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Maser-to-Laser Man

Charles Townes sketched out the basic design for the maser in 1951. It was not until 1953 that Townes, James Gordon and Herbert Zeigler arrived at the first maser; it operated at 24 GHz using ammonia. It found initial use as a UHF oscillator and precision clock. He immediately wanted to go to much shorter wavelengths.

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Townes (left) and Gordon (right)

Townes teamed up with his brother-in-law, Arthur Schawlow, and they generated the framework for infrared and optical masers.[1]

“The extension of maser techniques to the infrared and optical region is considered. It is shown that by using a resonant cavity of centimeter dimensions, having many resonant modes, maser oscillation at these wavelengths can be achieved by pumping with reasonable amounts of incoherent light. For wavelengths much shorter than those of the ultraviolet region, maser-type amplification appears to be quite impractical. Although use of a multimode cavity is suggested, a single mode may be selected by making only the end walls highly reflecting, and defining a suitably small angular aperture. Then extremely monochromatic and coherent light is produced. The design principles are illustrated by reference to a system using potassium vapor.”

Reflecting on the state of the art back in the late 1950’s is instructive. For example, “For a wavelength equal to 104 A, it was seen above that spontaneous emission produced a few milliwatts of power in a maser system of dimensions near one centimeter, assuming refectivities which seem attainable at this wavelength. Thus in the ultraviolet region at
wavelength equal to 1000A, one may expect spontaneous emissions of intensities near ten watts. This is so large that supply of this much power by excitation in some other spectral line becomes very difficult. Another decrease of a factor of 10 in wavelength would bring the spontaneous emission to the clearly prohibitive value of 100 kilowatts. These figures show that maser systems can be expected to operate successfully in the infrared, optical, and perhaps in the ultraviolet regions, but that, unless some radically new approach is found, they cannot be pushed to wavelengths much shorter than those in the ultraviolet region”

Townes in 2015, at 89 years, during an interview by Bonnie Azab Powell, “[The maser] was a new idea, a sudden visualization I had of what might be done to produce electromagnetic waves, so it’s somewhat parallel to what we normally call revelation in religion. Whether the inspiration for the maser and the laser was God’s gift to me is something one can argue about. The real question should be, where do brand-new human ideas come from anyway? To what extent does God help us? I think he’s been helping me all along. I think he helps all of us – that there’s a direction in our universe and it has been determined and is being determined. How? We don’t know these things. There are many questions in both science and religion and we have to make our best judgment. But I think spirituality has a continuous effect on me and on other people.”

A very nice and detailed obituary on Townes appeared in IEEE Spectrum on 28 January 2015, and it’s linked here.

References

1 A. L. Schawlow and C. H. Townes, “Infrared and Optical Masers,” Phys. Rev. 112, p.1940, 15 December 1958.