New instrument offers clearer solar head

By Astrobrat; Published 19 Aug 2007

A paradox of measuring solar rays without optic tools such as mirrors and lenses may have been solved by two physicists.

A new instrument, designed by Darrell Judge and Leonid Didkovsky, both at the University of Southern California, could provide a hassle-free technique for measuring the extreme ultraviolet (EUV) range of solar radiation.

Much important solar research deals with detecting and measuring the high-energy particles in this range, particularly those released during solar flares.

Immune to solar flares

Solar flares - abrupt emissions on the sun's surface that release massive amounts of energy - can render satellites temporarily useless. Major flares can knock out electricity grids and even affect our weather.

More generally, EUV-driven activity in the Earth's atmosphere has long-term effects on radio communications and climate. So scientists have good reason to point their light-measuring spectrometers toward the sun, although these instruments currently suffer from technological limitations.

A spectrometer measures electromagnetic intensity over a specified range of wavelengths, using metal filters to prevent all but the desired wavelengths of light from being captured. Unfortunately, the process necessarily causes a steady loss in instrument sensitivity.
Gaseous elements floating in the solar observatory spacecraft, such as NASA's Solar and Heliospheric Obervatory, become imprinted onto the optical surfaces and filters of spectrometers by rays of solar radiation - the very stuff being measured. As a result, the lenses, mirrors and prisms lose precision, and must be regularly calibrated.
"This is a problem with any EUV spectrometer," Didkovsky told "But the optics-free spectrometer may be totally free from this problem because we have no optical or filter-based elements."

Designed at the University of Southern California Space Sciences Center, the optics-free spectrometer (OFS) measures EUV rays without any of the traditional equipment that tends to degrade in space.

No optics needed

The OFS consists of a small cylinder whose main chamber is filled with neon gas. Upon interacting with solar photons, the neon molecules ionize to produce electrons.

An electric field focuses a narrow stream of these electrons to a detector at the back of the cylinder. This field can be adjusted to collect electrons from interactions across a range of photon wavelengths. The desired EUV activity is mapped by scanning through this range.

Having no optical surfaces to calibrate, the OFS should require no maintenance. "It can look at the sun day after day, year after year, without harm," Judge said.

The OFS could usher in a new generation of spectrometers that require little or no upkeep and that maintain a high level of sensitivity throughout their lives. These instruments would prove important for improving radio communications, preventing electricity blackouts and understanding climate change.
"These are real effects," Judge said, adding that a better understanding of solar flares could lead to the development of an early-warning system for weather forecasters, satellite operators, astronauts and others.