Today Ch.36 (Diffraction) Next week, Dec.6, Review This week off. hours:

Today Ch.36 (Diffraction) Next week, Dec.6, ReviewThis week off. hours: Th: 2:00-3:15pm; F: 1:00-3:00pmNext week off. hours:Tu:2-3:15pm,W:1-3pm,Th:1-3pmWebct homework is due by Dec.12.Check your Midterm Exams Grades on elearning!

Final Exam: (Ch.21-25, 27-29, 32,33,35,36)

Secs.511-515: December 9, Friday: 12:30-2:30 pmSecs.521-525, 528: December 12, Monday, 8-10 am

Lecture 24 (Ch. 36)

Diffraction1. Huygen’s principle, bending of the rays2. Fraunhofer’s diffraction3. Single slit4.Two slits with a finite width5. Resolution of the lens6. Diffraction grating7.Spectroscopy8. x-ray diffraction9. e diffraction

Huygen’s principle and bending of the rays

1788 – 1827

Augustin-Jean Fresnel

Joseph von Fraunhofer (1787 – 1826)

Single slit diffraction

How to describe the real picture?

Single slit diffraction

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Narrowing of the first fringe with increase of the slit width

Circular hole diffraction

The photographs of four very small sources of light taken made with a circular aperture in front of the lens

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Rayleigh’s criterion for resolution of two point objects: Two objects are barely resolved if the center of one diffraction pattern coincides with the first minimum if the other.

L

DLS

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For a microscop

1842 – 1919John William Strutt, 3rd Baron Rayleigh

Hubble vs Arecibo

Hubble: D=2.4m, nm500Arecibo: D=300m, cm75

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Giant Magellan Telescope (2016)

D1=8.5m, Deq=24m nm500

Interferometry: Arrays of telescopes

Two slits with a finite width

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Diffraction grating

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N-1 minima

With increase of N principal maxima becomes narrower

and their amplitude grows as 2N

Grating spectroscopySpectrum of sunlight produced by a diffraction grating has dark absorption lines due to absorption of the corresponding wavelength by the solar atmosphere. It allows to find out a chemical composition of the solar atmosphere.

x-ray diffraction

Wilhelm Röntgen (1845 – 1923)The 1st Nobel Prize,1901

nm101.0~

Bragg condition

nd sin2

An x-ray scattering pattern of DNA recorded by Rosalind Franklin led Watson and Crick to discovery of the DNA double helix structure

Louis de Broglie (1892 – 1987)

Electromagnetically induced transparency (EIT)

Two undistinguishable absorption passes for light result in cancellation of absorption (transparency).An electron has the wave property. It may be in a superposition of states 1 and 1’. Monohromatic light with a frequency resonant either to one or another atomic transition is absorbed.Bichromatic light containing two resonant frequencies goes through.

11’

1 2

O.K., Y.I.Khanin, JETP, 1986; O.K., P. Mandel, Phys. Rev. A. 1990. theory S.E. Harris, PRL, 1991. experiment

Electromagnetically induced transparency (EIT)Two undistinguishable absorption passes for light result in cancellation of absorption (transparency).An electron has the wave property. It may be in a superposition of states 1 and 1’. A circular polarized light interacts only with 1-2 (or 1’-2) state and absorbed. A linear polarized light interacts with both 1-2 and 1-2’ states and goes through the medium without absorption. To make medium transparent for light with given circular polarization send through the medium simultaneously light with another circular polarization.

The same is true for two beams of different frequenciesWhen the frequency difference coincides with the frequency of the atomic transition 1-1’.

1

1’

2

1

1’

1 2

O.K., Y.I.Khanin, JETP, 1986; O.K., P. Mandel, Phys. Rev. A. 1990. theory S.E. Harris, PRL, 1991. experiment