Is the optical Bloch equation violated in Pr3+ : LaF3?

Abstract

From measurements of various types of spin echoes of hyperfine transitions in 3H4 and photon echoes for the 1D2−3H4 transition in Pr3+:LaF3, we found that dephasings in both transitions are mainly due to the spectral diffusion. A correlated time τc of the fluctuating local fields is shown to be much longer than the usually used value of T2 = 21.7 μs. These results indicate that even in the absence of the excitation the dephasing cannot be described by the Bloch equation and therefore the anomalous power dependence of the optical FID observed by DeVoe and Brewer [Phys. Rev. Lett. 50 (1983) 1269] does not mean a violation of the optical Bloch equation in the strong excitation regime. Their results should be interpreted as a power dependence of the system whose decay is governed by the spectral diffusion. In this sense the standpoint of almost all theories proposed to explain this violation is not correct.