In 1983 the speed of light was set as an exact quantity. It is now one of the fundamental constants in physics, with the meter being directly related to this speed and the definition of the second. As such, experiments that calculate the speed of light with high precision are important in university undergraduate laboratories. In the experiment discussed here, a method is described that allows the speed of light to be calculated using an apparatus that fits onto a 1m bench-top. An advantage of this method is that a simple digital voltmeter can be used. This measures the amplitude-modulated output from a laser beam emerging from a multi-pass cell that is mixed with that from a reference beam. The relative phase shift is determined as the modulation frequency changes, allowing the speed of light to be ascertained. Full details of the apparatus and the electronics designed for the experiment are presented.

中文翻译：

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准确测量光速的本科实验室实验。

1983 年，光速被设定为一个精确的量。它现在是物理学中的基本常数之一，仪表与此速度和秒的定义直接相关。因此，高精度计算光速的实验在大学本科实验室中很重要。在这里讨论的实验中，描述了一种方法，该方法允许使用适合 1m 台式的设备来计算光速。这种方法的一个优点是可以使用简单的数字电压表。这测量了来自多通道单元的激光束的调幅输出，该激光束与来自参考光束的激光束混合。相对相移随着调制频率的变化而确定，从而可以确定光速。