Ultrafast polarization-dependent spectral hole-burning in a nearly amorphous fluoro-aluminum phthalocyanine thin film

We report the observation of a polarization-dependent spectral hole burned in the Q-band absorption peak of a nearly amorphous fluoro-aluminum phthalocyanine thin film by 130 fs optical pulses at room temperature. The hole is spectrally coincident with the pump pulse and observed only when the pump and probe pulses are temporally overlapped and polarized parallel. Coherent coupling effects appear to be responsible for the spectral hole. The observation of the polarization-dependent spectral hole implies that the two orthogonal polarization states of the system are decoupled, unlike inorganic semiconductors. The initially polarized population created by the pump pulse rapidly relaxes to the bottom of the excited-state manifold and depolarizes.