Chu朱棣文 Cohen-Tannoundji Phillips *The technique of laser cooling was developed by the winners of the 1997 Nobel Prize winners. *In the physical world,the lowest temperatures approach a limit of -273C.This is called the absolute zero.Nothing can be as cold as the absolute zero because all atomic and subatomic motions stop. *Laser cooling can get to the low temperature of 0.18uK. PDF created with pdfFactory trial version www.pdffactory.com
ÙThe technique of laser cooling was developed by the winners of the 1997 Nobel Prize winners. ÙIn the physical world, the lowest temperatures approach a limit of –273oC. This is called the absolute zero. Nothing can be as cold as the absolute zero because all atomic and subatomic motions stop. ÙLaser cooling can get to the low temperature of 0.18mK. Chu 朱棣文 Cohen-Tannoundji Phillips PDF created with pdfFactory trial version www.pdffactory.com
Ping-pong Balls *Photons are particles.They carry momenta like ping-pong balls. *You can slow the motion of an atom by bouncing laser light off the atoms. PDF created with pdfFactory trial version www.pdffactory.com
Ping-pong Balls ÙPhotons are particles. They carry momenta like ping-pong balls. ÙYou can slow the motion of an atom by bouncing laser light off the atoms. PDF created with pdfFactory trial version www.pdffactory.com
Tuning the Laser *Only laser light with the correct colour (frequency)can be absorbed by the atoms. *If the colour is wrong,the atoms cannot absorb the photons. PDF created with pdfFactory trial version www.pdffactory.com
Tuning the Laser ÙOnly laser light with the correct colour (frequency) can be absorbed by the atoms. ÙIf the colour is wrong, the atoms cannot absorb the photons. PDF created with pdfFactory trial version www.pdffactory.com
激光减速中性原子思想 运动的原子共振吸收迎面射来的光子，原子从基态跃迁到激发 态，动量和速度减小 hv 速度的减小△y= Mc 从激发态自发跃迁到基态放出光子，由于反冲又获得动 量。此后又吸收光子减小动量，又放出光子获得动量 吸收光子是来自同一束、同方向的激光，总使原子的动量减小 自发辐射出光子的动量是随机的，这样多次自发辐射的平均 效果并不增加原子的动量 PDF created with pdfFactory trial version www.pdffactory.com
Mc h v n D = - 激光减速中性原子思想 运动的原子共振吸收迎面射来的光子，原子从基态跃迁到激发 态，动量和速度减小 —— 从激发态自发跃迁到基态放出光子，由于反冲又获得动 量。此后又吸收光子减小动量，又放出光子获得动量 吸收光子是来自同一束、同方向的激光，总使原子的动量减小 速度的减小 自发辐射出光子的动量是随机的，这样多次自发辐射的平均 效果并不增加原子的动量 PDF created with pdfFactory trial version www.pdffactory.com
对于冷却钠原子的 波长为入=589nm的共振 光，减速效果相当于10 万倍的重力加速度 1985年贝尔实验室的朱 棣文小组用三对方 向相反射来的共振激光)=589nm照射钠原子，在六束激光的 交汇处钠原子团被冷却下来，温度2.4×108K 1995年左右，朱棣文等人利用钠原子喷泉方法将一群钠原子 降到2.4×10-11K(24pK)的温度 PDF created with pdfFactory trial version www.pdffactory.com
—— 对于冷却钠原子的 波长为l=589 nm的共振 光，减速效果相当于10 万倍的重力加速度 向相反射来的共振激光l=589 nm照射钠原子，在六束激光的 交汇处钠原子团被冷却下来，温度2.4×10-8 K 1985年贝尔实验室的朱 棣文小组用三对方 1995年左右，朱棣文等人利用钠原子喷泉方法将一群钠原子 降到2.4×10-11 K（24 pK）的温度 PDF created with pdfFactory trial version www.pdffactory.com