Electron Diffraction at Multiple Slits TABLE I.Intensity Distributions. N=2 I=4 cos (=xkd/2z) N=3I=(4c0sy-1)2 Cosr=士1 max. I=9 C0s=0 max. I=1 c0s5=±1/2 min. I=0 N=4I=162c03r-1)2c0327 c08=士1 max I=16 c03=士(1/6)1/2 max. I=32/27 cos=0 min. I=0 c0s=士(1/2)1g min. I=0 N=5I=(16cos灯-12c0s2r+1)9 c0s=士1 max. I=25 Co=士(3/8)1a max. I=25/16 C03r=0 max. I=1 c08r=±[(3士52)/8]% min. I=0 the second cylinder lens.With this arrangement lenses..When a camera was used to record the the width of the source image is reduced to 50 A diffraction patterns,the exposure time for fine- before it is allowed to diverge and coherently grain,fast film material was from 20 sec to 3 min. illuminate a region 60 u wide at the plane of the If the dimensions involved in this experiment slits.The diffraction pattern is projected onto were scaled into the realm of light optics,a slit the observation plane,located 350 mm beyond width of 5 cm and a grating spacing of 20 cm the slits,by means of a rotationally symmetric would be required since the wavelength of light electrostatic lens of large focal length. is 105 times greater than that of 50 kV electrons The diffraction pattern produced in the plane The distances between the source and the slits of observation is still so small that it must be and between the slits and the observation plane subsequently enlarged electron-optically up to would be 30 km and 40 km,respectively.The 100 times before it can be easily viewed on the width of the source would be 5 mm. fluorescent screen with the aid of a ten-power The sensitivity of this electron diffraction ap- optical microscope.The electron-optical enlarge- paratus is equivalent to that of an electron ment was achieved by using a cylinder lens as the microscope with a magnification of 105;thus it projector stage (in order to magnify preferentially responds strongly to fuctuations in voltage,to in a direction perpendicular to the interference mechanical vibrations,and to magnetic disturb- lines)together with two rotationally-symmetric ances.In order to eliminate the 50-Hz magnetic FIG.7.Electron-diffraction photograph from a single slit FIG.8.Electron-diffraction photograph from two slits (Fraunhofer region). (Fraunhofer region). AJP Volume 48 /9