  Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation
of collimated optical fields at 420 nm and 1324 nm. Input laser beams at 780 nm
and 776 nm enter a heated Rb vapor cell collinear and circularly polarized,
driving Rb atoms to the $5D_{5/2}$ state. Under phase-matching conditions
coherence among the $5S_{1/2}\rightarrow 5P_{3/2}\rightarrow 5D_{5/2}
\rightarrow 6P_{3/2}$ transitions produces a blue (420 nm) beam by four-wave
mixing. We also observe a forward and backward propagating IR (1324 nm) beam,
due to cascading decays through the $6S_{1/2}\rightarrow 5P_{1/2}$ states.
Power saturation of the generated beams is investigated by scaling the input
powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mW
power, almost an order of magnitude larger than previously achieved. We measure
the dependences of both beams in relation to the Rb density, the frequency
detuning between Rb ground state hyperfine levels, and the input laser
intensities.
