Abstract
The angular dependence of the diffraction efficiency of volume-type holographic gratings recorded in a single-domain light-sensitive liquid crystalline elastomer was investigated. Usually this dependence is expected to be very similar for intensity gratings and for polarization gratings. However, our measurements resolved a profound difference between the two types of the gratings: a typical Bragg peak of the diffraction efficiency is observed only for intensity gratings, while polarization gratings exhibit a profound dip at the Bragg angle. The appearance of this dip is explained by strongly anisotropic optical absorption of the actinic light during the recording process.
Highlights
Optical polarization gratings are periodic holographic structures that are recorded by optical interference patterns at constant intensity but spatially varying polarization states of the optical field [1,2]
Our results demonstrate that a strong linear dichroism at the actinic optical wavelength, which is characteristic for light-sensitive Liquid crystalline elastomers (LCEs) and for many other kinds of light-sensitive liquid crystalline materials, can drastically influence the volume-type polarization holographic recording in photo-responsive media
In combination with strongly nonlinear recording kinetics associated with photo-bleaching, dichroism can lead to diffractive structures exhibiting various unusual phenomena, such as a profound minimum of the diffraction efficiency at the Bragg angle, which was the subject of our present investigation
Summary
Optical polarization gratings are periodic holographic structures that are recorded by optical interference patterns at constant intensity but spatially varying polarization states of the optical field [1,2]. Polarization-responsive recording in liquid crystalline materials is usually based on optical-field-induced reorientation of the mesogenic molecules [10,11,12] Another common mechanism that leads to polarization-type LC gratings is holographic or some other type of patterning of surface layers that control the LC alignment [13,14,15,16,17,18,19,20]. They can change size and shape, flip between different shapes, oscillate, or even move on the supporting surface [25,26,27,28,29,30,31,32] Another interesting feature of light-sensitive LCEs is their strong opto-optical response that is observed as a large photoinduced modification of the optical birefringence. By extending our theoretical model developed for intensity gratings [40], we show that this dip is a consequence of anisotropic absorption of actinic light during the recording process
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