  Optomechanical thermometry is a precise and reference-free method to measure
absolute temperature. While pumping high optical power is needed to overcome
noise and reduce the integration time, there is actually an upper limit to the
useful optical power regardless of all other nonideal effects. Side-band
inequivalence is a nonlinear effect obtained by higher-order operator algebra
in quantum optomechanics and equivalent experiments, which causes asymmetric
frequency shifts in side-bands and also an additional difference in their
population. This chapter discusses previously unnoticed nonlinear effects
arising from side-band inequivalence in optomechanical and Raman thermometry,
which determines an upper bound in available optical power for temperature
readout.
