Phys 198

LAB IMAGES FOR DIFFRACTION AND INTERFERENCE - 1/22/97

Data:

The five images given below were all formed with light from a He-Ne Laser (wavelength = 633 nm)

Image 1: Single Slit Diffraction:

Image 2: Double Slit Interference (Young's Experiment):

Image 3: Square Set of Squares:

Image Analysis:

• Figure 1: What is the width of the slit? (A minor artifact shows up in Fig 1 because of the masking tape used to reduce the central spot brightness. I will let you figure it out.)
• Figure 2: The angle between the center bright fringe and the 3rd bright fringe is q₃ = 0.007718 rad.
  a) What is the width of the slits?
  b) What is the spacing between the slits?
  c) Where is the first missing order?
  d) Does this missing order corroborate your measurements of slit spacing and slit width?
• Figure 3:: What is the side dimension of one of the squares?
• Figure 4: What is the diameter of circular aperture?
• Figure 5: If the grating had 13,400 lines/in and the Lab screen was 6.3 cm from the grating, what is the magnification of your monitor image with respect to the original Lab screen image?

Hint: To solve for two unknowns you need two independent measurements. Thus, since the spacing of the single slit diffraction minima is constant, you won't gain much by measuring black line spacings. However, maxima are a different story. The secrets of the universe, as least as far as single slit diffraction is concerned, are obtainable from the following graph:

Circular diffraction is a different story, since there is no linearity in the spacing of either the maxima or the minima. Some values of the Bessel Function of the first order (not picked at random) are: J₁(u) = 0 when u = {0, 3.832, 7.016, 10.173, ...}