THE PRACTICE STUDIO
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PRACTICE / Diffraction gratings
A large grating helps only where light reaches it
A grating has 300 lines per millimetre. It must resolve two nearby lines around 600 nm separated by 0.25 nm in second order.
What minimum illuminated width is required under the ideal grating criterion?
Organize the givens & assumptions
- Line density = 300/mm
- λ ≈ 600 nm
- Δλ = 0.25 nm
- Order = 2
Ideal far-field diffraction, normal incidence on a regular transmission grating, equal coherent illumination over the stated width, and vacuum wavelengths in air. Resolution uses the stated ideal Rayleigh criterion; aberrations and detector limitations are neglected.
- A
- B
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- D
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