PORTLAND, Ore. Planet-searching capabilities got a 100-fold boost recently. A new ultra-fast, ultra-short-pulsed laser configured as a "gap-toothed" frequency comb was shown by the the National Institute of Standards and Technology (NIST) in cooperation with the University of Konstanz (Germany). Searching for Earth-like planets requires an ultra-precise technique for measuring different colors of light, which the new laser provides by virtue of widely separated "teeth"--about 20 GHz apart--each tuned to a known frequency of interest.
The new laser--the brain-child of researcher Albrecht Bartels at the Center for Applied Photonics of the University of Konstanz--sets the world's record in its combination of high speed, short pulses and high power. Only about the size of a dime, the laser blasts 10 billion pulses per second, each only 40 quadrillionths of a second (femtoseconds) long at an average power of 650 milliwatts. That's 10 times more pulses than NIST's standard comb filter lasers at comparable speeds, and yet it's 100 to 1000 times more powerful.
In searching for planets, it can spot slight variations in a distant star's color, as the planet's obit causes slight variations in its trajectory, producing minute shifts in its apparent color. By measuring the frequencies of that color with an ultra-precise comb filter--powered by the laser--these shifts can currently be detected with an accuracy of 1 meter per second. The new laser can potentially detect star wobble of just a few centimeters per second, for a 100-fold increase in sensitivity.
Most comb filters have teeth that are too finely space for astronomical instruments to detect such minute variations, but the new laser solved this problem with an invention by NIST astronomer Steve Osterman at the University of Colorado at Boulder. By bouncing the light between sets of mirrors, NIST and the University of Konstanz have eliminated periodic blocks caused by finely spaced teeth, creating a gap-toothed comb that leaves only every 10th or 20th tooth, making it an ideal ruler for astronomy, the researchers claim.
By combining the finely spaced teeth with the gaps, the technique enables a broad spectrum to be scanned while retaining detection of tiny variations. The researchers propose that astronomers launch such a comb filter on a satellite or space mission using up to five filtering cavities in parallel, to space out 25,000 teeth over the entire visible to near-infrared spectrum of 400 to 1100 nanometers.
The technique can also be used here on Earth in high-speed optical communications to sense gases, to study the atmosphere and for medical scanners.