Buchi NIRMaster Essential, Руководство по эксплуатации

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Büchi Labortechnik AG
Product description | 3
Operation Manual NIRMaster™ 11/46
3 Product description
3.1 Description of function
The instrument is a benchtop Fourier Transformation Near Infrared spectrometer
(FT-NIR) to identify and quantify analytes of interest. It generates an invisible near
infrared interferogram beam which interacts with the mole- cules of a sample,
generating a characteristic feedback. The feedback is picked up via a measurement
cell by a detector and mathematically processed via Fourier transformation into a
spectrum. This spectrum is charac- teristic for a given sample and allows
identification as well as quantification of its components.
How the interferogram is generated
An interferogram is an interference pattern of phase-shifted beams. The instrument
is a single-beam polarization interferometer, generating its interferogram in four
steps:
1. Polarization of the light source output
The polarizer
2
generates a well-defined polarization output of the undefined
polarized light, emitted by the light source
1
. Thus, only diagonally polarized
light is transmitted.
2. Beam splitting and orthogonal polarization
The polarized light enters a double refracting block (comparator)
3
. Here, the
light is broken down into two, orthogonally polarized components with a small,
static phase shift.
3. Generating the ongoing phase shift
An assembly of two double refracting wedges is arranged after the comparator.
Wedge
4
is stationary, while wedge
5
is constantly shifted back and forwards
by a fast linear-drive. The movement and the geometric arrangement provides a
change of thickness in the light path. This leads to an ongoing phase shift
between the light beams.
4. Beam recombination and interferogram output
A second polarizer
6
converts the phase shifted beams into a single light output
with intensity variation – the interferogram