JP2004101466A - Interferometer device comprising unnecessary light eliminator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interferometer device for eliminating the unnecessary light causing the noise in analyzing interference fringes, by mounting a light transmission-type light absorber on an optical path of the unnecessary light output from a half mirror. <P>SOLUTION: The light transmission-type light absorbers 41A, 41B are mounted on the optical path for the unnecessary light output from beam splitters 33A, 33B. The light absorbers 41A, 41B are mounted in a state of being obliquely intersecting axes L<SB>A</SB>, L<SB>B</SB>of the unnecessary light, and a light reflection preventing processing is performed on its unnecessary light incidence face. The light absorbers 41A, 41B eliminate the unnecessary light by absorbing the optical energy inside while converting the optical energy into the heat energy in a state of allowing the unnecessary light output from the beam splitters 33A, 33B to transmit therethrough. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention includes an unnecessary light remover for removing unnecessary light output from a half mirror disposed for changing the course of a light beam on the optical axis of an interferometer apparatus, and such an unnecessary light remover. Related to an interferometer device.
[0002]
[Prior art]
The interferometer device requires an optical system that guides the light beam output from the light source to the reference plane and the subject and guides the return light from the reference plane and the subject to the imaging unit. Half mirrors are widely used for changing the traveling direction of a light beam on a reciprocating optical path. Since the half mirror has the characteristic of splitting the input light beam into a transmitted light beam and a reflected light beam and outputting the split light beam, depending on the configuration of the interferometer device, the light beam transmitted or reflected by the half mirror may be measured and analyzed. In some cases, the light may be unnecessary light that is not used.
[0003]
Such unnecessary light may cause noise when performing interference measurement.However, in the conventional interferometer devices, for example, a light-blocking member that has been subjected to a black-painted alumite treatment or a malt plane is input. By arranging the light removing member for absorbing and scattering the unnecessary light to attenuate the unnecessary light at a position in front of the direction in which the unnecessary light is output, no substantial problem has occurred.
[0004]
[Patent Document 1]
JP-A-2000-222004 (FIG. 1)
[0005]
[Problems to be solved by the invention]
However, in recent years, the interference measurement has been performed by analyzing the interference fringes using a computer, and it has been required to obtain a very fine wavefront shape. In such a case, the interference fringe image has only slight brightness. Even the analysis is performed and the wavefront shape is calculated. Therefore, in the method for removing unnecessary light as described above, part of the light scattered by the light removing member becomes stray light and is superimposed on the interference fringe image, which becomes noise when performing interference fringe analysis, It has been confirmed that there is a possibility that the analysis result may be adversely affected.
[0006]
In general, as a means for removing unnecessary light, a type (horn structure) is known in which unnecessary light is taken in, and the taken-in unnecessary light is attenuated while being repeatedly reflected on an inner surface. However, this type of device has a problem that a large installation space is required.
[0007]
The present invention has been made in view of such circumstances, and unnecessary light output from a half mirror can be sufficiently removed so as not to be a cause of noise when analyzing interference fringes, and the installation space is small. An object of the present invention is to provide an unnecessary light remover and an interferometer device including such an unnecessary light remover.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, an interferometer device according to the present invention is an interferometer device including a half mirror on the optical axis for changing the path of a light beam, in order to remove unnecessary light output from the half mirror. An unnecessary light remover including a light transmission type light absorber that transmits and absorbs the input unnecessary light is disposed at a front position in a direction in which the unnecessary light is output. is there.
[0009]
In the interferometer device of the present invention, it is preferable that a surface of the light absorber facing the half mirror is subjected to a light reflection preventing process.
[0010]
Further, it is preferable that a surface of the light absorber facing the half mirror is disposed so as to be oblique to an axial direction of the unnecessary light.
The “light transmitting type light absorber” means a member that attenuates light by converting light energy into heat energy while transmitting light. For example, a color filter or an absorption type ND filter may be used. This is the case.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Overview of interferometer device>
FIG. 1 is a diagram illustrating an optical system of an interferometer device including an unnecessary light removing unit according to an embodiment of the present invention. In addition, in order to make the description easy to understand, in FIG. 1, the distance between the optical components and the size of each of them are appropriately changed and shown.
[0012]
The illustrated interferometer apparatus 10 includes a pair of interferometers 12A and 12B, an object holding member 14 for holding an opaque parallel flat plate (for example, a ceramic plate, a metal plate, a block gauge, etc.) 2 to be an object. In a state where a pair of interferometers 12A and 12B are arranged on both sides of the parallel plane plate 2 and the two sides 2a and 2b of the parallel plane plate 2 are to be measured, interference fringe measurement is performed. The absolute thickness and thickness unevenness of the face plate 2 are measured.
[0013]
Each of the interferometers 12A and 12B is a Fizeau-type interferometer, and diverges lenses 32A and 32B and laser beams output from tunable laser light sources 31A and 31B in its main body cases 20A and 20B, and a half mirror surface 35A. After passing through the beam splitters 33A and 33B provided with 35B, the collimator lenses 34A and 34B output the parallel light flux to the outside. Further, the output parallel light beam is made incident on reference surfaces 22Aa and 22Ba of reference plates 22A and 22B, and is divided into a transmitted light beam and a reflected light beam on the reference surfaces 22Aa and 22Ba. 2a and 2b, the reflected light is used as object light, and the reflected light on the reference surfaces 22Aa and 22Ba is used as reference light. Interference fringes generated by optical interference between the object light and the reference light are converted into beam splitters 33A and 33B. The images are taken into imaging devices 39A and 39B such as CCD cameras and the like via imaging lenses 38A and 38B. The beam splitters 33A and 33B are used for changing the course of the interfering return light in the direction of the imaging devices 39A and 39B. A low-pass filter, an IR cut filter, and the like are appropriately disposed on the imaging devices 39A, 39B side of the imaging lenses 38A, 38B, but are not shown.
[0014]
<Unnecessary light remover>
In the interferometer device 10 described above, the laser light output from the wavelength-variable laser light sources 31A and 31B passes through the beam splitters 33A and 33B in the direction of the collimator lenses 34A and 34B, so that the reference surfaces 22Aa and 22Ba and the test target are measured. When the laser beam passes through the beam splitters 33A and 33B, a part of the laser beam is opposite to the image pickup devices 39A and 39B on the half mirror surfaces 35A and 35B. (Upward in the figure), and is output as unnecessary light. When a part of the unnecessary light reaches the rough inner surfaces 20a and 20b of the main body cases 20A and 20B, it becomes scattered light, enters the imaging devices 39A and 39B, and causes noise. . In order to sufficiently remove such unnecessary light output from the beam splitters 33A and 33B, the interferometer apparatus 10 includes unnecessary light removers 40A and 40B in its main body cases 20A and 20B.
[0015]
The unnecessary light removers 40A and 40B are formed of light transmitting type light absorbers 41A and 41B disposed at a front position in a direction in which the unnecessary light is output, and, if necessary, the light absorbers 41A and 41B. An anti-reflection film (AR coating; the same applies hereinafter) provided on a surface facing the emission surfaces of the beam splitters 33A and 33B, and a radiation fin provided to prevent the light absorbers 41A and 41B from becoming hot. Consists of Further, even if unnecessary light reflected by the exit surface opposite to the surface of the beam splitter 33A, 33B, the axis L _A of the unnecessary _light, so as not to specular reflection in the direction of L _B, is the surface of its opposite, unnecessary light axis L _a of _the direction of L _B and oblique, that is, arranged to be tilted with respect to the axis L _a, a plane perpendicular to the L _B. As the light absorbers 41A and 41B, for example, an absorption type ND filter or a color filter can be used. In particular, when the light source light is ultraviolet light, optical glass plates such as BK7 whose surfaces have been subjected to a light reflection preventing treatment may be used as the light absorbers 41A and 41B.
[0016]
The light absorbers 41A and 41B absorb unnecessary light output from the beam splitters 33A and 33B while converting light energy into heat energy inside. In addition, since the surfaces of the light absorbers 41A and 41B are subjected to the anti-reflection treatment after being polished, unnecessary light is not scattered and reflected on the surfaces, and there is little possibility that the light is regularly reflected. Furthermore, still even when the specular reflection is unwanted light was present, the light absorber 41A, the surface of 41B, the axis L _A of the unnecessary _light, since the intersect L _B direction and obliquely, unnecessary light axis L _A, It is reflected in a direction different from the L _B direction. For this reason, it is also possible to prevent light interference with light reflected by the surface of another optical member arranged perpendicular to the optical axis. Therefore, according to the present embodiment, unnecessary light output from the beam splitters 33A and 33B can be sufficiently removed so as not to be a cause of noise when analyzing interference fringes. Further, the light absorbers 41A and 41B can be configured at low cost and in a space-saving manner using a compact general-purpose member.
[0017]
The embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment, and various aspects can be changed.
For example, in the above embodiment, a prism type half mirror is used, but a plate-like half mirror may be used.
[0018]
Further, the optical system of the above embodiment is configured to guide the light beam transmitted through the half mirror among the light beams from the light source to the subject, and to reflect the return light beam by the half mirror to the imaging device. Out of the light beams reflected by the half mirror may be guided to the subject, and the returned light beam may be transmitted through the half mirror and guided to the imaging device.
[0019]
Further, in the optical system of the above embodiment, the light beam from the light source is input to the half mirror as a divergent light beam, but a collimator lens is arranged in front of the half mirror, and the light beam from the light source is input to the half mirror as a parallel light beam. It is also possible to adopt a configuration in which these are performed.
[0020]
Further, in the above-described embodiment, an interferometer apparatus including two interferometers is described as an example so as to measure the absolute thickness and the thickness unevenness of the plane-parallel plate. Even so, the present invention can be applied.
[0021]
Further, in the above embodiment, the Fizeau-type interferometer device is illustrated, but other various interferometer devices in which unnecessary light is generated by using a half mirror, such as a Michelson type or a Twyman-Green type May be used.
[0022]
【The invention's effect】
As described above in detail, according to the interferometer apparatus of the present invention, the unnecessary light removing body including the light transmission type light absorber is disposed at the front position in the traveling direction of the unnecessary light output from the half mirror. By doing so, the following effects can be obtained.
[0023]
That is, the light absorber absorbs the unnecessary light output from the half mirror while converting the light energy into the heat energy while transmitting the unnecessary light. Therefore, the unnecessary light is suppressed while suppressing the generation of the scattered light due to the unnecessary light. It can be removed. For this reason, it is possible to prevent unnecessary light from being scattered and becoming stray light, which causes noise when performing interference fringe analysis. Further, as the light absorber, a commonly used inexpensive and compact one can be used, so that the cost is low and the installation space is small.
[0024]
Further, according to the interferometer apparatus of the present invention, since the unnecessary light removing body is provided, it is possible to suppress the occurrence of noise and the like, so that it is possible to perform highly accurate interference fringe analysis. .
[Brief description of the drawings]
FIG. 1 is a diagram of an optical system of an interferometer apparatus including an unnecessary light removing unit according to an embodiment of the present invention.
2 Parallel plane plates 2a, 2b Surface 10 to be inspected Interferometer device 12A, 12B Interferometer 14 Subject holding members 20A, 20B Body cases 20a, 20b Inner side surfaces 22A, 22B of body case Reference plates 22Aa, 22Ba Reference surfaces 31A, 31B Laser light sources 32A, 32B Diverging lenses 33A, 33B Beam splitters 34A, 34B Collimator lenses 35A, 35B Half mirror surfaces 38A, 38B Imaging lenses 39A, 39B Imaging devices 40A, 40B Unnecessary light removing members 41A, 41B Light absorber L _A , axis of L _B unwanted light

Claims (3)

In an interferometer device including a half mirror on the optical axis for changing the path of the light flux, in order to remove unnecessary light output from the half mirror,
An interferometer device comprising an unnecessary light remover provided with a light transmission type light absorber that transmits and absorbs the input unnecessary light at a position forward of the direction in which the unnecessary light is output. . The interferometer device according to claim 1, wherein a surface of the light absorber facing the half mirror is subjected to a light reflection preventing process. The interferometer device according to claim 1, wherein a surface of the light absorber facing the half mirror is disposed so as to be oblique to an axial direction of the unnecessary light.

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