  Photothermal effects can alter the response of an optical cavity, for
example, by inducing self-locking behavior or unstable anomalies. The
consequences of these effects are often regarded as parasitic and generally
cause limited operational performance of the cavity. Despite their importance,
however, photothermal parameters are usually hard to characterize precisely. In
this work we use an optical cavity strongly coupled to photothermal effects to
experimentally observe an optical back-action on the photothermal relaxation
rate. This effect, reminiscent of the radiation-pressure-induced optical spring
effect in cavity optomechanical systems, uses optical detuning as a fine
control to change the photothermal relaxation process. The photothermal
relaxation rate of the system can be accordingly modified by more than an order
of magnitude. This approach offers an opportunity to obtain precise in-situ
estimations of the parameters of the cavity, in a way that is compatible with a
wide range of optical resonator platforms. Through this back-action effect we
are able to determine the natural photothermal relaxation rate and the
effective thermal conductivity of the cavity mirrors with unprecedented
resolution.
