Impedance spectroscopy for measuring low optical absorption coefficients of nonlinear optical crystals

Abstract

Novel piezoelectric resonance laser calorimetry technique, based on impedance spectroscopy, is introduced for measuring low optical absorption coefficients of nonlinear-optical crystals. This method exploits dependence of crystal piezoelectric resonance frequencies on its temperature. Nonuniform temperature of the crystal heated by laser radiation is characterized by equivalent temperature that is directly determined by measuring frequency shift of certain piezoelectric resonance calibrated on temperature. Kinetics of crystal equivalent temperature during its interaction with laser radiation is obtained by measuring frequency kinetics of piezoelectric resonance. It is demonstrated that optical absorption coefficient can be determined from the linear slope of initial part of temperature kinetics. Basing on experiments with LiB 3 O 5 and LiNbO 3 crystals it was proved that values of optical absorption coefficients determined from initial part and full time kinetics of equivalent temperature have almost the same values.