  Thermal mode spectroscopy (TMS) has been recently proposed for accurately
measuring thermal diffusivity of solids from a temperature decay rate of a
specific thermal mode selected by three- dimensional (anti)nodal information
[Phys. Rev. Lett., 117, 195901 (2016)]. In this paper, we find out the
following advantages of TMS by use of perturbation analyses. First, TMS is
applicable to the measurement of high thermal diffusivity with a small size
specimen. Second, it is less affected by thermally resistive films on a
specimen in the sense that the resistance at the interface does not affect the
first-order correction of thermal diffusivity. Third, it can perform doubly
accurate measurement of the thermal diffusivity specified at a thermal
equilibrium state even if the diffusivity depends on temperature in the sense
that the measurement can be performed within tiny temperature difference from
the given state and that the decay rate of the slowest decaying mode is not
affected by the dependence.
