Stimulated Raman transitions between the ground-level hyperfine states of atoms have been used to manipulate slowly moving atoms in an atomic fountain. An ensemble of sodium atoms with an inferred velocity spread along one dimension of 270 jum/sec has been prepared by this technique. We also show that this velocity-selection method is effective in measuring ultracold temperatures of laser-cooled atoms in a regime where traditional ballistic methods fail.PACS numbers: 32.80.PjThere has been dramatic progress in the cooling and manipulation of atoms in recent years. For example, atoms in optical molasses 1 with polarization gradients 2 have been cooled to temperatures well below the Doppler limit kBT = hr/2. 3 Temperatures as low aswhere hk is the momentum recoil due to the photon used in the cooling process, have been observed for sodium 3 ' 4 ( -30 /iK) and cesium ( -2.5 pK). 5 Helium atoms have been "cooled" in one dimension to 2 pK, a factor of 2 below the recoil limit (hk) 2 /2M, by velocity-selective coherent population trapping. 6 In this paper, we describe a new type of optical velocity selection that has been shown to prepare a sample of atoms with a velocity spread 2 orders of magnitude below the velocity an atom would experience from the recoil of a single photon. This velocity spread can be characterized by an effective one-dimensional "temperature" of 24 pK. We further show that this technique will be useful in measuring the velocity spreads of atoms for AD< 1 cm/sec, where time-of-flight techniques 1,2 are no longer effective because of gravitational acceleration. Other applications of this velocity-selection method will also be indicated in this paper.The velocity-selected atoms are prepared as follows: Atoms with a ground-state hyperfine splitting v\2 and an optical interval vn as shown in Fig. 1 are first optically pumped into a single hyperfine level |l>. Two counterpropagating laser beams at frequencies V\L and VIL will induce a stimulated Raman transition to the |2) state if atoms are in resonance with the frequency difference vi2 as vi/, -V2L-7 The atoms excited into the |2) state will have a velocity spread given by the Doppler-shift formula Av/c SB AV/(V\L + V2L\ where Av is the linewidth of the transition. The velocity spread Av can be extremely narrow because the frequencies VIL,2L are optical frequencies and the linewidth of the 11>-• |2> transition can be narrow. If the laser frequency V2L = VIL +Vrf is generated by an electro-optic modulator or other radiofrequency technique, the frequency jitter of the laser is canceled out. The linewidth due to the finite transit time is greatly reduced with the use of slow atoms. For example, we have demonstrated a 2-Hz-wide resonance of the sodium ground-state hyperfine splitting with atoms in an atomic fountain. 8 Even with a modest measurement time of 10 msec, the expected spread in velocity Av is 30 ^m/sec for sodium atoms.The basic experimental apparatus has been previously described. 8 Atoms from a thermal beam were slowed with a counterpropagat...

We have captured 3.6 x 10(10) cesium atoms in a magneto-optic trap loaded from a vapor cell. The 300-fold increase in the number of trapped atoms compared with that of previous research was accomplished by using larger laser intensities and 4-cm-diameter laser beams. The loading time constant was as short as 0.2 s.

A novel superconducting single-photon detector ͑SSPD͒, intrinsically capable of high quantum efficiency ͑up to 20%͒ over a wide spectral range ͑ultraviolet to infrared͒, with low dark counts ͑Ͻ1 cps͒, and fast ͑Ͻ40 ps͒ timing resolution, is described. This SSPD has been used to perform timing measurements on complementary metal-oxide-semiconductor integrated circuits ͑ICs͒ by detecting the infrared light emission from switching transistors. Measurements performed from the backside of a 0.13 m geometry flip-chip IC are presented. Other potential applications for this detector are in telecommunications, quantum cryptography, biofluorescence, and chemical kinetics.

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