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Diffraction by N-slits

Diffraction by N-slits. Optical disturbance due to N slits. Contribution of j th slit. Contribution of N slits. Irradiance due to N-slits. I 0 = I rradiance by single slit at q =0. For principal maxima. or. For minima. Between consecutive principal maxima, there will be N-1 minima.

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Diffraction by N-slits

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  1. Diffraction by N-slits

  2. Optical disturbance due to N slits

  3. Contribution of jth slit

  4. Contribution of N slits

  5. Irradiance due to N-slits I0 = Irradiance by single slit at q=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. Slit Diffraction Pattern Pattern Diffraction from multiple slits

  11. Normal incidence Transmission grating

  12. Oblique incidence a

  13. For two wavelengths

  14. Width of principal maxima Dispersive power of grating

  15. Barely resolved (Dq)s It (Dq)w

  16. Chromatic resolving power of a grating

  17. Chromatic resolving power of a prism

  18. Reflection grating

  19. Diffractiongrating

  20. 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° .

  21. Atomic Force Microscope Image of CD 450 nm 0 nm 15m  15m

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

  23. Phase grating Bessel function Delta function

  24. Problem Consider a opaque screen with 5 equally spaced narrow slits (spacing between them is d) and with monochromatic plane wave (wavelength l) incident normally. Draw a sketch of the transmitted intensity vs. angle to the normal for q = 0 to q = 1/5 radian. Take Sinq = q over this range and assume d/l =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 q = 0.

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