A Raman spectrophotometer has four key components: a laser source, a sample holding system, a wavelength selector, and a detector.

The laser source emits a focused beam of monochromatic light, typically in the visible or near-infrared range, some of which is scattered by molecules in the sample.

Samples can be in various forms, including liquid, solution, transparent solid, powder, pellet, or gas.

The scattered light is collected and directed through a monochromator, excluding all but selected individual wavelengths. 

Optical band-rejection—or 'notch'—filters remove light from stray laser radiation and Rayleigh scattering that may interfere with the Raman signal.

Fiber-optic Raman spectrometers, in particular, use high-quality bandpass and notch filters to minimize the Rayleigh-scattered radiation that reaches the detector.

The detector—often a charge-coupled device or photomultiplier tube—converts the optical signal into an electrical one, producing a Raman spectrum.

Fourier-transform Raman instruments employ a continuous-wave laser source along with a Michelson interferometer instead of a monochromator, with the radiation focused onto a cooled photodiode for analysis.