特朗观测到氢 原子光谱中的最强一条谱线，并首先采用 10-8cm作为波长的单位，命名为埃(A)。还 绘制出近百种元素的光谱图。
实用光谱学的建立
• 1859年,德国物理学家基尔霍夫与德国化学 家本生研制分光镜。发现了每种元素不仅 发射、同时也吸收自己特征谱线的光，建 立了吸收光谱的基尔霍夫定律。
肖洛与激光光谱学
• A Carbide and Carbon Chemicals postdoctoral fellowship took Art to Columbia University to work with Charles H. Townes. • What a marvelous place Columbia was then, under I.I. Rabi's leadership! There were no less than eight future Nobel laureates in the physics department during Art’s two years there. • Working with Charles Townes was particularly stimulating. Not only was he the leader in research on microwave spectroscopy, but he was extraordinarily effective in getting the best from his students and colleagues. He would listen carefully to the confused beginnings of an idea, and join in developing whatever was worthwhile in it, without ever dominating the discussions. • Best of all, he introduced Art to his youngest sister, Aurelia, who became Art’s wife in 1951.
Phton detector Discharge tube
用于光谱研究的装置包含： •光源（激光器、单色光源等）
•收集光元件（透镜等）
•分光仪器（单色仪） •光学探测器（光电倍增管、CCD）、 •记录设备（计算机、记录仪）等
传统光谱学的局限性
• 使用普通光源，要提高探测分辨率，需要增强 光源的单色性，但增强光源的单色性，又以降 低光源的强度为代价，并影响到探测的灵敏度。 • 在弱光辐射情况下，光谱中的许多非线性效应 表现不出来，包含物质结构深层次的信息被阻 断。传统光谱学必须利用棱镜或光栅作为分光 器件，而这些器件的分辨率受到一定的限制， 因而谱线的许多细节不能被观察到。
诺贝尔奖与光学 Nobel Prize and Optics
激光光谱
Laser spectroscopists, photographed in front of Fudan University’s physics building in Shanghai, China, to mark the International Conference on Lasers held there and in Beijing in 1980. Participants included, from left to right, Yu-Fen Li, Zhi-Ming Zhang, John Hall, George Temmer, Aram Mooradian, Herbert Walther, Richard Brewer, an unidentified scientist, and Fu-Ming Li. Phys. Today 60, 1, 49 (2007); /10.1063/1.2709559
多普勒展宽
• 多普勒效应：原子朝观测者运动，发光频 率增大（蓝移）；原子远离观测者，发光 频率减小（红移） • 多普勒展宽：由于气体原子的速度有一定 分布范围，导致发光谱线有一定的宽度：
肖洛与激光光谱学
• This Doppler width, as a fraction of the line frequency is of the order of V/c, where V is the atomic velocity and c is the velocity of light, or typically about 10-5. • We were able to reduce it by a factor of ten or so, by using a roughly collimated beam of atoms, excited by an electron beam, and by observing the emitted light from a direction perpendicular to the atomic beam. • The hyperfine structures we sought could be resolved, but four hours exposure time on our photographic plates was required. It seemed that there really ought to be an easier method that would give still sharper spectral lines, and indeed a large part of our work in laser spectroscopy has been devoted to finding such methods.
量子力学与光谱学的发展
• 1892年，迈克耳孙就发现了巴耳末线 系中最强谱线实际上是由间隔0.14埃 的两条谱线组成。这一现象直到20世 纪量子力学建成后，才利用电子的轨 道的角动量与自旋角动量的结合获得 解释 • 1925年，在解释碱金属光谱的测量结 果时，荷兰裔美国物理学家乌伦贝克 正式引入电子自旋的概念
• 1885年，从事天文测量的瑞士科学家巴耳 末找到一个经验公式说明已知的氢原子谱 线的位置，这一组线称为巴耳末系（可见 光 H α 、 Hβ 、 H γ 、 H δ ）
2 n B n 3, 4, 5, 6... 2 n 4 B 3645 .6Å
• 1889年，瑞典光谱学家里德伯发现了许多 元素的线状光谱系，其中最为明显的为碱 金属原子的光谱系，和氢原子的光谱一样， 它们都能满足一个简单的公式：里德堡公 式（RH 为氢原子的里德伯常数）。
吸收光谱
发射与吸收光谱
发 射 与 吸 收 光 谱
荧光光谱
• 用波长较短的光照射到某种物质，物质吸 收光波后发出波长较长的光辐射（发射） 称为荧光
• 荧光光谱分析—— 利用某种物质受光照射 所产生的荧光的特性和强度，进行物质的 定性或定量分析
传统光谱分析法：放电管，加热炉等
Recorder Spectrometer High voltage
激光光谱
• 光源与光谱 • 光谱学 • 传统光谱学的建立与发展
– 发射与吸收光谱 – 荧光光谱
• 激光光谱学
– – – – 肖洛与激光光谱学 激光诱导荧光光谱 双光子、多光子荧光光谱 拉曼散射光谱
光源与光谱
• 光源——任何发光的物体 • 单色光—— 单一波长的光 • 非单色光 ：
dI λ代表波长在λ到λ＋d λ的光强 i (λ) = dI λ/d λ代表单位波长区间的光强
• 通过光谱的研究，可以得到原子、 分子等的能级结构、能级寿命、电 子的组态、分子的几何形状、化学 键的性质、反应动力学等多方面物 质结构的知识 • 光谱学技术不仅仅是一种科学工具， 在化学分析中它也提供了重要的定 性与定量的分析方法
传统光谱学的建立与发展
• 1666年牛顿 太阳光通过玻璃棱镜分解为红光到紫光的各 种颜色，发现白光是由各种颜色的光组成的---光谱学的开始
(布隆姆伯根主要贡献为非线 性光学的奠基人，肖洛主要 为激光光谱学的奠基人）
Bloemberge, （1920-）美国 Schawlow （19211999）美国
肖洛用激光打气球
肖洛与激光光谱学
• In the 1940s when Art was a graduate student at the University of Toronto, … use high-resolution optical spectroscopy to measure nuclear properties from their effects on the spectra of atoms. • The shifts and splittings of spectral lines from the interactions between electrons and nuclei were so small that they are known as hyperfine structures. • To resolve them, we needed to build high resolution spectroscopic equipment. We also had to reduce the widths of the spectral lines from our light source. • When the gas density is so low that collisions could be neglected, the principal source of the line widths is the Doppler-broadening from the thermal motions of the atoms.