We present the study of the dynamics of the recently reported photoinduced smectic-$C_{\alpha }^{*}$–smectic-$A$ transition. High resolution time-resolved dielectric dispersion measurements carried out during the photoisomerization process demonstrate that the magnitude of the uv intensity mimics the role played by temperature in determining the behavior of the soft mode relaxation. We also show that the uv intensity dependence of the soft mode relaxation frequency $f_R$ in the photoinduced smectic-$A$ phase can be described with a functional form similar to that derived for the temperature dependence of $f_R$ and compare the experimentally determined critical exponent with the theoretically predicted for the Ising and three-dimensional $\mathrm{XY}$ universality classes. Our study illustrates an interesting feature, namely, the magnitude of light intensity can be treated like a thermodynamic variable such as temperature and pressure to study phase transitions in general.

• Received 23 August 2002

DOI:https://doi.org/10.1103/PhysRevE.67.051701