Two-photon processes in the presence of phase- or frequency-telegraph noise: Experimental study

Stochastic fields with non-Gaussian Markovian phase or frequency jumplike noise are produced at microwave frequency and used to induce two-photon (TP) processes in a S=(1/2 spin system. The influence of the field statistics on the TP-induced second-order response is experimentally investigated in a system with very short relaxation times, in its stationary state and in the weak-field limit. In the case of frequency-telegraph noise the experimental spectra of the nonlinear response are found to reproduce roughly the spectral profiles of the corresponding driving fields but with a larger width. When the telegraph noise modulates the phase of the field, the relationship between input and output spectra depends on the phase-jump amplitude ${\phi }_0$. For ${\phi }_0$=π/4 the spectrum of the response is much broader than the input one, whereas it is much narrower for ${\phi }_0$=π/2. The experimental results are interpreted using the calculation of the TP-induced second-order response worked out in the preceding paper [Boscaino and Mantegna, Phys. Rev. A 40, 5 (1989)].