Optical cavity for gas sensor and gas sensor having the same

An optical cavity for a gas sensor having a space defined therein, comprising:

• a first parabolic reflective surface formed on one wall surface in the space;
• a second parabolic reflective surface which is formed at a position facing the one wall surface, and is configured to reflect again a light emitted from a light source disposed at a focus of the first parabolic reflective surface and reflected by the first parabolic reflective surface so as to change a traveling path of the light;
• and a hyperbolic reflective surface formed so that any one focus of two foci coincides with a focus of the second parabolic reflective surface, and is configured to reflect the light made incident from the second parabolic reflective surface to change the traveling path of the light, wherein, when a value of a vertex in an x-axis direction of a hyperbola forming the hyperbolic reflective surface is a, a value of the focus is c, and a value of a vertex in a y-axis direction is b (b=a), a value of c2−b2 of a hyperbola represented by Equation below is in a range of 0<c2−b2<4 mm
• y
• =
• (
• b
• 2
• c
• 2
• -
• b
• 2
• )
• ⁢
• x
• 2
• -
• b
• 2
• .