[en] Photothermal beam deflection technique has been employed for the measurement of thermal diffusivity of different compositions of semiconducting amorphous Ge_xSe_100-x thin films. Slope from the tangential component of the deflection signal with the pump-probe offset is used to evaluate the numerical value of thermal diffusivity (α). The mirage signal is analysed using the phase method and the result of the measurement is verified using the amplitude method. The experiments are carried out using carbon tetrachloride as the coupling medium for two different modulation frequencies, both of which have yielded the same value of thermal diffusivity. The variation in thermal diffusivity of the samples with composition is also investigated and is explained on the basis of structural changes taking place in the glass network