diffraction专用课件.pptVIP

Chapter31 Diffraction and Polarization “the bending of light around an obstacle” Width of the single-slit pattern Example: You pass 633-nm laser light through a narrow slit and observe the diffraction pattern on a screen 6.0 m away. You find that the distance on the screen between the centers of the first minima outside the central bright fringe is 32mm. How wide is the slit? 1. what is diffraction grating? An array of a large number of parallel slits, all with the same width a and spaced equal distances d between centers, is called a diffraction grating. 2. Intensity in the grating diffraction pattern 3. the characteristics of of the pattern 4. Grating Spectrometers(光栅光谱仪) If the grating is illuminated by white light with a continuous distribution of wavelengths, each value of k corresponds to a continuous spectrum in the pattern. The angle for each wavelength is determined by dsin?=k?; for a given value of k, long wavelengths lie at larger angles than do the shorter wavelengths . Example:The wavelengths of the visible spectrum are approximately 400nm to 700nm. Find the angular width of the first-order visible spectrum produced by a plane grating with 600 slits per millimeter when white light falls normally on the grating. Example: A transmission grating is illuminated by a monochromatic light of wavelength 6000?. Suppose the second-order lines is at angle ?30o , and the third-order lines are missed. What is the value of d? What is the value of a? How many principal maxima lines can you find? See you next term Example: An astronaut’s eye looking down on earth’s surface from a typical space shuttle altitude of 400 km. 1) Estimate the least linear width on earth’s surface that the astronaut can resolve. Pupil diameter 5 mm and wavelength of visible light to be 550 nm. 2) Can the astronaut resolve Great wall of china, which is over 3000km long, 5 to 10 m thick at its base, 4m thick at its top and 8 m in height? Solution: The minimum separation is The Rayleigh crit