ATM [Fwd: [ASTRO] New Optical Detector Could Revolutionize Astronomy]

[Mel Bartels <mbartels@efn.org>]

Ron Baalke wrote:

> Stanford University
>
> CONTACT: David F. Salisbury, News Service, (650) 725-1944;
> e-mail: david.salisbury@stanford.edu
>
> 9/2/98
>
> New optical detector could revolutionize astronomy
>
> Physicists at Stanford have developed a new optical detector so sensitive that
> it can clock the arrival of a single particle of light and measure its energy
> with exceptional precision.
>
> When applied to light coming from celestial objects, the device's ability to
> directly measure the location, arrival time, and energy of individual photons
> could have a revolutionary impact on optical astronomy, say its inventors,
> Stanford physics Professor Blas Cabrera and his research team.
>
> Not only can this detector measure all of an individual photon's important
> attributes, but it can do so throughout the infrared, optical and ultraviolet
> portions of the spectrum, the physicists report in the Aug. 10 issue of the
> journal Applied Physics Letters.
>
> The basic sensor, called a superconducting transition edge sensor (TES), was
> invented with Department of Energy support as part of a physics experiment
> called the Cryogenic Dark Matter Search and patented by Stanford in 1997. The
> experiment is being operated on campus and involves more than 40 scientists
> from eight institutions, Stanford, University of California-Berkeley,
> University of California-Santa Barbara, Case Western Reserve University,
> University of Santa Clara, San Francisco State University, Lawrence Berkeley
> National Laboratory and Fermilab.
>
> The sensor is a critical element in a new detector designed to detect
> elementary particles called WIMPs. These Weakly Interacting Massive Particles
> have been proposed as one possible explanation for the missing mass in the
> universe. Analyses of the rotation of visible galaxies have convinced
> scientists that as much as 50 percent of the matter that galaxies contain
> must be invisible to telescopes. Although WIMPS should be virtually invisible,
> scientists calculate that they should occasionally shake up the nuclei in
> crystalline material, and TES sensors have been developed to detect the heat
> produced by such interactions.
>
> The new optical version of TES, developed with support from the National
> Aeronautics and Space Administration, consists of squares of tungsten film
> that are 20 microns (about a human hair width) on a side. When the sheets are
> cooled down to a temperature of 80 thousandths of a degree above absolute
> zero, the tungsten becomes superconducting, able to carry electric current
> without resistance. Tungsten's transition between ordinary metal and
> superconductor is exceptionally sharp, so extremely small changes in the
> material's temperature give rise to large changes in its electrical
> properties.
>
> "The sharp resistive transition made it potentially an extremely sensitive
> calorimeter," says Cabrera, "but it was very difficult to keep it within the
> narrow temperature range required."
>
> In 1994, Cabrera and Kent Irwin, who is now at the National Institute for
> Standards and Technology in Boulder, solved the control problem by borrowing
> a technique that is widely used in the design of stereo amplifiers: negative
> feedback. They placed the sensor in a special circuit that produces a weak
> electrical current that automatically keeps the material at its critical
> transition temperature. The sensor is cooled slightly below the transition
> temperature and the electrical current raises its temperature to the critical
> value. When the energy from an individual photon reaches the tungsten, it
> heats up the electrons in the material. This heating causes a slight increase
> in the electrical resistance of the film. The greater resistance, in turn,
> causes a decrease in the electrical heating that exactly equals the amount of
> energy that the photon deposited. Not only does this keep the film at the
> right temperature but it also gives the scientists a precise measurement of
> the photon's energy and its arrival time.
>
> The new sensors have a number of potential uses. Irwin and his colleagues at
> NIST have customized TES detectors for use in an X-ray spectrometer. Using
> this technology, they have created the highest resolution, high-energy
> spectrometer in the world. The semiconductor industry is very interested in
> using this instrument to locate small-scale surface contamination that is a
> barrier to the continued miniaturization of integrated circuitry. According
> to current plans, the next generation X-ray satellite, called Constellation-X,
> will include a TES spectrometer to aid in the identification of the chemical
> compounds that make up the gas clouds that float between stars and galaxies.
>
> One of the most exciting applications for the sensors could come from mounting
> them on existing optical telescopes. "By providing us with information about
> the energy of each photon and the time when it arrives, these detectors can
> provide important information about some of the key questions in astronomy,"
> says physics Professor Roger Romani. He is working with Cabrera and graduate
> students Aaron Miller, Tali Figueroa and Sae Woo Nam on a trial application
> of the system on the 24-inch student telescope at Stanford this fall.
>
> Over the last 25 years, astronomers have converted their telescopes from
> photographic film to electronic CCD detectors similar to those used in
> camcorders. This conversion has increased the power of the telescopes by 30
> to 100 times. But, like film, CCDs only provide information about the position
> of photons. As with the human eye or a camcorder, many photons passing through
> various filters are needed to get a crude estimate of the color or average
> energy. More complicated electronic systems, called microchanneltrons, can
> obtain information about photon arrival times but not their energies.
>
> Currently, the physicists can only make TES detectors with a few pixels. Even
> with this limitation, however, they should be able to make meaningful new
> measurements of time-varying cosmic phenomena such as pulsars and gas-eating
> black holes, Romani says.
>
> Once they have a rudimentary TES array attached to Stanford's small student
> telescope, the scientists will make trial observations of the powerful pulsar
> in the Crab Nebula. A pulsar is a rapidly spinning neutron star that emits
> radio waves with clock-like regularity. By recording the way that the energy
> of the visible light from the pulsar varies on time scales as short as a
> thousandth of a second, the physicists hope to gain new insights into the
> outstanding question of how spinning neutron stars produce optical light. By
> examining how the distortion of the light pulses vary at different energies,
> it might also be possible to see evidence of the relativistic twisting of
> space that should take place in the neutron star's vicinity, Romani
> speculates.
>
> If the experiment with the small telescope is a success, the scientists hope
> to put a larger array of optical TES sensors on the 10-meter Hobby Eberly
> telescope in Texas. In addition to studies of faint black holes and neutron
> stars, the team also hopes to demonstrate that the device will be a powerful
> tool for measuring cosmic distances. Because the universe is expanding, the
> farther away objects are the faster they are receding. This motion causes
> redshift, the apparent reddening of light coming from receding objects. The
> larger an object's redshift the further away it must be. Because the speed
> of light is constant, objects with the highest redshifts are also the oldest
> objects in the visible universe. An array of TES devices could in principle
> obtain the redshift of every object in each image that a telescope makes.
> Currently, astronomers must follow up their initial observations of a new
> object with a lengthy spectrographic analysis to measure its redshift.
>
> An ultimate application of this new technology would be to equip the next
> generation of space telescope with a thousand-by-thousand element array of
> TES sensors. Such a system would allow astronomers the measure the redshift
> of even the most distant objects, those too faint for even the biggest
> telescopes on Earth to resolve. In its deep field mode, for example, the
> Hubble space telescope has produced images of objects that are a thousand
> times fainter than the glow of the dark night sky and are invisible to Earth-
> based telescopes. Redshift information about these and other similar objects
> could provide astronomers with a more complete picture of the size and shape
> of the universe, the distribution of galaxies within it, and how this has
> changed over time.
>
>                      -30-
>
> -------------------------------------------------------------
> Related Information:
>
> * Blas Cabrera group home page,
>   http://hep.stanford.edu/~cabrera/index.html
> * Roger Romani's home page,
>   http://astro.stanford.edu/users/rwr/home.html
> * Cryogenic Dark Matter Search web page,
>   http://cfpa.berkeley.edu/group/directdet/gen.html
> * Kent Irwin's home page,
>   http://emtech.boulder.nist.gov/div814/staff/stf_info/irwin/
> -------------------------------------------------------------
>
> PHOTO CAPTIONS:
> [http://www-leland.stanford.edu/dept/news/release/980902tesdetector.html]
>
> [Image 1]
> Two small white cylinders sitting on the horizontal shelf are new optical
> detectors so sensitive that they can measure the heat from a single photon
> that have been developed in Blas Cabrera's physics lab. The detectors are
> connected to a light source by optical fibers. Because they require an
> extremely low temperature to operate, they are immersed in a bath of liquid
> helium. Source: Cabrera laboratory.
>
> [Image 2]
> One of the first uses of the new detector will be to study the pulsar that
> sits at the heart of the Crab Nebula. The image on the left is a view of the
> Crab taken with the Palomar telescope and the image on the right is a blow up
> of the center of the Crab where the pulsar resides taken by the Hubble Space
> Telescope. Source: NASA.



--
Clear skies, Mel Bartels
http://www.efn.org/~mbartels