Just who turned on the light?

February 17, 2006

Lasers are all around us - in bar-code scans at supermarket checkouts, in compact disc players, in fibre optics for telecommunications and in laser pointers and printers and surgery, not to mention in holograms, laser light shows and movies such as Star Wars . In scientific research, three of the Nobel prizes in physics during the past ten years - in 1997, 2001 and 2005 - were awarded in recognition of work that would not have been possible without laser techniques. Yet when the laser was first conceived and demonstrated in the period 1957-60, as described in Beam: The Race to Make the Laser , no one was sure what it would be useful for. The joke among physicists was, in the words of one of the pioneers, that the laser was "a solution looking for a problem".

Einstein was the first to consider the key concept of stimulated emission of light - "laser" stands for "light amplification by stimulated emission of radiation" - in a paper published in 1917. But Einstein did not put forward a second key concept, the coherence of light. He predicted that one photon could stimulate an atom in a high-energy state to emit two photons of the same energy, but he did not indicate that they would be, so to speak, identical copies. Not only would they have the same frequency (because their energy was the same), they would also be in step with each other. In other words, the wave peaks and troughs would be similarly spaced, with a fixed phase relationship. A coherent beam of light consists of waves that are in phase; in an incoherent beam - that is, practically all light, including sunlight and lamplight - the peaks and troughs of the waves are not aligned in the same way. It is the coherence and the single frequency of light in stimulated emission that gives a laser beam its power.

Charles Townes, one of the inventors of the laser, wrote in his valuable memoir, How the Laser Happened (1999), that the laser was technologically possible in the 1920s. The reason it did not happen then is that theory lagged behind experiment. Physicists were trained to focus on the equilibrium states of atoms and molecules, and not on the non-equilibrium excited states created by the absorption of radiation that were more complex to describe theoretically. It took the development of radar and the detailed study of microwave radiation in the 1930s, the Second World War and the immediate postwar period to prepare minds to think about how to generate stimulated emission. The initial breakthrough came with the invention of the maser, for microwave rather than visible light amplification, in 1954.

Some Soviet physicists - notably Nikolai Basov and Alexander Prokhorov, who shared the first laser-based Nobel prize with Townes in 1964 - contributed to its invention and early development, as did two British physicists based in Oxford. In essence, though, the early history of the laser is an all-American story.

There were at least a dozen players, and the story has many twists, turns and blind alleys, but the chief contributors were: Townes and Arthur Schawlow (working for the highly prestigious and extremely wealthy Bell Laboratories); Gordon Gould (working for a private company, TRG, on a lucrative secret contract for the Pentagon's Advanced Research Projects Agency); and a dark horse, Theodore Maiman (working for the research laboratories started in California by the eccentric industrialist Howard Hughes).

In 1958, the three groups found themselves in a race. That year, Townes and Schawlow published the first description of how the laser should work, but Bell Labs, to their lasting chagrin, were beaten to the first working laser by Maiman in 1960, while Gould coined the name of the new invention and eventually established valuable patent rights that made him a multimillionaire, if a bitter man. Neither he - nor, surprisingly, Maiman - received a Nobel prize.

Jeff Hecht, a science journalist and correspondent for New Scientist who has been writing books on lasers for well over a decade, focuses on the rivalry in "the three dramatic years from the time Townes and Gould launched the high-stakes race for the laser to the recognition of Maiman as the winner". He draws on the books and papers of the pioneers, on interviews with them conducted by others in the 1980s, and on extensive interviews of his own to write the first detailed history of this crucial period. Although the book stops in the early 1960s, long before the arrival of current laser applications, anyone who wants to understand exactly who did what and when they did it must read Hecht's useful and worthwhile history.

Readers will, however, need stamina. His book is not easily accessible to the lay reader. Although there is no mathematics, considerable knowledge of physics is required. Unlike some other writers on lasers for non-specialists, Hecht makes hardly any attempt to introduce such concepts as electromagnetic radiation, the electronic structure of atoms and molecules or quantum theory. Within the first ten pages, along with Einstein's paper (cursorily dealt with), we are introduced to the quite challenging concepts of atomic population inversion and stimulated emission. A diagram of the electromagnetic spectrum arrives only on page 34. On page 98, "quantum efficiency" appears without preface; it is not explained for another 50 pages, and then only in passing. There is no glossary.

The writing style is also a drawback. In some places, the scientific explanations are crystal clear, in others they are much too concise and confusing. Cliche abounds, as in: "Intense and competitive, Maiman focused as tightly on his quest as a laser beam." Clumsy phrases are equally common: "The 'beep, beep, beep' from the orbiting Sputnik 1 threw a bucket of cold water in the faces of overconfident Americans." The source references, though impressively comprehensive with an excellent bibliography, are not keyed into the text, making it difficult to attribute quoted comments to a given source. There are too many typos. Most irritating of all is the frequent repetition of material to no purpose.

Even a light edit by the publishers would have removed many of these faults and greatly improved the readability of the book. One hopes that Oxford University Press will consider this if it is reprinted. Beam deserves to remain available for many years.

Andrew Robinson, literary editor of The Times Higher , is the author of Einstein: A Hundred Years of Relativity . He saw his first laser on a visit to Bell Labs as a boy in 1965.

Beam: The Race to Make the Laser

Author - Jeff Hecht
Publisher - Oxford University Press
Pages - 4
Price - £17.99
ISBN - 0 19 514210 1

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