A spectrometer is an optical system that transmits a specific band of electromagnetic spectrum. Dispersion of different wavelengths is accomplished with the separating capability of refraction (prism) or diffraction (diffraction grating). Typical applications are isolation of a narrow band of radiation from a continuum light source for absorption measurements, or analysis of the emission from excited atoms or molecules.
A typical monochromator design is shown below. It consists of the diffraction grating (dispersing element), slits, and spherical mirrors.
Schematic of a Czerny-Turner monochromator
Scanning is accomplished by rotating the grating.
- The wavelength range that the monochromator transmits.
- The wavelength dispersing power, usually given as spectral range / slit width (nm/mm). Dispersion depends on the focal length, grating resolving power, and the grating order.
- The minimum bandpass of the spectrometer, usually determined by the aberrations of the optical system.
- Acceptance angle (f/#)
- A measure of light collecting ability, focal length / mirror diameter
- Blaze wavelength
- The wavelength of maximum intensity in first order.
- A spectrometer that records a wide bandpass with a photographic plate or an array detector. The spectrometer requires a flat image field.
- A spectrometer with multiple detectors for simultaneous detection of multiple analytes.
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Copyright © 1996 by Brian M. Tissue