In our spectrometers, the Raman spectrum illuminates a linear array detector with 2048 pixels. When the software reads data from the spectrometer, it gets an intensity for each pixel. But Raman spectra are described in relative wavenumbers. In order to find the relationship between pixel number and wavenumber, we use a reference material. The system comes with a polystyrene cartridge with a well-known Raman spectrum. When you perform calibration, you are providing the software with the information needed to match pixel to wavenumber for proper spectral analysis.

Calibration should be performed any time the system is moved, and especially if it has experienced significant vibration or motion (an airplane, for example). The detector array can move slightly requiring realignment of the pixel to wavenumber relationship.