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-7 123 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
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Lecture%2041%202220%20Spring%202009 - Reminders and...

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