A small device in a crowded race
By the end of the 1950s, several well-funded teams in the United States and the Soviet Union were trying to build a working optical maser. The scientific groundwork had been laid by Townes, Schawlow and others. The first success came from a researcher who was not part of the best-known groups: Theodore Maiman, a physicist at Hughes Research Laboratories in Malibu, California.
According to the usual account, Maiman’s laser first operated on May 16, 1960. Some details of how and when different people were told are debated, but that date is the one most commonly given.
Why ruby
Ruby is a crystal of aluminum oxide with a small amount of chromium, which gives it its red color. Several scientists thought ruby was a poor choice. Calculations suggested that it would be hard to build up enough excited chromium atoms to get amplification, because the atoms in ruby follow what is called a three-level scheme, which requires a lot of pumping energy. Many groups concentrated on other materials as a result.
Maiman measured the properties of ruby himself and concluded that the problem could be overcome if the pump light was intense enough. He used a very bright flash from a photographic-style flash lamp, a coiled tube of xenon, wrapped around a small synthetic ruby rod. The ends of the rod were coated with a reflective layer, one end only partly reflective, to form a resonator.
How it worked
The flash lamp flooded the ruby with light for a brief moment. The chromium atoms absorbed energy and many jumped to an excited state. Some of them then decayed spontaneously and emitted light along the rod; that light stimulated other excited atoms to emit in step with it, and the mirrored ends sent the growing wave back and forth. A short pulse of deep red light, at a wavelength of about 694 nanometers, emerged from the partly reflective end.
The output was a pulse, not a continuous beam, since the flash lamp worked only briefly and the crystal could not handle continuous pumping at that level. Pulsed operation is a typical feature of early ruby lasers and one that later types, such as the helium-neon gas laser, avoided.
Announcement and reaction
Hughes announced the achievement at a press conference in New York in July 1960. News stories described it as a major advance, and some popular reports compared it with science fiction death rays. Maiman reported that a short paper on the work had been turned down by one physics journal, and the results were instead published in a different journal in August 1960. Accounts of the details vary, so this is best treated as a commonly told episode rather than a settled fact.
Before long other laboratories built ruby lasers of their own, and the first reports that mattered were those confirming that the effect could be repeated. Later in 1960 Ali Javan, with William Bennett and Donald Herriott at Bell Laboratories, reported a continuous gas laser using helium and neon. Q-switching, a technique for producing a much more intense short pulse from a ruby laser, was demonstrated within about a year or two.
First uses
The first ruby lasers were laboratory instruments, but ideas for using them came quickly.
- Drilling and machining. The pulse could be focused to burn a small hole in hard material. In the mid-1960s, Bell Laboratories researchers drilled holes in diamond dies used for wire drawing, an early industrial use often cited. Such dies were hard to drill by conventional methods.
- Range finding. Military and survey researchers used ruby laser pulses to measure distances by timing reflected light, and ruby lasers were used in early experiments tracking artificial satellites and bouncing light off the Moon.
- Photographic and holographic work. The short, bright pulses suited high-speed photography and early holography, which records interference patterns on photographic plates.
- Medicine. Eye doctors already relied on retinal examination to find problems, and in the early 1960s some experimented with ruby laser pulses on the eye and skin. Researchers at Columbia University in New York were reported to have treated retinal conditions with ruby pulses around 1961 to 1962, building on earlier work with intense light. Dermatologists also tested the beam on skin lesions. This was exploratory research in an early period, not an established treatment, and later laser types largely replaced ruby for these roles.
Hughes and the commercial side
Hughes was an aerospace and electronics company, and its interest was partly in military ranging and communications. Maiman later left to found his own laser company. Commercial ruby lasers were being sold within a few years to research laboratories, and the early companies that built lasers did not at first know who their customers would be.
Legacy of the ruby laser
Today the ruby laser itself is a rarity, as other lasers are more efficient. Its historic value is that it showed the principle could work in practice and set off a rapid search for new materials. Within a few years there were gas lasers, semiconductor lasers and lasers using glass and crystal doped with neodymium and other ions. Priority disputes around the first laser were mostly about the theory and the patents, while the first demonstration of a working device is generally credited to Maiman. His modest-looking apparatus is often cited as an example of how a simple experiment can succeed where larger programs had not.