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Why are lasers used as light sources in Raman spectrometers?

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Lasers are used as light sources in Raman spectroscopy primarily because the Raman effect is an inherently feeble phenomenon; for many compounds, the intensity of the scattered light is only 1/100,000 of the incident beam.1

Using a monochromatic visible laser provides two critical advantages for this technique:

High Intensity: The laser provides the high-intensity incident radiation necessary to produce a detectable signal from the weak scattering process.2
Precision: The monochromatic nature of the laser enables the observation of lines where the frequency shift is small, such as those resulting from rotational changes in a molecule.2

By utilizing a laser, researchers can effectively distinguish the scattered radiation from the incident beam, allowing for the accurate analysis of vibrational and rotational transitions that characterize the molecular species being studied.12