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Characterization of the Loading Dynamics of a Magneto Optic Trap Vilas Rao NASA SHARP 2001 Dr. Georg Raithel Assistant Professor of Applied Physics/Mentor What is Laser Cooling? It is the process of cooling, or slowing, atoms using lasers. How can light cool something down? Radiation Pressure - Light exerts a force! Light is made up of photons. A photon striking an atom slows the atom slightly. After the atoms absorb the photon, it remits it in a random direction. Called photon scattering. Absorption Reemission Photons atom atom What is a Magneto Optic Trap? What is a Magneto Optic Trap? Lasers coming from 6 directions cool the atoms into a ball of atoms in the center of the trap Collisions in the MOT The MOT is only able to trap atoms traveling slower than 30 meters/second. Faster atoms still move around in the MOT, sometimes hitting an atom out of the cluster of cooled atoms. Cooled atoms Fast-moving atom Atoms get knocked out Loading Time and Steady State of the MOT Loading Time - The average time that an atom stays in the cluster of atoms before getting knocked out. After a period of time, the number of atoms in the MOT becomes constant. Rate of Atoms Being Cooled = Rate of atoms being knocked out The constant number of atoms in the trap is known as the steady state atom number Calculating the Number of Atoms and Loading Time Reemission Absorption Photons atom atom The cluster of atoms can be seen as a bright ball of light due to the reemission of photons. A photodiode converts photons that hit its surface into a current. We place a photodiode such that the light from the atoms hit it, and measure the electric current. Using this value, we can calculate the steady-state atom number in the trap as well as the loading time. We found that 5.6 million atoms per second were trapped by the MOT. Application of Laser Cooling Studying Atoms: Atoms that are traveling slower can be studied more easily. Atomic Clock : Cesium atoms move back and forth between two energy states. Atomic clocks measure time based the oscillation between the states. This can be measured more accurately for cooled atoms than fastmoving atoms. Time can more accurately be measured. Conclusion Through the process of laser cooling, the MOT can trap atoms by cooling atoms in all directions. Potential Problems: • The light reemitted by the atoms is not bright enough to measure a current • The lasers are not aligned precisely. Cooling atoms has already revolutionized the study of atomic phenomena, and will continue to show applications.