A photo acoustic trace gas detector (100) is provided for detecting a concentration of a trace gas in a gas mixture. The detector (100) comprises a light source (101) for producing a light beam and a light modulator (103) for modulating the light beam into a series of light pulses at a chopping frequency for generating sound waves in the gas mixture. The amplitude of the sound waves is a measure of the concentration of the trace gas. The detector (100) further comprises an optical cavity (104a, 104b) with the gas mixture. The optical cavity (104a, 104b) amplifies the light intensity of the light pulses. A transducer (109) converts the sound waves into electrical signals. A feed back loop (110, 111, 113, 114) regulates a ratio of a length of the optical cavity (104a, 104b) and a wavelength of the light beam for amplifying the light intensity of the light pulses in the optical cavity (104a, 104b). The feedback loop (110, 111, 113, 114) comprises ratio modulating means (113, 114) for modulating the ratio at a modulation frequency, a photo detector (110) for measuring the light intensity of the light pulses and adjusting means (111), coupled to the photo detector (100) and to the ratio modulating means (113, 114) for, in dependence of the measured light intensity, adjusting an average of the ratio. The chopping frequency is higher than the modulation frequency.
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机译：提供了光声痕量气体检测器（ 100 ），用于检测气体混合物中痕量气体的浓度。检测器（ 100 ）包括用于产生光束的光源（ 101 ）和用于调制光束的光调制器（ 103 ）产生一系列斩波频率的光脉冲，以在混合气体中产生声波。声波的幅度是痕量气体浓度的量度。探测器（ 100 ）还包括一个光学腔（ 104 a， 104 b ）与混合气体。光学腔（ 104 a， 104 b ）放大光脉冲的光强度。换能器（ 109 ）将声波转换为电信号。反馈回路（ 110、111、113、114 ）调节光腔长度（ 104 a， 104 b ）和用于放大光腔中光脉冲的光强度的光束波长（ 104 a ，104 b ）。反馈回路（ 110、111、113、114 ）包括用于以调制频率调制比率的比率调制装置（ 113、114 ），光电检测器（ 110 ），用于测量光脉冲的光强度和调整装置（ 111 ），该装置与光电检测器（ 100 ）和比率调制装置（ 113、114 ），用于根据测得的光强度调整比率的平均值。斩波频率高于调制频率。
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