Theoretical background: Spectrometers
All AvaSpec spectrometers have no moving parts inside and are in nature extremely robust and stable.
The thermal stability of our spectrometers is part of our comprehensive Quality Control procedure and therefore closely monitored during the production and assembly process. All of our spectrometers undergo overnight thermal cycling, during which wavelength shift, intensity drop and spectral tilt are registered and checked against our QC acceptance norm.
More specifically, the following test are being carried out during the thermal cycling from 15°C to 25°C to 35°C back to 25°C:
Full Width Half Maximum
During the thermal cycling the average FWHM value is measured and has to fit with a certain standard deviation within the QC acceptance norm as can be found in this catalog for the different configurations.
During thermal cycling the shift of peaks is monitored and depicted as shift in pixels per °C.
Depending on the grating angle the maximum allowed peakshift is defined, for most gratings the below values are the QC acceptance norm. For gratings with many lines/mm starting at high wavelengths (VD, VE), the peak shift can double.
The max allowed peakshift =± 0.1 pixel per °C for an AvaSpec-ULS2048 with a pixel pitch of 14μm. Average peakshift is ± 0.04 pixel per °C for an AvaSpec-ULS2048
For an AvaSpec-ULS3648 with a pixel pitch of 8μm the max allowed peakshift is ± 0.17 pixel per °C.
For the AvaSpec-128 and for the AvaSpec-NIR256 with relative large pixels of 50μm the peakshift is limited to ± 0.03 pixel per °C.
For backthinned and NIR detectors with a 25μm pitch as in the AvaSpec-HS1024x58/122 and AvaSpec-NIR512 the peakshift is limited to ± 0.06 pixel per °C.
Intensity stability and Spectral tilt
Temperature sensitivity on the intensity axis can have a number of reasons. First the CCD detector itself has a temperature dependency, for most detectors there are black pixels that are read out and are subtracted from the rest of the data pixels, the so-called Correct for Dynamic dark (CDD). However, CDD will not correct for spectral tilt, which is partially also a detector property. The aluminum optical bench and the optical components are engineered in such a way that the thermal expansion does not lead to large increase in tilt or sensitivity.
For most spectrometers the average intensity increase/decrease is within ±4% for ± 10°C thermal cycling.
In the figure a typical test result for a thermal cycling can be seen.