Figure 8

(a) Raman spectroscopy performed with the upper Raman beam (Raman 2), for three different mean velocities selected with the lower Raman beam (Raman 1). The peaks correspond to three different Raman 1 frequencies incremented by 40 kHz steps. Inset: Raman 2 resonance as a function of Raman 1 frequency. The offset between the two frequencies is due to a difference in vertical velocity when the atoms cross the beam leading to a different Doppler shift. (b) Raman spectroscopy performed with the upper Raman beam (Raman 2), for four different velocity spreads selected with the lower Raman beam (Raman 1). The legend gives the corresponding effective temperatures deduced from a gaussian fit of the peak.