We investigate the spatial and quantum intensity correlations between the probe and Stokes optical fields produced via four-wave mixing in a double-Λ configuration, when both incoming probe and control fields carry non-zero optical orbital angular momentum (OAM). We observed that the topological charge of the generated Stokes field obeyed the OAM conservation law. However, the maximum values and optimal conditions for the intensity squeezing between the probe and Stokes fields were largely independent of the angular momenta of the beams, even when these two fields had significantly different OAM charges. We also investigated the case of a composite-vortex pump field, containing two closely-positioned optical vortices, and showed that the generated Stokes field carried the OAM corresponding to the total topological charge of the pump field, further expanding the range of possible OAM manipulation techniques.

We experimentally studied the characteristics of the collimated blue light (CBL) produced in 85 Rb vapor by two resonant laser fields exciting atoms into the 5D 3/2 state, using either the 5P 1/2 or the 5P 3/2 intermediate state. We compared the CBL output at different values of frequency detunings, powers, and polarizations of the pump lasers in these two cases, and confirmed the observed trends using a simple theoretical model. We also demonstrated that the addition of the repump laser, preventing the accumulation of atomic population in the uncoupled hyperfine ground state, resulted in nearly an order of magnitude increase in CBL power output. Overall, we found that the 5S 1/2 − 5P 1/2 − 5D 3/2 excitation pathway results in stronger CBL generation, as we detected up to 4.25 µW using two pumps of the same linear polarization. The optimum CBL output for the 5S 1/2 − 5P 3/2 − 5D 3/2 excitation pathway required the two pump lasers to have the same circular polarization, but resulted only in a maximum CBL power of 450 nW.

We experimentally investigate the effectiveness of the four-wave mixing suppression in a double-Λ interaction scheme by introducing an additional ladder-type two-photon Raman absorption resonance for one of the optical fields. We propose several possible interaction configurations involving either one or two isotopes of Rb, and experimentally demonstrate the possibility of efficient four-wave mixing suppression in both EIT and far-detuned Raman cases.