singleslit

Single-slit refers to the diffraction pattern produced when a plane wave of light passes through a narrow slit. The resulting intensity distribution on a distant screen consists of a central bright maximum flanked by progressively fainter secondary maxima and minima. The pattern is a fundamental example of Fraunhofer diffraction and is well described by the scalar diffraction theory for a rectangular aperture.

The angular intensity profile is given by I(θ) = I0 (sin β / β)^2, where β = π a sin θ / λ, a is the slit width, and λ is the light wavelength. Minima occur where sin β = 0 with β ≠ 0, i.e., a sin θ = m λ for m = ±1, ±2, … The central maximum spans roughly from −λ/a to +λ/a in angle (small-angle approximation: θ ≈ sin θ). As the slit becomes wider (larger a), the central maximum narrows and the overall pattern sharpens; conversely, a narrower slit broadens the pattern and reduces light throughput.

Physically, the pattern arises from the coherent superposition of light from across the slit; the shape is the Fourier transform of a rectangular aperture. In practical terms, the single-slit pattern sets a fundamental limit on the angular resolution of optical instruments, and slit width is a key parameter in spectroscopy and imaging, balancing spectral or spatial resolution against light throughput.

Historically, single-slit diffraction helped establish the wave nature of light and remains a standard demonstration in optics.