Modulation Transfer Spectroscopy for a Two-Level Atomic System with a Non-Cycling Transition

This paper reports the results of a theoretical study on modulation transfer spectroscopy in a system composed of two-level atoms with a non-cycling transition. In the case of a cycling transition, well-known in-phase and quadrature components of the modulation transfer signal could be obtained. In contrast, the modulation transfer signal was suppressed when the transition to a state other than the ground state was turned on. The most important item to consider when observing a strong modulation transfer signal is the long interaction time of atoms with laser light, which can be realized for strong cycling transitions.