Photon Echo Stimulated from Optically Induced Nuclear Spin Polarization

A new type photon-echo is reported which is stimulated from optically induced nuclear spin polarization in the electronic ground state of a molecular radical. The echo was observed in the 2A1 ← 2A1 electronic transition at 514.2 nm of triphenylmethyl in triphenylamine at 1.5 K. Evidence is also presented that intra-molecular spin cross-relaxation processes determine the relaxation of the normal stimulated photon echo in triphenylmethyl at low temperature