Abstract:
The present invention is adapted to make light beams emitted from a light source enter a photodetector both when interposing an optical element having known characteristics and when not interposing the optical element, and acquire a first output value and a second output value that are the output values of the photodetector with respect to each of light beams that respectively have predetermined multiple wavenumbers and are included in the incident light beams, and obtain an arithmetic expression for calculating intensity of incident light beams from an output value of the photodetector, using parameters that are a ratio between the first output value and the second output value at each of the predetermined wavenumbers and the wavenumber transmission or reflection characteristic of the optical element.