Test of the optical theory of Mössbauer quantum beats

Quantum-beat and sideband spectra of recoilless $\gamma$ radiation of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ were measured as a function of frequency and the voltage on the quartz crystal on which a ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ source was deposited. The sideband spectra were analyzed using a Rice distribution of the modulation index. The width of this distribution was shown to depend on the frequency; the narrowest distribution was found at 9.795 MHz. The results of the quantum-beat measurements are in agreement with the optical theory of Monahan and Perlow.