Signal‐beam amplification is achieved in degenerate two‐wave mixing experiments in liquid crystals at the wavelength &lgr;=10.6 &mgr;m of the cw CO2laser. The origin of the dynamic grating is the large thermal index change that arises when the cell operates near the phase transition temperature. Maxwell’s equations are analytically solved for the calculation of the amplitude variations of the incident waves (Ip@B:pump,Is@B:signal) and of the self‐diffracted wave (I−1). It is shown that energy transfer arises from the contribution of the &pgr;/2 component of the index modulation generated by the interference of (Ip,I−1). The resulting three‐wave model yields good agreement with the experimental results.