Flat-Field Calibration - Redback RS40k User Manual

6.4.8 Flat-Field Calibration

Spectrometers, like any optical instrument, can have non-uniformities in their detector
array and optical system. These non-uniformities can lead to variations in sensitivity
across different wavelengths or regions of the detector. Flat-field calibration helps to
compensate for these non-uniformities by normalising the response of the device
across the entire wavelength range. A complete data set acquired with the RS40k
spectrometer includes a science frame with real data, a flat-field (i.e. white-light) frame,
and a dark frame. The following steps describe how you acquire and process the data:
1. Switch off the light source or cover the single-mode fibre input.
2. Acquire an exposure with the same settings (exposure time, etc.) that will be
used for your measurement.
3. Click the Set Dark button in the toolbar.
4. Uncover the fibre and take an image of a broad-band light source, preferably use
a tungsten-quartz lamp (e.g. Thorlabs SLS201L or similar).
5. Acquire an exposure with an exposure setting lower than the overexposure limit
(typically around 170 kcounts at 650 nm). Stay below the exposure limit over the
entire range (→ observe overview plot).
6. Click the Set Flat button in the toolbar once the white-light spectrum is acquired.
After the dark and white-light frames have been set, the Show Flattened toolbar button
can be toggled to automatically flatten then spectrum any recorded science spectra.
Figure 15: Subtract Dark and Show Flattened icons simultaneously activated.
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