Velocity changing collisions in the laser saturation spectra of 87Rb D2 F″ = 2

The saturation absorption technique is applied to the 87Rb 2S1/2 F″ = 2 → 2P3/2 F′ = 1, 2 and 3 transitions to study the effect of velocity changing collisions (VCC). The VCC caused Doppler pedestal increases with argon pressure from 0 to 110 mTorr and decreases with modulation frequencies of 700–3200 Hz. The resonances of the velocity selective, saturated optical pumping are washed out for pressure of 110 mTorr. The magnitude of the Doppler pedestal relative to the homogeneous features, yields a rate for velocity changing collisions of 6.5 ± 0.2 × 10−10 cm3 s−1.

Research highlights
► We have observed collisional effects in the sub-Doppler spectrum of the Rb D2 line.
► The rate for velocity changing collisions has been measured.
► A hard sphere model for the collisional lineshape was used for both hyperfine and cross-over resonances.
► Twenty-four velocity groups are resolved.