Spectroscopic apparatus and gas detection apparatus

A spectroscopic apparatus comprising:

• a light source that outputs near-infrared light;
• an optical cavity that has a pair of opposing reflectors and can supply a gas to be measured between the reflectors, and in which incident light from the light source is introduced into between the reflectors;
• and
• a photodetector that detects intensity of emission light from the optical cavity for each wavelength,
• wherein a full width at half maximum of a wavelength spectrum of near-infrared light output from the light source and incident on the optical cavity is 15 nm or more, and
• the spectroscopic apparatus satisfies the following formula (1) in a specific concentration change range of the gas to be measured:
• [
• Math
• ⁢
• 1
• ]
• 
• α
• =
• 1
• L
• ⁢
• (
• I
• 0
• I
• -
• 1
• )
• ⁢
• (
• 1
• -
• R
• )
• (
• 1
• )
• R
• =
• R
• ⁢
• 1
• ×
• R
• ⁢
• 2
• (
• 2
• )
• in the formula (1), α represents an absorption coefficient of the gas to be measured, L represents a distance between optical centers of the pair of reflectors, I0 represents the intensity of the emission light from the optical cavity when the gas to be measured is not supplied to the optical cavity, I represents the intensity of the emission light from the optical cavity to which the gas to be measured is supplied, and R represents an effective reflectivity of the pair of reflectors represented by the formula (2), and
• in the formula (2), R1 represents the reflectivity of one of the pair of reflectors, and R2 represents the reflectivity of the other of the pair of reflectors.