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New Version_271 Exp6 Polarized Light Lab Manl

New Version_271 Exp6 Polarized Light Lab Manl - Experiment...

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Experiment VI Polarized Light I. Purpose In this lab you will study some of the properties of linearly polarized light. II. References (Course Textbooks) Optics, by Eugene Hecht, 4 th Edition III. Equipment Diode laser, < 1 mw, 670 nm Laser beam blocker (at end of optical bench) Laser beam blocker (near laser) Magnifying glass (lens, 5cm focal length) Quarter wave plate Lens,50 cm focal length Plane polarizer, simple, 2 each Swinging arm assembly with angles scale Swinging arm stabilizing rod Optical bench, sliders and holders Dielectric plate samples Computer with Logger Pro software Plane polarizer, calibrated, in rotating mount Light sensor with mini-screen and 3-level sensitivity box Baffle for light sensor (black electrical tape or black 35mm film can ) IV. Pre-Lab Questions (due at the start of lab class) 1. (a) If the incident light is unpolarized, about how much of the light intensity gets through a plane polarizer? (b) How much is passed by a combination of the first polarizer and a second which has its polarization axis at 45 0 with respect to the first? 2. If two polarizers are aligned so that they are perpendicular, then no light will pass through. If you insert another polarizer in between them at 45 0 with respect to both of them, what fraction of a beam of unpolarized light will get through all three? (Hint: its not zero!). 3. Explain how the experiment described in Prelab question 2 above shows the difference between filters which only remove light and polarizers which change the polarization. 4. Explain what Brewster’s angle is. Calculate Brewster’s angle for glass with an index of refraction of n = 1.5. V. Introduction Classically, light is a wave of oscillating electric and magnetic fields. For light which is propagating freely in space, the electric and magnetic fields always point in directions 71
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Fig. VI.1. Unpolarized light propagating along the +z axis has electric field pointing randomly in the x-y plane. If the light passes through a polarizer which is oriented at angle θ with respect to the y axis, the light will have an electric field which is polarized at angle θ. which are perpendicular to each other, and to the direction the light is traveling. We say that light is a “transverse wave”. In an unpolarized beam of light, such as that from an ordinary light bulb, the electric field points in random directions (of course all of these directions are always perpendicular to the direction in which the light is traveling). For linearly polarized light, the electric field points along one particular direction, called the “polarization direction”. For example, suppose a light beam is propagating in the z-direction and is linearly polarized in the x-direction. In this case, the electric field is oscillating in the ±x direction.
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