  We study the relaxation dynamics of a binary liquid mixture near a
light-absorbing Janus particle after switching on and off illumination using
experiments and theoretical models. The dynamics is controlled by the
temperature gradient formed around the heated particle. Our results show that
the relaxation is asymmetric: the approach to a nonequilibrium steady state is
much slower than the return to thermal equilibrium. Approaching a
nonequilibrium steady state is a two-step process leading to the behavior of
the spatial variance of concentration field similar to the initial overshoot in
response to an external field found in diverse soft materials. The initial
growth of concentration fluctuations after switching on illumination follows a
power law in agreement with the hydrodynamic and purely diffusive model. The
energy out-flow from the system after switching off illumination is well
described by a stretched exponential function of time with characteristic time
proportional to the ratio of the energy stored in the steady state to the total
energy flux in this state.
