| CPC G01N 21/3504 (2013.01) [G01N 2201/06113 (2013.01); G01N 2201/0636 (2013.01)] | 20 Claims |

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1. A gas detection device, comprising:
a first light source irradiating infrared;
a second light source irradiating visible light;
a low-pass filter transmitting the infrared irradiated from the first light source, reflecting the visible light irradiated from the second light source, and aligning an optical axis of the visible light with an optical axis of the infrared;
a first retroreflector on which the infrared and the visible light having the aligned optical axes are incident;
a first detecting part detecting the infrared reflected by the first retroreflector; and
a scattering body located at a center of the first retro reflector.
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