Optical heterodyne interference measurement device and optical heterodyne interference measurement method
An optical heterodyne interference measurement apparatus includes a beam generation unit, a beam splitter, a mirror, a first photodetector, a linear polarizer, a second photodetector, a linear polarizer, an AD conversion unit, and a computer. The beam generation unit generates and outputs a first light beam and a second light beam having polarizations orthogonal to each other. The first light beam and the second light beam have optical frequencies different from each other by a heterodyne frequency. The computer sets, when ω p is set to any peak frequency being temporally constant in a frequency spectrum of intensity noise included in the first light beam or the second light beam output from the beam generation unit, the heterodyne frequency ω h to a value of a rational multiple of the peak frequency ω p .
1 . An optical heterodyne interference measurement apparatus comprising:
a laser light source configured to generate and output a first light beam and a second light beam having optical frequencies different from each other by a heterodyne frequency and polarizations orthogonal to each other;
a first photodetector configured to detect a temporal change of an intensity generated by heterodyne interference between the first light beam and the second light beam after any one or both of the first light beam and the second light beam are reflected by or transmitted through a measurement object, and output a first detection signal; and
a computer configured to set, when ω p is set to any peak frequency being temporally constant in a frequency spectrum of intensity noise included in the first light beam or the second light beam output from the laser light source, the heterodyne frequency being a difference between the optical frequencies of the first light beam and the second light beam output from the laser light source to a value of a rational multiple of the peak frequency ω p , and configured to acquire information on the measurement object based on a phase of a component temporally changing sinusoidally at the heterodyne frequency in the first detection signal.
2 . The optical heterodyne interference measurement apparatus according to claim 1 , further comprising:
a beam splitter configured to collectively split the first light beam and the second light beam output from the laser light source into two light beams, and output as first split light and second split light; and
a second photodetector configured to detect a temporal change of an intensity generated by heterodyne interference between the first light beam and the second light beam included in the second split light, and output a second detection signal, wherein
the first photodetector is configured to detect the temporal change of the intensity generated by the heterodyne interference between the first light beam and the second light beam after any one or both of the first light beam and the second light beam included in the first split light output from the beam splitter are reflected by or transmitted through the measurement object, and output the first detection signal, and
the computer is configured to acquire the information on the measurement object based on the phase of the component temporally changing at the heterodyne frequency in the first detection signal, and a phase of a component temporally changing at the heterodyne frequency in the second detection signal.
3 . The optical heterodyne interference measurement apparatus according to claim 1 , wherein, when a ratio ω h /ω p between the heterodyne frequency ω h and the peak frequency ω p is represented by a rational number n/m (each of m and n is a positive integer which has only unity as a common divisor), the computer is configured to set the heterodyne frequency ω h in which n is set to 10 or less.
4 . The optical heterodyne interference measurement apparatus according to claim 3 , wherein the computer is configured to set the heterodyne frequency ω h in which n is set to 1.
5 . The optical heterodyne interference measurement apparatus according to claim 1 , wherein, when a ratio ω h /ω p between the heterodyne frequency ω h and the peak frequency ω p is represented by a rational number n/m (each of m and n is a positive integer which has only unity as a common divisor), the computer is configured to set the heterodyne frequency ω h in which m is set to 10 or less.
6 . The optical heterodyne interference measurement apparatus according to claim 5 , wherein the computer is configured to set the heterodyne frequency ω h in which m is set to 1.
7 . The optical heterodyne interference measurement apparatus according to claim 1 , wherein the computer is configured to set the heterodyne frequency ω h to the same value as the peak frequency ω p .
8 . The optical heterodyne interference measurement apparatus according to claim 1 , wherein the computer is configured to acquire the information on the measurement object based on the phase of the component temporally changing at the heterodyne frequency in the first detection signal, and a phase of an electric signal temporally changing at the heterodyne frequency generated in the laser light source.
9 . The optical heterodyne interference measurement apparatus according to claim 1 , wherein the laser light source includes a frequency shifter configured to generate and output the first light beam and the second light beam based on laser light output from the laser light source.
10 . The optical heterodyne interference measurement apparatus according to claim 1 , wherein the computer is configured to acquire, as the information on the measurement object, at least one information of a retardation of the measurement object, a displacement of the measurement object, a refractive index change of the measurement object, a surface shape of the measurement object, and a surface roughness of the measurement object.
11 . An optical heterodyne interference measurement apparatus comprising:
a laser light source configured to generate and output a first light beam and a second light beam having optical frequencies different from each other by a heterodyne frequency and polarizations orthogonal to each other based on light reflected by or transmitted through a measurement object;
a first photodetector configured to detect a temporal change of an intensity generated by heterodyne interference between the first light beam and the second light beam, and output a first detection signal; and
a computer configured to set, when Op is set to any peak frequency being temporally constant in a frequency spectrum of intensity noise included in the first light beam or the second light beam output from the laser light source, the heterodyne frequency being a difference between the optical frequencies of the first light beam and the second light beam output from the laser light source to a value of a rational multiple of the peak frequency ω p , and configured to acquire information on the measurement object based on a phase of a component temporally changing sinusoidally at the heterodyne frequency in the first detection signal.
12 . An optical heterodyne interference measurement method comprising:
generating and outputting a first light beam and a second light beam having optical frequencies different from each other by a heterodyne frequency and polarizations orthogonal to each other;
detecting a temporal change of an intensity generated by heterodyne interference between the first light beam and the second light beam by a first photodetector after any one or both of the first light beam and the second light beam are reflected by or transmitted through a measurement object, and outputting a first detection signal;
setting, when ω p is set to any peak frequency being temporally constant in a frequency spectrum of intensity noise included in the first light beam or the second light beam output in the beam generation, the heterodyne frequency being a difference between the optical frequencies of the first light beam and the second light beam output in the beam generation to a value of a rational multiple of the peak frequency ω p ; and
acquiring information on the measurement object based on a phase of a component temporally changing sinusoidally at the heterodyne frequency in the first detection signal.
13 . The optical heterodyne interference measurement method according to claim 12 , further comprising:
collectively splitting the first light beam and the second light beam output from the beam generation into two light beams by a beam splitter, and outputting as first split light and second split light; and
detecting a temporal change of an intensity generated by heterodyne interference between the first light beam and the second light beam included in the second split light by a second photodetector, and outputting a second detection signal, wherein
detecting the temporal change of the intensity generated by the heterodyne interference between the first light beam and the second light beam by the first photodetector after any one or both of the first light beam and the second light beam are reflected by or transmitted through the measurement object, and outputting the first detection signal includes:
detecting the temporal change of the intensity generated by the heterodyne interference between the first light beam and the second light beam by the first photodetector after any one or both of the first light beam and the second light beam included in the first split light output from the beam splitter are reflected by or transmitted through the measurement object, and outputting the first detection signal, and
acquiring the information on the measurement object based on the phase of the component temporally changing sinusoidally at the heterodyne frequency in the first detection signal includes:
acquiring the information on the measurement object based on the phase of the component temporally changing at the heterodyne frequency in the first detection signal, and a phase of a component temporally changing at the heterodyne frequency in the second detection signal.
14 . The optical heterodyne interference measurement method according to claim 12 , wherein
setting, when ω p is set to any peak frequency being temporally constant in the frequency spectrum of intensity noise included in the first light beam or the second light beam output in the beam generation, the heterodyne frequency being the difference between the optical frequencies of the first light beam and the second light beam output in the beam generation to the value of the rational multiple of the peak frequency ω p includes:
when a ratio ω h /ω p between the heterodyne frequency ω h and the peak frequency ω p is represented by a rational number n/m (each of m and n is a positive integer which has only unity as a common divisor), setting the heterodyne frequency ω h in which n is set to 10 or less.
15 . The optical heterodyne interference measurement method according to claim 14 , wherein when the ratio ω h /ω p between the heterodyne frequency ω h and the peak frequency ω p is represented by the rational number n/m (each of m and n is a positive integer which has only unity as a common divisor), setting the heterodyne frequency ω h in which n is set to 1.
16 . The optical heterodyne interference measurement method according to claim 12 , wherein
setting, when ω p is set to any peak frequency being temporally constant in the frequency spectrum of intensity noise included in the first light beam or the second light beam output in the beam generation, the heterodyne frequency being the difference between the optical frequencies of the first light beam and the second light beam output in the beam generation to the value of the rational multiple of the peak frequency ω p includes:
when a ratio ω h /ω p between the heterodyne frequency ω h and the peak frequency ω p is represented by a rational number n/m (each of m and n is a positive integer which has only unity as a common divisor), setting the heterodyne frequency ω h in which m is set to 10 or less.
17 . The optical heterodyne interference measurement method according to claim 16 , wherein when the ratio ω h /ω p between the heterodyne frequency ω h and the peak frequency ω p is represented by the rational number n/m (each of m and n is a positive integer which has only unity as a common divisor, setting the heterodyne frequency ω h in which m is set to 1.
18 . The optical heterodyne interference measurement method according to claim 12 , wherein
setting, when ω p is set to any peak frequency being temporally constant in the frequency spectrum of intensity noise included in the first light beam or the second light beam output in the beam generation, the heterodyne frequency being the difference between the optical frequencies of the first light beam and the second light beam output in the beam generation to the value of the rational multiple of the peak frequency ω p includes:
setting the heterodyne frequency ω h is set to the same value as the peak frequency ω p .
19 . The optical heterodyne interference measurement method according to claim 12 , wherein acquiring the information on the measurement object based on the phase of the component temporally changing sinusoidally at the heterodyne frequency in the first detection signal includes:
acquiring the information on the measurement object based on the phase of the component temporally changing at the heterodyne frequency in the first detection signal, and a phase of an electric signal temporally changing at the heterodyne frequency generated in the beam generation.
20 . The optical heterodyne interference measurement method according to claim 12 , wherein
generating and outputting the first light beam and the second light beam having optical frequencies different from each other by the heterodyne frequency and polarizations orthogonal to each other includes:
generating and outputting the first light beam and the second light beam by a frequency shifter based on laser light output from a laser light source.
21 . The optical heterodyne interference measurement method according to claim 12 , wherein acquiring the information on the measurement object based on the phase of the component temporally changing sinusoidally at the heterodyne frequency in the first detection signal includes:
acquiring, as the information on the measurement object, at least one information of a retardation of the measurement object, a displacement of the measurement object, a refractive index change of the measurement object, a surface shape of the measurement object, and a surface roughness of the measurement object.
22 . An optical heterodyne interference measurement method comprising:
generating and outputting a first light beam and a second light beam having optical frequencies different from each other by a heterodyne frequency and polarizations orthogonal to each other based on light reflected by or transmitted through a measurement object;
detecting a temporal change of an intensity generated by heterodyne interference between the first light beam and the second light beam by a first photodetector, and outputting a first detection signal;
setting, when ω p is set to any peak frequency being temporally constant in a frequency spectrum of intensity noise included in the first light beam or the second light beam output in the beam generation, the heterodyne frequency being a difference between the optical frequencies of the first light beam and the second light beam output in the beam generation to a value of a rational multiple of the peak frequency ω p , and
acquiring information on the measurement object based on a phase of a component temporally changing sinusoidally at the heterodyne frequency in the first detection signal.