Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 3.15: Time-of-flight profiles of the direct and reflected beams. The direct
beam is shown in black, while the reflected beam is shown in red. Both beams have
the same velocity and temperature, indicating good specular reflection of the beam
from the crystal. The reflected beam arrives earlier in time because the distance
from the nozzle to the rotor and on to the reflected beam detector is shorter than
the distance between the nozzle and the direct beam detector. This also explains
the slightly narrower time-of-flight profile of the reflected beam. Since the beams are
detected by different detectors, setup in different configurations, the amplitudes are
not comparable. Each curve is an average of 50 beam pulses.
3.4.1 Static Reflection
The first test of the rotor is to verify that the passivated Si crystals act as
good atomic mirrors. Time-of-flight profiles of the beam are examined for both the
direct and reflected beams, without spinning the rotor. Since the rotor is static, the
velocity profile of the beam should not change for atoms specularly reflected from the
crystal. To find the rotor position where the beam is reflected to the detector, the
motor controlling the rotor is turned off and the rotor is adjusted by hand to locate
the reflected signal on the detector. At this point, the servo motor is turned on and
the angle of the rotor is adjusted in .225 ◦ steps to empirically optimize the reflected
signal.
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