Polychromator
Encyclopedia
A polychromator is an optical device that is used to disperse light
into different directions to isolate parts of the spectrum
of the light. A prism
or diffraction grating
can be used to disperse the light. Unlike a monochromator
, it outputs multiple beams over a range of wavelength
s simultaneously. Monochromators have one exit slit and one wavelength at a time can pass through that slit. Polychromators have multiple exit slits, each of which allows a different wavelength to pass through it. A detector is placed after each slit so that the light at each wavelength is measured by a different detector. Polychromators are often used in spectroscopy
.
Spectrograph
is a closely related term. Spectrographs generally do not make use of exit slits. Instead, they use a single spatially selective detector (such as photographic film or a charge-coupled device
). Spectrographs are generally used to observe a continuous range of wavelengths, while polychromators are more commonly used to observe several discrete wavelengths, leaving gaps in-between.
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
into different directions to isolate parts of the spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
of the light. A prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
or diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
can be used to disperse the light. Unlike a monochromator
Monochromator
A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input...
, it outputs multiple beams over a range of wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s simultaneously. Monochromators have one exit slit and one wavelength at a time can pass through that slit. Polychromators have multiple exit slits, each of which allows a different wavelength to pass through it. A detector is placed after each slit so that the light at each wavelength is measured by a different detector. Polychromators are often used in spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
.
Spectrograph
Spectrograph
A spectrograph is an instrument that separates an incoming wave into a frequency spectrum. There are several kinds of machines referred to as spectrographs, depending on the precise nature of the waves...
is a closely related term. Spectrographs generally do not make use of exit slits. Instead, they use a single spatially selective detector (such as photographic film or a charge-coupled device
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
). Spectrographs are generally used to observe a continuous range of wavelengths, while polychromators are more commonly used to observe several discrete wavelengths, leaving gaps in-between.
External links
- Palmer, Christopher, Diffraction Grating Handbook, 6th edition, Newport Corporation (2005). http://gratings.newport.com/library/handbook/cover.asp
- Optical systems using plane gratings
- Optical systems using concave gratings