- Industry: Chemistry
- Number of terms: 265
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The mirror displacement at which the optical path difference for the two beams in an interferometer is zero. At ZPD, ZOPD, the detector signal is often very large, the centerburst.
Industry:Chemistry
An aperture placed in the beam to restrict the divergence to the maximum compatible with the selected resolution. When choosing lower resolution you can improve the S/N by opening the stop. Note that in many instances there is no physically separate stop but there will be some aperture, be it the source size, or the detector active area, that acts as the system J stop.
Industry:Chemistry
The mirror displacement at which the optical path difference for the two beams in an interferometer is zero. At ZPD, ZOPD, the detector signal is often very large, the centerburst.
Industry:Chemistry
1/wavelength, the units of wavenumbers are cm-1, and are most commonly used as the X axis unit in infrared spectra.
1 µm = 1,000 nm = 10,000 cm-1
5 µm = 5,000 nm = 2,000 cm-1
Industry:Chemistry
A spectral manipulation technique where the absorbances of a reference spectrum are subtracted from the absorbances of a sample spectrum. The idea is to remove the bands due to the reference material from the sample spectrum. This is done by simply calculating the difference in absorbance between the two spectra, then plotting this difference versus wavenumber. The reference spectrum is often multiplied by a subtraction factor so that the reference material bands subtract out properly.
Industry:Chemistry
A sampling method where the infrared beam passes through the sample before it is detected. Samples are typically diluted or flattened to adjust the absorbance values to a measurable range.
Industry:Chemistry
A spectral manipulation technique used to reduce the amount of noise in a spectrum. It works by calculating the average absorbance (or transmittance) of a group of data points called the “smoothing window,” and plotting the average absorbance (or transmittance) versus wavenumber. The size of the smoothing window determines the number of data points to use in the average, and hence the amount of smoothing.
Industry:Chemistry
The spectrum that is obtained after Fourier transforming an interferogram. Single beam spectra contain features due to the instrument, the environment, and the sample.
Industry:Chemistry
Spectral features that appear to the sides of an absorbance band as undulations in the baseline. Sidelobes are caused by having to truncate an interferogram, as a result of finite scan distance, and can be removed from a spectrum by multiplying the spectrum’s interferogram by an apodization function.
Industry:Chemistry
