Physicists Catch Best Waves Ever from New, Improved SURF III at NIST

Upgrades to the Synchrotron Ultraviolet Radiation Facility at the Commerce Department’s National Institute of Standards and Technology are yielding greatly improved calibrations for a wide variety of optic and photonic devices from satellite instruments to medical lasers and environmental monitoring devices.

The improved NIST synchrotron facility is designed to be the "nation’s standard light bulb," a resource for optical calibrations for U.S. industry, as well as government and academic researchers. The facility, known as SURF III, and which at more than 180 tons of solid steel may be the world’s heaviest "light bulb," soon will be helping manufacturers improve a variety of processes.

SURF III replaces SURF II, which served as the national synchrotron radiation standard from 1974 to 1998. Synchrotron radiation is the light emitted by electrons as they are propelled around a donut-shaped ring in a strong magnetic field. The light emitted from SURF III covers the infrared, visible, ultraviolet and extends into the X-ray region of the electromagnetic spectrum. It is exceptionally pure, and scientists can tune it to a desired wavelength to probe and measure a wide variety of materials and devices.

Scientists are able to use synchrotron radiation as a standard for various wavelengths of light because they can calculate very accurately the intensity radiated at each wavelength based on known properties of SURF’s magnet and electron storage ring. SURF is, essentially, an electron accelerator that propels electrons into and around a donut-shaped ring sandwiched between an upper and lower iron yoke to create a strong magnetic field. Electrons enter the ring and are forced into a circular orbit by the magnetic field.

As the electrons are accelerated, they gain energy. Eventually, they give up some of their energy in the form of a photon of light. Portals around the ring collect the emitted light and channel it down one of 13 beamlines for a variety of measurements and experiments. The accelerator resupplies the energy lost through radiation.

Measurements at SURF III will be much more accurate due to several improvements in the magnetic field, which is more uniform and much stronger than the magnetic field in SURF II. Since variations in the magnetic field are extraordinarily small (a difference of about 100 times smaller than the variations in the field in SURF II’s magnet), electrons in the storage ring move in nearly perfect circular orbits. The result is significant improvement in the uncertainty of irradiance measurements at any given wavelength. Additionally, SURF III has two more beamlines than SURF II and a new accelerator control system.

Each of the 13 beamlines at SURF III is dedicated to a particular purpose and set of users. The measurements and calibrations conducted at SURF II, including satellite calibrations for NASA, will continue with improved accuracy at SURF III. NIST scientists are adding new capabilities in two new beamlines to take advantage of SURF III’s ability to generate optical radiation at shorter wavelengths and higher energies to better measure properties of various materials.

For example, the U.S. semiconductor industry anticipates needing extremely smooth mirrors as it develops processes to manufacture the next generation of integrated circuits. Manufacturers would like to create smaller features for integrated circuits by using extreme-ultraviolet lithography. The mirrors needed for this process would have to be extremely smooth with alternating layers of reflective materials, all very uniform. A SURF beamline dedicated to reflectometry will help the semiconductor industry make the necessary measurements to characterize these mirrors.

Another beamline calibrates satellite instruments that measure solar output and make measurements of the Earth’s ozone layer. Other beamlines are used to calibrate diodes and measure the response of optical detectors. Such measurements ensure accuracy in curing polymers, processing microelectronics and using lasers in surgery.

More details on SURF III are available on the World Wide Web at http://www.physics.nist.gov/SURF. For further information, contact Andrew Hamilton at (301) 975-6381, andrew.hamilton [at] nist.gov (andrew[dot]hamilton[at]nist[dot]gov).

As a non-regulatory agency of the U.S. Department of Commerce’s Technology Administration, NIST strengthens the U.S. economy and improves the quality of life by working with industry to develop and apply technology, measurements and standards through four partnerships: the Manufacturing Extension Partnership, the Measurement and Standards Laboratories, the Advanced Technology Program, and the Baldrige National Quality Program.