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首页> 外文期刊>Physica Scripta: An International Journal for Experimental and Theoretical Physics >How many principles does it take to change a light bulb...into a laser?
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How many principles does it take to change a light bulb...into a laser?

机译：将灯泡转换成激光需要多少原理？

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Quantum optics did not, and could not, flourish without the laser. The present paper is not about the principles of laser construction, still less a history of how the laser was invented. Rather, it addresses the question: what are the fundamental features that distinguish laser light from thermal light? The obvious answer, 'laser light is coherent', is, I argue, so vague that it must be put aside at the start, albeit to revisit later. A more specific, quantum theoretic, version, 'laser light is in a coherent state', is simply wrong in this context: both laser light and thermal light can equally well be described by coherent states, with amplitudes that vary stochastically in space. Instead, my answer to the titular question is that four principles are needed: high directionality, monochromaticity, high brightness, and stable intensity. Combining the first three of these principles suffices to show, in a quantitative way-involving, indeed, very large dimensionless quantities (up to similar to 10(51))-that a laser must be constructed very differently from a light bulb. This quantitative analysis is quite simple, and is easily relatable to 'coherence', yet is not to be found in any textbooks on quantum optics to my knowledge. The fourth principle is the most subtle and, perhaps surprisingly, is the only one related to coherent states in the quantum optics sense: it implies that the description in terms of coherent states is the only simple description of a laser beam. Interestingly, this leads to the (not, as it turns out, entirely new) prediction that narrowly filtered laser beams are indistinguishable from similarly filtered thermal beams. I hope that other educators find this material useful; it may contain surprises even for researchers who have been in the field longer than I have.
机译：没有激光，量子光学就不会也不会繁荣。本文不是关于激光构造的原理，而是关于如何发明激光的历史。相反，它解决了一个问题：将激光与热光区分开的基本特征是什么？我认为，显而易见的答案是“激光光是连贯的”，它含糊不清，因此一开始必须将其搁置一旁，尽管稍后再进行讨论。在这种情况下，更具体的量子理论版本“激光处于相干状态”是完全错误的：激光和热光都可以用相干状态很好地描述，其振幅在空间上是随机变化的。相反，我对名义问题的回答是需要四个原则：高方向性，单色性，高亮度和稳定的强度。结合这些原理的前三个，足以以定量的方式表明确实涉及非常大的无量纲的量（最多类似于10（51）），激光器的构造必须与灯泡的构造大不相同。这种定量分析非常简单，并且很容易与“相干性”相关，但据我所知在任何有关量子光学的教科书中都找不到。第四个原理是最微妙的，也许令人惊讶的是，它是量子光学意义上与相干态有关的唯一原理：它暗示着以相干态进行描述是对激光束的唯一简单描述。有趣的是，这导致了（并非事实证明，这是全新的）预测，即窄过滤后的激光束与类似过滤后的热束无法区分。我希望其他教育工作者认为此材料有用。即使对于在该领域工作的时间比我更长的研究人员，它也可能会带来惊喜。

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