An explicit model from the matrix method is utilized to describe the measurement sensitivity of the photothermal detuning technique dependent on the polarization of the probe beam. Numerical results show that the optimal probe wavelengths and the slope of the main spectral band edges are different for both s- and p-polarized beams with the same incident angle. Compared with the random polarized probe beam at the larger incident angle, the measurement sensitivity can be improved approximately twice over with the p- and s-polarized probe beams under the optimal condition.