Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NIST technique could make sub-wavelength images at radio frequencies

18.06.2014

Imaging and mapping of electric fields at radio frequencies (RF)* currently requires the use of metallic structures such as dipoles, probes and reference antennas. To make such measurements efficiently, the size of these structures needs to be on the order of the wavelength of the RF fields to be mapped. This poses practical limitations on the smallest features that can be measured.

New theoretical and experimental work by researchers at the National Institute of Standards and Technology (NIST) and the University of Michigan suggests an innovative method to overcome this limit by using laser light at optical wavelengths to measure and image RF fields.


This is a laboratory apparatus for mapping and imaging of radio frequency (RF) electric fields at resolutions below the usual RF wavelength limit. Rubidium atoms are placed in the glass cylinder (on the right), which is illuminated at opposite ends by red and blue laser beams. The cylinder (2.5 by 7.5 centimeters in size) moves left on a track to enable the narrow laser beams to scan its entire width. The antenna (on the left) generates an RF field, which, depending on its frequency, has a certain effect on the spectrum of light absorbed by the atoms. By measuring this effect researchers can calculate and map the RF field strength as a function of position in the cylinder.

Credit: Holloway/NIST

The new technique uses a pair of highly stable lasers and rubidium atoms as tunable resonators to map and potentially image electric fields at resolutions far below their RF wavelengths (though not below the much shorter wavelengths of the lasers).

This advance could be useful in measuring and explaining the behavior of metamaterials and metasurfaces-structures engineered to have electromagnetic properties not found in nature, such as the illusion of invisibility. Imaging with sub-RF wavelength resolution also could help measure and optimize properties of densely packaged electronics and lead to new microscopy systems and imaging sensors.

Typically, RF field measurements are averaged over antenna dimensions of tens of millimeters (thousandths of a meter) or more. NIST's prototype technique has resolution limited by the beam widths of the two lasers used-in the range of 50 to 100 micrometers (millionths of a meter.) The technique was used to map RF fields with much longer wavelengths of 2863 and 17,605 micrometers (frequencies of 104.77 gigahertz and 17.04 gigahertz), respectively.**

The NIST and Michigan researchers mapped field strength as a function of position at resolutions as low as one-hundredth of an RF wavelength, far below normal antenna limits. Such data might be used to make colorized 2D images. In theory, the technique should work for wavelengths ranging from 600 to 300,000 micrometers.

The rubidium atoms are in a hollow glass cylinder (see photo), which is traversed down its length by two overlapping laser beams that act as stimulants and filters. First, a red laser excites the atoms, which initially absorb all the light. Then, a tunable blue laser excites the atoms to one of many possible higher energy ("Rydberg") states, which have novel properties such as extreme sensitivity and reactivity to electromagnetic fields.

Next an RF field-at the frequency to be mapped or imaged-is applied. This field alters the frequency at which the atoms vibrate, or resonate, altering the frequencies at which the atoms absorb the red light. This change in the absorption is easily measured and is directly related to the electric field strength at that part of the cylinder. By moving the cylinder sideways on a track across the narrow laser beams, researchers can map the changing field strength across its diameter. The blue laser can be tuned to excite the atoms to different states to measure the strength of different RF frequencies.

In the demonstration, researchers measured the strength of standing waves at specific locations inside the glass cylinder. For the two frequencies studied, measurements of the field agreed with results from numerical simulations.

The imaging technique is a spinoff of an ongoing NIST effort to develop a method that will, for the first time, directly link electric field measurements to the International System of Units (SI).

NIST developed the new measurement and imaging technique. University of Michigan co-authors provided the tunable blue laser and assisted in the measurements. The project is funded in part by the Defense Advanced Research Projects Agency.

###

* The term RF is used here to span the conventional radio, microwave, millimeter wave and terahertz frequency bands.
** C.L. Holloway, J.A. Gordon, A. Schwarzkopf, D. Anderson, S. Miller, N. Thaicharoen and G. Raithel. Sub-wavelength imaging and field mapping via EIT and Autler-Townes splitting in Rydberg atoms. Applied Physics Letters. 104, 244102; Posted online June 16, 2014. doi:10.1063/1.4883635

Laura Ost | Eurek Alert!

Further reports about: NIST cylinder frequencies lasers measurements micrometers properties wavelength wavelengths

More articles from Physics and Astronomy:

nachricht Fast and Accurate 3-D Imaging Technique to Track Optically-Trapped Particles
24.04.2015 | Korea Advanced Institute of Science and Technology

nachricht Tau Ceti: The next Earth? Probably not
23.04.2015 | Arizona State University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fast and Accurate 3-D Imaging Technique to Track Optically-Trapped Particles

KAIST researchers published an article on the development of a novel technique to precisely track the 3-D positions of optically-trapped particles having complicated geometry in high speed in the April 2015 issue of Optica.

Daejeon, Republic of Korea, April 23, 2015--Optical tweezers have been used as an invaluable tool for exerting micro-scale force on microscopic particles and...

Im Focus: NOAA, Tulane identify second possible specimen of 'pocket shark' ever found

Pocket sharks are among the world's rarest finds

A very small and rare species of shark is swimming its way through scientific literature. But don't worry, the chances of this inches-long vertebrate biting...

Im Focus: Drexel materials scientists putting a new spin on computing memory

Ever since computers have been small enough to be fixtures on desks and laps, their central processing has functioned something like an atomic Etch A Sketch, with electromagnetic fields pushing data bits into place to encode data.

Unfortunately, the same drawbacks and perils of the mechanical sketch board have been just as pervasive in computing: making a change often requires starting...

Im Focus: Exploding stars help to understand thunderclouds on Earth

How is lightning initiated in thunderclouds? This is difficult to answer - how do you measure electric fields inside large, dangerously charged clouds? It was discovered, more or less by coincidence, that cosmic rays provide suitable probes to measure electric fields within thunderclouds. This surprising finding is published in Physical Review Letters on April 24th. The measurements were performed with the LOFAR radio telescope located in the Netherlands.

How is lightning initiated in thunderclouds? This is difficult to answer - how do you measure electric fields inside large, dangerously charged clouds? It was...

Im Focus: On the trail of a trace gas

Max Planck researcher Buhalqem Mamtimin determines how much nitrogen oxide is released into the atmosphere from agriculturally used oases.

In order to make statements about current and future air pollution, scientists use models which simulate the Earth’s atmosphere. A lot of information such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

HHL Energy Conference on May 11/12, 2015: Students Discuss about Decentralized Energy

23.04.2015 | Event News

“Developing our cities, preserving our planet”: Nobel Laureates gather for the first time in Asia

23.04.2015 | Event News

HHL's Entrepreneurship Conference on FinTech

13.04.2015 | Event News

 
Latest News

Electrons Move Like Light in Three-Dimensional Solid

24.04.2015 | Materials Sciences

Connecting Three Atomic Layers Puts Semiconducting Science on Its Edge

24.04.2015 | Materials Sciences

Understanding the Body’s Response to Worms and Allergies

24.04.2015 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>