Researchers rely on Newton's interference for new experiment

Most people think of Sir Isaac Newton as the father of gravity. But for Lawrence Livermore National Laboratory physicist Henry Chapman and his colleagues, Newton's “dusty mirror” experiment served as a launching pad for them to keenly watch the X-ray induced explosion of microscopic objects.

Using the FLASH soft-X-ray free-electron laser (FEL) in Hamburg, Germany, the team blew up a plastic sphere, but used that same laser pulse to look at the sphere a split second later by placing an X-ray mirror right behind the object. A hologram (three-dimensional image of the object) formed through interference, which was caused when the light scattered through the sphere the first time combined with the light scattered through the sphere the second time (the light bounced back through the object from the mirror).

“We know from previous work we did at FLASH that the object did not explode during the initial 25-femtosecond pulse, and that forms the known reference wave of the hologram,” Chapman said. “The reference wave can be used to determine the unknown object wave, which is actually the same object, but a split second later.”

So where does Newton come in?

Newton created one of the earliest observations of interference in his “dusty mirror” experiment. In a darkened room, he used a prism and a small hole in a screen to form a quasi-monochromatic beam from sunlight, which he shone onto a back-quick silvered mirror. The mirror was angled to return the beam back through the hole and on the screen. Newton observed dark and light rings of light, which he found “strange and surprising.” It was 100 years later when the British scientist Thomas Young determined the rings were caused by interference at the screen between two paths of light scattering from dust particles on the mirror's front surface.

The research appears in the Aug. 9 edition of the journal, Nature.

Chapman designed the experiment after visiting the Chabot Space and Science Center with his wife (Sa_a Bajt, another author on the paper) and daughter. There was an optics exhibit that would let you see interference by looking down a long tube, which had a mirror at the bottom. When you held a small penlight close to the eye, you saw colored curved fringes in the mirror's reflection. The exhibit was described as the dusty mirror experiment. “It suddenly struck me that you could do the same thing with short pulses and X-ray mirrors, and it would be really interesting if the X- ray pulse was shorter than the time it takes for it to travel from the dust particle to the back of the mirror and back,” Chapman said.

And so the experiment was born.

The experiment is part of LLNL's Laboratory Directed Research and Development project: “Biological Imaging with Fourth-generation Light Sources” to develop the technique and determine the feasibility for single-molecule imaging experiments to be carried out at the Linac Coherent Light Source (LCLS) at Stanford when it comes on line.

Unlike the static conditions of Newton's experiment, in the recent experiment the object is ultimately vaporized by the X-ray pulse and the object size changes in the brief interval that the pulse takes to reflect back to the particle. The time it takes the pulse to return is encoded in the fringe pattern of the X-ray hologram, and this can be “read out” from the hologram to an accuracy of about 1 femtosecond. Coupled with the short wavelength of X-rays, the measurements give information simultaneously at the highest spatial resolution and time resolution for general noncrystalline materials.

“This experiment allows us to study the dynamics of material in the extreme conditions of intense FEL pulses, both during the pulse and as it turns into plasma,” Chapman said.

Plasma is considered to be a fourth state of matter, an ionized gas that has distinct properties. Until the recent experiment, there had been no structural methods to follow the early steps in plasma formation. Understanding these initial processes is crucial to future near atomic-resolution imaging experiments at LCLS. The key is to use short pulses to beam the damage and get a high-resolution image of the object before it explodes.

Source: Lawrence Livermore National Laboratory

Related stories:

Age-old magic tricks can provide clues for modern science
Revealing the science behind age-old magic tricks will help us better understand how humans see, think, and act, according to researchers at the University of British Columbia and Durham University in the U.K.
How carrots help us see the color orange
One of the easiest ways to identify an object is by its color -- perhaps it is because children's books encourage us to pair certain objects with their respective colors. Why else would so many of us automatically assume carrots are orange, grass is green and apples are red?
Newly discovered extrasolar planet is the smallest known and has smallest host star
Astronomers have discovered an extrasolar planet only three times more massive than our own, the smallest yet observed orbiting a normal star. The star itself is not large, perhaps as little as one twentieth the mass of our Sun, suggesting to the research team that relatively common low-mass stars may present good candidates for hosting Earth-like planets.
New light clock concept explains time dilation in special relativity
Joseph West, a physicist at Indiana State University, has recently proposed a method for intuitively visualizing and calculating the time dilation effects in special relativity—one of the stranger concepts in modern physics.
Old idea spawns new way to study dark matter
An international team of astronomers led by Ohio State University has examined dark matter in the outer reaches of our galaxy in a new way.
Gold catalysts are 'hot' because their electrons are heavy, chemist proposes
A University of California, Berkeley, chemist has found a mother lode of new and unique gold-catalyzed reactions by applying Einstein's theory of relativity to the rare and precious metal.
Goal of nanoscale optical imaging gets boost with new hyperlens
Scientists at the University of California, Berkeley, have developed a "hyperlens" that brings them one major step closer to the goal of nanoscale optical imaging. The new hyperlens, described in the Feb. 23 issue of the journal Science, is capable of projecting a magnified image of a pair of nanowires spaced 150 nanometers apart onto a plane up to a meter away.
Slowly does it as giant magnet goes underground at CERN
At 5:00 am GMT this morning the heaviest piece of the Compact Muon Solenoid (CMS) particle detector began a momentous journey into its experimental cavern, 100 metres underground at CERN, Geneva. You can watch it on the webcam link.

News discussion:

Physics news