Miniaturized spectrometer

Miniaturized spectrometer in the form of a probe for determination of the ingredients of a gaseous or liquid fluid with a light source (3) and a detector (2), with at least one measurement partial beam and at least one reference partial beam, characterized by the fact that the light of the light source (3) is optionally fanned out and focused, by means of at least one optical lens (8), into a substantially parallel beam, that at least one measurement partial beam is passed through a light-transparent window from the probe into the fluid being investigated and through an additional light-transparent window back into the probe, that at least one reference partial beam is guided in the probe interior, that a collecting optics device (14), comprising at least one lens, diverts the beams to the impingement point of a light guide (5) or an inlet of the detector (2), and that a beam selector (7, 7′) is provided in the area of the collecting optics (14) and passes through one of the partial beams and interrupts all the others.