John L. Hall
At MIT in the early 1960s, Ali Javan started a research project aimed at extending microwave frequency-measuring techniques into the infrared. He introduced the concept of an optical antenna of several wavelengths long which enables the near-complete confinement of an incident optical field coupled to it, and forming the antenna in nanoscale. For the first time an antenna was used to receive light and to transmit it to an infinitesimal receiving structure at its tip, observable only with an electron microscope. The antenna responded to infrared laser light and generated current vibrating at the frequencies of the incident beams. According to John L. Hall, during the 1962 American Physical Society meeting, Javan played a recording of the actual audio beat frequency between two of his lasers when they were tuned almost to the same optical frequency. Using this method Javan developed the first absolutely accurate measurement of the speed of light.