Gas detection apparatus

A gas detection apparatus comprising:

• a light emitting part;
• a light receiving part;
• and
• a light guiding part for guiding light from the light emitting part to the light receiving part, wherein
• a shape of at least a part of an inner surface of the light guiding part is composed of all or a part of n (n:
• one or more natural numbers) ellipsoids, and when:
• then ellipsoids are defined as ellipsoids E1, E2, . . . , E(n-1) and En;
• an ellipse having a maximum area in a cross-section of an ellipsoid Ei (i:
• a natural number satisfying 1≤i≤n) is defined as an ellipse Eci;
• an ellipsoid that passes through two focal points Fai and Fbi of the ellipse Eci and has a minimum volume having a scaling relationship with the ellipsoid Ei without being rotated is defined as an ellipsoid Esi;
• a region inside the ellipsoid Ei and not including the ellipsoid Esi is defined as a region Ri;
• the ellipsoid Ei including a light source region of the light emitting part is defined as an ellipsoid Es;
• the ellipsoid Ei including a light receiving region of the light receiving part is defined as an ellipsoid Ed;
• the region Ri of the ellipsoid Es is defined as a region Rin;
• and
• the region Ri of the ellipsoid Ed is defined as a region Rout;
• 60% or more of the light source region is present in the region Rin and 60% or more of the light receiving region is present in the region Rout,
• wherein the inner surface of the light guiding part is reflective;
• wherein, when a maximum length of the light source region is defined as Ls and a maximum length of the ellipsoid Es is defined as Lms, Ls≥Lms/50;
• and wherein, when a maximum length of the light receiving part is defined as Ld and a maximum length of the ellipsoid Ed is defined as Lmd, Ld≥Lmd/50.