Slitsbredden

Slitsbredden, in optics, is the width of a slit used to produce or sample a light beam. In many optical experiments, a slit with width a controls the angular distribution of diffracted light. In the Fraunhofer regime, the single-slit diffraction pattern on a screen shows minima at angles θm given by a sin θm = m λ, where λ is the wavelength of light and m is an integer not zero. The central bright region (central maximum) spans roughly 2 λ / a in small-angle approximation. The intensity envelope across the diffraction pattern is I(θ) = I0 [sin(π a sin θ / λ) / (π a sin θ / λ)]^2.

In practical instruments, changing slitsbredden changes resolution and light throughput. A smaller width yields a narrower diffraction envelope, improving spectral or angular resolution but reducing the total light and raising the minimum detectable signal. A larger width increases illumination and throughput but broadens features and can smear closely spaced spectral lines. In rectangular apertures, the full diffraction pattern is the product of two one-dimensional sinc-squared patterns; for a slit, one dimension corresponds to a sin θ, the other is effectively unbounded if the slit is tall.

Measuring and setting slitsbredden is common in laboratory optics and spectrometry, using precision micrometers or motorized slits. The concept is also important in astronomy, where slit width affects spectral resolution of slit spectrographs and the amount of light captured from faint sources.