90 years ago Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan first documented "A New Type of Secondary Radiation," which then became known as the Raman Effect [1, 2]. Raman spectroscopy is based on this effect and is used for qualitative and quantitative analysis of the chemical components and molecules of a sample. It is a nondestructive method that requires little, if any, sample preparation.
Nevertheless, Raman spectroscopy long remained a technique that was only performed in special laboratories. In recent years, however, it has been increasingly losing its outsider status. The reason for this is the development of the confocal Raman microscope, with which not only individual Raman spectra, but also complete images generated from thousands of spectra can be acquired. Through continuous development, commercially-available Raman microscopes are also becoming more user-friendly. For example, modern software interfaces guide the user through the Raman measurement and the subsequent data analysis.
There are several key factors that can be used as criteria for determining the quality of confocal Raman microscopes.
While in the past exposure times of minutes to hours were common for acquiring single Raman spectra, today these times are generally fractions of a second to less than one millisecond. In one second more than 1000 Raman spectra can be recorded. Thus a Raman image can be generated within a few minutes. To achieve this acquisition speed, the Raman imaging system should be equipped with optimized optics and an EMCCD camera.
High acquisition speeds are particularly important for measurements on sensitive and valuable samples in which the excitation energy must be as low as possible. Time-resolved investigations of dynamic processes can also benefit from rapid Raman spectral acquisition. Operating costs can also be reduced by shorter analysis times concurrent with increased data rates. Having a high system speed is also advantageous for time-critical work.
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