Optical measurement apparatus and calibration method

A calibration method executed by an optical measurement apparatus that includes a measurement probe, which irradiates a specimen with illumination light and optically receives returned light of the illumination light reflected and/or scattered from the specimen, and that performs optical measurement of the specimen, the calibration method comprising the steps of:

• calculating a background intensity of background light to be used in correcting the returned light from the specimen, from a product of a value and a third detection intensity, the value being of a ratio of a first detection intensity to a second detection intensity, the first detection intensity being an intensity of the returned light detected when a first medium having a refractive index that is the same as that of the specimen is irradiated with the illumination light by the measurement probe and detected in a state of not including the returned light from the first medium, the second detection intensity being an intensity of the returned light detected when a second medium is irradiated with the illumination light by the measurement probe and detected in a state of not including the returned light from the second medium, and the third detection intensity being an intensity of the returned light detected when a third medium is irradiated with the illumination light by the measurement probe and detected in a state of not including the returned light from the third medium;
• and
• subtracting the background intensity from a detection intensity of the returned light from the specimen.