US 8,559,015 B2 · Measuring apparatus

Abstract

The present invention provides a measuring apparatus for measuring an absolute distance between a reference surface an d a test surface, including a phase detection unit configured to detect an interference signal between light reflected by the reference surface and light reflected by the test surface, and detect, from the interference signal, a phase corresponding to an optical path length between the reference surface and the test surface, and a processing unit configured to perform processing of obtaining the absolute distance by controlling the phase detection unit so as to detect the phase corresponding to the optical path length between the reference surface and the test surface for each of a first reference wavelength and a second reference wavelength while changing the wavelength of light to be emitted by a first light source continuously from the first reference wavelength to the second reference wavelength.

A measuring apparatus for measuring an absolute distance between a reference surface and a test surface, the measuring apparatus comprising:

a first light source;
a wavelength reference element configured to set a wavelength of light to be emitted by the first light source to one of a first reference wavelength that is a known vacuum wavelength or a second reference wavelength that is a known vacuum wavelength different from the first reference wavelength;
a polarizing beam splitter configured to split the light from the first light source into light having a first polarization direction and light having a second polarization direction perpendicular to the first polarization direction, make the light having the first polarization direction enter the reference surface, and make the light having the second polarization direction enter the test surface;
a refractive index detection unit configured to detect a group index in a space between the reference surface and the test surface;
a phase detection unit configured to detect an interference signal between the light having the first polarization direction and reflected by the reference surface and the light having the second polarization direction and reflected by the test surface, and detect, from the interference signal, a phase corresponding to an optical path length between the reference surface and the test surface;
and
a processing unit configured to perform processing of obtaining the absolute distance by controlling said phase detection unit so as to detect the phase corresponding to the optical path length between the reference surface and the test surface for each of the first reference wavelength and the second reference wavelength while changing the wavelength of light to be emitted by the first light source continuously from the first reference wavelength to the second reference wavelength by using said wavelength reference element,
wherein letting λ1 be the first reference wavelength, λ2 be the second reference wavelength, φ1 be the phase detected by said phase detection unit at the first reference wavelength, φ2 be the phase detected by said phase detection unit at the second reference wavelength, M be the number of phase jumps that occur when the wavelength of light to be emitted by the first light source is continuously changed from the first reference wavelength to the second reference wavelength, Λl2 be a synthetic wavelength of the first reference wavelength and the second reference wavelength represented by λ1·λ2/|λ1−λ2|, ng be the group index detected by said refractive index detection unit, and k be the number of times the test surface reflects the light having the second polarization direction, said processing unit obtains the absolute distance D1 by:
D
1
=
1
2
⁢
k
·
n
g
⁢
(
M
+
ϕ
2
-
ϕ
1
2
⁢
π
)
⁢
Λ
12
,
wherein letting dλ2 be an error from a designed value of the second reference wavelength, dΛl2 be an error from a designed value of the synthetic wavelength of the first reference wavelength and the second reference wavelength, dφ be a detection error of said phase detection unit, and n2 be a refractive index at λ2, a range Dmax of the absolute distance measurable by the measuring apparatus satisfies:
2
⁢
d
⁢
⁢
ϕ
2
⁢
π
⁢
Λ
12
λ
2
+
2
⁢
k
·
D
max
λ
2
⁢
d
⁢
⁢
Λ
12
Λ
12
+
2
⁢
k
·
D
max
λ
2
⁢
d
⁢
⁢
λ
2
λ
2
<
1
2
,
and
said processing unit obtains the absolute distance D2 by:
D
2
=
λ
2
2
⁢
k
·
n
2
⁢
(
round
⁡
(
2
⁢
k
·
D
1
λ
1
-
ϕ
1
2
⁢
π
)
+
ϕ
1
2
⁢
π
)
.

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Measuring apparatus

Life of this patent

Measuring apparatus

Life of this patent

Abstract

Claims16