Lab Report

Topics: Light, Diffraction, Wavelength Pages: 6 (1991 words) Published: October 24, 2014
Introduction!

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The Michelson Interferometer is commonly used to determine the wavelength of light or measure very small distances. It was invented by Albert Abraham Michelson and is commonly used in optical interferometry, a branch of physics involving a family of techniques one could use to extract information about waves by superimposing them. !

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The original application of the Michelson Interferometer was to the famous Michelson-Morley experiment in 1887. Prior to Einstein's postulation that the speed of a light wave in vacuum has the same magnitude relative to all inertial frames, physicists thought that the propagation of light waves occurred in a medium called ether which permeated all space. The Michelson-Morley experiment disproved the existence of ether, baffling physicists everywhere until Einstein's postulation. !

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Another commonly used application of the Michelson Interferometer is in imaging cells. In this application, the Michelson Interferometer is mated to a microscope and the cell is in one arm of the interferometer. When light passes through the cell, it undergoes a phase shift which depends on the cell thickness and organelles within the cell. The fringe pattern produced can be used to construct a three dimensional image of the cell. !

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A commonly used set up of the Michelson Interferometer is shown in Figure 1 below. !

Figure 1 - Set Up of Michelson Interferometer!

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When two light sources have the same wavelength and frequency, they are said to be coherent with one another. If they were to be combined at a certain point, they are said to be superimposed at that point. When superimposed, the two (or more) light waves' properties can interact and interfere with one another which can lead to two scenarios; the superimposed light waves can reinforce each other to produce a brighter image or they can diminish one another to produce a dimmer image. When they produce a brighter image, it is known as constructive interference and when they produce a dimmer image, it is known as destructive interference.!

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In the Michelson Interferometer, constructive interference can be seen by the bright fringes on the screen and conversely, destructive interference can be seen by the dark fringes on the screen. As can be seen in Figure 1, a single laser source is split into two pathways by the half silvered mirror placed at an angle and is also known as a beam splitter. It allows half the light through unimpeded while reflecting the rest. Thus, the pattern of bright and dark fringes (interference pattern) can be manipulated by the optical pathway of one light source with respect to the other. By adjusting the optical pathway, taking careful measurements and observing the interference pattern, the wavelength of the source can be determined. !

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Aim!
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We are to determine the wavelength of the given laser source in the lab and compare that value to the value given by the manufacturer of the laser. !

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Methodology!
The set up is shown in Figure 2 below. (Picture for Reference in Appendix 2,Picture 1)!

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Figure 2 - Experimental Set Up of the Michelson Interferometer!

The laser source fires a beam of laser towards the beam splitter, reflecting half of the radiation towards the fixed mirror M1 and allowing the other half to pass through unimpeded towards the movable mirror M2. At M1, the radiation is reflected back to the beam splitter where only half the radiation will pass through unimpeded towards the screen. At M2, the radiation is reflected back to the beam splitter and half of the radiation will be reflected towards the screen. Thus, only 50% of the original beam recombines at the screen.!

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Before the experiment could be conducted, the laser beam and interferometer are aligned in the following steps.!

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1) The laser source is placed 15cm away from the beamsplitter. ! 2) White paper taped to the wall and serves as our viewing screen.! 3) With the...
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