Nov. 16, 2006, Andrew Szentgyorgyi

New Tools to Search for Planets Orbiting Stars Other Than the Sun

Since the discovery of the first exoplanet, 51 Peg, in 1995, research on exoplanets has exploded. The Harvard-Smithsonian Center for Astrophysics (CfA) has taken a leadership position in this field and is involved in a broad range of programs to further our understanding the census, dynamics and evolutionary history of planetary systems. In this talk I will briefly review the technique and methodology of exoplanet observation. I will then give a survey of some the tools the CfA has been developing to expand the horizons in this field. Finally, I will discuss and compare three CfA echelle spectrographs that illustrate some of the nuances and challenges of searching for the ultimate prize in exoplanet research, the detection of earth sized planets orbiting solar-like stars in the habitable zone.

Andrew Szentgyorgyi

Andrew Szentgyorgyi is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics (CfA) specializing in optical instrumentation. Andrew completed his Ph.D. in physics at the University of Wisconsin in 1986 , building an atmospheric Cherenkov telescope on Maui to search for sources of very high energy (1 TeV) gamma rays, After graduate school, he joined the Columbia University faculty, concentrating on X-ray astronomy instrumentation. Dr. Szentgyorgyi moved to Cfa to work on metrology for the Chandra grazing incidence X-ray optics, but in 1993 he joined the optical and infrared instrumentation group, building a number of cameras and spectrographs for CfA gorund based telescopes.


Oct. 27, 2006, James Phillips

Terrestrial and Spaceborne Tests of the Equivalence Principle of Gravity

Since before Galileo Galilei, experimenters have used free fall to investigate gravity. The motivation has varied. In 2006, we test general relativity. GR is founded upon the Einstein equivalence principle, which states that all sufficiently small test objects, subject only to gravity, fall the same, independent of their size, composition, location and the time. Theories of quantum gravity such as string theory and supersymmetry predict violations of the equivalence principle, setting the stage for modern experimental tests. The most sensitive test at present employs a torsion pendulum with a composition dipole, and is sensitive to small components of gravitational acceleration perpendicular to the suspension fiber. The highest sensitivity is Delta-g/g = 4x10^-13. These experiments are reaching the limit imposed by thermal noise in the fiber. Furthermore, various groups including our own are considering a space-based test achieving a sensitivity as high as 10^-20, and a torsion fiber suspension is a poor starting point. Therefore, we began a terrestrial equivalence principle test of the Galilean type, employing freely-falling masses. This experiment will improve the terrestrial limit on EP violation by one order of magnitude, and would serve as the basis for a space-based version. Significant obstacles must be overcome. For example, the test masses are launched at 5 m/s, but the transverse vibration must be held to 10 micron/s. Test mass separation must be measured with an accuracy of 10^-14 m incremental, and 3x10^-8 m absolute, which we will accomplish with optical metrology. Transverse velocity must be measured to 0.25 nm/s, which we will accomplish with capacitance gauges. We are building up these technologies, and expect to achieve state of the art sensitivity within a few years. Along the way, we have learned things we didn.t want to know about the friction in steel cable, and how inappropriate ball bearings are for this work.


James Phillips
Harvard-Smithsonian Center for Astrophysics

James Phillips obtained a Bachelor's degree in physics in 1975 from the University of Michigan and a Ph.D. in physics from Stanford in 1983. He did postdoctoral work at Stanford on a search for fractional electric charges (free quarks) on matter. In 1988 he came to the Harvard-Smithsonian Center for Astrophysics, where he is working on the equivalence principle and astronomical applications of ultraprecise laser metrology. He holds a patent on techniques for laser distance gauging, and is author of 39 scientific papers. His hobbies include dinghy sailing, science presentations in schools, and coaching and playing soccer.


Sept. 21, 2006, Bill Plummer

--- Two Easy Pieces: a Double Program with Two Presentations ---


I. An expedition through darkest optics, with gun and pinhole camera

You probably made a pinhole camera in the second grade, so of course you know what one is. Google returns more than 700,000 hits, starting from the 5th century BC.

But how much do you really know about a pinhole camera?

What did Petzval know? How was Rayleigh wrong? When can diffraction make an image sharper? Does a pinhole have a focal length? Can a pinhole have spherical aberration? Where does a pinhole camera show spurious resolution? What are dimensionless variables, and why are they useful? Will the pretty Cornu spiral help? What does the world actually look like, in the ultraviolet and in the infrared? Why did R. W. Wood make a fisheye camera with real water? How can you easily make really beautiful pinholes of any desired size? And will the pinhole camera be the last earthly refuge for photographic film?

II. A cool new way to mold lenses

Speaking of the infrared, the thermal IR spectrum is getting interesting again because of new digital image-forming technologies, such as uncooled bolometer arrays. These devices still need lenses to form their images, but if we want to use an aspheric surface here and there in an optical design, conventional wisdom only offers us expensive diamond-turned components or molded chalcogenide glasses. You will get an early look at some lens design options that will use a new (patent pending) technology: cold powder molding. You will see how an infrared lens can be made inexpensively, even one with a completely free-form shape!

This new approach to manufacturing offers lenses in high volume for the infrared, out to 20 or 50 microns wavelength, with excellent transmission and a variety of available material properties, for an attractively low cost. We can now make spherical and aspheric infrared lens components, diffractive infrared optical elements, and even infrared lens and prism arrays, with almost the same convenience we knew and loved when molding optical plastic!

Bill Plummer

Bill Plummer received his AB and PhD degrees in Physics from the Johns Hopkins University, where he worked with Prof. John Strong in infrared planetary astronomy. He joined Polaroid in 1969, in time to work closely with Edwin Land and Jim Baker on the SX-70 camera and a lot of other commercial products, and for more than twenty years was Director of Optical Engineering. He has published 40 papers and has given as many invited talks around the world. He has 96 US patents for optical, mechanical, electronic, and chemical inventions, with a few more pending. He has received the David Richardson Medal, the Joseph Fraunhofer Award, and the Robert M. Burley Prize from the Optical Society of America. He is a Fellow of the OSA and of the SPIE and is an elected member of the National Academy of Engineering. For some years he has also been a Senior Lecturer with the Mechanical Engineering Dept at MIT. Bill has been an optical engineering consultant since 2001, and is founder and president of WTP Optics, Inc.

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