monochromateurs

Monochromateurs, also known as monochromators, are optical devices that isolate a narrow range of wavelengths from a broad light spectrum. They are widely used in spectroscopy and analytical instruments that require wavelength-specific illumination or detection.

Principle and design: A dispersive element such as a diffraction grating or a prism separates light into its component wavelengths. An entrance slit defines the light beam, and an exit slit selects a narrow wavelength band that reaches the detector. By rotating the dispersive element, a chosen wavelength is scanned. Common configurations include Czerny–Turner and Ebert–Fastie designs.

Types and performance: Grating monochromators generally offer higher throughput and wider spectral coverage, while prism monochromators can reduce chromatic aberration in some regions. Double monochromators improve stray-light rejection by blocking unwanted light between stages.

Metrics: Key figures are spectral range, resolving power R = lambda/delta_lambda, and bandwidth delta_lambda. Slit widths, grating line density, and blaze angle influence resolution and signal level. Wavelength calibration uses reference lamps; higher orders may require sorting.

Applications and limitations: Used in UV–Vis, fluorescence, photoluminescence, Raman, and astronomical spectroscopy. Limitations include throughput loss, stray light, and order overlap. Solutions include careful alignment, shielding, and sometimes a double monochromator or filters.

Instruments often feature computer-controlled scanning and data acquisition for rapid spectral measurements.