The temperature profile and thermal-focusing effect induced by a high-order transverse mode laser beam in an internal element have been analyzed. We calculate the input-output power relationship for ordinary and extraordinary waves in a LiNbO3 crystal inside the resonator. Our calculations are in good agreement with the experimental results of P. G. Konvisar et, al., and, further, revise their calculated result for extraordinary waves. The internal thermo-optic hysteresis and focusing effect are also investigated experimentally.