Non-Linear Excitation Effect in Persistent Hole-Burning of Linear Frenkel Exciton System with Large Coherence Length

Abstract

Excitonic structure of J-bands of pseudo-isocyanine bromide J-aggregates in WEG glasses at 4.7 K has been investigated by persistent spectral hole burning. Clear crossover of hole line shape was observed in the intensity dependence of pulse laser burning (7ns, 10-Hz repetition). With decreasing the intensity the line shape changes from non-resonant red-shifted (∼3 cm−1 from the laser frequency ωB) broad hole to resonant sharp hole, which is similar to those obtained by cw-laser. With cw-laser light for burning, clear zero-phonon hole was formed with the width of 0.36 cm−1. The hole profile seems strongly dominated by the peak intensity of the burning light. We proposed the existence of the crossover is due to switching from the |1-ex) state resonance by one-photon absorption to the |2-ex) state resonance by two-photon absorption using real dipole-allowed |1-ex) state. The model provides the offset of the hole is equal to half of the difference of k = 2 and k = 1 exciton energy, from which we can deduce a coherence length N = 56 as typical order of magnitude. Further experiments are described, which basically support the interpretation.