Lenox Laser Helps Uncover Archimedes Palimpsest.

A spatial filter is an optical device which uses the principles of Fourier Optics to alter the structure of a beam of coherent light. Spatial filtering is commonly used to remove aberrations in the beam due to imperfect, dirty or damaged optics, or due to variations in the laser gain medium itself. This can be used to produce a laser beam containing only a single transverse mode of the laser’s optical resonator.

In spatial filtering, a lens is used to focus the beam. A beam that is not a perfect plane wave will not focus to a single spot, but rather will produce a pattern of light and dark regions in the focal plane. It can be shown that this two-dimensional pattern is the two-dimensional Fourier transform of the initial beam’s transverse intensity distribution. Light in the very center of the transform pattern corresponds to a perfect, wide plane wave. Other light corresponds to “structure” in the beam, with light further from the central spot corresponding to structure with higher spatial frequency. A pattern with very fine details will produce light very far from the transform plane’s central spot. This pattern is called an Airy pattern.

By altering the distribution of light in the transform plane and using another lens to reform the collimated beam, the structure of the beam can be altered. The most common way of doing this is to place an aperture in the beam that allows the desired light to pass, while blocking light that corresponds to undesired structure in the beam. In particular, a small circular aperture or “pinhole” that passes only the central bright spot can remove nearly all fine structure from the beam, producing a smooth transverse intensity profile. With good optics and precisely measured pinhole, one could even approximate a plane wave.

The diameter of an aperture is chosen based on the focal length of the lens, the diameter and quality of the input beam, and its wavelength. If the hole is too small, the beam quality is greatly improved but the power is greatly reduced. If the hole is too large, the beam quality may not be improved as much as desired.

The size of the aperture that can be used also depends on the size and quality of the optics. To use a very small pinhole, one must use a focusing lens with a low f-number, and ideally the lens should not add significant aberrations to the beam.

A commonly used spatial filter configuration is to use a microscope objective lens for focusing the beam, and an aperture made preferably by laser drilling a small, precise, hole in a piece of metal foil. Such apertures made in a variety of sizes and materials are readily available commercially from companies, such as, Lenox Laser, Inc., the leader in microhole technology.

Nasa Stereo Mission

NASA’s recent STEREO (Solar TErrestrial RElations Observatory) project is a mission to capture the sun in three dimensions. The two-year long project involves having two near-identical telescopes (one ahead of earths’ orbit and one behind) to record the behavior of the sun, studying phenomena like coronal mass ejections.

Lenox Laser fabricated custom parts for the Government and provided consulting services in support of testing the focus setting of one of the STEREO instruments during satellite integration at NASA/Goddard Space Flight Center.

Lenox Laser’s role was critical to a successful test. As a result, Lenox Laser was awarded the NASA/Goddard Space Flight Center Instrument Systems and Technology Division 2006 Contractor Team Spirit Award.

Lenox Laser Helps Uncover Archimedes Palimpsest.

Intensive efforts are underway to uncover centuries-old hidden writings of Greek mathematician Archimedes. Researches at the Stanford Linear Accelerator Center (SLAC) are utilizing advanced X-ray technology to uncover writings of Archimedes once completely unknown. Discovered in 1906 by then-Professor J.L. Heiberg of the University of Copenhagen, Denmark, the hidden text appeared within historical monastic prayer documents. The ancient practice of washing text away to make reuse material is called “Palimpsesting”.

The Archimedes Palimpsest writings lingered unseen for centuries, seemingly purged from the documents forever, until Professor Heiburg began to review small scrawls beneath the visible text. At SLAC, a revolutionary modern analysis of the writing medium has been made – revealing they do contain historically important information left behind by Archimedes, Hidden from the naked eye.

When confronted with an engineering challenge involving their Synchrotron X-Ray source, SLAC issued a request to Lenox Laser to produce microscopic laser-drilled holes in thin Tungsten film. These small apertures would prove critical to the team’s success in uncovering the Palimpsest’s “hidden treasure”.

Using a new X-Ray Fluorescence (XRF) technique, the team at SLAC, along with other collaborations, revealed writings involving mathematics and science once hidden for more than 1000 years. Conservation scientists are referencing this experiment to encourage similar new endeavors. Could many more documents in historical collections today hold hidden texts currently unknown? Time and Technology will tell.

The SLAC experiment has proven successful, and the story was featured on several prominent news and documentary programs. The Archimedes Palimpsest rests at the Walter’s Art Gallery in Baltimore, MD – continuously monitored by preservation professionals, and studied regularly by scholars from around the world.

Introduction to Young’s Double-slit Experiment

The double slit experiment, thought to have been first performed by English scientist Thomas Young circa 1800, generally refers to an experiment in which light is allowed to diffract through slits which produces fringes, or wave-like interference patterns on an opposing screen.

A similar experiment was performed by Claus Jonsson of the University of Tubingen where beams of electrons showed similar interference patterns. The results of this experiment are often taken as evidence of the “wave-particle duality” predicted by quantum physics. (a.k.a. Englert-Greenberger duality)

In the case two pinholes are used instead of slits, as in the original Young’s experiment, hyperbolic fringes are observed. This is because the difference in paths traveled by the light from the two sources is a constant for a fringe which is the property of a hyperbola. If the two sources are placed on a line perpendicular to the screen, the shape of the interference fringes is circular as the individual paths traveled by light from the two sources are always equal for a given fringe.

It is little wonder that the experiment performed by Dr. Jonsson (Young’s Double Slit applied to the interference of single electrons) ranks first in the list of the top ten most beautiful experiments as chosen by the readers of Physics World magazine.

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