Interferometric measurement method and interferometric measurement apparatus

An interferometric measurement method using an interferometric measurement apparatus,

• wherein the interferometric measurement apparatus comprises:
• a light source that outputs measurement light having a frequency included in a range of 0.1 THz to 50 THz;
• an interferometric optical system that includes:
• a beam splitter that splits the measurement light into a first split light and a second split light;
• a first optical path for the first split light from being output from the beam splitter to re-entering the beam splitter;
• and a second optical path, which is different from the first optical path, for the second split light from being output from the beam splitter to re-entering the beam splitter, the second optical path being configured to be switchable between a first state in which a sample is not disposed and a second state in which the sample is disposed, wherein the interferometric optical system combines the first split light and the second split light re-entering the beam splitter, and an optical path length difference between the first optical path and the second optical path is variable;
• a photomultiplier tube that outputs an electrical signal value corresponding to an incident light intensity of interference light of the measurement light, the interference light being generated by combination of the first split light and the second split light at the beam splitter;
• an interference intensity measurement unit that measures an intensity of the interference light based on the electrical signal value output from the photomultiplier tube;
• and
• an electric field amplitude calculation unit that determines an electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement unit, based on a relationship between a value of an electric field amplitude of light incident on the photomultiplier tube and a value of an electrical signal output from the photomultiplier tube,
• the method comprising:
• a first step of acquiring a first interference waveform indicating the intensity of the interference light for each optical path length difference in the first state, by performing the measurement by the interference intensity measurement unit while changing the optical path length difference in the first state;
• a second step of converting the first interference waveform into a first electric field amplitude waveform, which is a waveform of the electric field amplitude, by the electric field amplitude calculation unit;
• a third step of acquiring a second interference waveform indicating the intensity of the interference light for each optical path length difference in the second state, by performing the measurement by the interference intensity measurement unit while changing the optical path length difference in the second state;
• a fourth step of converting the second interference waveform into a second electric field amplitude waveform, which is a waveform of the electric field amplitude, by the electric field amplitude calculation unit;
• and
• a fifth step of acquiring a measurement value regarding a physical property of the sample, based on an electric field amplitude corresponding to each peak of the first electric field amplitude waveform and the second electric field amplitude waveform.