Light pipes for sensitive spectroscopy.

Light pipes for sensitive spectroscopy

Measuring the faint light emitted by a material confined within a massive, high-field magnet or in a refrigerator capable of attaining millikelvin temperatures is no simple matter. Often the probe necessary for collecting the data must snake through a tortuous access channel only a fraction of an inch wide. "A lot of science has been out of reach simply because of the difficulty of doing optical experiments in restricted environments," says Don Heiman of MIT's Francis Bitter National Magnet Laboratory. "It's like trying to look out of a peephole in your front door while standing in another room."

Heiman and his colleagues have solved the problem of access by using optical fibers as flexible pipes to carry light from confined samples to sophisticated spectrometers. Because these special silica fibers can transmit extremely weak optical signals amounting to less than one photon per second, researchers can detect a variety of subtle physical effects, even at temperatures as low as 50 millikelvins and in magnetic fields as high as 70 tesla. Researchers at MIT and a number of other laboratories now starting to use this optical-fiber technology have already discovered a number of novel optical effects in magnetic semiconductors and in fabricated structures known as quantum wells.