JP2015210241A - Wavefront measurement method, wavefront measurement device, and manufacturing method of optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a transmission wavefront of a specimen with high accuracy.SOLUTION: Specific light from a light source is divided into first light and second light, a first light receiving position when the first light is received by a wavefront sensor 81 and a second light receiving position when the second light is received by an imaging element 80 are measured, light transmitted through a specimen 60 is measured by the wavefront sensor 81, and an image of the specimen 60 is measured by the imaging element 80. A reference point on the wavefront sensor 81 is calculated on the basis of the first light receiving position, the second light receiving position, and the image of the specimen 60, and a transmission wavefront of the specimen 60 is calculated by using a measured value by the wavefront sensor 81 of the light transmitted through the specimen 60 and the reference point.

Description

  The present invention relates to a wavefront measuring method and a wavefront measuring apparatus for measuring a transmitted wavefront of an optical element.

  A mold lens manufactured by a mold has a refractive index distribution inside the lens. Since the refractive index distribution inside the lens adversely affects the optical performance, a technique for measuring the refractive index distribution in a non-destructive manner after molding is necessary for the production of a molded lens.

  In the measurement method disclosed in Patent Document 1, coherent light from a light source is incident on a test object immersed in a test solution having substantially the same refractive index, and an interference fringe is imaged on a detector. To calculate the transmitted wavefront. Then, the reference transmitted wavefront of the test object and the thickness in the optical axis direction of the test object are calculated from the design value of the test object, and the refraction of the test object is calculated from the transmitted wavefront of the test object, the reference transmitted wavefront and the thickness. The rate distribution is calculated. In order to form an interference fringe on the detector, the transmitted light of the test object must be substantially parallel light, so the test object is immersed in a test solution having a refractive index substantially equal to the refractive index of the test object. ing.

  In the measurement method disclosed in Patent Document 2, the first transmitted wavefront is measured by arranging the test object in the first medium having the first refractive index different from the refractive index of the test object, A test object is placed in a second medium having a second refractive index different from the refractive index of 1, and the second transmitted wavefront is measured. And each of the measurement results of the first and second transmitted wavefronts and the reference specimen having the same shape and specific refractive index distribution as the specimen are arranged in the first and second media. Using the transmitted wavefront, the shape component of the test object is removed, and the refractive index distribution projection value of the test object is calculated. Then, a refractive index distribution projection value is calculated in a plurality of arrangements having different angles of the test object with respect to light, and a three-dimensional refractive index distribution of the test object is calculated from the plurality of refractive index distribution projection values.

Japanese Patent Application Laid-Open No. 11-044641 JP 2011-247692 A

  In the method disclosed in Patent Document 1, a test solution having a refractive index substantially equal to the refractive index of the test object is required. However, a test solution having a high refractive index has a low transmittance. For this reason, when the interference fringes of the optical element having a high refractive index are measured by the measurement method disclosed in Patent Document 1, only a small signal is obtained from the detector, and the measurement accuracy of the transmitted wavefront is lowered. When the measurement accuracy of the transmitted wavefront decreases, the calculation accuracy of the refractive index distribution also decreases. In the method disclosed in Patent Document 2, since the refractive index of the test object is different from the refractive index of the medium, the wavefront transmitted through the test object has large aberration. In order to measure the transmitted wavefront of large aberration, it is necessary to accurately calculate a reference point (for example, a center point) of transmitted light. This is because if the calculated reference point is different from the original reference point, a non-rotationally symmetric wavefront error that should not exist is mixed in the measured transmitted wavefront. When the test object is tilted with the transmitted wavefront having large aberration as in the method disclosed in Patent Document 2, the transmitted light beam has a non-rotationally symmetric shape. It is difficult to accurately calculate the reference point from the transmitted light beam having a non-rotationally symmetric shape. Due to the displacement of the reference point, the accuracy of the measured transmitted wavefront is reduced, and the accuracy of calculating the refractive index distribution is also reduced.

  In order to calculate the refractive index distribution of the test object with high accuracy, it is necessary to measure the transmitted wavefront of the test object with high accuracy.

  An object of the present invention is to provide a wavefront measuring method and a wavefront measuring apparatus capable of measuring a transmitted wavefront of a test object with high accuracy.

  The wavefront measuring method as one aspect of the present invention divides specific light from a light source into first light and second light, and the first light reception when the first light is received by a wavefront sensor. A step of measuring a position and a second light receiving position when the second light is received by an imaging device; and light transmitted through the test object by causing light from the light source to enter the test object Is measured by the wavefront sensor, and an image of the test object is measured by the imaging device, based on the first light receiving position, the second light receiving position, and the image of the test object. Calculating a reference point on the wavefront sensor, and calculating a transmitted wavefront of the test object using the measurement value of the light transmitted through the test object by the wavefront sensor and the reference point. It is characterized by.

  An optical element manufacturing method including the steps of molding the optical element and evaluating the optical performance of the molded optical element by measuring the transmitted wavefront of the optical element using the wavefront measuring method described above. This constitutes another aspect of the present invention.

  According to another aspect of the present invention, there is provided a wavefront measuring apparatus that divides a light source, specific light from the light source into first light and second light, and the first light is a wavefront sensor. And measuring the first light receiving position when the second light is received by the imaging device and the second light receiving position when the second light is received by the imaging device, and measuring the light transmitted through the test object by the wavefront sensor. , Based on the measurement means for measuring the image of the test object imaged on the image sensor, the first light receiving position, the second light receiving position, and the image of the test object. A calculation means for calculating a reference point on the wavefront sensor and calculating a transmitted wavefront of the test object using the measurement value of the light transmitted through the test object by the wavefront sensor and the reference point; It is characterized by.

  According to the present invention, the transmitted wavefront of a test object can be measured with high accuracy.

The figure which shows schematic structure of the wavefront measuring apparatus of Example 1 in this invention. FIG. 3 is a diagram illustrating a correspondence relationship between a light receiving position of a wavefront sensor and a light receiving position of an image sensor in the first embodiment. 3 is a flowchart showing a procedure for calculating a transmitted wavefront of a test object in the first embodiment. The figure which shows the optical path of the light ray in the coordinate system defined on the to-be-tested object, and a measuring device. The figure which shows schematic structure of the wavefront measuring apparatus of Example 2 in this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of the wavefront measuring apparatus according to the first embodiment of the present invention. The measuring device includes a light source 10, an interference optical system, a container 50 that can store a test object 60 and a medium 70, an image sensor 80, a wavefront sensor 81, and a computer 90, and measures the transmitted wavefront of the test object 60. In this embodiment, the test object is a lens having a negative refractive power, but is not limited to a lens, and a transmitted wavefront can be measured if it is a refractive optical element such as a flat plate. The refractive index of the medium 70 serves to reduce the refractive power of the test object 60 and does not need to match the refractive index of the test object 60 (for example, the refractive index of the test object is 1. When it is about 9, the refractive index of the medium may be about 1.7).

  The light source 10 is a laser light source (for example, a HeNe laser). The light from the light source passes through the pinhole 30 to become a divergent wave, and passes through the collimator lens 40 to become parallel light.

  The interference optical system includes beam splitters 100 and 101 and mirrors 105 and 106. The interference optical system divides the light that has passed through the collimator lens 40 into reference light that does not pass through the test object and test light that passes through the test object, and causes the reference light and test light to interfere with each other. Is guided to the image sensor 80. The interference optical system guides the test light to the wavefront sensor 81.

  In the container 50, the test object 60, the medium 70, and the glass prism 110 are accommodated. It is preferable that the side surfaces 50a and 50b of the container 50 have the same and parallel thickness and a uniform refractive index.

  Part of the test light incident on the container 50 passes through the medium 70 and the test object 60, and part of the other test light passes through the medium 70 and the glass prism 110. Other test light incident on the container 50 transmits only the medium 70. On the other hand, the reference light transmitted through the beam splitter 100 passes through the side surface of the container 50 and the medium 70 and is reflected by the mirror 105. The reference light and the test light interfere with each other at the beam splitter 101 to form interference light.

  The refractive index of the medium 70 is calculated from the transmitted wavefront of the glass prism 110 having a known refractive index and shape disposed in the medium 70. The refractive index of the medium 70 may be calculated by a method in which the temperature of the medium 70 is measured using a thermometer instead of using the glass prism 110 and converted into the refractive index based on the measured temperature.

  The mirror 105 is driven in the direction of the arrow in FIG. 1 by a drive mechanism (not shown). The driving direction is not limited to the arrow direction in FIG. 1, and may be any direction as long as the optical path length difference between the reference light and the test light changes by driving the mirror 105. The drive mechanism of the mirror 105 is composed of, for example, a piezo stage. The driving amount of the mirror 105 is measured by a length measuring device (not shown) (for example, a laser displacement meter or an encoder) and controlled by the computer 90. The optical path length difference between the reference light and the test light is adjusted by the drive mechanism of the mirror 105.

  The interference light formed by the beam splitter 101 is detected by the image sensor 80 (for example, CCD or CMOS) through the imaging lens 45. The interference signal detected by the image sensor 80 is sent to the computer 90. The image sensor 80 is disposed at a conjugate position with respect to the position of the test object 60 and the glass prism 110 and the imaging lens 45. That is, the imaging lens 45 forms an image of the test object 60 and an image of the glass prism 110 on the image sensor 80.

  In the present embodiment, since the refractive index of the test object 60 and the medium 70 are different, the test light transmitted through the test object 60 becomes a divergent wave. Most of the interference fringes formed by the test light and the reference light that have become diverging waves are so dense that they cannot be resolved by the image sensor 80. Therefore, the image sensor 80 cannot measure most of the interference fringes formed by the test light that passes through the test object 60 and the reference light. However, in this embodiment, the image sensor 80 does not need to detect all interference signals transmitted through the test object 60. The image sensor 80 may detect an interference signal related to the transmitted light transmitted through the medium 70 and the glass prism 110 and an interference signal related to the transmitted light transmitted through the optical center of the test object 60. Since the transmitted light that has passed through the optical center of the test object 60 is parallel to the incident light incident on the test object 60 regardless of the tilt angle of the test object 60, it can be easily detected.

  A part of the test light transmitted through the test object 60 is reflected by the beam splitter 101 and detected by the wavefront sensor 81 (for example, Shack-Hartmann sensor). The signal detected by the wavefront sensor 81 is sent to the computer 90.

  The computer 90 has calculation means for calculating the transmitted wavefront of the test object based on the detection result of the image sensor 80 and the detection result of the wavefront sensor 81, and control means for controlling the driving amount of the mirror 105. It consists of CPU etc.

  In this embodiment, the position where the light beam from the light source is reflected by the beam splitter 101 and reaches the wavefront sensor 81 in a state where the test object is not arranged in the container, and the light beam passes through the beam splitter 101. The position reaching the image sensor 80 is measured in advance. FIG. 2A shows the correspondence between the light receiving position (u, v) on the wavefront sensor 81 and the light receiving position (p, q) on the image sensor 80 for a certain light beam. The correspondence relationship between the light receiving positions can be measured, for example, as follows.

  As a method for measuring the correspondence relationship between the light receiving positions, a pinhole is installed instead of the test object 60 in FIG. The light receiving position (u, v) on the wavefront sensor 81 and the light receiving position (p, q) on the image sensor 80 are measured while scanning the pinhole in a direction perpendicular to the test light. Then, for example, u = f (p), v = g (q) so that the light receiving position (u, v) on the wavefront sensor 81 can be calculated if the light receiving position (p, q) on the image sensor 80 is known. The correspondence is calculated as a function like

FIG. 3 is a flowchart showing a calculation procedure for calculating the transmitted wavefront of the test object 60. First, a test object is placed in a medium (S10). Next, specific light (light beam) in the test light is split into first light and second light by the beam splitter 101, the wavefront sensor 81 receives the first light, and the image sensor 80. Receives the second light. The first light receiving position (u ₀ , v ₀ ) that is the light receiving position of the first light on the wavefront sensor 81 and the second light receiving position (the light receiving position of the second light on the image sensor 80 ( p ₀ , q ₀ ) is measured (S20).

The position of the element of the measuring device in FIG. 1 changes with time due to thermal expansion or the like. The light receiving position measuring step in S20 is a step of calibrating the correspondence relationship u = f (p) and v = g (q) of the light receiving positions measured in advance. The calibration of the correspondence relationship only needs to have at least the correspondence relationship (u ₀ , v ₀ ) and (p ₀ , q ₀ ) for one ray. In addition, the specific light in a present Example refers to the light which does not permeate | transmit the test object 60 or the glass prism 110 among test light.

  The transmitted light of the test object 60 is measured by the wavefront sensor 81 (S30). When measuring the transmitted light of the test object 60, the test light that does not pass through the test object 60 and the reference light are unnecessary light, so that unnecessary light does not enter the wavefront sensor 81 with an aperture, a shutter, or the like. Shield the light.

  Then, the image of the test object 60 imaged on the image sensor 80 is measured (S40). The image formed on the image sensor 80 is an image in which an image showing the contours of the test object 60 and the glass prism 110 and an image of interference fringes formed by the test light and the reference light overlap. As described above, the interference signal related to the transmitted light transmitted through the medium 70 and the glass prism 110 and the interference signal related to the transmitted light transmitted through the optical center of the test object 60 are detected.

FIG. 2B shows the correspondence between the light receiving position (u ₁ , v ₁ ) on the wavefront sensor 81 and the light receiving position (p ₁ , q ₁ ) on the image sensor 80 in the light beam passing through the optical center of the test object 60. Showing the relationship. In FIG. 2B, the container 60, the medium 70, and the like are omitted for simplicity. Since the light transmitted through the optical center of the test object 60 travels in parallel to the light incident on the test object 60, it is easy to use it as a reference point when calculating the transmitted wavefront.

Imaging of light transmitted through the optical center measured from the function u = f (p), v = g (q) calibrated by the first light receiving position and the second light receiving position, and the image of the test object 60 Based on the light receiving position (p ₁ , q ₁ ) on the element 80, a reference point on the wavefront sensor 81 is calculated (S50). Finally, using the measured value of the transmitted light of the test object 60 by the wavefront sensor 81 and the reference point (u ₁ = f (p ₁ ), v ₁ = g (q ₁ )), the transmission of the test object 60 is performed. A wavefront is calculated (S60).

  In general, a signal measured by a wavefront sensor such as a Shack-Hartmann sensor does not have information on where the light that has passed through the test object has reached the wavefront sensor. Therefore, when calculating the wavefront, it is unclear where the reference point is. In particular, when the test object is tilted, the signal received by the wavefront sensor has a non-rotationally symmetric shape, making it difficult to accurately calculate the reference point. Since the exact reference point is not known, the calculated wavefront contains an error.

  On the other hand, in this embodiment, the coordinates at which the light passing through the optical center of the test object reaches the wavefront sensor are accurately specified, and the wavefront is calculated using the coordinates as a reference point. Can be calculated.

  In this example, the transmitted wavefront measured at the position of the wavefront sensor 81 was calculated. In general, the wavefront changes depending on the environment to be measured (for example, the distance between the test object 60 and the wavefront sensor 81, the refractive index of the medium 70, etc.). In order to evaluate the performance of the optical element, it is necessary to convert it into a physical quantity specific to the optical element that is not influenced by the environment. A method for calculating wavefront aberration (optical path length distribution) and refractive index distribution, which are one of the physical quantities peculiar to the optical element, is as follows.

The transmitted wavefront W _m (λ, x, y) of the test object 60 at the wavelength λ passing through the point (x, y) in the test object 60 shown in FIG. . A point (0, 0) in FIG. 4A indicates the optical center of the test object 60.

However, L _a (x, y), L _b (x, y), L _c (x, y), and L _d (x, y) are constituent elements along the light beam shown in FIG. The geometric distance between. The light ray in FIG. 4B indicates a light ray passing through the point (x, y) inside the test object 60 shown in FIG. L (x, y) is the geometric distance of the optical path of the light beam in the test object 60, that is, the thickness of the test object in the light beam direction. n ^sample (λ, x, y) is the refractive index of the test object 60 at the wavelength λ, and n ^medium (λ) is the refractive index of the medium 70 at the wavelength λ. Here, for simplicity, the thickness of the side surfaces 50a and 50b of the container 50 is ignored.

Next, the transmitted wavefront W _sim (λ, x, y) of the reference specimen having a specific refractive index distribution is calculated. Here, a test object (reference test object) having the same shape and uniform refractive index distribution n ^sample (λ, 0, 0) as the test object 60 is assumed, and the reference test object is the test object 60. The transmitted wavefront is calculated in the state where it is arranged at the same position. The transmitted wavefront W _sim (λ, x, y) of the reference specimen is expressed as Equation 2. In this embodiment, the refractive index n ^sample (λ, 0, 0) of the reference specimen is a known value.

When calculating the transmitted wavefront W _sim (λ, x, y) of the reference _specimen , the refractive index n ^medium (λ) of the medium 70 is required. The refractive index n ^medium (λ) of the medium 70 can be calculated from the transmitted wavefront of the glass prism 110 whose refractive index and shape are known. The transmitted wavefront of the glass prism can be measured using a phase shift method that drives the mirror 105.

Then, if the difference between the transmitted wavefront W _m (λ, x, y) of the test object 60 and the transmitted wavefront W _sim (λ, x, y) of the reference test object is taken, the wavefront aberration ( Optical path length distribution) W (λ, x, y) is obtained. If the wavefront aberration W (λ, x, y) is divided by the thickness L (x, y) of the test object, the refractive index distribution GI (λ, x, y) of the test object 60 is calculated. The wavefront aberration W (λ, x, y) and the refractive index distribution GI (λ, x, y) of the test object 60 are expressed as Equation 3.

  In Expressions 1 to 3, it is assumed that the test object 60 and the reference test object have the same shape L (x, y). When the shape of the test object 60 is different from the shape of the reference test object, the obtained wavefront aberration and refractive index distribution include errors. Therefore, it is desirable to use a method of measuring the shape of the test object 60 in advance and applying the shape to the shape of the reference test object. Alternatively, a design value L (x, y) may be applied as the shape of the reference test object, and a method of removing a shape error (shape component) δL (x, y) from the design value of the test object 60 may be used. Good.

The shape error δL (x, y) can be removed using wavefront aberrations at two different wavelengths. First, transmitted light is measured at a _first wavelength λ ₁ (for example, λ ₁ = 543 nm), and a transmitted wavefront W _m (λ ₁ , x, x) at the first wavelength is determined from the transmitted light at the first wavelength and the reference point. y) is calculated. Next, the transmitted light is measured at the second wavelength λ ₂ (for example, λ ₂ = 633 nm), and the transmitted wavefront W _m (λ ₂ , x at the second wavelength is measured from the transmitted light at the second wavelength and the reference point. , Y) is calculated. The transmitted wavefront W _m (λ _k , x, y) at the k-th wavelength is expressed as Equation 4. However, k = 1,2.

Similar to Equation 2, the transmitted wavefront of the reference specimen at the first wavelength and the transmitted wavefront of the reference specimen at the second wavelength are calculated. In addition, the wavefront aberration W (λ ₁ , x, y) of the test object 60 at the first wavelength and the wavefront aberration W (λ ₂ , x, y) of the test object 60 at the second wavelength are calculated. . The wavefront aberration W (λ _k , x, y) at the k-th wavelength is expressed as Equation 6 using the approximate equation of Equation 5.

Using the wavefront aberrations W (λ ₁ , x, y) and W (λ ₂ , x, y) of the test object 60 at the first and second wavelengths and the approximate expression of Equation 7, the shape component δL (x, y ), ΔL (0, 0) is removed. Accordingly, the refractive index distribution GI (λ ₁ , x, y) at the first wavelength and the refractive index distribution GI (λ ₂ , x, y) at the second wavelength are calculated as in Expression 8.

  The shape error δL (x, y) can be removed by immersing the test object in each of two types of media having different refractive indexes and measuring the transmitted wavefront instead of using two different types of wavelengths. The shape component removal method using two types of media is as follows.

  First, the first transmitted light of the test object 60 in a first medium having a first refractive index (for example, oil having a refractive index of 1.70) and the test image formed on the image sensor 80. A first image of the object 60 is measured. Next, the second transmitted light of the test object 60 in a second medium having a second refractive index different from the first refractive index (for example, oil having a refractive index of 1.75), and an image sensor A second image of the test object 60 imaged on 80 is measured.

  Then, a first reference point of the first transmitted light is calculated based on the first light receiving position, the second light receiving position, and the first image, and the first light receiving position, the second light receiving position, and the first light receiving position are calculated. The second reference point of the second transmitted light is calculated based on the two images. The first transmitted wavefront of the test object 60 is calculated using the first transmitted light and the first reference point, and the first transmitted wavefront of the test object 60 is calculated using the second transmitted light and the second reference point. Two transmitted wavefronts are calculated.

Similar to Equation 2, the transmitted wavefront of the reference specimen in the first medium and the transmitted wavefront of the reference specimen in the second medium are calculated. Further, the wavefront aberration W ₁ (λ, x, y) of the test object 60 in the first medium and the wavefront aberration W ₂ (λ, x, y) of the test object 60 in the second medium are calculated. . The wavefront aberration W _k (λ, x, y) in the k-th medium is expressed as Equation 9 using the approximation of Equation 5. Here, n _k ^medium (λ) is the refractive index of the kth medium.

Finally, from the wavefront aberrations W ₁ (λ, x, y) and W ₂ (λ, x, y) of the test object 60 in the first and second media, shape components δL (x, y), δL ( (0, 0) is removed, and the refractive index distribution GI (λ, x, y) is calculated as in Expression 10.

  The refractive index of the medium changes as the temperature of the medium changes. Therefore, if the present embodiment is performed under two different temperatures even with one type of medium, it is the same as the present embodiment performed with two types of media having different refractive indexes. Therefore, the shape component of the test object 60 may be removed using two types of temperatures.

  In this embodiment, a Shack-Hartmann sensor is used as the wavefront sensor 81. The wavefront sensor 81 may be any wavefront sensor that can measure a transmitted wavefront having a large aberration. As the wavefront sensor 81, a wavefront sensor using the Hartmann method or a wavefront sensor using a shearing interferometry such as a Talbot interferometer can be used.

  In this embodiment, a Mach-Zehnder interferometer is used for the interference optical system. Instead, any interferometer such as a Twiman Green interferometer that can know the optical path length difference between the reference light and the test light may be used.

  In this example, the first light receiving position and the second light receiving position in specific light were measured after the test object 60 was placed in the medium 70. Instead, the first light receiving position and the second light receiving position may be measured before placing the test object 60.

  In this example, the reference point was calculated based on the light transmitted through the optical center of the test object. Instead, the reference point may be calculated from the outer shape (contour) of the test object, or the reference point may be calculated by calculation based on the tilt angle of the test object and the design value of the test object. .

  In this example, a method for calculating the transmitted wavefront of the test object 60 without using the interference optical system used in Example 1 will be described. FIG. 5 is a diagram showing a schematic configuration of the wavefront measuring apparatus according to the second embodiment of the present invention. The wavefront sensor uses a Talbot interferometer including a two-dimensional diffraction grating 83 and a two-dimensional sensor 82 such as a CCD or CMOS. The light source 11 is a laser diode, and the test object 60 is a lens having a positive refractive power. The same configurations as those in the first embodiment will be described with the same reference numerals.

  The light from the light source 11 becomes a divergent wave through the pinhole 30 and becomes a parallel light through the collimator lens 40. In the container 50, a test object 60, a medium 70, and a thermometer (not shown) are arranged. The refractive index of the medium 70 is calculated using the temperature of the medium 70 measured by a thermometer and the temperature coefficient of the refractive index of the medium 70. A part of the light transmitted through the container 50 passes through the beam splitter 101 and is detected by the image sensor 80 through the imaging lens 45. A part of the light transmitted through the container 50 is reflected by the beam splitter 101 and detected by a Talbot interferometer including a two-dimensional diffraction grating 83 and a two-dimensional sensor 82. The image sensor 80 is disposed at a position conjugate with the position of the test object 60 and the imaging lens 45.

  A method for measuring the wavefront of the test object 60 in this embodiment will be described below. In the method of this embodiment, first, specific light is split into first light and second light by the beam splitter 101, and the first light is received by the Talbot interferometer (wavefront sensor). And the second light receiving position when the second light is received by the image sensor 80 are measured. After disposing the test object 60 in the medium 70, the transmitted light that passes through the test object 60 and converges is measured with a Talbot interferometer, and the image of the test object 60 imaged on the image sensor 80 is measured. To do.

  The center of the image of the test object 60 is calculated from the outer shape of the image of the test object 60 formed on the image sensor 80. A reference point of transmitted light is calculated based on the first light receiving position, the second light receiving position, and the center calculated from the image of the test object 60. The transmitted wavefront of the test object is calculated using the transmitted light and the reference point of the transmitted light.

  In this example, unlike Example 1 in which the reference point was calculated based on the interference fringes, the reference point was calculated based on the outer shape of the image of the test object 60. The reference point calculation method using interference fringes cannot measure the eccentricity of the refractive index distribution because the reference point shifts due to the influence of the refractive index distribution when the refractive index distribution is eccentric in the specimen. . On the other hand, since the reference point calculation method using the outer shape can calculate the reference point without being affected by the eccentricity of the refractive index distribution, the eccentricity amount of the refractive index distribution can also be calculated. However, it is necessary to obtain an image of the test object with high resolution.

  Using the apparatus and method described in the first and second embodiments, it is also possible to feed back the result of the measured transmitted wavefront to a method for manufacturing an optical element such as a molded lens.

  The optical element is manufactured through an optical element design process, a mold design process, and an optical element mold process using the designed mold. The molded optical element is evaluated for its shape accuracy, and when the accuracy is insufficient, the mold is corrected and the molding is performed again. If the shape accuracy is good, the optical performance of the optical element is evaluated. Incorporating the transmission wavefront calculation flow described with reference to FIG. 3 into the optical performance evaluation step enables mass production of optical elements molded using a high refractive index glass material as a base material. If the optical performance is low, the optical element whose optical surface is corrected is redesigned.

  The embodiments described above are merely representative examples, and various modifications and changes can be made to the embodiments when the present invention is implemented.

60 Test Object 80 Image Sensor 81 Wavefront Sensor 101 Beam Splitter

Claims (11)

Specific light from the light source is divided into first light and second light, and the first light receiving position when the first light is received by the wavefront sensor, and the second light is captured by the image sensor. Measuring a second light receiving position when light is received;
Making the light from the light source incident on the test object, measuring the light transmitted through the test object with the wavefront sensor, and measuring the image of the test object with the imaging device;
A reference point on the wavefront sensor is calculated based on the first light receiving position, the second light receiving position, and the image of the test object, and the light transmitted through the test object is generated by the wavefront sensor. A wavefront measurement method comprising: calculating a transmitted wavefront of the test object using a measured value and the reference point.   Based on the first light receiving position, the second light receiving position, and the light receiving position on the image sensor of the light transmitted through the optical center of the test object measured from the image of the test object, The wavefront measurement method according to claim 1, wherein the reference point is calculated.   The reference point is calculated based on the first light receiving position, the second light receiving position, and the center of the image of the test object calculated from the outer shape of the image of the test object. The wavefront measuring method according to claim 1.   When the light from the light source is incident on a pinhole, the light that has passed through the pinhole is divided into the first light and the second light, and the first light is received by the wavefront sensor 4. The wavefront measurement according to claim 1, wherein a first light receiving position and a second light receiving position when the second light is received by the imaging device are measured. 5. Method.   Calculating a wavefront aberration which is a difference between a transmitted wavefront of the test object and a transmitted wavefront when a reference test object having a specific refractive index distribution is arranged at the position of the test object, The wavefront measuring method according to any one of claims 1 to 4. Measuring the transmitted light of the test object at a first wavelength and the transmitted light of the test object at a second wavelength different from the first wavelength with the wavefront sensor;
Using the measured value of the transmitted light of the test object at the first wavelength and the reference point, the transmission wavefront of the test object at the first wavelength is calculated, and the test object at the second wavelength is calculated. Using the measured value of the transmitted light of the test object and the reference point, the transmitted wavefront of the test object at the second wavelength is calculated, and the transmitted wavefront of the test object at the first wavelength and the first wave 2. The method according to claim 1, further comprising: calculating a refractive index distribution of the test object by removing a shape component of the test object based on a transmitted wavefront of the test object at two wavelengths. 6. The wavefront measuring method according to any one of 5 above. The first transmitted light of the test object in the first medium having the first refractive index and the test in the second medium having a second refractive index different from the first refractive index. Measuring the second transmitted light of the object with the wavefront sensor;
Measuring a first image of the test object in the first medium and a second image of the test object in the second medium with the imaging device;
A first reference point of the first transmitted light is calculated based on the first light receiving position, the second light receiving position, and the first image, and the first light receiving position, A second reference point of the second transmitted light is calculated based on the second light receiving position and the second image, and the measured value of the first transmitted light, the first reference point, Is used to calculate the first transmitted wavefront of the test object, and the second transmitted wavefront of the test object is calculated using the measured value of the second transmitted light and the second reference point. And calculating a refractive index distribution of the test object by removing a shape component of the test object based on the first transmitted wavefront and the second transmitted wavefront. The wavefront measuring method according to any one of claims 1 to 5. Molding the optical element;
Evaluating the optical performance of the molded optical element by measuring the transmitted wavefront of the optical element using the wavefront measuring method according to any one of claims 1 to 7. A method for manufacturing an optical element. A light source;
Specific light from the light source is divided into first light and second light, and the first light receiving position when the first light is received by a wavefront sensor, and the second light is an image sensor. And measuring the second light receiving position when the light is received by the laser, measuring the light transmitted through the test object with the wavefront sensor, and measuring the image of the test object formed on the image sensor. Means,
A reference point on the wavefront sensor is calculated based on the first light receiving position, the second light receiving position, and the image of the test object, and the light transmitted through the test object is generated by the wavefront sensor. A wavefront measuring apparatus comprising: a calculation unit that calculates a transmitted wavefront of the test object using a measured value and the reference point.   The wavefront measuring device according to claim 9, wherein the wavefront sensor is a Shack-Hartmann sensor.   The wavefront measuring apparatus according to claim 9, wherein the wavefront sensor is a Talbot interferometer.

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