---
title: "光怎样把原子搬到不再吸光的状态里"
description: "一束偏振光怎样先制备原子，再让射频共振变成看得见的信号？"
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language: "zh-CN"
page_type: "story"
alternate_languages:
  en: "https://sandboxphysics.com/stories/quantum-evidence/optical-pumping-populations-double-resonance/"
last_modified: "2026-10-24"
---

[量子物理：读懂证据](https://sandboxphysics.com/zh/stories/quantum-evidence/)

诺奖 A · 证据与操控

# 光怎样把原子搬到不再吸光的状态里

Sandbox Physics · 2026-10-15

一束偏振光怎样先制备原子，再让射频共振变成看得见的信号？

## 越照，光反而越容易穿过去

设想一束选得合适的偏振光穿过一群原子。照了一会儿，原子吸收得越来越少，透过来的光反而更亮了。原子可以还在原处：反复吸光、发光，已经把许多原子搬进一个不大吸收这束光的内部状态。光在观察样品，也在改变样品。

这种搬动叫光抽运。所谓“布居”，说的就是某个状态里占了多少原子。选好跃迁和偏振，就能让不同状态中的原子数拉开差距，有时还能把差异保存在寿命较长的基态里。基态是原子内部能量最低的状态。

证据阅读：A. Kastler (1957), Optical Methods of Atomic Orientation and of Magnetic Resonance, JOSA 47, 460–465 — author abstract R. A. Bernheim (1965), Optical Pumping: An Introduction, chapters 2–3 — Berkeley-hosted excerpt

## 每次吸光和发光，都有一次换位的机会

基态还能细分成几个磁子能级，对应原子内部角动量的不同投影。光的偏振描述电场怎样摆动，也帮助决定它能激发哪些跃迁。处在不同子能级的原子，对同一束光便不一定同样容易吸收。

一个容易吸光的原子，吸收光子到达激发态，过一会儿再发出光子。回来时，它可能落进另一个基态子能级。反复循环，原子便可能从容易吸光的状态里被搬走，逐渐积到一个难以再被这束光激发的状态。这个状态相对所用光束，就是暗态。

暗不暗取决于整套跃迁和光的偏振。其他能级分支、偏振不纯，或意外激发，都能让原子继续参加吸光循环。追踪角动量时，入射的偏振光、原子本身，以及原子发出的光，都有份。

证据阅读：A. Kastler (1957), Optical Methods of Atomic Orientation and of Magnetic Resonance, JOSA 47, 460–465 — author abstract R. A. Bernheim (1965), Optical Pumping: An Introduction, chapters 2–3 — Berkeley-hosted excerpt

## 碰撞会把刚排好的状态重新打散

原子彼此碰撞，或撞上器壁，会逐渐丢掉光建立的不平衡，回到较接近未制备时的分布。这个恢复过程叫弛豫。实验里最终看到的布居，是两种作用互相竞争的结果：光不停搬动原子，弛豫又把它们混回去。

关掉抽运光，刚建立的差异逐渐消退；重新开光，差异又慢慢长起来。追踪吸收或荧光怎样变化，便能从光学信号研究制备和弛豫。怎样减少弛豫，和怎样选对能级一样，都是实验要解决的实际困难。

证据阅读：R. A. Bernheim (1965), Optical Pumping: An Introduction, chapters 2–3 — Berkeley-hosted excerpt Laboratoire Kastler Brossel, Birth of Double Resonance and Optical Pumping — institutional history

## 射频能打乱光先排好的队伍

加上磁场，相邻磁子能级有了能量差。再施加频率合适的振荡场，就能让原子在它们之间转移，这叫磁共振。如果转移把原子重新送回容易吸光的状态，扫过共振时，透射或荧光信号便跟着改变。

用一种作用驱动，再用另一种作用观察，就是双共振。Brossel 和 Bitter 在 1952 年的实验里，用偏振光给汞原子的激发态建立不均匀布居，再看磁共振怎样改变出射光的偏振。基态光抽运发展了相关想法，把可利用的不平衡放在寿命更长的较低状态里。

证据阅读：J. Brossel and F. Bitter (1952), A New Double Resonance Method for Investigating Atomic Energy Levels, Phys. Rev. 86, 308–316 — abstract A. Kastler (1957), Optical Methods of Atomic Orientation and of Magnetic Resonance, JOSA 47, 460–465 — author abstract

## 从 Kastler 的想法，到钠原子束上的信号

按实验室的历史记述，Kastler 在 1950 年提出基态光抽运，Brossel 在 1952 年用钠原子束看到了信号。中间有失败的尝试，照射和弛豫条件都得反复处理。后来发展出的蒸气泡技术，又往实用实验推进了一步。

Kastler 在 1966 年获奖，表彰的是用光学方法研究原子的射频共振。光成了整理内部状态、灵敏读出响应的工具。整理好内部状态的原子，质心仍可能飞得很快；激光冷却接着处理的，是怎样把这种运动也慢下来。

证据阅读：Laboratoire Kastler Brossel, Birth of Double Resonance and Optical Pumping — institutional history A. Kastler (1957), Optical Methods of Atomic Orientation and of Magnetic Resonance, JOSA 47, 460–465 — author abstract Alfred Kastler — official 1966 award facts

## 接着操作模型

下面这些教学 Lab 产生的是模拟数据，和上文讨论的历史观测不是一回事。

- [用偏振光抽运原子，再看它们在暗处弛豫](https://sandboxphysics.com/zh/labs/optical-pumping-relaxation/)
- [用 Hanle 效应求激发态寿命](https://sandboxphysics.com/zh/labs/hanle-lifetime-spectrometer/)

## 来源与阅读说明

Kastler 1957 年的本人总结和 Brossel–Bitter 1952 年论文的摘要，都在出版方网站上读到。钠原子束的时间线依据实验室自己的历史记述；简化的抽运图景参照伯克利托管的 Bernheim 导论。1966 年诺奖讲稿的 PDF 返回 403，我们不声称已经通读。

1. [A. Kastler (1957), Optical Methods of Atomic Orientation and of Magnetic Resonance, JOSA 47, 460–465 — author abstract](https://opg.optica.org/josa/abstract.cfm?uri=josa-47-6-460)
2. [J. Brossel and F. Bitter (1952), A New Double Resonance Method for Investigating Atomic Energy Levels, Phys. Rev. 86, 308–316 — abstract](https://journals.aps.org/pr/abstract/10.1103/PhysRev.86.308)
3. [Laboratoire Kastler Brossel, Birth of Double Resonance and Optical Pumping — institutional history](https://www.lkb.fr/en/laboratory/presentation/history/birth-of-double-resonance-and-optical-pumping/)
4. [R. A. Bernheim (1965), Optical Pumping: An Introduction, chapters 2–3 — Berkeley-hosted excerpt](https://experimentationlab.berkeley.edu/sites/default/files/OPT/References/OPTPumpingintroduction.pdf)
5. [Alfred Kastler — official 1966 award facts](https://www.nobelprize.org/prizes/physics/1966/kastler/facts/)

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