JPS61128104A - Fringe scanning shearing interferometer - Google Patents

Abstract

PURPOSE:To enable extension of measuring range, reduction of size and weight of an apparatus, by bisecting the forward travelling direction of a specimen surface and, developing images and irradiating the integrated both surfaces by folding back individually onto an area sensor. CONSTITUTION:A reflected ray of light of a specimen surface 6 is irradiated onto a bench-type prism 7 to be bisected and one of the wove fronts is reflected twice by a right-angle prism 8 to be irradiated onto a bench-type prism 9 to reach an area sensor 12 through an image developing lens 11. The other wave front is reflected twice by a right-angle prism 10 to be transmitted through the prism 9 and reaches the sensor 12 through the lens 11 to be integrated with the other wave front. By this arrangement, interference fringes are produced on the sensor 12 by allowing the prism 7 to be displaced in the X direction by a driving means 14 and giving sideward displace ment to the wave front in the X direction and at the same time, the prism 8 is dis placed in the Z direction by a driving means 13 for a phase modulation. And, a shear ing intersecting with the X direction of the prism 7 through a right angle is performed by the Y direction displacement of a prism 10 by a driving means 15 and this kind of shearing in X, Y directions make measurement of a shape of curved of the speciment possible.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a fringe-scanning noring interferometer, and more specifically, to a fringe-scanning noring interferometer, and more specifically, to measurement of high rt degrees of flat, spherical, and aspherical shapes, and measurement of wavefront aberration and eccentricity of optical elements. , relates to a fringe scanning noring interference needle that can be applied to focal length measurements, etc.

(Prior Art) FIG. 25 shows the configuration of a conventional fringe scanning shearing interferometer.

In the figure, numeral 21 is a laser light source, 22 is a collimator lens system, and 26 is a course of the laser light. The beam splitter 24 directs the object to be measured ζ, and the converter lens 24 is a converter element that converts the measured wavefront generated by projecting light onto the curved surface 25 to be measured into a nearly parallel wavefront. I will show you each one.

Further, reference numeral 26 indicates a supporting portion i of the corner cube prism from the beam sinter 26, 30 indicates a driving means for the corner cube prism, 52 indicates a lens, and 53 indicates an area sensor.

Here, the light emitted from the laser light source 21 passes through the collimator lens system 22 and becomes parallel light, and the beam sinter 23
After turning to the left at , the wave is converted into a spherical wave of the reference spherical surface by the converter lens 24 , and is incident on the curved surface 25 to be measured (C).

However, here is the reference ball! What is Compartare/Z24?
It is a spherical surface whose radius R is the distance from the focal point 700 to the apex on the optical axis of the curved surface to be measured 250.

If the deviation from the reference spherical surface at any point on the curved surface 25 to be measured is d/2, then the wavefront reflected from the white surface 25 to be measured will have a spherical aberration of d. This d
? By measuring, it is possible to know the shape of the curved surface 25 to be measured.

Now, the anti-l from the curved surface 25 to be measured? tff is a source (hereinafter referred to as a wavefront) containing detailed information regarding the surface shape IC of the identified m-plane 25, and again, the converter lens 2
4. Pass through the beam splitter 23 and head toward the beam splitter 26.

By the way, this wavefront is slightly shifted from a plane wave, and the amount of shift is exactly f4! This corresponds to twice the amount of deviation between the I constant curved surface and the reference spherical surface.

Beam gooseberry ivy 26[j] The wavefront is split into two directions in its traveling direction, one goes straight and is reflected five times by the corner cube prism 28, and then the wavefront is reflected by the beam splitter 2.
6, it is reflected again and reaches the lens 32.

For convenience, this wavefront is referred to as wavefront A.

The other wavefront is reflected by the beam slitter 26, enters the corner cube prism 27, is reflected five times, enters the beam splitter 2bVC, and goes straight to the junction I/Z3.
Leading to 2. For convenience, this wavefront will be referred to as wavefront B.

The wavefront B is laterally shifted by 2 S to the corner cube prism 27. This lateral shifting operation is performed by shifting the corner cube prism 27 by 1/2S from the position indicated by the solid line.

As a result, interference fringes are generated on the photoelectric detection device 33 between the wavefront A and the wavefront B, which corresponds to a wavefront that is conventionally shifted by S.

At the same time, the corner cube prism 28 is driven by the driving means 30.
By moving a small amount in two directions at , the phase of wavefront A ? It can be modulated.

By the way, Figure 1-6 is a top view of the corner cube prism used in the conventional fringe scanning shearing interferometer described above, and the off-line diagram is a top view of the corner cube prism used in the conventional fringe scanning shearing interferometer.
Figure 8 shows a view viewed from the direction of arrow 1, and Figure 8 shows an off view viewed from direction 0 of arrow C.

This corner cube prism has an illusion of mutual V on each ridgeline.
c The angle formed by two adjacent surfaces is set to 9QO, and each ridgeline (for example, OF) is set as shown in the off diagram.
And the surface (
The angle θ formed by the plane surrounded by ORQ is set to 90°.

Here, in Figure 6, you can see the top, 4 o, and three ridgelines, OP, OQ, and OR, but in Figure 8, each of the five ridgelines is reflected on the opposing surface. For.

In addition, three lines O'P',o'q', and o'* are visible. this? For convenience, this is called a reflection ridge.

When such a corner-V-Ape prism is used in a fringe-scanning shearing interferometer, it is necessary to prevent the light beam from being applied to the reflection ridges as well as the ridgelines, because the source is not reflected at the ridgelines.

Therefore, only one fan-shaped area obtained by dividing the circumference into six equal parts can be used.

Now, the diameter of the circle inscribed in one 7 sector section is d.

Assuming the diameter of a corner cube prism.

The relationship between d and D is d=D/3 button<VC. Note that the derivation of this relational expression will be omitted for the sake of convenience.

This relational expression means that when a corner cube prism is used, only the original light of 1/6 of its diameter can enter, and from this, the measurement v! of the surface to be measured is determined. , the range is limited and narrow.

(Objective) An object of the present invention is to provide a fringe scanning/alling interferometer that divides a wavefront into two parts, in which the effective light flux of the wavefront can be set to be large in order to expand the measurement range. In addition, it is an object of the present invention to provide a fringe scanning noring interferometer in which the optical device of the interferometer can be downsized.

(Structure 13:) The present invention achieves the above objectives in two ways! ! In order to achieve this, one trapezoidal prism Vcx divides the traveling direction of the measured wavefront into two, and the two divided wavefronts are folded into the first right-angle prism and second right-angle prism Vcj, respectively. The wavefront is integrated with another trapezoidal prism, and both sides emitted from this prism are combined into 1! The idea is to inject the ℃ area sensor K through the lens.

The present invention will be explained below based on a leprosy example.

Figure 21 shows a plan view of the base part of the fringe scanning noring interferometer according to the present invention, and Figure 3-2 shows a view of the device part as seen from the direction of arrow F in Figure 1. ing.

In both figures, the light emitted from the laser light source 1 is as follows.

Collimator lens 2, 5? The light then becomes parallel light, turns left at the beam sinter 4, is transformed into a spherical wave (reference sphere WJ) by the converter lens 5 as a conversion element, and enters the curved surface 6 to be measured.

The light reflected from the curved surface to be measured 6 becomes a source of information regarding the surface shape of this curved surface (hereinafter referred to as a wavefront), and is again transmitted to the converter lens 5. The light passes through the beam splitter 4 and enters the first trapezoidal prism 7.

The first trapezoidal prism 7 is made by pasting together two large and small one-sided prisms, and allows approximately 50% of the transmitted light to be reflected or transmitted through this pasted surface. , Also, is the beam splitter 4 (7) pasted? ) The characteristics of the mating surfaces are also the same.

The wavefront incident on the first trapezoidal prism 7 is divided into two here, and one wavefront is advanced by 1 and is arranged in the 1st direction.
It is reflected twice by the right angle prism 8.

The two spears enter the trapezoidal rhythm 9. In this way, the first angle prism 8 achieves the function of folding back one of the wavefronts divided by X into the first trapezoidal prism 7, and the second trapezoidal prism 9 has the same configuration as the first trapezoidal prism 7 or can be custom-made. The wavefront incident on the prism 9 is reflected twice here, passes through the imaging lens 11, receives the moat imaged by this lens, and is transferred to the tth area sensor 12Vc, which converts the optical base. The wavefront that reaches the area sensor 12 via such a route.

Hereinafter, it will be referred to as wavefront A.

Another wavefront that is incident on the first trapezoidal prism 7 and reflected by this bonded surface travels downward, is reflected again, and is incident on the double-sided prism 10 arranged in the reflection direction iC.

Another wavefront incident on the second rectangular prism 10 is reflected twice by this prism 10, and is reflected twice by the second rectangular prism 10.
The light passes through the r-image forming lens 11 and reaches the area 1 sensor 12. The wavefront that reaches the rear sensor 12 via such a route is hereinafter referred to as wavefront B.

As understood from the above points, the 2-2 trapezoidal prism 9
is coupled with the function of reintegrating the two wavefronts reflected by the first and second monogonal prisms 8.10, respectively.

In FIGS. 1 and 2, the 3-1 right angle prism 8 is provided with a first driving means 16 that holds the prism 8 and drives the condensing lens 110 in the axial direction (Z direction). As this driving means, for example, a piezo element can be used.

The first trapezoidal prism 7 holds the above 'yt,
A drive means 14 for driving the spear 2 in a first direction (X direction) perpendicular to the axis is provided.

The second rectangular prism 10 also has a third rectangular prism 10 that holds it and drives the VC in a second direction (Y direction) perpendicular to the original axis VC and perpendicular to the first direction. Drive means 15 are provided. Examples of driving means for the spear 2 and the spear 5 include a pulse motor and means for screw feeding using a screw shaft driven by an X-axis.

Here, the first trapezoidal prism 7 is moved by the second driving means 14.
When moved from K in the X direction in FIG.

Wavefront B is laterally shifted in the X direction (by the prism,
Interference fringes are generated between the wavefront A and the wavefront B on the eliase/sustainer 12. In this sense, the present interferometry is a shearing interferometry.

At the same time, the first right angle prism 8 is
By slightly moving the driving means 13Vcj in two directions (2 μm to 1/2000 μm), the phase of the wavefront A can be modulated. In this sense, the present interferometry is fringe scanning interferometry.

The shear in the direction perpendicular to the X direction of the first trapezoidal prism 7 moves the second rectangular prism 10 to
This is done by moving in the Y direction. According to the present invention, the shape of the curved surface to be measured can be measured by performing /ar in the X and Y directions.
The optical path length from the first trapezoidal prism 7 to the rectangular prism l0VC is made equal to the optical path length from the first trapezoidal prism 7 to the rectangular prism l0VC,
The first trapezoidal prism 7 and the second trapezoidal prism 9 in the figure? An actual winding example is shown where the windings are arranged as close together as possible. According to this example, the optical path length of the wavefront A, which is divided into 13 parts, becomes shorter.
Durability and maximum performance are improved. That is, the ratio of the optical paths of the two wavefronts to each other (common path ratio) is improved, the anti-corrosion performance is improved, and the device can be made smaller.

Figure 4 is an example of Figure 3, in which the mutually opposing surfaces of the first right angle prism 8 and the second right angle prism 10 are tilted as shown in the figure, and the two prisms have 7.99 faces. between the
The angle θ1. An actual example is shown in which θ2 is set to make these planes non-parallel.

If the surfaces of the prism 7.90 and the surfaces of the prism 8.10 are in a parallel state, the original light will be repeatedly reflected between these surfaces and reach the area sensor 12 as a ghost. In the actual winding example, such a problem is prevented. Note that the angle θ1. θ2 is 3° & up to 8°
The moderation is good.

In this actual coffin example, the rectangular prism 8.10 itself was provided with an inclined surface, but in addition to this, the trapezoidal prism 7.
9 may be tilted to set such θ.

Here, is a corner cube prism used in a conventional interferometer?
However, when such a prism is used,
As mentioned earlier, there is a drawback that only 115 luminous fluxes of light can be incident on the prism.
(See figure) The interferometer of the present invention allows the original incidence of a light beam having the same diameter as 1/2 of the input long side or the short side of the 5 trapezoidal prism and the rectangular prism.
This makes it possible to enlarge the light flux of the wavefront that passes through a set of optical systems consisting of a trapezoidal prism and a right-angle prism, making it possible to measure objects with a large diameter. By increasing the conversion rate, it is possible to improve the camera resistance performance and also make the device itself smaller6.
On the other hand, with conventional interferometers, when performing 7-ar in the X or Y direction, one corner cup grism itself must be moved in those two directions, so it is not possible to make the movement stage independent. 6 For example, the X stage moves in the X direction relative to the main body base, but the
As for the stage, it is necessary to move it in the Y direction with respect to the There must be.

In the interferometer of the present invention, since 77- in the X and Y directions can be performed independently on the main body base, the product i1a! It is lighter in weight and can be moved at higher speeds.

(Effects) According to the present invention, in a fringe shearing interferometer that divides a wavefront into two, it is possible to expand the measurement range of a surface to be measured, and also to make the device smaller and lighter. It is possible to provide a fringe scanning noring interferometer that can be used for a wide variety of applications.

[Brief explanation of drawings]

Fig. 1 is a Q-F plane view of the optical device of a fringe scanning noring interferometer according to an embodiment of the present invention, and Fig. 2 is a front view of the same optical device. Figure 4 shows an example of the arrangement of a trapezoidal prism and a rectangular prism, and Figure 5 shows a conventional stripe distortion/
Figure 6 of the optical device of the Arinog interferometer is a plan view of the corner cube prism used in the above interferometer. Figure 7 is a front view of the corner cube prism shown above.
Figure 8 is a diagram for explaining that the effective luminous flux cannot be set large in the corner chiave prism. 5... Conoverta lens, 6... 111 fixed surface, 7
...first trapezoidal prism, 8...first right angle prism,
9...Second trapezoidal prism, 10...Second right angle prism, 11...Yuiyo lens, 12...Area sensor, 1
3..., 1-1 driving means, 14... 2nd driving means, 15... 3-3 driving means

Claims (1)

[Scope of Claims] A conversion element that converts a wavefront to be measured generated by projecting light onto a surface to be measured into a nearly parallel wavefront; a first trapezoidal prism that divides the traveling direction of the wavefront to be measured into two directions; a first right-angle prism that folds back a first wavefront divided by the first trapezoidal prism; a second right-angle prism that folds back a second wavefront divided by the first trapezoidal prism; and the first and second right-angle prisms. a second trapezoidal prism that reintegrates the respective reflected first and second wavefronts, an imaging lens that forms an image of the first and second wavefronts emitted from the second trapezoidal prism, and the imaging lens an area sensor that receives and photoelectrically converts the image formed by the area sensor, and the first rectangular prism, which forms an image of the
second driving means for holding the trapezoidal prism and driving it in a first direction perpendicular to the optical axis; and third driving means for driving in a second direction perpendicular to the first direction.