Two Americans and a German won the Nobel Prize in physics yesterday for pioneering research in the behavior of light and its use in creating measuring techniques accurate enough to build clocks of unprecedented precision and to probe the structure of atoms.

The Royal Swedish Academy of Sciences awarded Harvard University's Roy J. Glauber, 80, half of the $1.3 million prize for developing a mathematical framework based on quantum physics to describe the behavior of particles of light known as photons.

Theodor W. Haensch, 63, of the Max Planck Institute of Quantum Optics, and John L. Hall, 71, of the University of Colorado and the National Institute of Standards and Technology, split half the prize for building laser tools and measuring the frequency of light with what are now 15 decimal points of precision.

Glauber's theoretical work forms much of the mathematical underpinning of the science known today as quantum optics, while techniques and instruments developed by Haensch and Hall, particularly the "optical frequency comb," allow scientists to define everything from the speed of light to the length of a meter with unprecedented accuracy.

The development of lasers in 1960 profoundly affected the work of all three scientists, prompting Glauber to investigate the structure of light and giving Haensch and Hall the tools for their subsequent discoveries.

"I'm absolutely delighted," said Harvard physicist Gerald Gabrielse, a Glauber colleague and Haensch collaborator. "Many of us grew up learning about the quantum nature of light from Roy Glauber. Ted Haensch has done wonderful things with lasers, and John Hall is one of my heroes -- a tremendously clever laser jock whose techniques are used everywhere."

Haensch was at work in his Munich offices when the Academy called him. "I was speechless but of course very happy, exuberant," he told the Associated Press. "Now, I am trying to get used to this."

Glauber, asleep on the other side of the Atlantic, said someone with "a perceptibly Swedish accent" awakened him with a phone call at 5:30 a.m. Eastern time at his Arlington, Mass., home to tell him there was "some good news."

"He said it involved the Nobel Prize, then I heard the voices of two Swedish scientists who I am acquainted with -- which at least raised the possibility that it was a joke," Glauber told a Harvard news conference. "But there was something very persuasive about it," he added, and "then the phone began ringing incessantly."

In Boulder, Colo., Hall, a night owl who had fallen asleep in his office, missed the 3:30 a.m. Mountain time call, which was answered by his wife. She listened for a moment, then hung up, thinking it was a crank. "But they called back immediately," Hall said in a telephone interview, "saying, 'Wait, wait, this is serious.' "

The three scientists' work grew out of the formulation early in the 20th century that light was not only "waves" but was also composed of packets of energy called "quanta," later identified as photons. When a photon hit a metal, it delivered its energy to one electron and could be measured as an electric current.

In "classical" optics, developed in the 19th century, scientists conceived of light only as waves, creating the theory known today as electromagnetism. For the better part of a century, and even today for many activities, classical optics "is perfectly fine," said University of Florida physicist John R. Klauder, co-author of a textbook on quantum optics.

But lasers offered a ready-made source of "coherent" light, in which frequency, phase and direction could be strictly controlled. Incandescent light bulbs, by contrast, display a wide range of all three characteristics.

"With lasers or complex materials, you would be foolish" to start with traditional analysis, Klauder said. "You want to go straight to the problem at hand." Glauber in the early 1960s provided the mathematical framework that described the new things that could be done with lasers.

"The question was, how do you describe those [phenomena] in theoretical terms?" Glauber said. "I puzzled over that for the better part of a year." The advent of lasers, he added, "made a whole new world of experiments possible."

This was also apparent to Hall, interested in using lasers to research with greater precision the speed of light. Knowing that all light travels at the same speed in a vacuum, he and a colleague built a 30-yard-long vacuum chamber in a never-used gold mine near Boulder and measured the frequencies of two laser beams traveling its length.

"It was a clear demonstration that lasers were stable," Hall said, particularly when they were deep in the ground far away from atmospheric disturbances.

Hall went on to develop the methane-stabilized laser, one of several inventions that have led to precision measurements, including time (the cesium clock) and distance (a meter, computed by Hall with a krypton laser, is the distance traveled by light in 1/299,792,458 of a second.)

Haensch determined that high-precision measurements could be achieved with a laser that emits a large number of different frequency oscillations. By building a "comb" in which each tooth represented a different frequency, Haensch, with a later assist from Hall, produced a tool that could determine an optical frequency in terms of the cesium second -- unprecedented precision.

"It's like an old radio with a knob," Gabrielse said. "But instead of changing stations, you turn the knob and get different light frequencies. And the great thing is that it fits on a tabletop."

Roy J. Glauber, 80, of Harvard University will get half of the $1.3 million prize money.John L. Hall, 71, of the University of Colorado will split the other half with Haensch.Theodor W. Haensch, 63, of the Max Planck Institute of Quantum Optics was speechless.