Equivalent temperature concept in laser physics and its correspondence with thermodynamic temperature

The concept of the equivalent temperature of the crystal interacting with laser radiation, which was recently introduced in laser physics, is based on the dependence of the crystal sample eigenfrequencies on its temperature. This concept was successfully applied for measurements of low absorption coefficients of different optical materials. In this paper, we present an accurate identification of the equivalent temperature of the sample with its thermodynamic temperature basing on both mathematical modelling and experimental verification. (paper)