This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. The remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.
This paper reports an experiment on laser cooling of STRb atoms in pulsed diffuse light, which is the key step towards a compact cold atom clock. It deduces an empirical formula to simulate the pulse cooling process based on the loading of cold atoms in cooling time and the loss in the dead time, which is in agreement with the experimental data. The formula gives a reference to select the parameters for the cold atom clock.
We discuss the feasibility of realizing a cold atom space clock with counter-propagating cold atoms in microgravity. The design of the space clock is based on an atomic beam clock with Ramsey cavity, except that magneto-optical trap （MOT） is placed at each side. Cold atoms are launched simultaneously from the MOTs at both sides of the clock and they move at the counter-direction towards each other. The velocity of the launched atoms is precisely controlled to Ramsauer-Townsend resonance so that no additional collision frequency shift takes place. Such configuration can efficiently cancel the frequency shift resulting from cavitv phase shift and increase the signal-to-noise ratio （SNR）.
The magnetic field in the microwave interaction zone of the fountain atomic clock was measured by stimulated Raman transitions. By measuring the two-photon transition frequency between the Zeeman levels of the two ground states, we achieved a magnetic field measurement accuracy of the order of 0.28 nT, This method is immune to the Doppler shift and the AC Stark shift. The second order Zeeman shift of the fountain clock is 170.7 × 10^-15, with the uncertainty of 7,2 × 10^-16.
An experiment on measuring the magnetic field in Ramsey interaction region of the atomic fountain clock by detecting the Zeeman frequency shift of 87Rb hyperfine transition is presented.By mu-metal shielding and coils compensating,the magnetic fluctuations resulting from asymmetry and instability are less than 10 and 0.025 nT,respectively.The relative frequency uncertainty of atomic fountain clock caused by the magnetic field is less than 5.4×10-16.
