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Optical Spectrometers
Introduction
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.
Monochromator designs
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.
Monochromator parameters
- Bandpass
- The wavelength range that the monochromator transmits.
- Dispersion
- 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.
- Resolution
- 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.
Related instruments
- Spectrograph
- A spectrometer that records a wide bandpass with a photographic
plate or an array detector. The spectrometer requires a flat
image field.
- Polychromator
- A spectrometer with multiple detectors for simultaneous detection
of multiple analytes.
Related Topics