Measurement apparatus and measurement method

A measurement method comprising:

• outputting a frequency-modulated laser beam with a plurality of modes from a laser apparatus having a laser resonator;
• branching the frequency-modulated laser beam into (i) a portion of the frequency-modulated laser beam as a reference light and (ii) at least some of the remaining portion of the frequency-modulated laser beam as a measurement light;
• generating a beat signal by mixing the reference light and a reflected light that is reflected by radiating the measurement light onto an object to be measured;
• extracting a signal component corresponding to a resonator frequency of the laser resonator and superimposed on the frequency-modulated laser beam;
• generating a first clock signal on the basis of the signal component;
• converting the beat signal into a first digital signal using the first clock signal;
• and
• calculating a difference in a propagation distance between the reference light and the measurement light on the basis of the first digital signal.

A light measurement apparatus, comprising:

• a laser having a laser resonator and configured to output a frequency-modulated laser beam with a plurality of modes;
• a branch configured to branch the frequency-modulated laser beam into (i) a portion of the frequency-modulated laser beam output by the laser as a reference light and (ii) at least some of a remaining portion of the frequency-modulated laser beam as a measurement light;
• a beat signal generator configured to generate a beat signal by mixing the reference light and a reflected light that is reflected by radiating the measurement light onto an object to be measured;
• an extractor configured to extract a signal component corresponding to a resonator frequency of the laser resonator and being superimposed on the frequency-modulated laser beam output from the laser;
• a clock signal generation circuit configured to generate a first clock signal on the basis of the signal component;
• a convertor configured to convert the beat signal into a first digital signal using the first clock signal;
• and
• a calculation circuit configured to calculate a difference in a propagation distance between the reference light and the measurement light on the basis of the first digital signal.