1. Chapter 11: Fraunhofer Diffraction Chapter 11: Fraunhofer Diffraction

2. Diffraction Geometric optics: If you look carefully:
Light does not bend
If you look carefully:
It does

5. The world is finite

6. Our hero of the day: Frauenhofer
Joseph von Fraunhofer demonstrating the spectroscope. Photogravure from a painting by Richard Wimmer.

7. Joseph von Fraunhofer (6 March 1787 – 7 June 1826)
Born in Straubing, Bavaria; became an orphan at the age of 11, and he started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger.
In 1801, the workshop in which he was working collapsed and he was buried in the rubble. The rescue operation was led by Maximilian IV Joseph, Prince Elector of Bavaria. The prince entered Fraunhofer's life, providing him with books and forcing his employer to allow the young Joseph Fraunhofer time to study.
After eight months of study, Fraunhofer went to work at the Optical Institute at Benediktbeuern, a secularised Benedictine monastery devoted to glass making. There he discovered how to make the world's finest optical glass and invented incredibly precise methods for measuring dispersion. In 1818, he became the director of the Optical Institute. Due to the fine optical instruments he had developed, Bavaria overtook England as the centre of the optics industry. Even the likes of Michael Faraday were unable to produce glass that could rival Fraunhofer's.
In 1824, he was awarded the order of merit, became a noble, and made an honorary citizen of Munich. Like many glassmakers of his era who were poisoned by heavy metal vapours, Fraunhofer died young, in 1826 at the age of 39. His most valuable glassmaking recipes are thought to have gone to the grave with him.

8. Single point source

9. Double point source

11. Huygens principle
Details that we did not discuss yet

13. Big aperture, first zero line is at a small angle
Narrow aperture you get a big angle

16. 2D sinc function (Hecht)

21. Photographs of a pinhole (<0
Photographs of a pinhole (<0.5 mm diameter) in a sheet of aluminum foil illuminated by a lamp and viewed through a distant (50 feet away) well corrected 75 mm diameter by 1000 mm focal length achromatic lens stopped to a small aperture (7.1 mm) of a CCD camera

26. Try this with you own eyes!

29. Phase change due to angle
r=r0
The phase of the two sections is opposite but amplitudes are roughly the same
Cosine function

33. Two Slits and Spatial Coherence
If the spatial coherence length is less than the slit separation, then the relative phase of the light transmitted through each slit will vary randomly, washing out the fine-scale fringes, and a one-slit pattern will be observed.
Fraunhofer diffraction patterns
Good spatial coherence
Poor spatial coherence

34. Young’s Two Slit Experiment and Quantum Mechanics
Imagine using a beam so weak that only one photon passes through the screen at a time. In this case, the photon would seem to pass through only one slit at a time, yielding a one-slit pattern.
Which pattern occurs?
Possible Fraunhofer diffraction patterns
Each photon passes through only one slit
Each photon passes through both slits

35. Dimming the light incident on two slits
Dimming the light in a two-slit experiment yields single photons at the screen. Since photons are particles, it would seem that each can only go through one slit, so then their pattern should become the single-slit pattern.
Each individual photon goes through both slits!

36. How can a particle go through both slits?
“Nobody knows, and it’s best if you try not to think about it.”
Richard Feynman

37. Exercises
You are encouraged to solve all problems in the textbook (Pedrotti3).
The following may be covered in the werkcollege on 6 October 2010:
Chapter 11:
1, 3, 4, 10, 12, 13, 22, 27