The slit resolution of a monochromator refers to the ability of the monochromator to resolve or distinguish between different wavelengths of light. It is determined by the width of the entrance and exit slits in the monochromator. Slit resolution is usually measured in nm.

When light passes through the entrance slit of a monochromator, it is narrowed down into a beam. This narrow beam of light then interacts with a dispersing element (such as a diffraction grating or a prism) that separates the different wavelengths. After dispersion, the light exits through the exit slit, which is also typically narrow.

The resolution of the monochromator is determined by the width of these slits. A narrower slit allows the monochromator to separate closely spaced wavelengths more effectively, resulting in higher resolution.