1. diffraction (Physical optics)
Chapter 36
diffraction (Physical optics)

2. Single slit Diffraction

3. Wavelength dependence
Longer wavelength, larger diffraction

4. Near-Field and Far-Field
Fresnel diffraction (near-field):
Source, obstacle, screen are all close to each other.
Fraunhofer diffraction (far-field):
Source, obstacle, screen are far from each other. Light rays can be considered parallel to a good approximation. This is the case we will study.

5. Intensity of Diffraction

6. Characteristic of diffraction
Central peak twice as wide

7. Angular width

8. Minima

9. Find the dark fringe

10. Find the slit width

11. Diffraction through a circular aperture

12. Resolvability for different α
Cannot be resolved
Can be resolved

13. Large angular separation
Can resolve the two stars easily α

14. Small angular separation
Cannot resolve the two stars α

15. Rayleigh’s Criterion α
Just able to resolve the two stars when the maximum falls directly on the first minimum α

16. Resolvability (Resolving Power)

17. Different Aperture

18. Example θR

19. Diffraction Grating (Multiple Slits)

20. Diffraction Gratings
Peaks much narrower than a double slit. N is the total number of slits.

21. Different number of slits
The width of the peaks decreases as N increases.

22. Different colors (wavelength) diffract differently

23. Example: White light on a Grating
Find the angular spread of the first order bright fringe when white light falls on a diffraction grating with 600 slits per millimeter. The wavelengths of the visible spectrum are approximately 400nm (violet) to 700nm (red).

24. X-ray Diffraction
X-rays is an EM waves with very short wavelength (λ ≈10-10m). This is about the same as the separation between some crystalline solid.

25. Conditions for constructive interference

26. Deriving the intensity for a Grating

27. Derivation (Cont.)