| 摘要 |
PURPOSE:To suppress noises due to optical standing waves, by making the amplitude of wavelength modulation to be X times the interval of the optical standing wave, which is generated in an optical system. CONSTITUTION:A sawtooth wave signal having a specified period is generated 21 and supplied to a laser 1 as a bias current. The oscillating wavelength of the signal is determined. The oscillating output undergoes A/D conversion 22 and the result is inputted into a ROM 25. The data of the modulating amplitude from the ROM 25 are read. D/A conversion 24 of the data is performed. The result is multiplied 29 by the amplitude of a sine wave from an oscillator 23. The amplitude of the sine wave is changed at every oscillating wavelength. Thus condition, under which X times of the period of the optical standing wave that is generated in an optical system are obtained, is satisfied in all wavelength [X satisfies J2(piXX)=0 and J is a quadratic Bessel function]. The multiplied output and the sawtooth signal are added 26, and the current of the laser 1 is set. As a result, noises due to the optical standing waves, which are generated in a long optical path cell 28 for measuring gas to be measured 2, can be suppressed.
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