A spectrometer including a source emitting an electromagnetic radiation, a selection device configured for selecting a monochromatic radiation based on the electromagnetic radiation, a focusing device configured for defining a focusing point associated with a wavelength of the electromagnetic radiation emitted by the source and configured for displacing the focusing point with respect to an input of the selection device, a vessel containing a sample intended to receive the monochromatic radiation, and an analyzer of a radiation transmitted or emitted by the sample.