| 摘要 |
<p>A photo acoustic detector for detecting a concentration of a sample in a sample mixture, the photo acoustic detector has a light source for producing a light beam for exciting molecules of the sample, a light modulator for modulating an intensity of the light beam for generating pressure variations in the sample mixture, an amplitude of the pressure variations being a measure of the concentration of the sample, and an acoustic cell with an acoustic resonator for amplifying the pressure variations. Furthermore, the photo acoustic detector has a resonant pickup element for converting the pressure variations inside the acoustic resonator into a detector signal, and a processing section for processing the detector signal to generate 1) a sample signal caused by the pressure variations, and 2) a background signal caused by direct excitation of the pickup element by the light beam. The acoustic cell and the pickup element are arranged in such a way that a phase difference between the background signal and the sample signal is close to 90 degrees.</p> |
