Physics 6805: Diffraction 101

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Recent changes to this page:

• 21-Aug-2017 --- Revised 2017 version from LaTeX version.

Contents

• Diffraction 101 (review?)
• Intensity as a Function of Angle
• Diffraction from a circular hole
• Diffraction and resolution
• Wavelength and resolution
• Consequences
• Quantum Mechanics and Resolving Power

Slides

Diffraction 101 (review?)

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Intensity as a Function of Angle

Single-slit diffraction: first minimum when sin θ_min = λ/a ⇒ pattern widens as λ increases.

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Diffraction from a circular hole

The diffraction pattern of a circular hole of diameter d is similar to that of a single slit of width a. The bright spot in the middle is the Airy disk. It has about 85% of the power in the pattern. Minima are at:
sin θ₁ = 1.22 λ/d
sin θ₁ = 2.23 λ/d
sin θ₁ = 3.24 λ/d

What is the diffraction pattern from a solid disk? (Hint: Babinet)

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Diffraction and resolution

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Wavelength and resolution

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Consequences

   

For a slit of width a, θ_min = sin^-1(λ/a), so if λ>a, you don't learn anything about the details of the slit.

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Quantum Mechanics and Resolving Power

    

The de Broglie relation is λ = h/p.
For λ≈10^-10m ⇒ probe atoms
For λ≈10^-14m ⇒ probe nucleus
For λ≈10^-18m ⇒ probe quarks

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