| 摘要 |
PURPOSE:To measure the concentration of gas at a relavtively high speed with high precision by superposing a modulated current having a lower frequency than a fine sine wave current on light from a semiconductor laser in addition to a DC current and the fine sine wave current, and making a wavelength scan with the modulated current of low frequency. CONSTITUTION:The power source 2 of a laser diode 1 is controlled by a DC power source 3, power source 4 for wavelength scanning, and power source 5 for differential modulation. Laser light 6 is absorbed by a specific gas 7 and inputted to a detector 8. The reception signal of the detector 8 is inputted to a phase detector 10 through a filter 9 which passes only the higher harmonic 2f1 of frequency twice as high as a modulation frequency f1, and phase-detected with the synchronizing signal of the power source 5. The phase-detected signal is supplied to a phase detector 12 through a filter 11 which passes the higher harmonic 2f2 of frequency twice as high as a frequency f2 for wavelength scanning and phase- detected with the synchronizing signal of the power source 4. The phase-detected signal is passed through a smoothing filter 13 and outputted as a signal 14 proportional to the concentration gas. Thus, the gas concentration is measured at a relatively high speed with high precision. |
