Notes to the presenter This is an interactive presentation best done for a

small group (15-20 maximum) Practice setting up the interferometer first, so you

know how to do it. With practice, you can set it up in 5-10 minutes

Total talk & demo can be done in 30-50 minutes Participants should be encouraged to interact

with the interferometer (which is why small groups work better)

Don’t forget to turn in an ambassador outreach form!

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www.MetrologyCareers.com

PRESENTINGthe

NCSLI Michelson Interfe

rometer

in a Pizza Box!

Objectives

The roots of the metric system The definition of the meter Albert Michelson’s contribution to optics Principles of interferometry The geometry of the Michelson interferometerAnd you will interact with a working interferometer

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You will learn about

Origins of the metric system Prior to the French revolution, each region

in France had its own standards• Different “yard” units for textiles (toise)• Different “bushel” units for grain• Different “pint” measures for beer

Idea of rationalizing units from 1670: Abbé Mouton proposes 1 minute of arc of the circumference of the earth as the primary standard of length; decimal divisions

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More on the history of the meter Other proposals (including Thomas

Jefferson) based on the period of a pendulum; also proposals to use base 12 divisions

During the revolution (1780s-1790s), the French Academy of Sciences is commissioned to reform units• Meter: 1 part in 10,000,000 of the meridian

(longitude line) from the North Pole to the Equator, passing through Paris

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The early metric system 1 meter (1×10-7 of the earth quadrant) Area and volume derived from the meter Mass derived from volume: 1 gram = mass of

water (at 0°C) in a volume of 1 cm3

Metric system not in widespread use until 1875 (May 20, 1875—signing of the Convention of the Meter)

meter is based on the Platinum-Iridium meter at BIPM in Paris; kilogram based on the international prototype in Paris; each signing nation has copies

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The meter in the US 1875: US signs the Convention of the

Meter 1890: US receives K-4 and K-20 (kilogram

standards) and meter 21 and 27 1893: T. C. Mendenhall, Superintendent of

Weights & Measures in the US orders the adoption of the international prototype meter and kilogram as US standards.

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Albert A. Michelson 1852-1931 Grew up in Northern California & West Nevada Appointed to US Naval Academy; returned as an

instructor, then, to Case School of Applied Science, Clark University, and finally University of Chicago

Did experiments to measure the speed of light, and also the Michelson-Morley experiment to determine the speed of travel of earth in the “aether” (1887)

Visited BIPM to set up interferometers for measuring the meter bars!

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The 1907 Nobel Prize in Physics

The Royal Academy of Sciences has decided to award this year's Nobel Prize for Physics to Professor Albert A. Michelson of Chicago, for his optical precision instruments and the research which he has carried out with their help in the fields of precision metrology and spectroscopy.

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Interference and light

Light exhibits constructive and destructive interference

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Incoming light Reflected light

Dark Band

Bright Band

Dark Band

Michelson’s interferometer

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The LASER

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Laser interferometer

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Mirror (moving)

LASER SOURCE

beamsplitter

Mirror (fixed)

DETECTOR

Beamsplitter

Laser light is:• Monochromatic (all the same wavelength)• Coherent (all the “peaks” and “valleys” are

in phase with each other)

Michelson interferometer with laser

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Demo time!

In 1960, the meter was redefined to Krypton light wavelength

In 1983, the meter was redefined to be the distance traveled by light (in a vacuum) in 1/299 792 458 second• c ≡ 299 792 458 m/s

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For more information

www.metrologycareers.com www.ncsli.org www.bipm.org NBS SP447 (from www.nist.gov) American Institute of Physics

(www.aip.org)

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