JP2000356508A - Interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interferometer which can readily detect the amount and direction of the location deviation of an object to be measured from a reference reflecting member even when the location deviation is large. SOLUTION: An interferometer is provided with a reference wave front creating means 6 which divides light emitted from a light source 1 into reference light and measuring light and a reference reflecting member 8 provided with a reflecting surface having almost the same shape as the wave front of light emitted from an optical system 7 to be measured when the measuring light is made incident to the system 7 and obtains the optical characteristic of the system 7 by causing the measuring light reflected by the reflecting member 8 and reference light to interfere with each other. The interferometer is also provided with a reflecting member 15 which is positioned near the wave front condensing point of the measuring light emitted from the optical system 7 or its vicinity, passes at least part of the measuring light emitted from the optical system 7, and reflects at least part of the measuring light reflected by the reflecting member 8 and a detecting means 14 which detects the condensing position of the measuring light reflected by the reflecting member 15 and the measuring light passed through the reflecting member 15 from the optical conjugate relation between the condensing position and the wave front condensing point of the measuring light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer which can be used for an optical element inspection device and the like.

[0002]

2. Description of the Related Art In recent years, optical elements are often required to have extremely high optical performance. In particular, a condensing lens for exposing an optical disk master is one of the typical objects requiring high optical performance. . When performing the adjustment inspection of the optical performance of such a condenser lens, an interferometer is used as an inspection unit.
An interferometer is a useful device that can accurately measure the wavefront aberration of an object to be measured.

The interferometer will be described with reference to FIG. The light beam emitted from the light source unit 31 passes through the beam splitter 35 and enters the reference wavefront generation unit 36. Part of the incident light is reflected by the reference wavefront generation surface 36a of the reference wavefront generation means 36, and becomes reference light. The remaining incident light passes through the measured optical system 37 and is used as measurement light. The measurement light is transmitted through the measured optical system 37 again after being reflected by the reference reflection member 38. And the reference reflecting member 3
The light reflected at 8 interferes with the reference light reflected at the reference wavefront generation surface 36a, and generates interference fringes. The interference fringes are observed by the light receiving unit 39.

If the reference wavefront generating surface 36a and the reflecting surface of the reference reflecting member 38 are manufactured with high precision and there is no positional deviation or attitude deviation of the optical system 37 to be measured, the interference fringe is measured. It represents the disturbance of the wavefront due to an object, and can quantitatively measure the optical performance of the object to be measured. By the way, the positioning of the optical system to be measured must be performed by the measuring operator every time the object to be measured is replaced. In particular, the displacement due to the optical axis direction of the measured optical system 37, that is, the relative distance between the measured optical system 37 and the reflecting member 38, and the displacement in a plane perpendicular to the optical axis of the measured optical system 37. That is, both lateral displacement must be performed.

In the former case, the measuring light reflected by the reference reflecting member 38 is condensed on a plane different from the plane that transmits and condenses the measured optical system 37. In the latter case, the measuring light reflected by the reference reflecting member 38 passes through the measured optical system 7 and is condensed in the above-described condensing plane, but passes through the measured optical system 37. The deviation between the condensing position where the light is condensed and the condensing position of the measurement light reflected by the reference reflecting member 38 causes a position deviation twice as large as the relative position deviation between the object 37 and the reflecting member 38. .

[0006]

As described above, in the conventional interferometer, when the position deviation and the posture deviation of the measured optical system 37 are extremely large, the condensing position of the measuring light reflected by the reference reflecting member 38 is not reflected. In some cases, the interference fringes cannot be observed outside the field of view of the measurement optical system 37.

For example, when a condensing lens for exposing an optical disk master is measured by a conventional interferometer, when the numerical aperture of the lens is 0.9, the field of view of the optical system is at most about 0.05 mm in diameter. It is. Therefore, when the relative position deviation (deviation in a plane perpendicular to the optical axis) between the measured optical system 37 and the reference reflecting member 38 in the direction perpendicular to the optical axis exceeds 0.025 mm, the light passes through the measured optical system 37. Therefore, the light reflected by the reference reflecting member 38 cannot reach the light receiving section 39. Therefore, the position deviation cannot be measured on the light receiving section 39.

Therefore, for example, in the case of a lens having a narrow field of view, such as a condenser lens for exposing an optical disk master, if the measured optical system has a large positional deviation, the measured light is reflected by the reference reflecting member 38, The light cannot pass through the object to be measured again, and the position deviation cannot be detected by the focal point detecting means. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems and to provide an interferometer capable of easily detecting a position deviation amount and a direction even when a position deviation between an object to be measured and a reference reflection member is large.

[0009]

According to the present invention, there is provided a reference wavefront generating means for separating light emitted from a light source into reference light and measurement light, and the measurement light is transmitted to an optical system to be measured. A reference reflection member having a reflection surface of substantially the same shape as the wavefront of light emitted from the optical system to be measured when the light enters, causing the measurement light and the reference light reflected by the reference reflection member to interfere with each other,
In the interferometer for obtaining the optical characteristics of the optical system to be measured, the interferometer is provided at or near the wavefront condensing point of the measuring light emitted from the optical system to be measured, and passes at least a part of the measuring light emitted from the optical system to be measured A reflection member that reflects at least a portion of the measurement light reflected from the reference reflection member, and a light-condensing position of the measurement light reflected by the reflection member and the measurement light that has passed through the reflection member. A detecting means for detecting a point having an optically conjugate relationship with the point is provided.

As described above, the measurement light from the optical system to be measured and the measurement light emitted from the optical system to be measured and reflected by the reference reflecting member are taken out from the optical system of the interferometer main body, and each is measured. By detecting where there is an optically conjugate relationship with the focal point of the optical system, even if the measured optical system has a large positional deviation or posture deviation, the position deviation or posture between the measured optical system and the measuring device Deviation can be detected.

According to a second aspect of the present invention, a reference wavefront generating means for separating light emitted from a light source into a reference light and a measurement light, and a measurement wavefront when the measurement light enters an optical system to be measured. A reference reflection member having a reflection surface having substantially the same shape as the wavefront of light emitted from the optical system, and causing the measurement light and the reference light reflected by the reference reflection member to interfere with each other, thereby reducing the optical characteristics of the optical system to be measured. In the interferometer to be obtained, a light spot obtained by irradiating the measurement light emitted from the optical system to be measured is provided at or near the wavefront focal point of the measurement light emitted from the optical system to be measured, and reflected from the reflecting member. And a forming member that forms a light spot obtained by illuminating the measured light, and condenses light from the light spot formed by the forming member to form an image, and is emitted from the optical system to be measured. Of the light spot obtained by irradiating the measurement light When, it was it comprises a detection means for detecting the position of the image of the light spot obtained by illuminated measurement light reflected from the reflective member.

As described above, instead of the reflecting member, for example, a forming member coated with a fluorescent paint that emits light that can be detected by the detecting means is applied to the wavefront condensing point of the measuring light emitted from the optical system to be measured or to the wavefront condensing point. A light spot obtained by irradiating the forming member with the measuring light emitted from the optical system to be measured and a light spot obtained by illuminating the measuring light reflected from the reflecting member are formed in the vicinity. Keep it. The light spots formed on the forming member are condensed to form an image, and the light spots can be similarly formed by providing detection means for detecting the position of the image of each light spot.

Next, the present invention will be described in more detail with reference to embodiments. In addition, the present invention
The present invention is not limited to the embodiments described below.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An interferometer according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of an interferometer according to a first embodiment of the present invention. The interferometer according to the first embodiment has the following configuration. This interferometer comprises a coherent light source 1 and a folding mirror 2
A beam expander optical system including a lens 3 and a lens 4, a beam splitter 5, and a reference wavefront generating means 6.
, A reference reflection member 8, a light receiving optical system including a lens 9 and a lens 10, and a light receiving element 11.

Further, in the interferometer according to the first embodiment, a reflection member 15 is provided at or near the focal position of the optical system 7 to be measured. A lens 16 for reflecting the passed measurement light and the measurement light reflected by the reference reflection member 8 and further reflected by the reflection member 15
And mirrors 17 and 18 that reflect the measurement light passing through the measured optical system 7 and the reference reflecting member 8 to the light receiving element 14 and further guide the measuring light reflected by the reflecting member 15, and passed through the measured optical system 7. A light receiving element 14 is provided for detecting the condensing position of the measurement light and the measurement light reflected by the reference reflection member 8 and further reflected by the reflection member 15.

The coherent light source 1 is a light source that emits laser light having a long coherent distance. The reference wavefront generating means 6 is made of a material that transmits light emitted from the coherent light source 1. Then, the reference wavefront generation surface 6
In (a), the light from the coherent light source 1 is partially reflected, and its surface shape is substantially the same as the wavefront of the incident measurement light.

The reference reflecting member 8 is provided on the optical system 7 to be measured.
Has ideal optical characteristics, it has a reflecting surface having substantially the same shape as the wavefront obtained when the light transmitted through the reference wavefront generating means 6 passes through the optical system 7 to be measured. In such an interferometer, the light emitted from the coherent light source 1 has its exit direction changed by the turning mirror 2 and passes through the lenses 3 and 4 constituting the beam expander optical system. Then, a parallel light beam having a predetermined size is incident on the beam splitter 5, passes therethrough, and is incident on the reference wavefront generating means 6. The reference wavefront generating means 6 has a reference wavefront generating surface 6a.
Thereby, the parallel light beam from the coherent light source 1 is separated into reference light and measurement light. At this time, each of the wavefronts of the reference light and the measurement light is a plane.

Next, the measuring light then enters the optical system 7 to be measured. Then, the measurement light is condensed at the focal position of the measured optical system 7, diverges again, and enters the reference reflecting member 8.
By the way, the reference reflection member 8 has the same reflectance as the reference wavefront generation surface 6, and a part of the measurement light passes through the reference reflection member 8. Therefore, a part of the measuring light is transmitted through the reference reflecting member 8 and the other measuring light is reflected, thereby improving the sharpness of the interference fringes.

The light reflected from the reference reflecting member 8 is collected again at a position substantially the same as the focal position of the measured optical system 7 when the deviation of the position and orientation of the measured optical system 7 is not so large. Light. Thereafter, the light passes through the optical system to be measured 7 and the reference wavefront generating means 6, is reflected by the half mirror 5, passes through the lenses 9 and 10, and reaches the light receiving element 11. The reference light is also reflected by the half mirror 5,
The light passes through the lenses 9 and 10 and reaches the light receiving element 11. The optical characteristics of the optical system 7 to be measured are observed by observing the interference image by the two lights of the reference light and the measurement light with the light receiving element 11.

By the way, in the interferometer according to the first embodiment of the present invention, the reflection member 15 is provided at the position where the measurement light emitted from the optical system 7 to be measured is focused. This reflection member 15
Is provided with an opening at the center, and the measurement light collected by the measured optical system 7 passes through this opening and reaches the reference reflecting member 8. A reflection film is formed on the surface of the reflection member 15 on the side of the reference reflection member 8, and the optical system 7 to be measured is
When the position of the reference reflection member 8 is shifted with respect to the measurement light, the measurement light reflected by the reference reflection member 8 is reflected by the reflection member 15.

Therefore, in the lens 16, a part of the measurement light from the measured optical system 7 that has passed through the opening of the reflection member 15 is
A part of the measurement light reflected by the reference reflection member 8 and a part of the measurement light reflected by the reflection member 15 is condensed, and the respective light spots are formed on the light receiving surface of the light receiving element 14 via the mirrors 17 and 18. I have. It is to be noted that a wider field of view of the lens 16 than the field of view of the optical system 7 to be measured can detect even a larger displacement amount.

By the way, when there is no relative position deviation or posture deviation between the measured optical system 7 and the reference reflecting member 8, the light spot formed on the light receiving element 14 passes through the opening of the reflecting member 15. It becomes the measurement light from the measurement optical system 7.
When there is a relative positional deviation or a posture deviation between the measured optical system 7 and the reference reflecting member 8, a light spot of the measuring light from the measured optical system 7 that has passed through the opening of the reflecting member 15,
The light spot of the measurement light reflected by the reference reflection member 8 and reflected by the reflection member 15 does not coincide with the light spot, and the light condensing position is shifted or not converged at one point. By detecting this, the position deviation and the posture deviation between the measured optical system 7 and the reference reflecting member 8 can be known.

When correcting the positional relationship between the reference reflecting member 8 and the optical system 7 to be measured, an XYZ stage (not shown) on which the reference reflecting member 8 is mounted is driven to By moving the optical system 8 or moving the mounting position of the optical system 7 to be measured with respect to the interferometer of the present embodiment, the light spot formed on the light receiving element 14 is condensed at one point and approaches each other. Thus, the position can be adjusted.

Next, an interferometer according to a second embodiment of the present invention will be described with reference to FIG. In addition, among the configurations shown in FIG. 2, those having the same reference numerals as those in FIG. 1 are the same as those in the first embodiment of the present invention, and a description thereof will be omitted. By the way, in the interferometer according to the second embodiment of the present invention, the measuring light received by the light receiving element 14 is a part of the measuring light passing through the reflecting member 15 or a part of the measuring light reflected by the reflecting member 15. And a reflecting mirror 20. Further, a lens 19 is provided for condensing the measurement light passing through the reflection member 15 and the measurement light reflected by the reflection member 15, and is incident on the light receiving element 14 via the mirror 18.

By doing so, the reference reflecting member 8
Since there is no need to transmit the measuring light, there is no need to pay attention to the material of the reference reflecting member 8 and the homogeneity of the material. In particular, in the interferometer according to the first embodiment of the present invention, when the coherent light source 1 is not visible light but ultraviolet light or infrared light, it is necessary to pay attention to the transmittance at each wavelength. . Further, there is a disadvantage that the material constituting the reference reflecting member 8 is limited according to the wavelength of the coherent light source 1. However, unlike the interferometer according to the second embodiment of the present invention, by not using the measurement light passing through the reference reflecting member 8, it can be used without being concerned with the material and homogeneity of the reference reflecting member 8. There are advantages.

In each of the embodiments of the present invention, the reflecting member 15 has a hole having substantially the same diameter as the converging diameter of the measuring light emitted from the optical system 7 to be measured. The present invention is not limited to this, and a reflective member formed of a partially reflecting mirror may be used. When using such a reflecting member 15, attention must be paid to the material, thickness and internal homogeneity of the reflecting member 15. In this way, the position of the light spot composed of a part of the measurement light emitted from the measured optical system 7 and the position of the light spot composed of a part of the measurement light emitted from the reference reflecting member 8 are measured. Thus, the positions of the reference reflecting member 8 and the measured optical system 7 can be adjusted.

The interferometer according to each embodiment of the present invention has been described on the assumption that the measurement light transmitted through the optical system to be measured 7 is condensed at one point, and the reference reflecting member 8 is spherical. However, the present invention is not limited to this. For example, an optical system in which the measurement light passing through the optical system to be measured 7 does not converge at one point may be measured. Even if the reference reflecting member 8 is not spherical, the effect of the present invention is not changed at all. Absent.

When light other than visible light is used for the coherent light source 1, a fluorescent material is applied to a transparent plate instead of the reflecting member 15 so that the reference reflecting member 8 and the lens 1 can be used.
6. The mirrors 17 and 18 need only consider transmission and reflection in the visible light range, and the detector 14 can use a detector that detects only visible light. Further, in the case of the interference system shown in the second embodiment of the present invention, a plane reflecting mirror is used as the mirror 20, but a curved mirror such as a parabolic mirror may be used. When using a curved mirror such as a parabolic reflector, the lens 1
9 may be downsized or omitted. Also, the first of the present invention
Also in the case of the interferometer described in the embodiment, the lens function can be positively added by making the bottom surface of the reference reflecting member 8 a curved surface, and the lens 16 may be downsized or omitted. .

When the interferometer according to each embodiment of the present invention is used for measuring the optical characteristics of a condensing lens for exposing an optical disk master, it is common to use ultraviolet light as a light source for the optical system. The wavefront aberration of about 1/20 of the used wavelength is typical. Even in the measurement of such an optical system,
The alignment between the measured optical system 7 and the reference reflecting member 8 was facilitated, and the measurement time was shortened.

In the case where the ultraviolet light is used for the interferometer as described above, a thin quartz glass parallel flat plate is used for the reflecting member 15 in order to facilitate manufacture and reduce transmitted wavefront aberration. Is preferred. In addition, an inexpensive fluorescent film is preferable for the light receiving element 14 and visual inspection is easy, but precise alignment may be performed using a two-dimensional array imaging element.

[0031]

As described above, in the interferometer according to the present invention, even if the position deviation and the posture deviation between the optical system to be measured and the interferometer are large, each of the position deviation and the posture deviation can be easily obtained. The amount and direction can be detected, which can save labor and shorten the inspection time. Therefore, it is possible to easily position the object to be measured and the interferometer in a short time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an interferometer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an interferometer according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional interferometer.

[Explanation of symbols]

 1: Light source 2, 17, 18, 20: Reflecting mirror 3, 4, 9, 10, 16, 19: Lens 5, 35: Beam splitter 6, 36: Reference wavefront generating means 6a, 36a: Reference surface 7, 37: Optical system to be measured 8, 38: Reference reflecting member 11, 14: Light receiving element 15: Reflecting member 31: Light source unit 39: Light receiving unit

Claims (2)

[Claims] 1. A reference wavefront generating means for separating light emitted from a light source into reference light and measurement light, and light emitted from the measured optical system when the measurement light enters the measured optical system. A reference reflection member having a reflection surface of substantially the same shape as the wavefront of the reference light, the interference between the measurement light and the reference light reflected by the reference reflection member, to obtain an optical characteristic of the measured optical system in an interferometer Provided at or near the wavefront condensing point of the measurement light emitted from the measured optical system, allowing at least a part of the measurement light emitted from the measured optical system to pass therethrough and reflected from the reference reflecting member. A reflection member that reflects at least a part of the measurement light that has been reflected; and a light-condensing position of the measurement light reflected by the reflection member and the measurement light that has passed through the reflection member. Have a conjugate relationship Interferometer characterized by comprising a detecting means for detecting for. 2. A reference wavefront generating means for separating light emitted from a light source into reference light and measurement light, and light emitted from the measured optical system when the measurement light enters the measured optical system. A reference reflection member having a reflection surface of substantially the same shape as the wavefront of the reference light, the interference between the measurement light and the reference light reflected by the reference reflection member, to obtain an optical characteristic of the measured optical system in an interferometer A light spot obtained by irradiating the measurement light emitted from the measured optical system, provided at or near the wavefront focal point of the measurement light emitted from the measured optical system, and A forming member that forms a light spot obtained by illuminating the reflected measurement light; condensing light from the light spot formed by the forming member to form an image, and emitting the light from the optical system to be measured Is irradiated with the measurement light The image of the light spot is, the interferometer characterized by comprising detecting means for detecting the position of the image of the light spot obtained illuminated is reflected the measurement light from said reflecting member.