Calibration and Data Processing

Raman spectroscopy has been revolutionised in the past 10 years by the advent of new photon detectors and the increasing use of microprocessors and minicomputers to perform Raman data collection and processing. The aim of this Chapter is to set out in a systematic fashion the important aspects of data handling. Digital computers are used exclusively today, therefore, the first consideration should be to establish how accurately analogue-to-digital convertors can represent real photon data and how this influences subsequent treatment of that data. The question of wavelength or frequency calibration is also relevant, particularly to Raman spectral data sets recorded using array detectors. The Raman spectroscopist has many favourite ‘standard’ materials that are used to check instrument resolution and accuracy, but measurements of instrumental throughput and the polarising effects of gratings and slits are often ignored. Fortunately, digital methods can facilitate the normalisation of individual spectra and it should now be possible to compare the spectra from different Raman instruments easily and successfully. Once a Raman spectrometer or spectrograph’s complete instrument function has been measured, it becomes possible to apply very powerful data fitting, estimation and filtering techniques to extract as much information from a Raman spectrum as possible.

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