Origin of optical nonlinearity of photo-responsive liquid crystals revealed by transient grating imaging

Abstract

A large optical nonlinearity has been observed for the photo-responsive liquid crystals under the condition that the nematic phase is close to the isotropic condition. The direct observation of the photo-response of a liquid crystal by the time-resolved transient grating phase imaging technique revealed that the optical nonlinearity was caused by the transiently generated phase formed inside the photo-induced isotropic region. A shock-like flow was observed for the formation of the transiently generated phase. Based on the theoretical calculation, we propose that a flow generated at the disordered/ordered interface induced the reorientation of the liquid crystal molecules, thereby generating a larger polarization and ultimately causing the optical nonlinearity.

Pattern-illumination time-resolved phase microscopy and its applications for photocatalytic and photovoltaic materials

“…This method was successfully applied to observe millisecond dynamics in photo-responsive liquid crystals. 88 However, in our research, 25 we discovered that the image quality achieved with Talbot self-imaging was almost same level as that of Schlieren imaging. In Talbot self-imaging, the image is slightly defocused by a few microns to transition the phase image into an amplitude image, yielding a spatial resolution of about 3 mm in our optical setup.…”

“…To demonstrate the measurement technique, a stripe pattern identical to the transient grating excitation was used. 88…”

Tutorial: Characterizing Microscale Energy Transport in Materials with Transient Grating Spectroscopy

“…TGS with nanosecond and microsecond resolutions is naturally suitable for investigating dynamics in soft matter and biological materials. A recent example utilized TGS coupled with imaging to probe the photo-induced flow and phase transition in a liquid crystal [113].…”

Analysis of Molecular Disordering Processes in the Phase Transition of Liquid Crystals Observed by Patterned-Illumination Time-Resolved Phase Microscopy

“…The principle of the PI-PM method was described in previous papers and is shown in Figure S1 in Supporting Information (SI) [ 38 , 39 ]. In brief, an arbitrary pump light pattern is irradiated to a sample, causing photoisomerization and the following molecular rotation and disordering for the LCs.…”

“…In recent years, we have studied the origin of the optical nonlinearity from the dynamics of the LCs by using time-resolved methods and found that the enhancement occurred on the millisecond time scale [ 37 ]. Furthermore, a new time-resolved imaging technique was developed, and the origin was clarified by visualizing the images of the optically induced flow of the LCs [ 38 ].…”