Depth profile of optically recorded patterns in light-sensitive liquid-crystal elastomers.

Area of Science:

• Materials Science
• Polymer Chemistry
• Optics

Background:

• Liquid-crystal elastomers (LCEs) exhibit unique photoresponsive properties.
• Azobenzene moieties are widely used photosensitive dopants in polymers.
• Understanding light-induced transformations in LCEs is crucial for optical applications.

Purpose of the Study:

• To investigate nonlinear absorption and photobleaching in azobenzene-doped LCEs.
• To analyze the depth of UV light penetration and molecular isomerization.
• To model the spatial distribution of molecular conformers and diffraction efficiency.

Main Methods:

• Recording a one-dimensional holographic grating using crossed UV laser beams.
• Analyzing the angular dependence of diffraction efficiency near the Bragg peak.
• Employing a numerical model with beam propagation and rate equations for molecular conformers.

Main Results:

• Determined the progression of trans to cis isomerization depth as a function of UV irradiation time.
• Computed the spatial distribution of trans and cis conformers using a numerical model.
• Observed that recording depth increases logarithmically with time due to residual cis conformer absorption.

Conclusions:

• The depth of holographic grating recording in azobenzene-doped LCEs progresses logarithmically with UV irradiation time.
• The process is fundamentally limited by the thermal relaxation rate from the cis to trans conformation.
• Nonlinear absorption and photobleaching significantly influence light penetration and isomerization dynamics in these materials.