4 research outputs found
Depth Profile of Optically Recorded Patterns in Light-Sensitive Liquid Crystal Elastomers
We investigated nonlinear absorption and photobleaching processes in a liquid
crystal elastomer (LCE) doped with light-sensitive azobenzene moiety. A
conventional one-dimensional holographic grating was recorded in the material
with the use of two crossed UV laser beams and the angular dependence of the
diffraction efficiency in the vicinity of the Bragg peak was analyzed. These
measurements gave information on the depth to which trans to cis isomerisation
had progressed into the sample as a function of the UV irradiation time. Using
a numerical model that takes into account the propagation of writing beams and
rate equations for the local concentration of the absorbing trans conformer, we
computed the expected spatial distribution of the trans and cis conformers and
the shape of the corresponding Bragg diffraction peak for different irradiation
doses. Due to residual absorption of the cis conformers the depth of the
recording progresses logarithmically with time and is limited by the thermal
relaxation from the cis to trans conformation.Comment: 19 pages (incl. figs), 6 figure
Kinetics of Holographic Recording and Spontaneous Erasure Processes in Light-Sensitive Liquid Crystal Elastomers
The optical mechanism for imprinting one-dimensional grating structures into thin films of a light-sensitive monodomain liquid crystal elastomer is investigated by analyzing the time dependence of optical diffraction properties. The recording kinetics shows an irregular oscillatory behavior, which is most expressed at small grating spacings and at temperatures close to the nematic-isotropic phase transition. The oscillations are attributed to the opto-mechanical response of the film, i.e., to contraction of the film during the recording process. At temperatures far below the nematic-isotropic phase transition, the spontaneous erasure kinetics exhibits exponential relaxation with relaxation time following the Arrhenius activation law. However, at temperatures close to the nematic-isotropic phase transition, the erasure process shows an interesting nonmonotonic behavior that we attribute to the non-linear relation between the concentration of the photo-transformed chemical groups and the nematic order parameter
Kinetics of Holographic Recording and Spontaneous Erasure Processes in Light-Sensitive Liquid Crystal Elastomers
The optical mechanism for imprinting one-dimensional grating structures into thin films of a light-sensitive monodomain liquid crystal elastomer is investigated by analyzing the time dependence of optical diffraction properties. The recording kinetics shows an irregular oscillatory behavior, which is most expressed at small grating spacings and at temperatures close to the nematic-isotropic phase transition. The oscillations are attributed to the opto-mechanical response of the film, <em>i.e</em>., to contraction of the film during the recording process. At temperatures far below the nematic-isotropic phase transition, the spontaneous erasure kinetics exhibits exponential relaxation with relaxation time following the Arrhenius activation law. However, at temperatures close to the nematic-isotropic phase transition, the erasure process shows an interesting nonmonotonic behavior that we attribute to the non-linear relation between the concentration of the photo-transformed chemical groups and the nematic order parameter
Kinetics of holographic recording and spontaneous erasure processes in light-sensitive liquid crystal elastomers
The optical mechanism for imprinting one-dimensional grating structures into thin films of a light-sensitive monodomain liquid crystal elastomer is investigated by analyzing the time dependence of optical diffraction properties. The recording kinetics shows an irregular oscillatory behavior, which is most expressed at small grating spacings and at temperatures close to the nematic-isotropic phase transition. The oscillations are attributed to the opto-mechanical response of the film, i.e., to contraction of the film during the recording process. At temperatures far below the nematic-isotropic phase transition, the spontaneous erasure kinetics exhibits exponential relaxation with relaxation time following the Arrhenius activation law. However, at temperatures close to the nematic-isotropic phase transition, the erasure process shows an interesting nonmonotonic behavior that we attribute to the non-linear relation between the concentration of the photo-transformed chemical groups and the nematic order parameter