If cavity spectral transmission response is asymmetric with respect to scan direction (i.e, red scans versus blue scans), then most likely the cavity resonance wavelength depends upon temperature. When light is absorbed in a cavity, resonance wavelength is shifted through a combination of the thermal expansion coefficient and the dependence of the refractive index upon temperature (dn/dT). In silica, it is the latter effect that is dominant. The graph (immediate right) and the movie (bottom right) show how this effect influences the measured transmission spectra in micro-cavities.
In the movie, the scanning pump (red) induces thermal drift of the resonant lineshape (blue). The intersection point between the pump line and the cavity Lorentzian draws the hysteretic absorption (black).
• For parameters and governing equations, please see: T. Carmon, L. Yang, and K. J. Vahala, “Dynamical thermal behavior and thermal self-stability of microcavities”
• Substitute your cavity parameters and get the hysteretic wavelength response of your cavity (or vice versa, fit your experimental hysteretic wavelength response to the theoretical prediction and get the heat conductivity, heat capacity and thermal dynamics of your cavity )