Optical cavity-enhanced photo acoustic trace gas detector with variable light intensity modulator

A photo acoustic trace gas detector (100) for detecting a concentration of a trace gas in a gas mixture, the photo acoustic trace gas detector (100) comprising

• a light source (101) for producing a light beam,
• a light modulator (103) for modulating the light beam into a series of light pulses for generating sound waves in the gas mixture, an amplitude of the sound waves being a measure of the concentration,
• an optical cavity (104a, 104b) for containing the gas mixture and for amplification of a light intensity of the light pulses,
• a transducer (109) for converting the sound waves into electrical signals, and
• a feed back loop (110, 111) for regulating the amplification of the light intensity of the light pulses in the optical cavity (104a, 104b), the feedback loop (110, 111) comprising a photo detector (110) for measuring the light intensity of the light pulses, characterized in that
• the light modulator (103) is arranged for modulating the light beam between a non-zero lower intensity level and a higher intensity level.