Four-level polarization beats with broadband noisy light

Four-level polarization beats (FLPBs) with broadband noisy light are investigated by use of chaotic field, phase-diffusion, and Gaussian-amplitude models. The polarization beat signal is shown to be particularly sensitive to the statistical properties of the Markovian stochastic light fields with arbitrary bandwidth. Different stochastic models of the laser field affect only the fourth-order coherence functions. The constant background of the beat signal originates from the amplitude fluctuation of the Markovian stochastic fields. The Gaussian-amplitude field shows fluctuations larger than the chaotic field, which in turn exhibits fluctuations much larger than for the phase-diffusion field with pure phase fluctuations caused by spontaneous emission. It is also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced dispersion effects between the two arms of an interferometer and to the Doppler width do not affect the overall accuracy when FLPBs are used to measure the energy-level difference between two states that are dipolar forbidden from the ground state.