Lecture%2041%202220%20Spring%202009

# Lecture%2041%202220%20Spring%202009 - Reminders and...

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1 Reminders and Announcements HW 23 is due tomorrow; HW 24 is optional (extra credit) and is due Friday • Help Room Hours (Physics 117): Help Room Hours (Physics 117): – M 4-8 pm, T 3-6:30, W 3-6:30, R 4:30-8, F 2-6 Michelson Interferometer The interferometer was invented by an American physicist, A. A. Michelson • The interferometer splits light into two parts The interferometer splits light into two parts and then recombines the parts to form an interference pattern The device can be used to measure wavelengths or other lengths with great precision Michelson Interferometer, Schematic A ray of light is split into two rays by the mirror M o The mirror is at 45 o to the incident beam The mirror is called a beam splitter It transmits half the light and reflects the rest Consider 500 nm light in an interferometer with 1 m arms. What fractional change in the length of one arm causes a shift of one fringe? 33% 33% 33% 1. 5 e-7 2. 2.5 e-7 1 2 3 0 of 5 3. 1 e-6 Michelson Interferometer – Applications The Michelson interferometer was used to disprove the idea that the Earth moves through an ether Modern applications include – Fourier Transform Infrared Spectroscopy (FTIR) – Laser Interferometer Gravitational-Wave Observatory (LIGO) Fourier Transform Infrared Spectroscopy This is used to create a high-resolution spectrum in a very short time interval The result is a complex set of data relating light intensity as a function of mirror position This is called an interferogram The interferogram can be analyzed by a computer to provide all of the wavelength components This process is called a Fourier transform

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2 Laser Interferometer Gravitational- Wave Observatory General relativity predicts the existence of gravitational waves In Einstein’s theory, gravity is equivalent to a distortion of space – These distortions can then propagate through space The LIGO apparatus is designed to detect
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