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Name: Anurag
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I was performing diffraction and interference experiment using constant power diode laser. The fringes thus obtained in the double slit experiment are not of same width and intensity. Please tell me the reason for this difference in intensity and width of fringes. Is it due to non-perfect monochromatic source (laser)?


There are two factors that apply. First is the blend of different colors. When you mix paints of different colors, you do not always use equal quantities of each color. When light is emitted with a blend of frequencies, the blend does not have to be equally distributed. Second is the effect of angle. The light is initially moving forward. Some, but not all, is bent to form the later harmonics, the repeated colors. A lower portion of the light energy is bent than is passed forward. More must be done to the light to form the second harmonic. Therefore, less of the light energy is directed at the larger angles. This goes back to single-slit diffraction, where the center line is definitely brightest.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

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