The Effect Of Saturation And Velocity Selective Populationin 5S_1/2â†'5P_3/2 Laser Excitation In Rb Vapor

Availability of single-mode tunable lasers having line widths much smaller than the thermal Doppler width of the spectral lines of atoms in a vapor, gave rise to many investigations that require velocity-selective excitation. In the case of predominant inhomogeneous e.g. Doppler broadening, atoms do not absorb monochromatic radiation with equal probability. In a word, the probability of absorption depends upon each atom's velocity. Only a little atoms with narrow velocity group can be pumped to excited state and those atoms have the same velocity component along the pump-laser propagation direction. Velocity-selective pumping has important applications in saturation spectroscopy , line shape studies , laser cooling of atoms , and the study of velocity-changing collisions .Excited state population distribution created by 5S1/2→5P3/2 laser excitation in room temperature rubidium vapor was quantitatively analyzed applying absorption and saturation spectroscopy. When the laser linewidth was much smaller than the Doppler linewidth, the absorption coefficients were measured for a series of P780 powers between 40μW and 5mW. Population in the 5P3/2 level obtained from the saturation measurements was also determined by the absorption measurement of narrow spectral line from a Rb hollow cathode lamp. The agreement between the results obtained in these two ways is very good. It was shown that 2% of the ground state population could be transferred to the first excited state by pumping the Doppler broadened line with a single-mode narrow-band laser.