OPTI 380A Lab 9 Interference - Prelab

# OPTI 380A Lab 9 Interference - Prelab - Revision 10/7/2010...

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Revision 10/7/2010 Optics 380A Interference 1 OPTICS 380A Lab 7: Interference Prelab Questions to consider in your preparation: (1) What are the differences between interference by division of wavefront and interference by division of amplitude? (2) In Young’s double slit experiment, how does the fringe spacing change with the separation of the two slits for a fixed wavelength of light? (3) What are the conditions for constructive and destructive interference for a monochromatic coherent light wave? This lab is an introduction to interference of light waves by division of wavefront. In the next lab, we will look at interference by division of amplitude. Three experiments will be done this week--Young’s Double Slit (a classic!), Lloyd’s Mirror (simple but elegant) and two-point interference. Briefly, we will use the Lloyd’s Mirror experiment to measure the wavelength of a He-Ne laser, and Young’s Double Slit is cast into a “real-world” type of problem, complete with error analysis. INTERFERENCE AND INTERFEREROMETERS An interferometer is an optical device which takes an input beam of light, splits it into two (or more) beams, and then recombines the two beams back into one. This process of recombining is known as interference . The beam output by the interferometer exhibits a spatially-varying pattern of light and dark regions known as fringes . The intensity of a bright fringe may be greater than the sum of the intensities of the individual two beams, and a dark fringe may have zero intensity (totally dark). This process occurs when the light waves of the two beams have a predictable phase relationship with each other--i.e., when the beams are coherent with each other. A laser beam has a high degree of coherency, so we will use a laser as the source in our two experiments. The basic principle of how an interferometer works is shown in Figure 7.1. Figure 7.1. Block diagram of an interferometer.

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Revision 10/7/2010 Optics 380A Interference 2 There are two general ways of splitting the input beam into two beams to pass through an interferometer. The first method physically splits the input beam into two separate beams, and is called division of wavefront. This is usually done by placing two apertures in the beam, as shown in Figure 7.2. The second method
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## This note was uploaded on 10/30/2010 for the course OPTICS 380a taught by Professor Staff during the Spring '10 term at Arizona.

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OPTI 380A Lab 9 Interference - Prelab - Revision 10/7/2010...

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