Measurement apparatus and measurement method using a laser and beat signals

A measurement method of a measurement apparatus for measuring a distance to an object to be measured, the method comprising:

• outputting a frequency-modulated laser beam with a plurality of modes from a laser apparatus having a laser resonator;
• branching a portion of the frequency-modulated laser beam as a reference light and at least some of the remaining portion of the frequency-modulated laser beam as a measurement light;
• generating a plurality of beat signals by mixing the reference light and a reflected light that is reflected by radiating the measurement light onto an object to be measured;
• converting the plurality of beat signals into digital signals by sampling the beat signals at a frequency greater than or equal to four times a resonator frequency of the laser resonator;
• and
• calculating a distance from the measurement apparatus to the object to be measured on the basis of the digital signals,
• wherein the converting includes a frequency converting that converts the digital signals into frequency information, and
• the calculating further includes:
• dividing the frequency information converted by the frequency converting into a plurality of pieces of frequency information corresponding to a plurality of bands having a predetermined bandwidth,
• converting a plurality of pieces of divided frequency information into frequency information corresponding to one predetermined frequency band and then integrating signal levels for each frequency,
• detecting a frequency position of the beat signal of the integrated frequency information, and
• calculating the distance from the measurement apparatus to the object to be measured on the basis of the detected frequency position of the beat signal.

A measurement apparatus for measuring a distance to an object to be measured, the measurement apparatus comprising:

• a laser that has a laser resonator and outputs a frequency-modulated laser beam with a plurality of modes;
• a branch that branches a portion of the frequency-modulated laser beam output by the laser as a reference light and at least some of the remaining portion of the frequency-modulated laser beam as a measurement light;
• beat signal generator that generates a plurality of beat signals by mixing the reference light and a reflected light that is reflected by radiating the measurement light onto an object to be measured;
• convertor circuitry that converts the plurality of beat signals into digital signals by sampling the beat signals at a frequency greater than or equal to four times a resonator frequency of the laser resonator;
• and
• calculation circuitry configured to calculate a distance from the measurement apparatus to the object to be measured on the basis of the digital signals,
• wherein the convertor circuitry includes a frequency conversion circuitry that converts the digital signals into frequency information, and
• the calculation circuitry is further configured to:
• divide the frequency information converted by the frequency conversion circuitry into a plurality of pieces of frequency information corresponding to a plurality of bands having a predetermined bandwidth,
• convert a plurality of pieces of divided frequency information into frequency information corresponding to one predetermined frequency band and then integrate signal levels for each frequency,
• detect a frequency position of the beat signal of the integrated frequency information, and
• calculate the distance from the measurement apparatus to the object to be measured on the basis of the detected frequency position of the beat signal.