1. Diffraction by N-slits

2. Optical disturbance due to N slits

3. Contribution of j th slit

4. Contribution of N slits

5. Irradiance due to N-slits I 0 = I rradiance by single slit at  =0

6. For principal maxima or

7. For minima Between consecutive principal maxima, there will be N-1 minima

8. Subsidiary maxima (N-2) subsidiary maxima between consecutive principle maxima

9. For large N, irradiance of first subsidiary maxima

10. Diffraction from multiple slits Slit Diffraction Pattern

11. Normal incidence Transmission grating

12. Oblique incidence a

13. For two wavelengths

14. Dispersive power of grating Width of principal maxima

15. Barely resolved ItIt  s  w

16. Chromatic resolving power of a grating

17. Chromatic resolving power of a prism

19. Reflection grating

20. Diffraction grating

21. The nominal track separation on a CD is 1.6 micrometers, corresponding to about 625 tracks per millimeter. This is in the range of ordinary laboratory diffraction gratings. For red light of wavelength 600 nm, this would give a first order diffraction maximum at about 22°.

22. 15  15  0 nm 450 nm Atomic Force Microscope Image of CD

23. Bragg’s law X-ray diffraction from crystals: 2d Sin θ = n λ

24. Phase grating Delta function Bessel function

25. Problem Consider a opaque screen with 5 equally spaced narrow slits (spacing between them is d) and with monochromatic plane wave (wavelength ) incident normally. Draw a sketch of the transmitted intensity vs. angle to the normal for  = 0 to  = 1/5 radian. Take Sin  =  over this range and assume d/ =10. What is the ratio of least intense to the most intense peak? What is the angular distance of the first intense peak away from  = 0.