| 摘要 |
<p>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 13CO2 concentration and ratio of 13CO2 and 12CO2 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 12CO2 and 13CO2, and a reference cell (122) containing a reference sample of gas having a known concentration of 12CO2 and 13CO2. The laser section employs a distributed-feedback (DFB), single-frequency diode laser emitting at, for example, between 2 to 3 micrometer (νm) to probe molecular absorption lines of 12CO2 and 13CO2. The 2 to 3 νm beam emitted from the laser is split into a sample (124) and a reference path signal. The reference path signal passes through th e 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 12CO2 and 13CO2 absorption lines is selected from the synchronously detected signal and compared to determine relative compound concentrations of 12CO2 and 13CO2 in the breath sample.</p> |
