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Double Slit Fringe Spacing Calculator
Calculate double-slit fringe spacing in the far-field small-angle approximation. Choose input units and calculate one value within the stated conditions.
Inputs
Calculations run in this browser. Scientific notation such as 1.2e-3 is supported. Do not group thousands.
Result
Adjacent bright fringe spacing Δy
Enter values and select Calculate.
Δy ≈ λL/d
Assumptions
Required: positive inputs, monochromatic coherent light, d≫λ and L≫d in the far-field small-angle limit. Slit-width envelope, diffraction intensity and near-field patterns are excluded.
Displayed values are floating-point approximations. Design safety factors and unprovided error contributions are not calculated.
Formula references and credits
NaNa Lab created the code, descriptions, icons and preview images. Text, figures and code from the linked references have not been reproduced.
Physical constants: NIST / CODATA 2022. The values of μ₀ and ε₀ are measured recommendations, not exact defining constants. Values and precision notes are in the source record.
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