Collisional loss rate measurement of Cesium atoms in MOT Speaker : Wang guiping Date : December 25

Outline: Introduction Experiment setup Experimental results and analysis Conclusion

Outline: Introduction Experiment setup Experimental results and analysis Conclusion

I I spontaneous emission do take place during the collision. cold collisions are sensitive to long-range forces Kinetic energy of the colliding partners is low

Cold and ultracold collisions occupy a strategic position at the intersection of several powerful themes of current research in chemical physics, in atomic, molecular, and optical physics, and even in condensed matter. The nature of these collisions bear critically in optical manipulation of inelastic and reactive processes, precision measurement of molecular and atomic properties, matter-wave coherences and quantum-statistical condensated of dilute, weakly interacting atoms.

An inelastic collision, which released energy, is a “bad collision”, atoms gain in kinetic escape the trap. Determination the collision rate coefficient Trapping laser intensity dependence Collisions processes are thus a limiting factor for attaining high densities and low temperatures in all traps.

Outline: Introduction Experiment setup Experimental results and analysis Conclusion

852.35nm 6 2 P 3/2 5.2MHz 6 2 S 1/2 F= F=4 3 cooling repumping 133 Cs, alkali metal, I=7/2 SP OI AOM PBS Laser: DL100 SAS 1 Controller Laser: 6017 SAS 2 Lock-in 6 Trapping beams Repumping beam Oscilloscope TDS 1012 MOT

Background pressure in glass MOT: 1×10 -7 Pa Magnetic field grads: 15Gauss/cm Trap laser power: 4mW Diameter of trap lasers: 10mm Repumping laser power: 5mW Diameter of repumping lasers: 15mm Dimension of cold atoms cloud: 0.8mm Number of the trapped atoms: 1×10 7 Density of cold atoms cloud: 4×10 10 atoms/cm 3 Temperature of cold atoms: ~100μK Our experimental parameters:

Outline: Introduction Experiment setup Experimental results and analysis Conclusion

36mW 28mW 20mW 14mW 4mW

The time dependence of the number of atoms: Loss rate constant due to collisions between trapped atoms. The atomic density Rate constant for collisions with thermal background gas The capture rate

Radiation trapping If the density becomes very high in a MOT, there is a larger probability that a scattered photon will be re-absorbed by an other atom. This will result in a repulsive force between the two atoms. This will limit the maximum density in a MOT. Eventually, the density becomes constant, and continued filling only leads to a growth of the cloud.

L.Marcassa.et al.,Rhys.Rev.A.47,6 The slope equal to

Gallagher-Pritchard model radiative escape fine-structure-changing collision

Outline: Introduction Experiment setup Experimental results and analysis Conclusion

 We measure the collision loss rate for ultracold cesium atoms in MOT as a function of the trapping laser intensity.  We interpreted the results with collision theory.