![]() In fact, controlling the wavelength is the key operational element of this clock, says Liberman. This accuracy is primarily the result of keeping the diode laser centered at 852.1 nm (the cesium absorption line). However, the Westinghouse clock is still 1000 times more accurate than comparably priced crystal oscillators, which are used in many applications considered appropriate for a compact atomic clock. ![]() ![]() "We are trying to bring atomic clocks to the world." "NIST is going for performance, while we are going for practicality," says Liberman. The Westinghouse clock, on the other hand, boasts a millionth of a second accuracy in a day. For example, NIST-7 will neither gain nor lose one millionth of second in a year, which makes it invaluable for setting and maintaining time and frequency standards. What the Westinghouse clock gains in size and cost, however, it loses in accuracy-relatively speaking, that is. A microwave electromagnetic field excites electrons in the cesium vapor, partially restoring the atoms to their base energy level when the circuit`s frequency precisely matches the resonant frequency (about 9.2 gigahertz) of the cesium atoms. An 852-nm diode laser pumps the cesium atoms to a higher energy level, producing a population imbalance. The device combines an integrated electronic circuit with an aspirin-sized, cylindrical glass cell filled with cesium vapor. In contrast, the most advanced version of the Westinghouse clock will be about the size and weight of a walnut (see photo). And though rubidium-cell clocks are optically pumped, they use a lam¥fitted with an isotopic filter to eliminate undesired wavelengths. Until NIST-7, all NIST atomic clocks isolated the atoms by passing the cesium vapor through a magnetic field. Other cesium-beam and rubidium-cell clocks employ even more complex pumping devices. In addition, though NIST-7 uses a diode laser for pumping, "the setu¥takes u¥a small bench," says Liberman. "After performance, size, power, and cost are secondary issues for them." For example, the glass cylinder in NIST-7 (a cesium-beam clock that is NIST`s first optically pumped clock) is 10 ft long and 1 1/2 ft in diameter. ![]() "NIST is the nation`s timekeeper, and they want the best," says Liberman. Historically, accuracy has been the most important feature of atomic clocks. Westinghouse has tried several types of diode lasers and currently favors vertical-cavity devices because of their lower power requirements. "We need only a microwatt diode, but they are hard to find," says Liberman. We also project that it will cost one-tenth as much as atomic clocks now on the market," which range from $3000-$10,000 for a rubidium-cell clock to $20,000-$60,000 for a cesium-beam clock.īecause diode-laser prices are so volume-dependent, the actual price of the Westinghouse clock will be determined largely by the cost of the laser. "It will be one-tenth the size and 100 times lighter than any atomic time standard now available, and it will draw one-tenth the power (about one-third of a watt). "We`re talking about a clock that could revolutionize communications and location applications," says Irving Liberman, manager of Westinghouse`s time-standards program. When formally introduced in 1997, the device is expected to bring high-accuracy time-keeping capabilities to a number of applications for which this technology has previously been too expensive and cumbersome. Westinghouse claims its miniature laser-pumped cesium-cell frequency standard is smaller, less costly, and more efficient than any currently available atomic clock. Researchers from Westinghouse Electric Corp.`s Science & Technology Center (Pittsburgh, PA) are developing the first diode-pumped atomic clock intended for commercial use. Low-power diode lasers expand atomic-clock applications
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