Based on the density matrix equations with 3-j symbol expression, we calculated the intensities and lineshapes of fluoresence signals for two-photon transitions between homonuclear diatomio molecular singlet electronic states, which have a near-resonant intermediate enhancing level. Calculations were made for interactions between a variety of polarization modulated laser fields with three level systems. Signals obtained by the phase-sensitive detection method showed that either the circular polarization modulated method (LPMTPS) could be used to eliminate the Doppler broadening background caused by the adsorption of two photons from one beam. In addition these methods could be used to identify the specific branches of the two photon lines from their ixregnler spectral strnotirres without the need of knowing the upper ΙθτθΙ constants. Signal ratios of eqnal-frequenoy two-photon transitions under circular polarization modulation condition to those with linear polarization modulation wore listed for all the branches with AJ =±2，±1 and 0. Differences of the results might be orders of magnitude fox a resonable large J value. On the other hand signal ratios of two-photon branches in the intensity modulated circulax polarization laser field to those in linear polarization fields (shown in another list) are all in the same order. Furthermore, a table is presented to show the relative signal intensities of unequal-frequency polarization modulated two-photon transitions between various eleotronio states. It might be useful for determining intermediate or upper electronic states of a resolved two-photon absorption line. PMTPS is thus expected to be a usefal method for ruoleonlax spectroscopy or highresolution laser spectroscopy.