Diffraction Optical Path
Intensity Distribution I(θ) = I₀·[sin(β)/β]²
Simulated Diffraction Pattern on Screen
Diffraction Parameters
Slit Properties
Light Properties
Display Options
Quick Presets
Diffraction Formulas
What is Single Slit Diffraction?
Single slit diffraction is a wave phenomenon where light spreads out after passing through a narrow aperture. Unlike the ray model of light, which would predict a sharp shadow, wave optics predicts that light bends around corners and creates a characteristic pattern of bright and dark fringes on a screen.
Diffraction Mechanism
When a plane wave encounters a single slit of width a, each point in the slit acts as a source of secondary spherical wavelets (Huygens' principle). These wavelets interfere with each other, creating a pattern on the screen. The central maximum is the brightest and widest region where most of the light is concentrated. Secondary maxima appear on either side but are much dimmer (approximately 4.5%, 1.6%, 0.8% of central intensity for the first three orders). Dark fringes (minima) occur where destructive interference cancels the light.
Intensity Pattern
The intensity distribution follows the sinc² function: I(θ) = I₀·[sin(β)/β]² where β = (πa·sinθ)/λ. At θ = 0, β = 0 and using the limit sin(β)/β = 1, we get maximum intensity I₀. Minima occur when β = mπ (m = ±1, ±2, ...), corresponding to angles where a·sinθ = mλ. The central bright fringe has angular width 2λ/a (distance between first minima on both sides). Secondary maxima occur approximately at β ≈ (m + ½)π.
Effect of Slit Width
The slit width a inversely affects the spread of the diffraction pattern: narrower slits produce wider patterns (Δx ∝ 1/a), while wider slits produce narrower patterns. In the limit a ≫ λ, the diffraction becomes negligible and ray optics applies. Conversely, when a ≈ λ, the pattern becomes very wide with pronounced wave behavior. This is a general principle in wave physics: smaller apertures or obstacles cause more diffraction.
Effect of Wavelength
Longer wavelengths (red light) diffract more than shorter wavelengths (blue light), producing wider patterns. This is why Δx ∝ λ. This wavelength dependence is why we see rainbows from CD/DVD reflections (diffraction grating) and why prism effects occur. In white light diffraction, each wavelength creates its own pattern, resulting in colored fringes with red diffracted most on the outer edges.
Applications
Single slit diffraction has numerous applications: measuring the width of thin objects (hair, wire) by analyzing their diffraction pattern, determining the wavelength of unknown light sources, studying crystal structures using X-ray diffraction (though typically with multiple slits/gratings), optical instrument design (telescope and microscope resolution limits), and understanding the fundamental wave nature of light and matter. The diffraction limit determines the maximum resolution of any optical system: resolution ≈ 1.22λ/D for circular apertures.