GAS SENSOR

PURPOSE:To switch a gas sensor at a high speed so as to improve the gas sensing speed of the sensor by hourly changing modulating signals given to the 1st and 2nd semiconductor laser devices which emits laser light having slightly different wavelengths. CONSTITUTION:Signals having a frequency (f) (Hz) oscillated by an oscillator 5 modulate intensity of laser light emitted from a laser oscillator 1 through a drive device 2. At the same time, the oscillate signals from the oscillator 5 modulate the intensity of another kind of laser light emitted from another laser oscillator 3 through another drive device 4 as signals whose phase is shifted by pi (rad) through a phase modulator 6. The two kinds of laser light of two different wavelengths emitted from the oscillators 1 and 3 are scattered at a scattering section 13 through a half mirror 7 and reflecting mirror 8 and received by a photoreceptor 10 through a condensor lens 9. At the photoreceptor 10 the received two kinds of laser light are converted into electric signals and sent to an amplitude measuring instrument 12 through a BPF 11, where the laser light having different laser intensity distributions and two kinds of wavelengths are synthesized to each other and the amplitude of the synthesized light is measured.