Distances Measured with Picometer Accuracy

Photo: The vacuum chamber developed at NIST

This level of precision is akin to measuring the distance from New York to Los Angeles with an uncertainty of just 1 millimeter. The technique may have applications in nanotechnology, remote sensing and industries such as semiconductor fabrication.

Laser light is typically used to measure distances by counting the number of wavelengths of light between two points. Because the wavelength is very short with 633 nanometers for the red light most often used, the method is intrinsically very precise. Modern problems in nanotechnology and device fabrication, however, require uncertainty far below 633 nm.

A more precise method involves measuring the frequency of laser light rather than the wavelength. The laser light is stored between two highly reflective mirrors, to create the optical analogue of an organ pipe. The length of an organ pipe can be measured by driving the pipe with sound waves of a known frequency. The sound emitted by the pipe is loudest when it is driven at one of its "natural" frequencies, commonly called harmonics. When one or more of these frequencies is identified, the pipe length can be determined. In the NIST work, light is transmitted through both mirrors only when the frequency of the light matches a harmonic frequency. This frequency can be used to determine the distance between the mirrors.

While this approach has been used previously for the measurement of short distances of the order of 1 micrometer, the new work extends it 25,000-fold by demonstrating a range of 25 millimeters.

COMPAMED.de; Source: National Institute of Standards and Technology (NIST)