Comparison of collimated blue-light generation in 85Rb atoms via the D1 and D2 lines

We experimentally and theoretically studied the characteristics of the collimated blue light (CBL) produced in Rb85 vapor by two resonant laser fields exciting atoms into the 5D3/2 state, using either the 5P1/2 or the 5P3/2 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 found that in general the CBL yield was higher for the the D1 excitation scheme compared to the D2 excitation scheme under similar conditions. We also demonstrated the importance of the repump laser, preventing the accumulation of atomic population in the uncoupled hyperfine ground state, which resulted in nearly an order of magnitude increase in CBL power output. One interesting finding was the existence of the optimal power ratios between the two pump lasers, leading to the maximum blue-light power, observed both in the experiment and in the calculations.