JP4857619B2 - Method for measuring eccentricity of reflective aspherical optical element, method for manufacturing optical system, reflective aspherical optical element, and optical system - Google Patents

Description

  The present invention relates to an optical system including at least one reflective aspherical optical element such as a Ritchie-Cretian type or a Cassegrain type, and a method for manufacturing the same. The present invention also relates to a reflective aspheric optical element constituting the optical system and a method for measuring the eccentricity thereof.

Aspherical mirrors such as hyperboloids and paraboloids are used in reflection optical systems such as Ritchie-Cretian type and Cassegrain type in order to effectively suppress aberrations. An aspherical mirror having only one optical axis needs to be devised such as using the back surface of the mirror as a reference when assembling the aspherical mirror.
Therefore, it is effective to accurately measure the eccentricity with reference to the back surface of the aspherical mirror prior to assembly. A similar technique is disclosed in Patent Document 1. Patent Document 1 describes a function of detecting an inclination of a reference plane applied to a test lens while measuring a wavefront aberration of the test lens in a Twiman-Green type or Fizeau type interferometer. It is added.

Prior to assembly, it is also effective to process the reflecting surface and back surface of the aspherical mirror with high accuracy so that the eccentricity of the aspherical mirror can be suppressed. The technique of the high precision processing is disclosed in Patent Document 2.
JP 2004-340663 A JP-A-5-57606

  However, in order to measure the eccentricity of the aspherical mirror using the technique of Patent Document 1, it is necessary to insert a null optical element suitable for the shape of the reflecting surface (aspherical surface) into the optical path of the interferometer, In that case, since the optical axis adjustment error of the null optical element is superimposed on the measurement result, high-precision measurement is difficult. Moreover, even if the technique of Patent Document 2 is used, there is a limit, and the eccentricity can be suppressed only to the mechanical accuracy of the grinding machine / polishing machine.

Therefore, an object of the present invention is to provide a method for measuring the eccentricity of a reflective aspheric optical element that can measure the eccentricity of the reflective aspheric optical element with high accuracy.
Another object of the present invention is to provide an optical system manufacturing method capable of manufacturing a high-performance optical system.
It is another object of the present invention to provide a reflective aspheric optical element whose eccentricity is measured with high accuracy or a highly accurate reflective aspheric optical element whose eccentricity is suppressed.

  Another object of the present invention is to provide a high-performance optical system.

The eccentricity measuring method of the present invention includes a procedure of disposing a reflective aspherical optical element having a first reference surface and a null optical element having a second reference surface in a measurement light beam of an interferometer, and the reflection The reflection aspheric surface, the first reference surface, and the second reference surface of the reflection aspheric optical element are shared by the interferometer while maintaining the positional relationship between the aspheric optical element and the null element. And a procedure for obtaining the eccentricity of the reflective aspherical optical element based on the first reference surface based on the result of each detection.

The first reference plane is a plane fixed in parallel with the back surface of the reflective aspheric optical element, and the second reference plane is a plane fixed perpendicular to the optical axis of the null element. Is desirable. The light source of the interferometer is preferably a light source capable of modulating the wavelength of the emitted light.
The optical system manufacturing method of the present invention is an optical system manufacturing method including at least one reflective aspherical optical element, wherein the eccentricity of at least one reflective aspherical optical element constituting the optical system is determined. The method includes the steps of measuring with the eccentricity measuring method of any reflective aspherical optical element of the present invention, and assembling the optical system according to the result of the measurement. The optical system manufacturing method may further include a step of reworking the reflective aspherical optical element according to the measurement result.

The reflective aspheric optical element of the present invention is measured by the eccentricity measuring method for any of the reflective aspheric optical elements of the present invention.
The reflective aspherical optical element of the present invention is characterized by being measured by the eccentricity measuring method for any of the reflective aspherical optical elements of the present invention and reworked according to the measurement result.
The optical system of the present invention is manufactured by any one of the optical system manufacturing methods of the present invention.

ADVANTAGE OF THE INVENTION According to this invention, the eccentricity measuring method of the reflective aspherical optical element which can measure the eccentricity of a reflective aspherical optical element with high precision is implement | achieved.
In addition, according to the present invention, an optical system manufacturing method capable of manufacturing a high-performance optical system is realized.
In addition, according to the present invention, a reflective aspherical optical element whose eccentricity is measured with high accuracy or a highly accurate reflective aspherical optical element with reduced eccentricity is realized.

  Further, according to the present invention, a high-performance optical system is realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present embodiment is an embodiment of a manufacturing method of a Ritchie-Cretian reflective optical system.
FIG. 1 is a diagram illustrating a reflective optical system manufactured in the embodiment. As shown in FIG. 1, the reflecting optical system includes a primary mirror 11 that is a concave aspherical mirror and a secondary mirror 12 that is a convex aspherical mirror. Of these, the primary mirror 11 is a perforated mirror. Further, because of the Richie-Cretian equation, the reflecting surface 11a of the primary mirror 11 and the reflecting surface 12a of the secondary mirror 12 are higher-order aspheric surfaces that are close to hyperboloids, respectively.

FIG. 2 is a flowchart showing the overall flow of the manufacturing method. As shown in FIG. 2, the manufacturing method includes a processing step S1, a measurement step S2, and an assembly step S3.
In the processing step S1, each of the primary mirror 11 and the secondary mirror 12 is processed. In the processing, not only the reflecting surface 11a of the primary mirror 11 and the reflecting surface 12a of the secondary mirror 12, but also the back surface 11b of the primary mirror 11 and the back surface 12b of the secondary mirror 12 are processed. In that case, those back surfaces are polished so as to be a smooth plane. In the processing, the optical axis (aspheric surface axis) of the reflecting surface 11a of the primary mirror 11 and the back surface 11b of the primary mirror 11 are brought close to each other vertically, and the optical axis (aspherical surface) of the reflecting surface 12a of the secondary mirror 12 is obtained. Axis) and the back surface 12b of the secondary mirror 12 are brought close to vertical.

In the measurement step S2, the eccentricity of the primary mirror 11 with respect to the back surface 11b and the eccentricity of the secondary mirror 12 with respect to the back surface 12b are measured. Here, in particular, the angular deviation between the optical axis and the back surface normal is measured as the eccentricity. Therefore, in the following, “eccentricity” is used to mean the angular deviation. Details of the eccentricity measurement of the primary mirror 11 and the eccentricity measurement of the secondary mirror 12 will be described later.
In the assembly step S3, the positional relationship between the primary mirror 11 and the secondary mirror 12 is adjusted with reference to the back surfaces 11b and 12b of both. At that time, using the information on the eccentricity of the primary mirror 11 measured in the measurement step S2 and the information on the eccentricity of the secondary mirror 12, the positions of the back surfaces 11b and 12b are set so that the optical axes of both are parallel to each other. The relationship is adjusted. Further, the relative positions of the primary mirror 11 and the secondary mirror 12 are shifted while maintaining the postures of the two so that the optical axes of the two mirrors coincide. Thereafter, the primary mirror 11 and the secondary mirror 12 are assembled to complete the reflection optical system (FIG. 1).

<Eccentricity measurement of primary mirror 11>
Hereinafter, the eccentricity measurement of the primary mirror 11 will be described in detail.
FIG. 3 is a diagram for explaining the eccentricity measurement of the primary mirror 11. In the eccentricity measurement, as shown in FIG. 3, a Twiman-Green interferometer is used. The interferometer includes a light source 21, a collimator lens 22, a beam splitter 23, a reference plate 24 having a reference surface 24a, an observation lens 25, an image sensor 26, a monitor (not shown), a computer (not shown), and the like.

The null optical element 13 and the main mirror 11 are arranged in a predetermined positional relationship in the measurement light beam of the interferometer. The null optical element 13 is an element that converts the wavefront (plane) of the measurement light beam from the interferometer into a wavefront (aspherical surface) incident substantially perpendicular to the reflecting surface 11a of the main mirror 11, and includes a refractive lens and diffractive optics. An element or a combination of a refractive lens and a diffractive optical element is used.
In this interferometer, when the measurement light beam incident on the reflecting surface 11 a of the main mirror 11 via the null optical element 13 is reflected by the reflecting surface 11 a, the optical path is folded back and returned to the interferometer via the null optical element 13.

Here, a reference mirror 14 having a reference plane 14 a is fixed to the back surface 11 b of the primary mirror 11. The reference mirror 14 presses the reference plane 14a against the back surface 11b, thereby matching the optical axis of the reference plane 14a with the normal line of the back surface 11b. At least a part of the reference plane 14a is exposed to the null optical element 13 side.
On the other hand, an annular mirror 15 having a reference plane 15 a is fixed around the null optical element 13. The annular mirror 15 is composed of a parallel plane plate having a high degree of parallelism, the reference plane 15 a faces the interferometer side with respect to the null optical element 13, and the reference plane 15 a is perpendicular to the optical axis of the null optical element 13. It is adjusted in advance to become.

  However, since there is a possibility that eccentricity may remain in the null optical element 13, when the annular mirror 15 is attached, if the holding member of the null optical element 13 is used as it is as a reference, the annular mirror 15 The reference plane 15a and the optical axis of the null optical element 13 may not be exactly perpendicular. For this reason, in the present embodiment, as shown in FIG. 4, the null optical element 13 itself is cored so that light is projected while the null optical element 13 is rotated on a rotating stage and the focal position does not fluctuate. It is desirable to attach the annular mirror 15 after taking out.

Now, the annular mirror 15 shown in FIG. 3 reflects a part of the measurement light beam traveling from the interferometer to the periphery of the null optical element 13 by its reference plane 15a. The reflected measurement light beam then returns to the interferometer by turning back its optical path.
Further, the reference mirror 14 reflects the measurement light beam traveling from the interferometer toward the main mirror 11 without passing through the null optical element 13 at the reference plane 14a. Then, the reflected measurement light beam returns its optical path and returns to the interferometer without passing through the null optical element 13.

In the following, as shown in FIG. 3, the annular mirror 15 is made of a transmissive member (a member that is transparent to the measurement light beam), and the measurement light beam transmitted through the annular mirror 15 The description will be made assuming that the light is incident on the perforated portion and the reference plane 14a provided on the perforated portion reflects the measurement light beam incident thereon.
Each measurement light beam returned to the interferometer is directed to the observation surface 26a of the interferometer (the imaging surface of the image sensor 26) and interferes with the reference light beam reflected by the reference surface 24a. As a result, interference fringes are formed in two types of regions as shown in FIG. 5 on the observation surface 26a.

FIG. 5A is an interference fringe formed in a circular area E1 at the center of the observation surface 26a. The interference fringes indicate the shape of the reflecting surface 11a. The interference fringes are formed by the light reflected by the reference surface 24a and the light reflected by the reflecting surface 11a reaching the circular region E1 and interfering with each other.
FIG. 5B is an interference fringe formed in the ring-shaped region E2 around the circular region E1 in the observation surface 26a. This interference fringe mainly indicates the inclination of the primary mirror 11 and the null optical element 13 with respect to the reference surface 24a. The interference fringes are such that the light reflected by the reference surface 24a, the light transmitted through the annular mirror 15 and reflected by the reference plane 14a, and the light reflected by the annular mirror 15 reach the annular zone E2 and interact with each other. It is formed by interfering with. Specifically, the light that reaches and interferes with the ring-shaped region E2 is at least:
(1) light reflected by the reference surface 24a,
(2) light reflected by the reference plane 14a,
(3) light reflected by the reference plane 15a,
(4) Light reflected from the back surface 15b of the annular mirror 15 (noise light)
There are four lights. Incidentally, the inclination of the back surface 11b of the primary mirror 11 is an interference fringe formed by the two lights (1) and (2), and the inclination of the null optical element 13 is indicated by (1), (3 ) Are two interference fringes.

The observation surface 26a on which the above interference fringes are formed is imaged by the image sensor 26, and the image data acquired by the image sensor 26 is displayed on a monitor (not shown) in real time. Therefore, the measurer can view the interference fringes in real time.
In order to increase the contrast of the interference fringes, it is desirable that at least the reflectance of the reference plane 14a, the reflectance of the reference plane 15a, and the reflectance of the reference surface 24a are set to be substantially the same (for example, 4%). . In general, in order to increase the contrast of interference fringes formed by two light beams reflected by a certain two surfaces, the reflectances of the two surfaces should be close to each other. In order to reduce the contrast of interference fringes that become noise, it is desirable to apply an antireflection film to the back surface 15b of the annular mirror 15 to reduce its reflectance (for example, 0.1%).

(Placement adjustment)
First, the inclination of the null optical element 13 with respect to the reference surface 24a is adjusted. In this tilt adjustment stage, the primary mirror 11 is out of the optical path of the measurement light beam of the interferometer, or is shielded by the light shielding means 16 as shown in FIG. In this state, the measurer can visually observe the interference fringes indicating the inclination of the null optical element 13 from the annular region E2 of the observation surface 26a.

The measurer adjusts the inclination of the null optical element 13 while visually checking the interference fringes, and fixes the null optical element 13 when the interference fringes become one color. By this adjustment, the tilt error of the null optical element 13 is suppressed to some extent.
At the time of this tilt adjustment, the light (noise light) reflected by the back surface 15b of the annular mirror 15 also reaches the annular region E2, so that necessary interference fringes (reflected light from the reference surface 24a and the reference plane 15a are reflected). In addition to the interference fringes), noise interference fringes also occur, but since the reflectance of the back surface 15b is low, the necessary interference fringes have higher contrast and can be identified.

Subsequently, the position and tilt of the primary mirror 11 with respect to the interferometer are adjusted. At this time, the measurer can visually observe interference fringes (see FIG. 5A) indicating the shape of the reflecting surface 11a from the circular region E1 of the observation surface 26a.
The measurer adjusts the position and inclination of the primary mirror 11 while viewing the interference fringes, and fixes the position and inclination of the primary mirror 11 when the interference fringes become one color. By this adjustment, an arrangement error of the primary mirror 11 is suppressed to some extent.

(Interference measurement)
In the interference measurement, the observation surface 26a is imaged by the image sensor 26 while maintaining the state after the arrangement adjustment. The image data acquired by the image sensor 26 is taken into a computer (not shown).
The computer indicates, from the captured image data, an interference fringe indicating the shape of the reflecting surface 11a (see FIG. 5A), an interference fringe indicating the inclination of the null optical element 13, and the inclination of the back surface 11b of the primary mirror 11. Interference fringes (see FIG. 5B) are individually recognized.

Among these, the interference fringes indicating the shape of the reflecting surface 11a are formed independently in the circular area E1, as shown in FIG. 5A, and therefore can be directly recognized from the image data of the circular area E1. Can do.
On the other hand, the interference fringes indicating the inclination of the null optical element 13 and the interference fringes indicating the inclination of the back surface 11b of the primary mirror 11 are superimposed on the same annular region E2 as shown in FIG. These interference fringes cannot be directly recognized from the image data of the annular region E2.

Moreover, at least the interference (four-beam interference) caused by the four lights (1), (2), (3), and (4) described above occurs on the annular zone E2.
Among these, in order to separate only the interference fringe data formed by two specific lights from the other interference fringe data, for example, the following separation method can be applied.
(Interference fringe separation method)
The wavelength of the light source 21 (see FIG. 3) of the interferometer is previously made variable. Therefore, a semiconductor laser is preferably used for the light source 21. The wavelength of the interferometer can be controlled by controlling the injection current of the semiconductor laser.

  In the interference measurement, imaging by the image sensor 26 is repeated while appropriately controlling the injection current and modulating the wavelength with a predetermined modulation waveform, thereby acquiring image data for a plurality of frames. When a semiconductor laser having a wavelength of 830 nm is used as the light source 21 and the annular mirror 15 having a thickness of 10 mm is used, the wavelength modulation width is, for example, 0.025 nm or more. The acquired image data for a plurality of frames is taken into a computer.

After data acquisition, calculation is performed based on the acquired image data for a plurality of frames and the modulation pattern of wavelength modulation, and only interference fringe data formed by two specific lights is extracted. In order to simplify the calculation, it is preferable that the wavelength modulation is linear with respect to the injection current and the modulation waveform is sawtooth.
Here, when the wavelength is modulated during interference measurement, the phase of the interference fringes is modulated. However, in the two light interference fringes having substantially the same optical path length (geometric optical path length), the phase hardly changes even if the wavelength changes. On the other hand, in the interference fringes of two lights having different optical path lengths, the phase changes uniformly when the wavelength changes. Therefore, the interference fringes due to the two lights flow and cannot be recognized as the fringes when the wavelength modulation speed is high. Therefore, the following adjustment is performed before the interference measurement.

  That is, when the interference fringes to be separated are interference fringes indicating the inclination of the null optical element 13 (interference fringes formed by the reflected light of the reference surface 24a and the reference plane 15a. See FIG. 6), the beam splitter 23. The position of the reference plate 24 in the optical axis direction is adjusted so that the optical path length from the beam splitter 23 to the reference plane 15a coincides with the optical path length from the beam splitter 23 to the reference plane 15a. However, care should be taken not to change the inclination of the reference plate 24 during the adjustment.

  When the interference fringes to be separated are interference fringes indicating the inclination of the back surface 11b of the main mirror 11 (interference fringes formed by the reflected light of the reference surface 24a and the reference plane 14a), from the beam splitter 23 to the reference surface 24a. The position of the reference plate 24 in the optical axis direction is adjusted so that the optical path length of the reference plate 24 matches the optical path length from the beam splitter 23 to the reference plane 14a. However, care should be taken not to change the inclination of the reference plate 24 during the adjustment.

(Calculation of eccentricity)
As described above, from the data of the interference fringes (FIGS. 5A and 5B) of the circular region E1 and the annular region E2, the inclination data of the null optical element 13, the shape data of the reflecting surface 11a, the primary mirror 11 Tilt data of the back surface 11b is obtained. These data are data based on the common reference plane 24a.

Therefore, the computer calculates the eccentricity of the primary mirror 11 with respect to the back surface 11b based on the tilt data of the null optical element 13 with respect to the reference surface 24a and the tilt data of the back surface 11b of the primary mirror 11 with respect to the reference surface 24a. . Although the inclination of the null optical element 13 is small because it is adjusted with respect to the reference surface 24a, the eccentricity of the primary mirror 11 with respect to the back surface 11b is required more accurately.
<Eccentricity measurement of secondary mirror 12>
Hereinafter, the eccentricity measurement of the secondary mirror 12 will be described in detail. Similarly to the eccentricity measurement of the primary mirror 11, the eccentricity measurement of the secondary mirror 12 is performed with high accuracy by the same procedure using a Twiman-Green type interferometer. Here, only differences from the eccentricity measurement of the primary mirror 11 will be described. The difference is in the optical system around the secondary mirror 12 arranged in the interferometer.

  FIG. 7 is a diagram showing an optical system around the secondary mirror 12 arranged in the interferometer. In FIG. 7, components having the same functions as those shown in FIG. In this optical system, the null optical element 13 converts the wavefront of the measurement light beam from the interferometer into a wavefront that is incident substantially perpendicular to the reflecting surface 12 a of the sub-mirror 12. Since the reflecting surface 12 a of the secondary mirror 12 is a convex surface, the positional relationship between the secondary mirror 12 and the null optical element 13 is such that the reflecting surface 12 a is positioned in front of the focal point of the null optical element 13. At this time, the measurement light beam incident on the reflecting surface 12a is not a divergent light beam but a condensed light beam. In order to make such a measurement light beam enter the entire reflecting surface 12a, the diameter of the null optical element 13 is set to be large in advance according to the size of the reflecting surface 12a.

Further, since the secondary mirror 12 is a non-perforated mirror, the reference plane 14a of the reference mirror 14 protrudes to the periphery of the secondary mirror 12 so that the measurement light beam directed to the periphery of the secondary mirror 12 can be reflected.
Here, when the diameter of the secondary mirror 12 is large, for example, an optical system as shown in FIG. 8 may be used. In FIG. 8, the same elements as those shown in FIG.
In the optical system shown in FIG. 8, the reflecting surface 12a of the secondary mirror 12 is arranged behind the focal point of the null optical element 13, and the secondary mirror 12 has two conjugate points having no aberration for inspection. I do. Therefore, in this optical system, a folding reflection mirror 16 with a hole is added, and the optical path of the reflected light beam is folded by the folding reflection mirror 16.

In the eccentricity measurement using this optical system, it is considered that the measurement error increases by the addition of the folding reflection mirror 16, but the unique information (shape of the reflecting surface, arrangement error, etc.) of the folding reflection mirror 16 is separately measured. In this case, the eccentricity measurement can be performed with the same accuracy as the eccentricity measurement described above.
<Iteration>
After execution of the measurement step S2 shown in FIG. 2, the primary mirror 11 and / or the secondary mirror 12 are evaluated using the eccentricity information acquired in that step, and if it is determined that it is necessary, the processing step S1. The primary mirror 11 and / or the secondary mirror 12 may be reworked. If this is repeated, the eccentricity of the primary mirror 11 and / or the secondary mirror 12 can be kept small, and the precision of the primary mirror 11 and / or the secondary mirror 12 can be improved (see the dotted line portion in FIG. 2). When the eccentricity is sufficiently reduced by this iteration, the eccentricity may be regarded as zero in the assembly step S3.

  In addition, after the execution of the measurement step S2, the reflection surface of the primary mirror 11 and / or the secondary mirror 12 is evaluated using the shape data of the reflection surface acquired in that step. Returning to step S1, the reflecting surfaces of the primary mirror 11 and / or the secondary mirror 12 may be re-polished. By repeating this, the surface accuracy of the reflecting surface of the primary mirror 11 and / or the secondary mirror 12 can be improved (see the dotted line portion in FIG. 2).

<Effect of embodiment>
As described above, in the present embodiment, by appropriately using the interferometer, the annular mirror 15, the null optical element 13, and the reference mirror 14 in the measurement step S2, the primary mirror 11 and the secondary mirror, which are one type of aspherical mirror, are used. Each of the 12 eccentricities is measured with high accuracy. Further, in the assembly step S3, since the eccentricity information measured with high accuracy is used, the primary mirror 11 and the secondary mirror 12 can be aligned with high accuracy. Therefore, the completed reflection optical system (see FIG. 1) has high performance.

<Others>
In the present embodiment, as shown in FIG. 3, the annular mirror 15 is made of a transmission member, and the measurement light beam transmitted through the annular mirror 15 is incident on the reference plane 14a of the reference mirror 14 (FIG. 3). Reference) is described, but the present invention is not limited to this.
For example, the radial width of the annular mirror 15 is narrowed, and the measurement light beam that has passed further outside the annular mirror 15 is directly incident on the reference plane 14a of the reference mirror 14, and the annular mirror 15 is used as a non-transmissive member. Also good. In this case, in that case, interference fringes indicating the inclination of the null optical element 13 (interference fringes formed by the reflected light of the reference surface 24a and the standard plane 15a) and interference fringes indicating the inclination of the back surface 11b of the main mirror 11 (reference surface 24a). And the interference fringes formed by the reflected light of the reference plane 14a are separated on the observation surface 26a, so that the above-described three types of interference fringes can be easily recognized.

  Further, the shape of the annular mirror 15 is adjusted to an appropriate shape capable of reflecting the measurement light beam incident on the periphery of the null optical element 13 (it does not need to be an annular shape). However, the shape is selected so that the measurement light beam incident on the null optical element 13 and the measurement light beam incident on the reference mirror 14 are prevented as much as possible, and the tilt data of the null optical element 13 can be generated as accurately as possible. It is desirable that In that respect, it is desirable to have a ring shape.

As a method for separating the interference fringes, various known methods can be applied in addition to the method using wavelength modulation. Various known methods for improving detection accuracy can be applied to the interference fringe detection method.
Further, although the Twiman Green type is shown as the form of the interferometer, other types of interferometers may be used as long as the present invention can be applied.

In the above-described embodiment, the Ritchie-Cretian type reflection optical system is manufactured. However, the present invention can also be applied to the manufacture of the Cassegrain type reflection optical system. The present invention can also be applied to the production of other optical systems as long as at least one reflective aspherical optical element is provided.
Incidentally, the optical system shown in FIG. 3 can be applied to the decentration measurement of the concave reflective aspheric surface, and the optical system shown in FIGS. Applicable.

It is a figure which shows the reflective optical system manufactured in embodiment. It is a flowchart which shows the flow of the whole manufacturing method. It is a figure explaining the eccentric measurement of the main mirror. It is a figure explaining attachment of null optical element 13 and annular zone mirror 15. FIG. It is a figure explaining the interference fringe which arises in an interferometer. It is a figure explaining the interference fringe which arises in an interferometer at the time of inclination adjustment of the null optical element. It is a figure which shows the optical system of the periphery of the submirror 12 arrange | positioned at an interferometer. It is a figure which shows the modification of the optical system of the periphery of the submirror 12.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Primary mirror, 12 ... Secondary mirror, 11a, 12a ... Reflecting surface, 14 ... Reference mirror, 15 ... Ring zone mirror, 14a, 15a ... Reference plane

Claims (8)

Placing a reflective aspheric optical element having a first reference surface and a null optical element having a second reference surface in a measurement beam of the interferometer;
Each of the reflective aspheric surface, the first reference surface, and the second reference surface of the reflective aspheric optical element is placed in the interferometer while maintaining the positional relationship between the reflective aspheric optical element and the null element. Detecting on a common reference plane,
A method of measuring the eccentricity of the reflective aspherical optical element based on the result of each detection, and determining the eccentricity of the reflective aspherical optical element based on the first reference surface . In the decentration measuring method of the reflective aspherical optical element according to claim 1,
The first reference surface is a plane fixed in parallel with the back surface of the reflective aspheric optical element,
The second reference plane is a plane fixed perpendicular to the optical axis of the null element. A method for measuring the eccentricity of a reflective aspheric optical element. In the decentration measuring method of the reflective aspherical optical element according to claim 1 or 2,
The method for measuring the eccentricity of a reflective aspherical optical element, wherein the light source of the interferometer is a light source capable of modulating the wavelength of outgoing light. A method of manufacturing an optical system comprising at least one reflective aspheric optical element,
A procedure for measuring the eccentricity of at least one reflective aspherical optical element constituting the optical system by the eccentricity measuring method for a reflective aspherical optical element according to any one of claims 1 to 3,
Assembling the optical system according to the measurement results;
The manufacturing method of the optical system characterized by the above-mentioned. In the manufacturing method of the optical system according to claim 4,
A method of manufacturing an optical system, further comprising a step of reworking the reflective aspherical optical element according to the measurement result.   A reflective aspheric optical element, which is measured by the eccentricity measuring method for a reflective aspheric optical element according to any one of claims 1 to 3.   Reflective aspherical optics, characterized by being measured by the eccentricity measuring method for a reflective aspherical optical element according to any one of claims 1 to 3 and reworked according to the measurement results. element.   An optical system manufactured by the optical system manufacturing method according to claim 4 or 5.

Images