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.
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