Two Slit Interference
The double-slit intensity pattern: interference fringes inside a single-slit diffraction envelope, on a constant background. Use it for light intensity measured across a two-slit pattern.
Parameters
- Intensity at the center of the pattern, above the background.
- Envelope parameter: the envelope’s first zeros are at xₒ ± π/k₁.
- Fringe parameter: neighboring bright fringes are π/k₂ apart.
- Center of the pattern.
- Constant background.
Tips
- Here sinc(u) = sin(u)/u.
- The automatic starting values for k₁ and k₂ are fixed numbers, not estimates from your data. Enter guesses from the pattern: k₂ ≈ π divided by the fringe spacing, and k₁ ≈ π divided by the distance from the center to the first zero of the envelope.
- For small angles, with x the position on a screen a distance L from the slits, k₁ = πa/(λL) and k₂ = πd/(λL), where a is the slit width, d the slit separation and λ the wavelength.