Sub-RF Imaging Advanced by Lasers

Laser-enhanced radio-frequency mapping could lead to better assessment of metamaterials.

Traditional field mapping requires the use of millimeter-scale antennas and dipoles, similar in size to the radio frequencies they measure. This poses practical limitations on the smallest features that can be measured.

A technique developed by a team from the National Institute of Standards and Technology and University of Michigan overcomes these limitations using laser light at optical wavelengths. The technique is sensitive to wavelengths from 600 µm to 300,000 µm, the researchers said.

The new sub-RF wavelength resolution technique allows more efficient imaging and mapping of electricmagnetic fields at radio frequencies. Courtesy of NIST.

In the study, a red laser excited rubidium atoms in a hollow glass cylinder. Next, a tunable blue laser excited the atoms into a higher-energy Rydberg state, making them extremely sensitive to electromagnetic fields.

An RF field was then applied, altering the frequencies at which the atoms absorbed the red light. This change in absorption is easily measured and is directly related to the electric field's strength at that part of the cylinder.

The technique could be used in assessing and understanding the properties of metamaterials and metasurfaces. It could also measure and optimize properties of densely packaged electronics, the researchers said, and even lead to the development of new microscopy systems and imaging sensors.

The work was funded in part by the Defense Advanced Research Projects Agency. The research was published in Applied Physics Letters (doi: 10.1063/1.4883635).

For more information, visit www.nist.gov.