Linear dispersion (LND), often referred to as spectral resolution, determines the wavelength range that passes through the exit slit of a monochromator. The dispersion power depends on the monochromator’s focal length (f) and the groove density of the diffraction grating (d). The exact value of LND is characteristic of each selected wavelength (λ₀) and is influenced by the grating angle (β) and the monochromator’s construction angle (α). Linear dispersion is typically expressed in nm/mm, representing the spectral width (Δλ) that passes through a 1 mm-wide exit slit.
This means that if a linear detector with a width of 30 mm is installed at the exit slit of the MO 250 monochromator, and the selected central wavelength (λ₀) is 550 nm, the captured spectral width will depend on the groove density of the diffraction grating used. The corresponding spectral range isdetermined as follows:
- 300 grooves/mm λmin – λmax = 354 – 746nm
- 600 grooves/mm λmin – λmax = 450 – 650nm
- 1200 grooves/mm λmin – λmax = 500 – 600nm
