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


Further Information


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Copyright © 1996 by Brian M. Tissue

updated 2/21/96