Advanced Measurement Options

Detector

The detector is a device inside the spectrometer that produces an electrical signal in response to the infrared beam striking it.

The detector setting is updated automatically based on your spectrometer setup.

Nicolet Summit: DTGS.

Nicolet Summit Pro: TEC DTGS.

Optical velocity

Determines the optical velocity in the interferometer. The default value is determined by the type of detector you are using, and can only be changed on certain spectrometers.

On the Nicolet Summit spectrometer, the default value is 0.4747 and cannot be changed.

Zero fill

Interpolates data points between the collected data points. This doesn’t increase the actual resolution of the data, but can smooth out sharp features and improve the line shape of a spectrum.

Collect your sample and background spectra using the same Zero Fill setting.

Options

None: No zero filling is done.

1: One data point is added between each collected data point

2: Three data points are added between each collected data point

2

Source

The component inside the spectrometer that emits the infrared radiation that travels to the detector.

The source type is determined by your spectrometer setup. See your spectrometer user guide for details on the source.

Apodization

Apodization refers to a mathematical function that is applied to the single beam data to reduce or remove peak side-lobes that can occur because the interferogram is not an infinite set of data.

Strong apodization reduces more noise but can also reduce the resolution of the data and broaden peaks.

You may want to consider weaker apodization, such as Boxcar, if you are measuring spectra with very narrow peaks, such as high-resolution gas spectra.

See "Apodization Functions" for a description of each type of apodization.

Norton-Beer Strong

Automatic Atmospheric Suppression

Suppresses the effects of water vapor and carbon dioxide on the spectra you have collected.

In general, it is better to control for atmospheric conditions using a current background spectrum. If you measure the background frequently or if atmospheric conditions change slowly, there is no need to use this feature.

Use this feature only if you measure the background infrequently or when atmospheric conditions change rapidly.

Deselected

Range Limits

Sets the limits for the range of frequencies, in wavenumber, included in the collected spectrum.

Max: 4,000

Min: 400

Aperture

Controls the intensity of the infrared radiation that reaches the sample.

Aperture can only be changed when using spectrometers with adjustable apertures.

In general, larger apertures will result in a better signal-to-noise ratio while smaller apertures result in better stability and accuracy. Small apertures are better for high-resolution measurements.

You may need to use small apertures to acquire true high-resolution spectra.

Scan rejection and peak alignment

During data acquisition, the data may naturally shift slightly. This setting tells the system whether and how to ignore, correct, or reject scans with shifted peaks. 

• None: This setting assumes that there is no shift in the data and scans are treated exactly as they are scanned without any correction. This can sometimes result in poorer quality data or show signs of “peak hop”, where the peak appears to shift. This may be useful for measuring emissions or similar cases where there is no or only a small peak initially.
• Simple: This option is best for most applications. With this setting, the first scan is used as a standard and each new scan is compared to it. If the peak on new scans is close to the position of the original peak, the peaks are aligned, and the data is used. If the peak is shifted too far, the scan is rejected.
• Strong: With this option, the system first checks if the peak is in the correct location and then checks the size of the peak. If the peak is large enough and in the correct position, the system aligns the peak and uses the scan. Otherwise, the scan is rejected.
• Peak alignment only: With this setting, the system aligns the peaks but does not reject any scans. This is useful in mapping applications where parts of the sample surface will correctly show poor data.

Boxcar

The interferogram is unweighted; that is, the data are simply truncated at the beginning and end. Use this type when you are measuring a gas sample, want maximum resolution and are not concerned about ringing effects (side lobes). The greatest amount of ringing will be present with this type.

Cosine

This setting suppresses side lobes and only moderately degrades the resolution of the spectrum. This setting is similar to the Happ-Genzel and Norton-Beer medium apodization. Cosine is normally used only to reproduce the results of other experiments that used it.

Happ-Genzel

Suppresses side lobes more effectively than the Triangular type and with less reduction in resolution than that type. (It results in more reduction in resolution than the boxcar type.)

Norton-Beer Weak

This setting has a less pronounced smoothing effect on data than do the Norton-Beer Medium and Norton-Beer Strong types and degrades the resolution less than those types. Side lobes appear on both sides of peaks and are more pronounced for sharper peaks.

Use this setting only when the best possible resolution is required. This setting is generally not recommended and is normally used only to reproduce the results of other experiments that used it.

Norton-Beer Medium

This type has a smoothing effect on data which is between that of the Norton-Beer Weak and Norton-Beer Strong types. It suppresses side lobes as much as possible given that it only moderately degrades the resolution of the spectrum. The side lobe suppression is more significant than for Norton-Beer Weak apodization. This setting is suitable for most normal samples; it gives results virtually identical to those obtained with Happ-Genzel.

Norton-Beer Strong

Norton-Beer Strong is the recommended apodization for the Nicolet Summit and Summit Pro spectrometers.

This setting has a greater smoothing effect on data than do the Norton-Beer Weak and Norton-Beer Medium types and degrades the resolution of the spectrum more. The side-lobe suppression is more significant than for Norton-Beer Medium apodization.

Triangular

Mathematically weights interferogram data to reduce ringing effects (side lobes), resulting in lower resolution than that obtained with the boxcar and Happ-Genzel types. Some ringing will usually be present with this type. This setting is normally used only to reproduce the results of other experiments that used it.

Blackman-Harris

The 4-term Blackman-Harris function is a strong apodization function that is better than any of the others at suppressing side lobes. However, it results in greater line broadening than any of the others. In practice this has the effect of reducing random noise in a spectrum while causing band broadening.