近代光学15-Nov7th讲义.pptVIP

* * * * * * Image/Text/Data from the University of Illinois WW2010 Project. /(Gh)/wwhlpr/coronas.rxml?hret=/guides/mtr/opt/mch/diff.rxmlprv=1 * 上册P208）2,5,9 * Diffraction patterns for a number of holes ranging in diameter from 1mm to 4mm as they appeared on a screen 1m away To map the rest of the pattern, we now move the sensor along any line perpendicular to the axis. For off-axial point P, some zones are partially obscured. At certain position, the sum of all partial zones “saw” by P is zero. As P move radically outward, we detects a series of relative maxima and minima. Fresnel Diffraction * * * * * 下册P30)2,5,7 It seems to have been invented by the American astronomer David Rittenhouse in about 1785. Some years later, Joseph von Fraunhofer quite independently rediscovered the principle, and went on to make a number of important contributions to both the theory and technology of gratings. * * * * * * * * * This large, unmarked spectrometer is at Denison University in Granville, Ohio. It dates from ca. 1900, and appears to have been equipped with a holder for a diffraction grating at some later date. Student-type spectrometers like this one have been in common use since 1900, although computer-based devices are beginning to take their place. Verniers allow the angular positions of the arm to be read to the nearest minute or two. From /EarlyApparatus/Optics/Spectrometers/Spectrometers.html * * * * * * * * * * * * * * * 4. Three-dimensional grating There seems to be no particular conceptual difficulty for the possibility of a three-dimensional grating. A regular spatial array of scattering centers would certainly yield interference maxima in preferred direction. In 1912, Max von Laue conceived the ingenious idea of using the regularly spaced atoms within a crystal as a 3-dimensional grating. Diffraction Grating The constructive interference occurred whenever the angle between the beam (X-ray) and a set of atomic planes within the crystal obeyed B