Description:
<jats:title>Abstract</jats:title><jats:p>The expression of the two‐photon absorption coefficient in crystals is discussed using explicitly the Wigner‐Eckart theorem for finite symmetry groups. It is discussed how to separate the dynamical part, which contains appropriate reduced matrix elements of the momentum operator, from the geometrical part, which depends on the polarization vectors of both the radiation beams. For the geometrical part the standard results of the literature are recovered; detailed new information for the two‐photon absorption rate is supplied by the dynamical part. To illustrate the procedure, the case of TICI is considered as a specific example.</jats:p>