with positive dielectric anisotropy have been studied. It is shown that the maximum wavelength of the Bragg reflection of blue phases, BP II and BP I, shifts to longer wavelength with increasing electric field. The electric field influences more strongly on BP II: a reversible shift of (lambda) 0 up to 80 nm was observed.
The color change electrooptic effect in dual frequency addressable cholesteric liquid crystals (LCs) with an initial planar orientation was investigated. A field induced increase of the pitch was observed for the switching between low and high frequency fields. The investigations allow new conclusions on the origin of blue and red shift observed in an electric field applied parallel to the helix axis. In cholesteric LCs and polymer-dispersed cholesteric LCs with positive dielectric anisotropy, a colored texture with unusual properties was observed for pitch values of P approximately 0.8 micrometers and under certain conditions. This texture appears after the reduction of the electric field during the transition from the homeotropic nematic structure into the cholesteric one. The angular and the electrified dependencies of the spectral characteristics indicate that this state possesses diffractive grating properties. A voltage controlled color shift and a laser beam deflection were investigated.
A new electro-optic effect in an optically active nematic chiral structure beyond Mauguin's region has been studied. This structure rotates the polarization plane of incident light, and a liquid crystal with positive dielectric anisotropy sandwiched between crossed polarizers is switched from transparent into dark state in electric field. The characteristic features of this structure are: (a) the absence of oscillations in the transmission-voltage characteristics, (b) low demands on surface conditions (including nonrubbed cells), (c) the ability to function in any position between crossed polarizers, and (d) wide viewing angle.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.