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1、1,FIG. 3. Schematic diagram of the energy levels of the 由铯原子内的双光子跃迁图示。6S1/2-8S1/2 two-photon transition in atomic Cs. The two-photon 双光子跃迁能量达到了411纳米。transition energy v0 corresponds to 411 nm. The excited atoms 激发态原子自发的衰减到7P的低水平，spontaneously decay to the ground level through the 7 P level, so 以至于双光
2、子跃迁通过荧光信号能够被直接的观测到that the two-photon transitions can be directly observed through the measurement of the fluorescence signal vfl at ;460 nm. The 6S1/2 and the 8S1/2 levels are split into two hyperfine states, but only two 这两个水平分裂成两种超精细状态，但是只有两种跃迁是可以transitions are allowed, one from each of the subl
3、evels of the 的，一种是从基态各低能级达到激发态。在实验中，ground state to the corresponding excited state. In the experiment 所有的信号都达不到几皮秒，all signals were shorter than a few picoseconds, too short to observe 如此之短以至于不能观察到这两个跃迁到次能级的任何动态变any dynamics between the two transitions corresponding to the two 化，sublevels. We there
4、fore considered the ground and excited states as 我们由此认为这两个状态是同一个状态single states. 2,where g(v) is the line-shape function. Assuming a wide line 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 1 页，共 5 页 - - - - - - - - - 这里是线性函数，limit, we have 我们假设一个宽的极限，我们有如下公式，which c
5、an be shown to yield 而它可以得到如下的结果Similarly, in this case for N-photon transitions, 同理，在有 N个光子跃迁的时候，我们便得到了这个结果， IN(t)dt. These well-known results simply reflect the 那些熟悉的结果很容易折射出这个事实，那就是fact that here TPA and multiphoton transitions depend on the TPA（？）和多光子跃迁决定于激发脉冲，而与相位无关intensity of the exciting pul
6、ses and not on their phase as in Eq.(6). 3, III. EXPERIMENTAL RESULTS 实验结果To demonstrate coherent control with this approach, we 为了论证，performed experiments with the 6S1/2-8S1/2 two-photon transitions 我们用铯原子的，做双光子跃迁实验of atomic cesium, at a wavelength of 411 nm, induced 在飞秒脉冲中心波长为822纳米的情况下，产生了波长为411纳b
7、y femtosecond pulses centered at 822 nm, as shown schematically 米光谱，正如预测，图示的一样。in Fig. 3. Each of the excited atoms decays spontaneously 每个处于激发态的原子通过7P态自发的衰减到基态，名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 2 页，共 5 页 - - - - - - - - - to the ground level through the
8、 7P level, so that 以至于双光子跃迁能够通过双光子荧光直接the two-photon transition can be directly monitored through 监测到。the measurement of the two-photon fluorescence TPF! signal at 460 nm. The experimental system, shown in Fig. 4, was similar to 在Fig,4中所用的试验系统和Ref.16.中使用的相似that described in Ref.16. The setup was com
9、posed of a 装置由可编程的脉冲整形仪器，一个铯原子气态单元，programmable 4-f pulse shaper 14, a Cs gas cell, a photomultiplier, 一个光电倍增光，和一个同步的放大器。and a lock-in amplifier. A mode-locked Ti:sapphire 一台钛蓝宝石激光器为铯双光子跃迁产生了31飞秒谱宽laser produced 31 fs FWHM transform-limited sech2 的脉冲，经过整形仪器后测量，中心波长为822纳米。intensity pulses, centered a
10、t 822 nm, measured at the output 可编程的脉冲整形仪器有一对1200线每毫米的光栅of the pulse shaper. The programmable 4-f pulse shaper was composed of a pair of diffraction gratings with 1200 和一对焦距为 100毫米的消色透镜组成。lines/mm and a pair of achromat lenses with a 100 mm focal 第一快透镜和光栅在傅里叶平面上输入复杂光谱length. The first lens and grat
11、ing spatially map the complex 脉冲，那里有立体的过滤装置spectrum of the input pulse at the Fourier plane, where a spatial filter was inserted. The second lens and grating reassemble 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 3 页，共 5 页 - - - - - - - - - 第二块透镜和光栅组成一定结构去产生对时间进行修
12、改the spectral components to form a modified timeshaped 后的脉冲，pulse. A programmable one-dimensional liquidcrystal 一个可编程的液晶体空间光调节器SLM spatial light modulator SLM! array SLM-256, CRI!, 由电脑控制的 128个独立结构组成，composed of computer-controlled 128 discrete elements, was 被放在整形器的傅里叶平面上，placed at the Fourier plane
13、of the shaper, and was used as a 用来只让特定相位的脉冲透过。dynamic filter for spectral phase manipulation of the pulses. 每单元的宽度是 97毫米而且各单元之间的间隔是3毫米。The width of each pixel is 97 mm and the interpixel gap is 整形后的脉冲用焦距为50的透镜聚焦在气态铯原子团3 mm. The shaped output pulses were focused using a lens 上，而且在 460纳米的荧光信号被光电倍增仪器w
14、ith a 50 mm focal length into the Cs gas cell, and the 和放大器所检测到。fluorescence signal at ;460 nm was detected by the photomultiplier 1P28, Hamamatsu! and a lock-in amplifier. FIG. 4. Experimental arrangement for two-photon transitions in Cs gas. The programmable 4-f pulse shaper was composed of a pair
15、 可编程脉冲整形装置由一对每毫米1200条线的衍射光栅，和一of diffraction gratings with 1200 lines/mm, and a pair of achromat 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 4 页，共 5 页 - - - - - - - - - 对焦距是 100毫米的消色透镜组成lenses with a 100-mm focal length. A programmable onedimensional 一个可编程的，由电脑控制各
16、部分的SLM（空间光调节器）被SLM with 128 computer controlled discrete elements 放在整形仪器的傅里叶变换平面，was placed at the Fourier plane of the shaper, and was used as a 它用作动态的控制只透过特定的脉冲。dynamic filter for spectral phase manipulation of the pulses. The 经过整形后的脉冲通过焦距长度为50毫米的透镜后shaped output pulses were focused using a lens with a 50 mm focal 聚焦于气态铯原子团上。length into the Cs gas cell. The fluorescence signal at ;460 nm 波长为 460纳米的荧光信号被光电接收器和放大器所检测到。was detected by the photomultiplier and the lock-in amplifier. 4, 名师资料总结 - - -精品资料欢迎下载 - - - - - - - - - - - - - - - - - - 名师精心整理 - - - - - - - 第 5 页，共 5 页 - - - - - - - - -