1. PHY 1371Dr. Jie Zou1 Chapter 38 Diffraction and Polarization (Cont.)

2. PHY 1371Dr. Jie Zou2 Outline The diffracting grating Diffraction grating spectrometer A compact disc Diffraction of x-rays by crystals

3. PHY 1371Dr. Jie Zou3 The diffraction grating Diffraction grating: A useful device for analyzing light sources, which consists of a large number of equally spaced parallel slits. How does a diffraction grating work? Each slit produces diffraction. The diffracted beams interfere with one another to produce the final pattern. Condition for maxima in the interference pattern at angle  : d sin  = m, m = 0,1,2,3… d = slit spacing. m = the order number

4. PHY 1371Dr. Jie Zou4 Diffraction grating spectrometer Basic operating principle: The collimated beam incident on the grating is diffracted into the various orders at the angles  that satisfy the equation d sin  = m, m = 0,1,2,3… The wavelength can be determined by measuring the precise angles at which the images of the slit appear for the various orders.

5. PHY 1371Dr. Jie Zou5 A compact disc A compact disc is a diffraction grating. The light reflecting from the regions between the closely spaced grooves interfere constructively only in certain directions that depend on the wavelength and on the direction of the incident light.

6. PHY 1371Dr. Jie Zou6 Example 38.7 Monochromatic light from a helium- neon laser ( = 632.8 nm) is incident normally on a diffraction grating containing 6000 lines per centimeter. Find the angles at which the first-order, second-order, and third-order maxima are observed.

7. PHY 1371Dr. Jie Zou7 Diffraction of x-rays by crystals Bragg’s law: The condition for constructively interference (maxima in the reflected beam) is: 2d sin  = m, m = 1,2,3…(d is the spacing between atomic planes).

8. PHY 1371Dr. Jie Zou8 Homework Ch. 38, P. 1236, Problems: #24, 32.