A time-resolved, spectroscopic study of the third-order nonlinear optical response of rare-earth hexagonal manganites $R{\mathrm{MnO}}_3$ $(R=\mathrm{Sc},$ Y, Er) was performed in the range of 1.45 to 1.62 eV nearby the first $d–d$ transition in ${\mathrm{Mn}}^{3+}$ ions. The nonlinearity was shown to result in a transient perturbation $\Delta \varepsilon \left(\omega \right)$ of the dielectric permittivity tensor, whose antisymmetric part decays within less than 100 fs through the relaxation of excited electrons. The symmetric part of $\Delta \varepsilon \left(\omega \right)$ was found to depend upon two distinct relaxation processes with decay times of about 360 fs and more than 70 ps, which were attributed to phonon thermalization and lattice cooling, respectively.

• Received 29 June 2001

DOI:https://doi.org/10.1103/PhysRevB.64.201103