Washington, October 30 Scientists have built the first optical frequency comb-a tool for precisely measuring different frequencies of visible light-that actually displays comb-like 'teeth'.

It has been built by scientists at the University of Konstanz in Germany and the National Institute of Standards and Technology (NIST) in the United States.

The "teeth" of the new frequency comb are separated enough that when viewed with a simple optical system-a grating and microscope-the human eye can see each of the approximately 50,000 teeth spanning the visible color spectrum from red to blue.

A frequency comb with such well-separated, visibly distinct teeth will be an important tool for a wide range of applications in astronomy, communications and many other areas.

A basis for the 2005 Nobel Prize in physics, frequency combs are now commonplace in research laboratories and next-generation atomic clocks.

But until now, comb teeth have been so closely spaced that they were distinguishable only with specialized equipment and great effort, and the light never looked like the evenly striped pattern of the namesake comb to the human eye.

A frequency comb can be used like a ruler to measure the light emitted by lasers, atoms, stars or other objects with extraordinarily high precision.

Other frequency combs with finer spacing are highly useful tools, but the new comb with more visibly separated teeth will be more effective in many applications such as calibrating astronomical instruments.

The new comb is produced by a dime-sized laser that generates super-fast, super-short pulses of high-power light containing tens of thousands of different frequencies.

As in any frequency comb, the properties of the light over time are converted to tick marks or teeth, with each tooth representing a progressively higher number of oscillations of light waves per unit of time.

The shorter the pulses of laser light, the broader the range of frequencies produced.

In the new comb, the laser pulses are even shorter and repeated 10 to 100 times faster than in typical frequency combs.

The laser emits 10 billion pulses per second, with each pulse lasting about 40 femtoseconds, or quadrillionths of a second, producing extra-wide spacing between individual comb teeth.

Another unusual feature of the new comb is efficient coupling of the laser pulses into a "nonlinear" optical fiber, which dramatically expands the spectrum of frequencies in the comb.

The ability to directly observe and use individual comb teeth will open up important applications in astronomy, studies of interactions between light and matter, and precision control of high-speed optical and microwave signals for communications. (ANI)