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The quantisation of electronic energy into subbands in low-dimensional structures originates many interesting physical effects, one of which is the electrophonon resonance effect. In this work, we investigate the electrophonon resonance by theoretically calculating the optical absorption power in n 􀀀 i 􀀀 p 􀀀 i superlattices (SLs) subjected to a high frequency electromagnetic wave. The absorption power is calculated up to the first-order nonlinear term using the projection operator technique taking account of the effect of electron – optical phonon interaction. Numerical results are obtained and discussed for the GaAs:Si/GaAs:Be SL. The linear and nonlinear optically detected electrophonon resonance (ODEPR) peaks are observed in the absorbance. The full width at half maximum (FWHM) of ODEPR peaks increases with increasing the doping concentration as well as temperature. In particular, the results show that the two-photon absorption is of great importance and should be considered in nonlinear optics. This investigation provides