Fluorescence fluctuations from a multilevel atom in a nonstationary phase-diffusion field: Deterministic frequency modulation

It is well known that a field’s quantum noise can have a profound effect on the fluctuations of laser-induced fluorescence (LIF). However, though previous studies have led to a good understanding of this process in the case of stationary fields, many of the important applications of LIF employ some form of laser modulation, yielding a field of nonstationary stochastic character. Here, we discuss the results from numerical experiments that examine the influence of a nonstationary field on the LIF noise. Specifically, we consider a phase-diffusion field and LIF from a beam of alkali-metal-like atoms with ground and excited-state Zeeman splitting when the field undergoes deterministic frequency modulation. Our computational results show that deterministic modulation at high Fourier frequencies (i.e., 10 MHz) can significantly increase the LIF noise at low Fourier frequencies (e.g., 1 Hz), and that the amount of LIF noise amplification depends on a complicated interplay among the laser’s linewidth, the modulation frequency, the modulation index, and the multilevel atomic system’s energy-level spacing. Interestingly, we find that certain values of the atom’s Zeeman splitting significantly decrease the magnitude of LIF noise.