def Lambda_type_minus_r_over_t(g1d, gprime, gm, Delta1, Deltap, Omega):
    """
    Minus the reflection coefficient of a Lambda-type atom divided
    by the transmission coefficient. The transfer matrix for the
    Lambda-type atoms will be written in terms of this ratio.
    """
    #Assume real Omega
    return g1d*(Delta1-Deltap+0.5j*gm)\
           /((gprime-2j*Delta1)*(Delta1-Deltap+0.5j*gm)+2j*Omega**2)