Author: Dr. Light outside the pass band is usually absorbed in the device. Alternatively, the input light may be delivered through an optical fiber. That way, one obtain substantial flexibility, e. Output The transmitted light is available at the output port, which is also often having the form of a slit, from which relatively divergent light is obtained. In some cases, the output is again coupled into an optical fiber.
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Author: Dr. Light outside the pass band is usually absorbed in the device. Alternatively, the input light may be delivered through an optical fiber. That way, one obtain substantial flexibility, e.
Output The transmitted light is available at the output port, which is also often having the form of a slit, from which relatively divergent light is obtained. In some cases, the output is again coupled into an optical fiber. Design Requirements The design of a monochromator should ideally fulfill a number of requirements; the most fundamental ones are: wide enough wavelength tunability high transmission in the pass band strong attenuation of light with any other wavelengths independence of the center wavelength on the direction or alignment of the input beam Typical devices e.
Their transmission band should depend only weakly on the alignment of the input beam. Additional useful features can be: adjustable bandwidth of the pass band a well defined filter function, e. The input light is focused onto the input slit and therefore divergent after the slit. It is collimated by a curved mirror and hits a diffraction grating , which deflects different wavelength components in slightly different directions. A second curved mirror translates different beam directions into different positions on the exit slit, so that only light in a narrow wavelength region can get through that slit.
One may again collimate that light e. A careful design is needed for suppressing stray light, which is particularly important for applications like Raman spectroscopy. The whole setup is placed in a box, containing additional apertures and black shields not shown in the figure in order to minimize effects of stray light, which might otherwise get to the output in irregular ways.
Such measures are particularly important in cases where very weak light in the presence of intense light at another wavelength needs to be analyzed — for example, in Raman spectroscopy.
In some cases, one needs to use a dual monochromator i. Another solution may be to use a notch filter before the monochromator for attenuating light at the unwanted wavelength.
The diffraction grating is normally placed on a rotational stage; its position determines the center wavelength of the pass band. The rotational stage is often motorized, so that it can be computer-controlled. Some devices have a scale for the rotational position, possibly calibrated in nanometers. Simpler monochromators have a micrometer screw, and the user has to translate its scale readings into wavelength values. Unfortunately, the dependence of pass band wavelength or optical frequency on the rotational angle is nonlinear; that may have to be compensated with software — for example, on a computer or a built-in microprocessor.
Spherical mirrors are actually problematic in conjunction with a large slit height due to their spherical aberrations.
One may therefore either use toroidal collimating mirrors a kind of aspheric optics or curved slits to avoid such problems. Typical achievable wavelength resolutions of such monochromators are about 0. Devices with particularly high resolutions tend to be larger using mirrors with long focal length and a grating with larger area ; they also need to be built with high mechanical and thermal stability.
Within some limits, relatively compact setups can be obtained by folding the beam path. The quality of the diffraction grating can be important for the performance: Its diffraction efficiency determines the power losses.
Depending on the application, a blazed grating or a holographic grating may offer better performance. In that respect, blazed gratings a kind of ruled gratings are better than holographic gratings. Light scattering on the grating should be as weak as possible, because otherwise one obtains some background transmission for any wavelengths. In that respect, holographic gratings are usually best.
One may also suppress effects from additional diffraction orders with an additional prism. Based on these considerations, one can decide which type of diffraction grating is most appropriate for a particular application. Prism Monochromators Similar monochromators as discussed above can be realized with a prism instead of a diffraction grating; the transmission bandwidth is then substantially larger due to the smaller angular dispersion of a prism.
On the other hand, a prism causes lower power losses and can be used in wider wavelength regions, e. Optical Resonators Within a very limited range of optical frequencies, an optical resonator can also serve as a monochromator, transmitting light only in resonance. The width of the usable frequency range is the free spectral range , which depends on the around-trip time of light in the resonator. Applications of Monochromators In the early times of optics, monochromators were often used for obtaining quasi- monochromatic light.
This was of course very inefficient in conjunction with a broadband light source, as required for generating widely tunable monochromatic light. For a fixed wavelength, one could use certain low-pressure gas discharge lamps and transmit one of the prominent emission lines. Nowadays, that application is somewhat less common, because it is often better to use a laser as quasi-monochromatic light source. Still, the principle is used e.
Monochromators are often used in spectroscopy. A common application is in combination with a photodetector ; with such a setup one can record the optical spectrum of a light source by recording the transmitted intensity while scanning the transmission band scanning spectrometer. Without the exit slit, a monochromator may be used in a spectrograph.
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Your question or comment: Spam check: Please enter the sum of thirteen and three in the form of digits! By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. If you later retract your consent, we will delete those inputs. As your inputs are first reviewed by the author, they may be published with some delay. Suppliers APE The principle task of the spectrum slicer or laser monochromator pulseSlicer is to cut out a very narrow spectral part of an ultrashort laser pulse.
Essentially, it acts as a tunable bandpass filter. For example, it can be used as a simple solution for narrowing broadband laser pulses.
It is made by slabs of  oriented Germanium crystals which are inclined towards each other in order to focus down the Bragg reflected beam. A device that can produce monochromatic light has many uses in science and in optics because many optical characteristics of a material are dependent on wavelength. Although there are a number of useful ways to select a narrow band of wavelengths which, in the visible range, is perceived as a pure color , there are not as many other ways to easily select any wavelength band from a wide range. See below for a discussion of some of the uses of monochromators.