Signals and noise in lasers and atom-field interactions

Arielle Little, Michael C. Y. Huang, James C. Camparo

Pump-probe experiments are ubiquitous in atomic, molecular, and optical physics, where a strong pump field induces some change in a quantum system that is probed by a much weaker field. Often, high intensity of the pump field is at a premium with all other characteristics of the strong field subordinate. As a particular example, of relevance to atomic clocks and atomic magnetometers, a strong broad-linewidth laser optically pumps an atomic vapor, which is then probed by a much weaker narrow-linewidth laser. Though the broad-linewidth field suffers laser phase noise (PM) to amplitude noise (AM) conversion, the narrow-linewidth probe by itself produces a much quieter signal. Here, we consider the question of whether the noisy pump field maps its (PM-to-AM) absorption cross-section fluctuations onto the quiet probe field's transmission. Our results show that PM-to-AM noise does not transfer directly: atoms interacting with the pump field are instantaneously distinct from those interacting with the probe field. However, the broad-linewidth laser can influence the quiet field's transmission through the vapor due to optical pumping, resulting in fluctuations in the number density of atoms in the absorbing states. Nevertheless, there is a saving grace for this ``PM-to-AM induced optical pumping'' noise transfer: for very high noisy-field intensities (where optical pumping saturates) this type of noise on the probe field becomes negligible.

K. Wódkiewicz

K. Wódkiewicz, Joseph H. Eberly

We discuss relations between different jump processes used by us and other workers for the description of external electromagnetic field fluctuations. We show that the shot noise, the random telegraph signal, and the Poisson process are examples of a general class of fluctuations described by the relevant Burshtein-Chapman-Kolmogorov-Smoluchowski equation. We establish general conditions for which all these processes lead to the same atomic response in strong field-atom interactions.

C. J. Joachain

P. L. Knight

Yi Mu

Based on a master equation method, a two-photon laser is modeled as a single noninverted three-level atom interacting via a two-photon transition with a single resonant-cavity field mode. The laser exhibits the bistability switching between vacuum and lasing states in the high pump power without injected signal. Such a feature is accompanied by intensity-noise quenching and lasing without inversion. The bistability is forbidden in a similar ordinary laser---a Raman laser.