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Laser Diffraction

The document describes how to use a diffraction grating and laser to experimentally determine the wavelength of light using Bragg's law of diffraction, which relates the wavelength to the angle of diffraction and spacing of the grating. Students will measure the angle of diffraction for different orders of maxima from a laser hitting a grating, then use those angles and the known grating spacing to calculate the wavelength and check it against the theoretical value. The procedure is then repeated at a different grating location for additional data points.

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121 views2 pages

Laser Diffraction

The document describes how to use a diffraction grating and laser to experimentally determine the wavelength of light using Bragg's law of diffraction, which relates the wavelength to the angle of diffraction and spacing of the grating. Students will measure the angle of diffraction for different orders of maxima from a laser hitting a grating, then use those angles and the known grating spacing to calculate the wavelength and check it against the theoretical value. The procedure is then repeated at a different grating location for additional data points.

Uploaded by

throckmi
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOC, PDF, TXT or read online on Scribd
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Physics Online Laser Diffraction

Introduction Diffraction occurs when light waves interfere with each other. A diffraction grating consists of a thin piece of opaque glass or plastic with a pattern of equally-spaced, transparent slits. If a beam of monochromatic light (that is, light of only one wavelength) is incident on a diffraction grating at !", then a series of bright and dar# bands (called fringes) will emerge. $he location of the bright bands is given by %nell&s law of diffraction' d*sin() = m* (m = 0, 1, 2,....).

$he variable d is the distance between the centers of the grooves in the diffraction grating, is the angle between the line connecting the center of the grating and the bright band and the line perpendicular to the grating, m is called the order of the band and is the wavelength of the light. (otice that the angle of diffraction depends on the wavelength. )ed light (longer wavelength) is diffracted through a larger angle than blue light (shorter wavelength). $his means that %nell*s law can be used to calculate the wavelength of monochromatic light, such as that from a laser. $he purpose of this lab is to test the theoretical value for the wavelength of a red laser. Equipment You Procure $ape measure or meter stic# x $ape An assistant Equipment from Kits Diffraction grating +aser (do not aim at anyone*s eyes) E periment!" Procedures ,) %olve the above equation for , the wavelength of the light. -) .alculate d, the distance between grooves (in meters), given that there are /!! grooves0mm. 1) $ape the diffraction grating to a hori2ontal surface so that the grating is vertical. $he grating should be a large distance from a wall and parallel to the wall. 3) 4easure the distance between the diffraction grating and the wall, L. /) $urn off the lights. 5) Aim the laser at the diffraction grating. 6ou should notice an odd number of dots on the wall, typically /. $he one in the center should be the brightest (m 7 !).

8) 4easure the distance between the center dot and one near it, x. $his is a location for m 7 ,. 9) :se the definition of sin(;), x, and + to calculate sin(;). ) .alculate the wavelength of the light and compare it to the theoretical value of 5/! < ,! nm. ,!) )epeat steps 8 through using a dot that is - dots away from the center. $his will be m 7 -. ,,) )epeat steps 1 through ,! using a different location for the diffraction grating. $his will give you a total of 3 calculations of the wavelength.

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