tecan infinite 200 Instructions For Use Manual page 68

5. Optical System
Description of how a Monochromator Works
Fiber Optic Bundle
Flash Monitor
68
A monochromator is an optical instrument that enables any wavelength to be
selected from a defined optical spectrum. Its method of operation can be
compared to a tunable optical filter, which allows both the wavelength and
bandwidth to be adjusted.
A monochromator consists of an entrance slit, a dispersive element and an exit
slit. The dispersive element diffracts the light into the optical spectrum and
projects it onto the exit slit. A dispersive element can be realized by using a glass
prism or an optical grating. Modern monochromators such as those used in the
®
are designed with optical gratings.
infinite M200
Rotating the optical grating around its vertical axis moves the spectrum across
the exit slit and only a small part of the spectrum (band pass) passes through the
exit slit. This means that when the monochromator entrance slit is illuminated with
white light, only light with a specific wavelength (monochromatic light) passes
through the exit slit. The wavelength of this light is set by the rotation angle of the
optical grating. The bandwidth is set by the width of the exit slit. The bandwidth is
defined as full width at half maximum (FWHM).
Monochromators block undesired wavelengths, typically amounting to 10
means when the monochromator is set for light with a wavelength of 500 nm and
the detector detects a signal of 10,000 counts, light with different wavelengths
creates a signal of only 10 counts. For applications in the fluorescence range, this
blocking is often not sufficient, since the fluorescence light to be detected is
usually much weaker than the excitation light. To achieve a higher level of
blocking, two monochromators are connected in series, i.e. the exit slit of the first
monochromator acts as the entrance slit of the second monochromator
simultaneously. This is known as a double monochromator. In this case, the
blocking count reaches a factor of 10
filters.
®
In the , a double monochromator is installed on both the excitation
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and detection side. This opens the opportunity for easy selection of excitation and
fluorescence wavelengths with no limitations by cut off filters.
From the exit slit of the Excitation Monochromator the light will be coupled into a
fiber optic bundle guiding the light either to the top measuring optics or the bottom
measuring optics (see 5.1). The lower end of each fiber bundle acts as a color
specific light source. In both cases a small portion of the light is always guided to
the flash lamp monitor diode.
The light energy of single flashes may fluctuate slightly. To take these variations
into account, a silicon photodiode monitors the energy of every single flash.
Fluorescence and Absorbance measurement results are compensated
correspondingly.
Instructions for Use for infinite® 200 No. 30017581 Rev. No. 1.4
6
, a value typically achieved by Interference
3
. This
2008-07