| 摘要 |
A diode laser-based trace-gas monitor system (100) accurately measures molecular content and a ratio of molecular content for a trace-gas in a gas sample. A particular monitoring system measures <13>CO2 concentration and ratio of <13>CO2 and <12>CO2 in a breath sample with a sensitivity of approximately one hundred parts per billion. The system includes a sample acquisition section, a cell section, a laser section and a detector section. The sample acquisition section includes a pump (128) and two valves (V1, V2) under the control of a processor. The sample acquisition section causes a sample cell (124) to be filled with a breath sample from a breath-input stream (132). The cell section includes the sample cell containing the sample of breath to be measured for concentrations of <12>CO2 and <13>CO2, and a reference cell (122) containing a reference sample of gas having a known concentration of <12>CO2 and <13>CO2. The laser section employs a distributed-feedback (DFB), single-frequency diode laser emitting at, for example, between 2 to 3 micrometer ( mu m) to probe molecular absorption lines of <12>CO2 and <13>CO2. The 2 to 3 mu m beam emitted from the laser is split into a sample (124) and a reference path signals. The reference path signal passes through the reference cell, and then detected for calibration. The sample path signal passes through the sample cell and modulation from molecular absorption is synchronously detected. A pair of <12>CO2 and <13>CO2 absorption lines is selected from the synchronously detected signal and compared to determine relative compound concentrations of <12>CO2 and <13>CO2 in the breath sample.
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