JPH07167738A - Aspherical surface measurement method - Google Patents

Abstract

PURPOSE:To provide a method for measuring an apsherical surface which can easily and rapidly adjust alignment with a simple configuration without adding a complex device when measuring an optical element, especially an aspherical surface. CONSTITUTION:A measuring optical system for light flux from a laser oscillator 1, applying it an aspherical surface 21a to be detected of an aspherical surface lens 21 through a focusing lens 19, overlapping reflection light from the aspherical surface 21a to be detected to reference light where the light flux from the above last oscillator 11 is split by a hologram 23, and then forming interference fringes by interference on an observation surface 53 after diffraction is provided to measure the shape of the aspherical surface 21a to be detected based on the above interference fringes and a stage for compensating the inclination for the light axis of the focusing lens 19 of the light axis of the aspherical surface lens 21 by adjusting the direction of the above reference light toward the hologram 23 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical surface measuring method for measuring an aspherical surface shape by using a holographic technique.

[0002]

2. Description of the Related Art In recent years, aspherical lenses have been widely used in optical devices such as photographing lenses of cameras. This is because the aspherical lens can be mass-produced relatively inexpensively due to the progress of the optical plastic molding technology. At the mass production stage of aspherical lenses, it is necessary to quickly measure whether or not the aspherical shape is formed with high precision as designed.

Conventionally, as a method for measuring an aspherical surface, a method utilizing a holographic technique has been known. The applicant of the present invention has also previously developed and applied for an aspherical surface measuring method and measuring device (Japanese Patent Laid-Open No. 4-240534). The aspherical surface measuring device previously developed by the applicant of the present invention is a hologram that is obtained by superimposing and photographing the reflected light from the aspherical surface prototype that is formed with high accuracy in advance according to the design value and is accurately arranged, and the reference light. To form. Next, after returning this hologram to the shooting position after the development processing and disposing the aspherical lens, which is the surface to be inspected, at the same position as the aspherical prototype, the interference fringes observed on the observation surface are The shape error from the design value, which is the difference from the aspherical prototype, can be easily measured.

However, in reality, the interference fringes obtained include an alignment error due to a molding error of the outer shape of the aspherical lens, a mounting error when mounting the aspherical lens on the measuring device, and the like. The adjustment work for removing this alignment error is extremely difficult, and a large amount of time is required for the adjustment. That is, in the spherical surface measurement, only the translational adjustment of the three axes of the XYZ coordinate system was sufficient, but for the aspherical surface, it is necessary to further adjust a total of five axes including the inclinations Δθx and Δθy about the X and Y axes. was there. Here, the Z axis is the incident direction of the test light to the test lens, that is, the optical axis direction of the measurement optical system in which the test lens is placed, and X and Y are two orthogonal directions perpendicular to the optical axis O.

Generally, assuming that the surface to be inspected is deviated by δx in the X-axis direction and δy in the Y-direction, the interference fringes have a tilt component (tilt fringe) and a coma aberration component (coma fringe) in each direction. The included pattern (interference fringe) is observed. On the other hand, when tilted about the X and Y axes by Δθx and Δθy, a pattern including most of the tilt component and a slight coma component is observed in the interference fringes. The appearance of interference fringes due to only the tilt component and only coma is shown in FIGS. 2B and 3B. If coma is included in the tilt component,
It appears as shown in. Further, the deviation of the surface to be inspected in the Z-axis direction causes a defocus component in the interference fringes. Generally, these three errors are overlapped with each other, and interference fringes are observed.
Here, unlike other errors, the defocus component appears as an axially symmetric pattern, and thus can be adjusted relatively easily (see FIG. 4B).

However, errors due to lateral displacement and inclination of the surface to be inspected generate interference fringes that are close to each other and are difficult to separate from each other. Therefore, the alignment adjustment of the lens increases the number of trial and error steps and the adjustment time becomes long. , There was a problem.

Further, there is known a method of manually adjusting up to a point where interference fringes having a certain degree of coarseness are obtained, and the remaining alignment error is obtained and adjusted by an interference fringe analysis method such as a fringe scanning method using a computer and a scanning means. Has been. However, according to this method, there is a problem that the apparatus becomes expensive as a whole and the fringe analysis time becomes long, and it is difficult to apply the method on a mass production site.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aspherical surface which can be easily and quickly adjusted in a short time with an inexpensive and simple structure without adding a complicated device when measuring an optical element, particularly an aspherical surface. It is intended to provide a measuring method of.

[0009]

SUMMARY OF THE INVENTION To achieve this object, the present invention divides a light beam from a coherent light source and irradiates the test surface of a test optical element with the test light, which is reflected light from the test surface. , Having a measurement optical system for forming interference fringes by causing interference with the reference light obtained by dividing the light flux from the coherent light source by the hologram after being diffracted by the hologram, and based on the interference fringes. A measuring method for measuring the shape of a surface to be inspected, characterized by having an adjusting step of tilting the reference light from an initially set direction.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments. FIG. 1 is an optical path diagram of an aspherical surface measuring apparatus to which the aspherical surface measuring method of the present invention is applied. The laser emitted from the laser oscillator 11 as a light source for projecting the coherent light becomes a parallel light flux having a large diameter by the objective lens 13 and the collimator lens 15. This light flux passes through the second half mirror 33 and the first half mirror 17, is focused by the condenser lens 19, and is reflected by the aspherical surface (test surface) 21a of the aspherical lens 21 arranged at the test position. The optical path travels in the opposite direction, passes through the condenser lens 19, and is reflected by the first half mirror 17 in a direction substantially at a right angle. Then, the light passes through the hologram 23 arranged on the recording surface 51 and is imaged on the photosensitive surface (observation surface 53) of the CCD image sensor 27 by the imaging lens 25. Here, the direction in which the test light is incident on the aspherical lens 21, that is, the optical axis of the condenser lens 19 is the optical axis O of the measurement optical system.
And the Z axis of the X, Y, Z coordinate system.

The aspherical lens 21 is the lens holder 1 to be tested.
Held on 00. Here, in the case of measurement in a mass production process, in consideration of workability, the measuring device necessarily has a vertical shape, and the lens holding table 100 is arranged vertically below,
The measuring optical system and the measuring device are arranged vertically above. The lens holding base 100 includes a lens mounting recess 101 for fitting and holding the aspherical lens 21, and a circular hole 104 formed in a bottom 103 of the lens mounting recess 101.
The inner peripheral surface of the lens mounting concave portion 101 constitutes a lens guide surface 102 that abuts on the peripheral edge portion of the aspherical lens 21 and guides the aspherical lens 21 so as to be vertically dropped straight. If the contact surface of the aspherical lens is convex,
The upper peripheral edge portion 105 of the hole 104 contacts the aspherical lens to hold the aspherical lens, and when the contact surface of the aspherical lens is concave, the bottom surface 103 contacts the peripheral edge portion of the aspherical lens and the aspherical lens. Hold. In the present embodiment, the second surface 21b of the aspherical lens 21 is held in contact with the upper end peripheral portion 105.

Further, the lens holding base 100 can be moved in the optical axis O (Z-axis) direction by a moving stage or the like.
They are supported so as to be capable of translational movement in directions (X-Y axis directions) orthogonal to the axes. The movement in the Z-axis direction adjusts the defocus, and the movement in the XY-axis direction adjusts the lateral shift.

The hologram 23 uses an ultra-high-resolution photosensitive material as a medium. An aspherical prototype (not shown) is placed on the lens holding table 100, and the high-resolution photosensitive material is placed on the recording surface 51. The recording (exposure and development) is performed by irradiating the reflected light from the aspherical prototype and the reference light.

On the other hand, a part of the parallel light flux emitted from the laser oscillator 11 and transmitted through the second half mirror 33 is
The light is reflected by the half mirror 17 in the direction opposite to the CCD image sensor 27, further reflected by the fixed reference mirror 29 and the movable reference mirror 31, passes through the first half mirror 17, and enters the hologram 23. And
The light beam incident on the hologram 23 is diffracted by the hologram 23, travels in the same direction as the test light from the aspherical lens 21, and is moved by the imaging lens 25 to the CCD image sensor 27.
Imaged above. The parallel light flux reflected by these reference mirrors 29 and 31 becomes reference light.

Here, in this embodiment, the movable reference mirror 3 is used.
1 is configured to be rotatable in two directions orthogonal to the normal line of the reflecting surface. It should be noted that these two directions are an in-plane direction (parallel to the paper plane) and a direction orthogonal to the paper plane in FIG.

The CCD image sensor 27 captures an interference fringe resulting from superposition of the test light reflected by the aspherical surface 21a of the aspherical lens 21 and the reference light reflected by the reference mirrors 29 and 31. This interference fringe is obtained as a difference from the aspherical shape of the aspherical prototype 55, that is, a difference from the design shape. Therefore, the CCD image sensor 2
By reproducing this interference fringe imaged by 7 on the TV monitor 41 for observation or measurement, the aspherical lens 21
It is possible to know the processing accuracy and state of. The interference fringes observed here use the same optical system for recording the aspherical prototype and for measuring the lens under test, that is, the condensing lens 19 and the first half mirror 17 are used. Since the light flux passes, the aberrations of the optical system cancel each other during recording of the aspherical prototype and measurement of the lens shape to be inspected, and no measurement error due to the optical system of the measuring device occurs.

Further, the aspherical surface 21a (test surface) and the hologram 23 (recording surface) are arranged in a conjugate relationship, and the hologram 23 and the CCD image sensor 27 (observation surface).
And are arranged in a conjugate relationship. By arranging in such a conjugate relationship, the coordinates on the surface to be inspected and the coordinates on the observation surface correspond one-to-one, and the inclination of the reference light (angle of incidence on the hologram 23 when measuring the lens to be inspected). ) Is not affected by the aberration, and alignment adjustment becomes easy.

In this embodiment, it is possible to measure a spherical lens. A part of the parallel light flux emitted from the collimator lens 15 is reflected by the second half mirror 33 in a direction substantially at a right angle, and further reflected by the third mirror 35 that produces the second reference light flux, and travels backward in the optical path. Half mirror 3
After passing through 3, the image is formed on the CCD image sensor 39 by the image forming lens 37. The light flux that has passed through the second half mirror 33 is reflected on the surface to be inspected by the condenser lens 19, passes through the condenser lens 19 and travels backward in the optical path, is reflected by the second half mirror 33, and forms the imaging lens 37. An image is formed on the CCD image sensor 39 by. An interference fringe is obtained on the CCD image sensor 39 by superimposing these two lights. By imaging this interference fringe with the CCD image sensor 39 and displaying it on the TV monitor 42, the spherical shape of the spherical lens can be measured.

When the surface to be inspected is an aspherical lens, it is reflected by the aspherical surface 21a of the aspherical lens 21 and focused on the focusing lens 19.
A part of the light beam that has passed through the first half mirror 17 travels backward in the optical path to the second half mirror 33 as a parallel light beam, is reflected by the second half mirror 33 toward the imaging lens 37, and the CCD image sensor 39 up. Therefore, the light reflected by the third mirror 35 and the test light reflected by the aspherical lens 21 interfere on the light receiving surface of the sensor 39 to form an interference fringe. By observing this interference fringe, the alignment state of the aspherical lens 21 can be checked. However, since the rough portion of the interference fringes can be formed into an annular shape, it is difficult to measure depending on the surface to be inspected. When the tilt, coma and various aberrations of the aspherical lens 21 do not exist, the interference fringes are concentric.

Now, if there is an alignment error of the aspherical lens 21, that is, an error that occurs when the set position is relatively different from the aspherical prototype with respect to the measuring device, there is tilt, coma aberration, and defocusing, which causes an observation surface. Interference fringes are generated on 53. 2 to 4 show only the tilt,
The states of the wavefronts when only coma and only defocus are generated respectively are shown.
In the figure, reference numeral (A) is a three-dimensional plot of the wavefront aberration on the observation surface 53, and reference numeral (B) is the observation surface 5.
3 is a front view showing the appearance of interference fringes on FIG. 3, and symbol (C) is a diagram showing wavefront aberration in a vertical cross section passing through the optical axis O and the Y axis in FIG.

When measuring the aspherical shape of the aspherical lens, usually, as described above, first, the hologram 23 is formed by exposing and developing with a reference aspherical prototype. As the hologram 23, a computer generated hologram which does not require an aspherical prototype may be used.

When the hologram 23 is completed, the hologram 23 is set at a predetermined position, and then the aspherical lens 2 to be inspected is set.
1 is placed on the lens holding table 100, and X of the aspherical surface 21a,
Adjust the deviation in the Y and Z axis directions. Lens holder 100
Is arranged vertically below, and the measuring optical system and the measuring device are arranged vertically above. Here, not only the eccentricity (lateral deviation) or inclination of the aspherical surface itself but also the facing surface 21 of the aspherical lens 21 on the lens holding edge portion 104 of the lens holding base 100.
Since b is abutted, the aspherical lens is inclined with respect to the abutting part with respect to the optical axis O, and further, the clearance between the lens guide surface 102 and the peripheral contour of the aspherical lens 21 inevitably causes the aspherical lens 21 to be tested. With respect to the optical axis O of the measuring apparatus, the inclinations Δθx, Δθy and the lateral deviation δx,
yields δy.

Next, the adjusting method in this embodiment will be described in comparison with the conventional adjusting method. The aspherical lens 21 to be tested is an aspherical lens having an effective radius of 7.20 mm and an aspherical surface 21 a having an aspherical surface expression 1.

[Equation 1] Paraxial r: -27.682 (mm) k: 0.00000 α ₄ : -2.79670 × 10 ^-5 α ₆ : 7.25141 × 10 ^-8 α ₈ : -6.30504 × 10 ^-9 α ₁₀ , α ₁₂ : 0.00000 × 10 ^-0

The aspherical surface 21a to be tested has an effective radius (h
= Hmax) and the amount of aspherical surface is 0.111 mm and λ = 0.6328 μm, the aspherical surface produces a wavefront aberration of 350 λ back and forth. Here, as an alignment error of the aspherical surface 21a to be tested, an interference fringe (hereinafter referred to as “interference fringe” based on a tilt error (hereinafter, referred to as “an inclination error Δθ” of 1 ′ exists and a lateral deviation δ (direction is arbitrary) of 10 μm) exists. The interference fringes based on the "tilt fringes") and coma aberration (hereinafter referred to as "coma aberration fringes") are observed in the number shown in Table 1.

[Table 1]

Table 1 shows the relationship between the tilt Δθ and the lateral deviation δ of the aspheric surface to be tested and the tilt fringes and coma fringes of the observed interference fringes. In this example, if a tilt Δθ of 1'occurs on the aspheric surface to be tested, tilt fringes will be 13.2.
And 0.65 coma fringes appear, and if a lateral deviation δ of 10 μm occurs on the aspherical surface under test, 16.4 tilt fringes and 6.70 coma fringes appear.

What is characteristic here is that the influence of the inclination Δθ of the surface to be inspected is largely related to the number of tilt fringes and is hardly related to the coma aberration fringes (however, it is not 0) and the lateral shift. δ has a great relation to the number of coma fringes.

The relationship between the conventional adjustment procedure and the wavefront aberration under such conditions will be described with reference to Table 2. In the conventional alignment adjustment method for an aspherical lens to be inspected, the surface to be inspected is tilted with respect to the optical axis and laterally offset in the direction orthogonal to the optical axis for adjustment, and the tilt and lateral offset are independently adjusted. It was done in stages. Where the slope Δθ
1 ', a lateral deviation δ of 10 μm occurs, and the error caused by each is in the same direction, 29.6 tilt fringes (13.2 + 16.4 = 29.6) and 7.35 coma aberration fringes (0.65+).
3.7 = 7.35) The conventional adjustment method in the case where it appears (see (1) in Table 2) will be described with reference to Table 2.

[Table 2]

First, in order to confirm the number of coma aberration fringes, which are aberrations caused by the alignment error, the number of tilt fringes, which are more numerous than the coma aberration fringes, is reduced. Therefore, due to the characteristics of the interference fringes with the surface to be inspected, the inclination of the surface to be inspected is first adjusted. Here, the inclination .DELTA..theta.a of the aspherical surface to be tested is rotationally adjusted by .DELTA..theta.a = (29.6 / 13.2) .apprxeq.2.4 'in the direction in which the number of generated tilt fringes decreases. By adjusting this inclination Δθa, the inclination Δθ =
-1.2 ', tilt fringes are 0, and coma aberration fringes are 5.89 (-2.2 x 0.65 + 7.35 = 5.89) (see Table 2 (2)).

Next, in order to eliminate the 5.89 comatic aberration fringes, δa =
(5.89 / 6.70) × 10 ≒ Move by 8.8 μm. By adjusting the lateral deviation δa, the lateral deviation δ = 1.2 μm and the coma fringes become 0, but −14.4 tilt fringes occur (see Table 2 (3)). Here, originally, the remaining coma fringes become 0, but since many tilt fringes are generated, the situation cannot be visually recognized.

Therefore, this time, the inclination Δθa of the aspheric surface to be tested is rotationally adjusted by Δθa = (14.4 / 13.2) ≈1.1 ′ in the direction in which the tilt fringes are reduced so that the number of tilt fringes is zero. By adjusting this inclination Δθa, the inclination Δθ = −0.1
′, Tilt fringe is 0, but coma fringe is about 0.7
One occurs (see Table 2 (4)).

Then, again, in order to make the coma aberration fringes zero, the aspherical surface to be inspected in the direction of canceling the coma aberration fringes, δa = 10 ×
(0.71 / 6.70) ≒ Move by 1.1 μm. However, this lateral deviation adjustment results in lateral deviation δ = 0.2 μm, and coma aberration fringes are reduced to 0, but tilt fringes of −1.7 are generated (see Table 2 (5)). Here, since the number of tilt fringes has decreased, it can be visually recognized that the number of coma aberration fringes has finally reached 0.

In this manner, the adjustment of the inclination Δθa of the aspherical surface under test and the adjustment of the lateral deviation δ in the direction orthogonal to the optical axis are alternately performed until the number of tilt fringes and the number of coma aberration fringes fall below the allowable values. It repeats.

In the conventional adjusting method described above, the lateral deviation δ does not occur when adjusting the inclination of the optical axis of the aspherical surface to be inspected.
However, this assumption holds only when the rotation axis of the surface to be inspected coincides with the apex (optical center) of the aspherical surface to be inspected. Actually, this assumption is not always satisfied, and there is a problem that if this condition is broken, adjustment takes a lot of time. Moreover, since the conventional adjustment method cannot separately adjust the interference fringes due to the tilt error and the interference fringes due to the coma aberration, the adjustment is complicated when the conditions are broken as described above.

From this conventional measuring method, what is important for alignment adjustment is how to facilitate visual recognition by preventing the coma aberration component, which is the necessary information, from being buried in the tilt component, which is the unnecessary information. It can be seen that the ease of visual recognition determines the adjustment time.

The present invention made based on the above analysis will be further described with reference to FIGS. 6 to 8. The state of the interference fringes passing through the optical axis in the observation plane is shown in the graph of FIG. In FIG. 6, the horizontal axis ρ indicates the aspherical lens 21.
Where h is the height (radius) from the optical axis and hmax is the effective radius (effective radius D), the value is expressed by h / hmax, and the vertical axis Δω (book) is the deformation of the interference fringes. Is the amount. The values of Table 1 already mentioned are the values of ρ = 1 in this graph. From this graph, the amount of deformation Δω of the interference fringe is the lateral deviation δ of the aspherical surface.
It can be seen that the amount of dependence on the slope Δ is sufficiently smaller than the lateral deviation δ of the aspherical surface.

The measuring apparatus of the present invention made by paying attention to this point is characterized in that the coma aberration component and the tilt component can be separated and independently adjusted. In other words, tilt the reference beam that was initially set during alignment adjustment,
Only the tilt component caused by the alignment error of the aspherical surface to be inspected is independently corrected to improve the adjustment efficiency. Specifically, the coma aberration component is adjusted by moving the aspherical lens to be inspected, and the tilt component is adjusted by inclining the reference light without tilting the aspherical lens to be inspected. . As described above, in the apparatus of the present embodiment, all coma aberration components of the aspherical surface to be tested can be eliminated only by adjusting the translational deviation of the aspherical lens to be tested.

The operation principle of the embodiment for realizing the idea of the present invention will be further described with reference to FIG. In FIG. 7, the direction orthogonal to the paper surface is the X axis, and the axis orthogonal to the X axis and the optical axis O in the paper surface is the Y axis. The movable reference mirror 31 is configured to be rotatable about an X-axis direction axis and a Y-axis direction axis whose axes extend in a direction perpendicular to the center of the reflecting surface. Here, consider a case where the movable reference mirror 31 is inclined by Δφ about the X-axis direction axis. As shown in FIG. 7, when the movable reference mirror 31 is tilted by Δφ, the hologram 2
The reference light entering 3 has an incident angle inclined by 2Δφ. Further, the reference light diffracted by the hologram 23 passes through the imaging lens 25 and enters the observation surface 53 at the incident angle α. here,
When the hologram 23 and the observation surface 53 are conjugate to the imaging lens 25, the imaging magnification of the imaging lens 25 is m.
Then, the incident angle α is α = 2mΔφ.

Further, in this example, the surface to be inspected and the observation surface are naturally conjugated. Here, the light beam diffracted by the hologram and transmitted through the imaging lens 25 is merely inclined by α,
The wavefront shape of the diffracted wavefront itself does not change. Therefore, the reference light incident on the observation surface 53 at this incident angle α is
The light (object light) that has passed through the hologram 23 due to the reflected light from the aspherical surface 21a to be inspected and the light that has passed through the imaging lens 25 and then overlaps on the observation surface 53, resulting in the formation of interference fringes.
At this time, if the diameter of the light beam on the observation surface 53 is D, only k fringes of the number k = Dα, that is, interference fringes generated by the tilt are observed, and no coma aberration occurs. It can be seen that nine tilt fringes are generated in the embodiment shown in FIG.

The present embodiment is characterized in that the movable reference mirror 31 is tilted to perform alignment adjustment. The movable reference mirror 31 is tilted 1 '.
Table 3 shows the number of interference fringes that sometimes occur. This table 3
When the tilt Δφ of the movable reference mirror 31 increases or decreases by 1 ′,
Although 31.9 tilt fringes are generated, the coma aberration fringe is 0.

[Table 3]

Next, the adjustment by the adjusting method and the adjusting device of the present invention will be described with reference to Table 4 and FIG. The present embodiment is characterized in that the aspherical lens 21 is moved only in the optical axis O and the direction orthogonal thereto, and that the movable reference mirror 31 is rotationally adjusted.

[Table 4]

First, the aspherical lens 21 to be inspected is set on the lens holder 100 to be inspected (step (S) 11). If defocus occurs, the aspherical lens 2
1 (lens holder 100 to be inspected) is moved and adjusted in the Z-axis direction to set defocus to 0 (S13).

After the defocus adjustment, it is assumed that the inclination Δθ and the lateral deviation δ are in the same direction as the alignment error of the aspherical surface 21a to be tested, and the inclination Δθ is 1'and the lateral deviation δ is 10 μm. This is the same condition as (1) in Table 2. At this time, the number of tilt fringes was 29.6 and the number of coma fringes was 7.35 (see (1) in Table 4).

Therefore, first, the movable reference mirror 31 is rotationally adjusted in order to reduce the tilt fringes to 0 (S15). Here, since the number of tilt fringes is 29.6, the movable reference mirror 31 is moved in the direction of canceling the tilt fringes (29.6 / 31.9).
.Apprxeq.0.93 'rotation to make the tilt .DELTA..phi. Of the movable reference mirror 31 from the initial setting direction -0.9' and set the tilt fringe to zero. As a result of this operation, the lateral shift δ of the aspherical lens 21 remains unchanged, and 7.35 coma aberration fringes remain (Table 4).
(See (2)).

Next, in order to reduce the coma aberration fringe to 0, the aspherical lens 21 is moved by 11 μm in the direction in which the coma aberration is canceled (S17). By this movement, the lateral shift δ becomes −1 μm, but the coma aberration fringe becomes zero. Tilt fringes are generated in this process, but if the movable reference mirror 31 is tilted independently of the adjustment of the surface to be inspected, the number of tilt fringes does not increase, and
It can also be a book. By the above operation, the tilt fringes and the coma fringes become almost zero. The tilt Δφ of the movable reference mirror 31 is reduced by 0.6 ′ to about 0.4 ′.

When the absolute value of the remaining amount after adjustment of the tilt fringes and the coma fringes becomes less than the allowable value by the above adjustment, the shape error of the surface to be inspected caused by the processing error or the like is measured, and the aspherical surface to be inspected is measured. 21a is judged to be good or bad (S19, S2
1, S23). When the judgment is completed, the aspherical lens 2 to be inspected
1 is removed from the lens holder 100, and processing is performed based on the above determination. Then, a new aspherical lens to be tested is placed on the lens holder 100, and the processes of S11 to S23 are performed.

As described above, in this aspherical surface measuring device, the inclination of the aspherical surface 21a to be measured (the aspherical lens 21 with respect to the optical axis O) is measured.
Of the optical axis), that is, the tilt fringes are adjusted by changing the incident angle of the reference light by adjusting the angle of the movable reference mirror 31 without tilting the aspherical surface 21a to be measured. All you have to do is adjust the lateral shift. Moreover, tilting the reference beam does not affect the coma fringes, so
The tilt fringes and the coma fringes can be separated and adjusted independently, and the alignment adjustment time of the aspherical surface to be tested can be significantly shortened.

As described above, in the present embodiment, the movable reference mirror 31 is rotated in order to tilt the reference light. However, the movable reference mirror 31 and the fixed reference mirror 29 may be replaced with each other. However, it is only necessary that the hologram be adjusted so that the angle of incidence on the observation surface (angle with respect to the optical axis O) can be adjusted.

[0048]

As is apparent from the above description, according to the present invention, in the aspherical surface measuring method using the hologram, the alignment adjustment of the aspherical surface to be inspected, that is, the adjustment of the lateral deviation and the inclination with respect to the optical axis is performed. The adjustment is performed by moving the aspherical surface to be inspected in a direction orthogonal to the optical axis, and the inclination is adjusted by adjusting the inclination of the reference light without moving the aspherical surface to be inspected. It has become possible to significantly reduce the alignment adjustment time for the aspheric surface to be tested.

[Brief description of drawings]

FIG. 1 is an optical path diagram of an embodiment of an aspherical surface measuring device using a hologram to which the present invention is applied.

FIG. 2 is a diagram showing the appearance of interference fringes due to the tilt of the aspherical surface under test, which is shown on the observation surface of the measurement apparatus, in three-dimensional, planar, and cross-sectional views.

FIG. 3 is a diagram showing a state of interference fringes due to coma aberration of an aspherical surface under test, which is shown on an observation surface of the same measuring apparatus, in three-dimensional, planar, and cross-sectional views.

FIG. 4 is a diagram showing a state of interference fringes due to defocusing of an aspherical surface under test, which is shown on an observation surface of the same measuring apparatus, in three-dimensional, planar, and sectional views.

FIG. 5 is a plan view showing a state of interference fringes due to tilt and coma aberration of a surface to be inspected, which appears on an observation surface of the measuring apparatus.

FIG. 6 is a graph showing how interference fringes bend when tilt Δθ is 1 ′ and lateral deviation δ is 10 μm.

FIG. 7 is a diagram illustrating the relationship between the rotation angle of the movable reference mirror and the deflection of the reference light in the present embodiment.

FIG. 8 is a flowchart illustrating a measurement procedure of this embodiment.

[Explanation of symbols]

 11 laser oscillator (coherent light source) 19 condensing lens 21 aspherical lens (optical element to be inspected) 21a aspherical surface (aspherical surface to be inspected) 23 hologram 27 CCD image sensor 30 movable reference mirror 51 recording surface 53 observation surface 100 inspection Lens holder O Optical axis (optical axis of measurement optical system)

[Procedure amendment]

[Submission date] September 9, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

SUMMARY OF THE INVENTION The present invention to achieve this purpose is to divide the light beam from the coherent light source irradiates the test surface of the test optical element, and the test light that is a reflection from該被test surface , a measuring optical system for forming an interference pattern by interference superimposed on the observation plane after the reference light and that the light beam is divided is diffracted by the holograms from the coherence light source, based on the interference fringes A measuring method for measuring the shape of a surface to be inspected, characterized by having an adjusting step of tilting the reference light from an initially set direction.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is an optical path diagram of an embodiment of an aspherical surface measuring device using a hologram to which the present invention is applied.

FIG. 2 is a diagram showing the appearance of interference fringes due to the tilt of the aspherical surface under test, which is shown on the observation surface of the measurement apparatus, in three-dimensional, planar, and cross-sectional views.

FIG. 3 is a diagram showing a state of interference fringes due to coma aberration of an aspherical surface under test, which is shown on an observation surface of the same measuring apparatus, in three-dimensional, planar, and cross-sectional views.

FIG. 4 is a diagram showing a state of interference fringes due to defocusing of an aspherical surface under test, which is shown on an observation surface of the same measuring apparatus, in three-dimensional, planar, and sectional views.

FIG. 5 is a plan view showing a state of interference fringes due to tilt and coma aberration of a surface to be inspected, which appears on an observation surface of the measuring apparatus.

[6] tilt Δθ 1 ', is a graph showing a state of bending of the interference fringes when the lateral deviation δ occurs 10 [mu] m.

FIG. 7 is a diagram illustrating the relationship between the rotation angle of the movable reference mirror and the deflection of the reference light in the present embodiment.

[8] Flowchart illustrating the measurement procedure of this embodiment
It is a figure .

Claims (5)

[Claims] 1. A light beam from a coherent light source is split and applied to a test surface of an optical element to be tested, and the test light reflected by the test surface and the light beam from the coherent light source are split. With a measurement optical system that forms interference fringes by causing reference light and the hologram to be diffracted by the hologram and then superimposing and interfering on the observation surface, a measurement method for measuring the shape of the surface to be inspected based on the interference fringes. Then, there is an adjusting step of tilting the above-mentioned reference light from the initially set direction;
And an aspherical surface measuring method. 2. The aspherical surface measuring method according to claim 1, further comprising a step of moving and adjusting the optical element to be inspected only in an incident direction of the inspected light. 3. The aspherical surface measuring method according to claim 1, wherein the adjusting step is a step of adjusting a direction in which the reference light is incident on the hologram. 4. The method according to claim 1, further comprising moving and adjusting the optical element to be tested only in a direction parallel to a plane orthogonal to an incident direction of the light to be tested. An aspherical surface measuring method including an adjusting step. 5. The aspherical surface measuring method according to claim 1, wherein the surface to be inspected, the hologram, and the observation surface have a conjugate relationship with each other.