{"id":43,"date":"2022-04-27T07:12:54","date_gmt":"2022-04-27T11:12:54","guid":{"rendered":"https:\/\/pressbooks.library.upei.ca\/danceofphotons\/chapter\/4-photons-diffract\/"},"modified":"2022-05-12T17:39:05","modified_gmt":"2022-05-12T21:39:05","slug":"4-photons-diffract","status":"publish","type":"chapter","link":"https:\/\/pressbooks.library.upei.ca\/danceofphotons\/chapter\/4-photons-diffract\/","title":{"raw":"PHOTONS DIFFRACT","rendered":"PHOTONS DIFFRACT"},"content":{"raw":"
\r\n

p. 10<\/p>\r\nStreams of particles don\u2019t swerve when they meet a barrier - they either pass or not:\"\"\r\n\r\nBecause photons vibrate, those passing too close to an edge encounter a slight electron field drag<\/em> on their edge side causing them to swerve behind it. 3<\/sup>\r\n\r\n<\/div>\r\n

How much they swerve depends on their wavelength and phase as they encounter the edge. Look closely. Notice the slight color fringe in the bent rays. Like the last rays from a sun below the horizon, long wavelengths are bent more than short ones due to longer proximity to the edge:4<\/sup><\/p>\r\nSuch \u201cbending\u201d around an edge is characteristic of waves in general. e.g. Long wavelength (low frequency) sound waves bend around walls and rocks. However, sound waves bend as a result of spreading air or water pressure behind an edge. Photon diffraction does not depend on the medium it travels through.<\/span>\r\n\r\nAltough<\/strong> it<\/strong> occurs<\/strong> for<\/strong> a<\/strong> different<\/strong> reason<\/strong> than<\/strong> the<\/strong> bending<\/strong> of<\/strong> sound<\/strong> waves,<\/strong> this<\/strong> similar<\/strong> bending<\/strong> of<\/strong> light<\/strong> around<\/strong> an<\/strong> edge<\/strong> was<\/strong> an<\/strong> early<\/strong> clue<\/strong> to<\/strong> its<\/strong> wave-like<\/strong> nature.<\/strong>\r\n\r\n \r\n

p. 11<\/p>\r\nWhile these fringes are scarcely noticeable with a single edge, this effect from hundreds of edges close together (a diffraction<\/em> grating<\/em>) adds up producing vivid spectra:\r\n\r\n\"\"\r\n\r\nSimilar spectral effects also appear in reflections from the fine grooves on compact audio disks.\r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n

p. 12<\/p>\r\nMore compelling evidence of the wave properties of photons appears when photons of a single wavelength are directed at two adjacent slits:\r\n\r\n\"\"\r\n\r\nWith two edges, each slit diffracts photons in both directions. At various locations photons diffracted in the same direction from each slit cross paths. When these photons are in the opposite phase of vibration, their energies cancel producing darkness at that location. At another location photons from each slit will arrive in phase, and their energies sum resulting in brightness.\r\n\r\nTreating streams of photons like linear rays is great for visualizing how images are formed and lighting application. Yet<\/strong> it<\/strong> is<\/strong> their<\/strong> vibration<\/strong> that<\/strong> determines<\/strong> what<\/strong> they<\/strong> do<\/strong> and<\/strong> how<\/strong> to<\/strong> control<\/strong> them.<\/strong>\r\n

<\/p>","rendered":"

\n

p. 10<\/p>\n

Streams of particles don\u2019t swerve when they meet a barrier – they either pass or not:\"\"<\/p>\n

Because photons vibrate, those passing too close to an edge encounter a slight electron field drag<\/em> on their edge side causing them to swerve behind it. 3<\/sup><\/p>\n<\/div>\n

How much they swerve depends on their wavelength and phase as they encounter the edge. Look closely. Notice the slight color fringe in the bent rays. Like the last rays from a sun below the horizon, long wavelengths are bent more than short ones due to longer proximity to the edge:4<\/sup><\/p>\n

Such \u201cbending\u201d around an edge is characteristic of waves in general. e.g. Long wavelength (low frequency) sound waves bend around walls and rocks. However, sound waves bend as a result of spreading air or water pressure behind an edge. Photon diffraction does not depend on the medium it travels through.<\/span><\/p>\n

Altough<\/strong> it<\/strong> occurs<\/strong> for<\/strong> a<\/strong> different<\/strong> reason<\/strong> than<\/strong> the<\/strong> bending<\/strong> of<\/strong> sound<\/strong> waves,<\/strong> this<\/strong> similar<\/strong> bending<\/strong> of<\/strong> light<\/strong> around<\/strong> an<\/strong> edge<\/strong> was<\/strong> an<\/strong> early<\/strong> clue<\/strong> to<\/strong> its<\/strong> wave-like<\/strong> nature.<\/strong><\/p>\n

 <\/p>\n

p. 11<\/p>\n

While these fringes are scarcely noticeable with a single edge, this effect from hundreds of edges close together (a diffraction<\/em> grating<\/em>) adds up producing vivid spectra:<\/p>\n

\"\"<\/p>\n

Similar spectral effects also appear in reflections from the fine grooves on compact audio disks.<\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

p. 12<\/p>\n

More compelling evidence of the wave properties of photons appears when photons of a single wavelength are directed at two adjacent slits:<\/p>\n

\"\"<\/p>\n

With two edges, each slit diffracts photons in both directions. At various locations photons diffracted in the same direction from each slit cross paths. When these photons are in the opposite phase of vibration, their energies cancel producing darkness at that location. At another location photons from each slit will arrive in phase, and their energies sum resulting in brightness.<\/p>\n

Treating streams of photons like linear rays is great for visualizing how images are formed and lighting application. Yet<\/strong> it<\/strong> is<\/strong> their<\/strong> vibration<\/strong> that<\/strong> determines<\/strong> what<\/strong> they<\/strong> do<\/strong> and<\/strong> how<\/strong> to<\/strong> control<\/strong> them.<\/strong><\/p>\n

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