Comparison of collimated blue light generation in ${}^{85}$Rb atoms via the D${}_1$ and D${}_2$ lines

TL;DR

This study compares blue light generation in rubidium-85 atoms via two different excitation pathways, demonstrating that the pathway through the $5P_{1/2}$ state yields stronger blue light, especially with the addition of a repump laser.

Contribution

It provides a comparative experimental analysis of blue light generation via D1 and D2 lines in rubidium-85, including the effects of polarization, detuning, and repumping on output power.

Findings

The $5S_{1/2} - 5P_{1/2} - 5D_{3/2}$ pathway produces up to 4.25 μW of blue light.

Adding a repump laser increases CBL power output nearly tenfold.

The D2 pathway with circular polarization yields a maximum of 450 nW of blue light.

Abstract

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 $4.25~\mu$W 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.