Two-Photon Polarization Spectroscopy in CuCl

Highly sensitive momentum-space spectroscopy, named two-photon polarization spectroscopy (TPPS), is presented in the Z 3 exciton resonant region of CuCl. This spectroscopy is based on the induced optical anisotropy associated with the formation of \( ₁\) excitonic molecules (EM's). By this method the following facts are confirmed: the upper branch polaritons (UBP's) and the lower branch polaritons (LBP's) coexist in the wide energy range above the longitudinal exciton energy; the conversion of UBP into LBP occurs in the reflection at the sample boundary; the EM relaxation depends on the wave number in the large wave number region. From the quantitative analysis of the spectra, it has been found that the damping of the Z 3 exciton depends strongly on its energy in the L-T gap region. The prospects of the ABC problem are also discussed.