Researchers from the Commerce Department's National Institute of Standards and Technology and Bell Laboratories of Lucent Technologies have teamed to produce a more precise method for measuring the frequency of visible and infrared light.
The new technology may help facilitate the development of future generations of atomic clocks, improve the ability to identify molecules and elements by spectroscopy, and provide more reliable frequency standards for use by the telecommunications and related industries. This technology also provides a new level of control over ultrashort light pulses.
Reported in tomorrow's Science, the technique uses a single laser to measure optical frequency instead of a cumbersome and expensive multiple laser system.
The measurements made by the NIST/Lucent system have a higher level of precision than conventionally derived ones because they are compared to the well-defined primary frequency standard of a cesium-133 atomic clock.
Eventually, the researchers believe that the level of precision for their technology will be limited only by the performance of the primary standard itself.
The experiments were conducted at JILA, a joint research endeavor of NIST and the University of Colorado at Boulder.
The researchers "locked" a radio-frequency-clock-stabilized titanium- sapphire laser in a manner that generated a repetitive train of ultrashort optical pulses (referred to as a "repetition frequency"). Each pulse is so short that it contains only about three cycles of light.
The output spectrum of such a laser is a series of sharply defined spectral lines, separated by the repetition frequency. The scientists call this spectrum a "comb" because it has the appearance of a common pocket comb.
Ordinarily, there would be no fixed relationship between the envelopes of the pulses and the wavelength of the laser light, but in this work, the envelope and the wavelength are locked together with a controlled phase relationship.
In addition, the repetition rate of the pulses is locked to the standard cesium microwave frequency (9.2 gigahertz). This makes it possible to determine the absolute frequency of each of the "teeth" of the comb, and provides a means of measuring optical frequencies with a single laser.
A visible continuum of lightwave frequencies is generated within a novel air-silica microstructure fiber. Light is very tightly confined to the glass fiber's solid core by a ring of air holes surrounding the core.
This unusual fiber creates an extremely small effective area, possesses special characteristics for light dispersion and keeps light loss to a minimum. This allows for generation of a frequency continuum with only one thousandth of the power previously needed.
