Spectrometer with multiple Fabry-Perot filters for gas analysis

A method of spectrometric gas analysis, comprising:

• passing a light source through a filter arrangement having a plurality of Fabry-Perot filters arranged behind one another;
• setting the frequency properties of the light by changing the transmission spectrum of the filter arrangement in accordance with a scanning scheme;
• guiding the light into a measurement cell having a gas to be investigated;
• and
• measuring the absorption of the light by the gas in the measurement cell,
• wherein the absorption is measured a plurality of times after a respective adjustment of at least one of the plurality of Fabry-Perot filters and is thereby measured a plurality of times with light of different frequency properties, the scanning scheme providing a respective transmission spectrum having a narrow band maximum at a scanning frequency, modulating the amplitude of the narrow band maximum at the scanning frequency over a plurality of cycles, and systematically varying the scanning frequency in order to successively evaluate a spectrum at different frequencies with a lock-in-method based on the known modulation.