Image: Hot electron bolometer
TU Delft
Colored scanning electron microscope image showing a superconducting "hot electron bolometer" (HEB) for detection of terahertz radiation. The superconducting niobiumnitride nano-bridge is shown at the center which connects to the on-chip (partly shown) gold spiral antenna via additional contact pads. The strip covering the bridge is a left-over from the processing.
updated 1/31/2007 5:51:33 PM ET 2007-01-31T22:51:33

A miniscule sensor could lead to a better understanding of the formation of new stars, planets, and the hole in the ozone layer by studying an obscure wavelength of radiation.

Scientists at Delft University of Technology in the Netherlands have built the pinpoint-size detector, which senses the least explored region of the electromagnetic spectrum, to measure molecules and gases in planet's atmospheres.

"The sensor is especially suited to detect molecules in interstellar gas clouds, but also to detect trace gases in atmospheres in planets, including our own," said instrument scientist Merlijn Hajenius of Delft's Kavli Institute of Nanoscience.

The technology works by detecting terahertz radiation, the most common form of radiation in the universe if not one of the least publicized.

The electromagnetic spectrum runs from long-wavelength radio at one end to high-energy, short-wavelength X-rays and gamma rays on the other. Between microwaves and X-rays, lie T-rays, or terahertz radiation.

When heated, the detector, called a hot electron bolometer or HEB, becomes sensitive enough to obtain information on the terahertz signal.

"The Delft group is one of the prominent groups in advancing that [HEB] field," said electrical engineer Daniel Mittleman, of Rice University's T-ray lab. "This latest work extends the performance of HEB mixers to higher frequencies."

A gold antenna attached to the detector catches terahertz radiation and sends it to the small superconducting bridge, where scientists can read the frequency of the received signal. The latest detectors developed by Hajenius are more sensitive than previous HEBs due to better contacts between the extremely thin superconducting film and the antenna.

"In Delft, we have set a world record with this detector in the frequency area above 1.5 terahertz," Hajenius said.

The sensor's first mission is slated for 2008. It will measure the Earth's atmosphere on the second flight of Delft's balloon instrument, TELIS. The goal: to study the hydroxyl radical and other molecules in the sky above Brazil, an important step toward understanding the thinning of the ozone layer.

Astronomers will also employ these detectors in the new HEAT observatory in Antarctica, for a detailed study of the interstellar matter of the Milky Way. They will also use the sensors to better understand the formation of new stars.

T-rays coming of age
T-rays have other applications as well.

The Herschel Space Observatory, a satellite due to launch in 2008 is the terahertz version of the Hubble telescope. In Chile, one of the world's largest telescope arrays, the Atacama Large Millimeter Array, is being constructed; it will monitor terahertz wavelengths in hopes of spotting objects in the very early universe.

Many everyday materials, such as clothing, plastics, and wood look transparent under terahertz imaging, so the technology can be used to spot concealed weapons. In addition, materials will absorb the radiation at varying frequencies, depending on the type of material.

Pharmaceutical companies and tobacco companies are researching ways to use T-ray cameras for quality control in the factory. Researchers have been able to identify specific explosives and drugs that have unique "fingerprints" based on absorption frequencies.

The Delft detectors show most promise for astronomical and atmospheric applications. However, Hajenius imagines the technology may have other practical uses.

"Maybe breath analysis will be a new application for terahertz spectroscopy in the future," Hajenius told

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