JP3206948B2 - Interferometer and interferometer alignment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer having an alignment function for generating a suitable number of interference fringes on a light-receiving surface when measuring the shape of a surface to be measured, and this interferometer. The alignment method.

[0002]

2. Description of the Related Art One method of measuring the shape of an object on the order of the wavelength of light or less is a spatial fringe scanning method using an interferometer. In the spatial fringe scanning method, a light beam from a single light source is divided into two and reflected by a measured surface and a reference surface, and these reflected lights are combined to generate an interference fringe on an imaging surface of a television camera. Then, one of the measured surface and the reference surface is moved in the optical axis direction to analyze a change in the amount of light for each pixel of the camera, and the surface shape of the measured surface is measured.

When an algorithm for fringe analysis by the spatial fringe scanning method is used, in order to simplify the algorithm, the number of pixels of the television camera is set to n / 4m (m = 1,
It is preferable to generate (2, 3 ...) interference fringes. Therefore, the measured surface, so that the number of interference fringes suitable for the measurement,
Alternatively, the interferometer is aligned by tilting the reference plane.

[0004]

Conventionally, in order to measure the number of interference fringes, the output of a television camera is displayed on a monitor, the number of interference fringes is counted by a human eye on the monitor, and a predetermined number of interference fringes is measured. Therefore, there is a problem that the adjustment work is very complicated and the work efficiency is poor.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has been made in view of the above-mentioned circumstances. An object of the present invention is to provide an interferometer capable of easily adjusting the tilt and an alignment method thereof.

[0006]

Means for Solving the Problems An interferometer according to the present invention, in order to achieve the above object, the present of the interference fringes formed by the reference light from the reference surface and the test light from the measurement surface
First light receiving means for adjusting the number to a predetermined number and measuring,
Wherein a condenser lens to form a light spot by focusing with said reference light and test light, the subject formed by the condenser lens
A second light receiving unit that receives two light spots, a light spot based on light and a light spot based on the reference light, and a deflecting unit that deflects at least one of the test light and the reference light. It is characterized by having.

Further, in the method for aligning an interferometer according to the present invention, a light spot is formed by converging a test light from a measured surface of the interferometer and a reference light from a reference surface, and forming a light spot between the light spots At least one of the test light and the reference light is deflected so that the distance becomes a predetermined distance.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

[0009]

First Embodiment FIGS. 1 and 2 show a first embodiment of the present invention.

In the interferometer shown in FIG. 1, a light beam emitted from a light source 1 is converted into a parallel light beam by a collimator lens 2, and is transmitted by a first half mirror 3 to a plane mirror 4 and a reference mirror 5 which are surfaces to be measured. Divided toward The luminous flux reflected by each mirror is superimposed on the first half mirror 3, and
The light enters the second half mirror 6.

The component transmitted through the second half mirror 6 forms an image on an imaging surface 8 of a CCD camera as a first light receiving surface disposed on a pupil plane conjugate with the pupil via an imaging lens 7, Form interference fringes. On the other hand, the component reflected by the half mirror 6 is converged by the condenser lens 9 and corresponds to each reflected light on a screen 10 as a second light receiving surface located on the Fourier surface.
Two light spots P1 and P2 are formed.

The reference mirror 5 is provided so as to be tiltable with respect to the optical axis, and has a function as a deflecting means for deflecting the reference light. By setting the inclination angle of the reference mirror 5 to an appropriate value, the number of interference fringes formed on the imaging surface 8 and the interval δ between light spots on the screen 10 can be adjusted.

Here, two light spots P1, P2 on the screen 10
The relationship between the interval Δ and the number n of interference fringes formed on the imaging surface 8 of the CCD camera will be described.

In order to generate n interference fringes, the light source 1
Is a monochromatic light source having an emission wavelength λ, and the diameter of the light beam reflected from the flat mirror 4 which is the object to be measured is D, and the inclination angle θ of the light beam due to the inclination of the reference mirror 5 needs to be set as follows: .

[0015]

[Equation 1] θ = (nλ) / D [rad]

If the focal length of the condenser lens 9 is f, the interval δ between the light points P1 and P2 on the screen 10 is as follows.

[0017]

## EQU2 ## δ = fθ = (nλf) / D

As described above, the interval δ between the light spots is determined by the number of interference fringes.
n is a function of n, and the interval δ for generating a predetermined number of interference fringes is uniquely determined. By doing so, n interference fringes can be formed on the imaging surface 8 of the CCD camera.

In the first embodiment, in order to indicate set values for generating a predetermined number n of interference fringes,
Cross-shaped indices S1 and S2 as shown in FIG. The distance between the centers of these indices is the set value δ0, and the light spots P1 and P2
To match the center of each index
By adjusting the angle, a predetermined number of interference fringes are generated on the imaging surface 8 of the CCD camera.

Although the second half mirror is fixed in the optical path in the above example, it is set in the optical path only during alignment, and is inserted and removed so as to retreat from the optical path when measuring interference fringes. It is good also as a structure provided freely. With such a configuration, it is possible to reduce a light amount loss at the time of measurement and to make it less susceptible to noise. Further, when a mirror is provided so as to be freely inserted and removed, a total reflection mirror may be used instead of the half mirror 6.

[0021]

Second Embodiment FIGS. 3 and 4 show a second embodiment of the present invention.

In the first embodiment, the positions of the two light spots are directly confirmed visually on the screen. In the second embodiment, the positions of the light spots are measured by a light receiving element such as a PSD or an image sensor. The measured surface and the reference surface are driven via an actuator based on the measurement result, and the light spot interval is automatically set to a predetermined distance.

The configuration of the optical system is almost the same as that of the first embodiment, and as shown in FIG.
Instead, a light receiving element 11 such as a PSD (position sensing device) or an image sensor is used. PSD is
Since the element detects the coordinates of the portion where the amount of light is the largest, two elements are required at each position where each light point converges in order to obtain the coordinates of the two light points. When an image sensor is used, one element can detect the coordinates of two light spots.

An electric signal including coordinate information of a light spot is input to the drive control circuit 12 by the light receiving element 11. Drive control circuit
The controller 12 controls the actuators 13 and 14 that drive the mirrors 4 and 5 based on the information.

FIG. 4 is a flowchart showing the procedure of measurement by the interferometer.

First, in step (denoted by S. in the drawing) 1, a mirror as a surface to be measured is arranged at a predetermined position, and in step 2, the distance between light points P1 and P2 is determined based on the output of light receiving element 11. δ
Is measured. In step 3, it is determined whether or not the measured interval δ is equal to a set value δ0 corresponding to the predetermined number of interference fringes, and if not, the actuators 13 and 14 are controlled in a direction in which they are equal in step 4 Then, the mirrors 4 and 5 are tilted, and the distance δ is measured again in step 2.
Steps 2, 3, and 4 are repeated until the interval Δ becomes equal to the set value Δ0. After the intervals become equal, the analysis of interference fringes is started in Step 5.

According to the configuration of the second embodiment, the alignment of the interferometer can be automated.

[0028]

Third Embodiment FIG. 5 shows a third embodiment of the present invention. Example
Examples 1 and 2 are examples in which the present invention is applied to a Twyman-Green interferometer, while Example 3 is an example in which this is applied to a Mach-Zehnder interferometer.

In the interferometer shown in FIG. 5, a light beam emitted from a light source 1 is converted into a parallel light beam by a collimator lens 2, and a parallel plate 4 'having a surface to be measured and a reference mirror 5 by a first half mirror 3. And divided into Parallel plane plate
Test light transmitted through 4 'and reflected by mirror 20 and reference mirror
The reference light reflected by 5 enters second half mirror 6.

The reference light transmitted through the second half mirror 6 and the component of the test light reflected by the half mirror 6 pass through the first pupil plane conjugate with the pupil via the imaging lens 7. An image is formed on an imaging surface 8 of a CCD camera as a light receiving surface to form interference fringes. On the other hand, the reference light reflected by the half mirror and the component of the test light transmitted through the half mirror are converged by the condenser lens 9 and are reflected on the screen 10 as the second light receiving surface located on the Fourier surface. Form two light spots corresponding to the light.

The reference mirror 5 is provided so as to be tiltable with respect to the optical axis, and has a function as a deflecting means for deflecting the reference light. By setting the inclination angle of the reference mirror 5 to an appropriate value, the number of interference fringes formed on the imaging surface 8 and the interval between light spots on the screen 10 can be adjusted.

As the deflecting means, besides the reference mirror 5, a mirror 20 may be provided rotatably.

[0033]

As described above, according to the present invention, the interference fringes are obtained by converging the test light from the surface to be measured and the reference light from the reference surface and measuring the interval between the light spots. And the number of interference fringes can be easily set to a predetermined number without performing an operation such as counting the number of interference fringes.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical system showing a configuration of a first embodiment.

FIG. 2 is an explanatory view showing a screen of the apparatus shown in FIG.

FIG. 3 is an explanatory diagram of an optical system showing a configuration of a second embodiment.

FIG. 4 is a flowchart illustrating an operation of a second embodiment.

FIG. 5 is an explanatory diagram of an optical system showing a configuration of a third embodiment.

[Explanation of symbols]

 1 ... Light source 4 ... Measurement surface 5 ... Reference surface 8 ... Imaging surface (first light receiving surface) 10 ... Screen (second light receiving surface) 11 ... Light receiving element (second light receiving surface)

Claims (4)

(57) [Claims] The number of interference fringes formed by the test light from the surface to be measured and the reference light from the reference surface is adjusted to a predetermined number.
A first light receiving means for measuring and integer, based on the a condenser lens to form a light spot by focusing with said reference light and test light, the test light that is formed by the condenser lens Light spot
And a second light point that receives two light points of a light point based on the reference light .
An interferometer, comprising: a light receiving unit; and a deflecting unit that deflects at least one of the test light and the reference light. Wherein said second light receiving means is a screen that is visible to the light spot, the screen, the two
An index is provided at a position where the light spot should be located in order to set the interval between the light spots to a predetermined value.
The interferometer according to 1. 3. The second light receiving means is a light receiving element that photoelectrically converts and detects the coordinates of the light spot , and measures an interval between the two light spots based on an output of the light receiving element. 2. The interferometer according to claim 1, further comprising a deflection control unit that controls the deflection unit so that the interval has a predetermined value based on a result. 4. The method according to claim 1, wherein the test light from the surface to be measured of the interferometer and the reference light from the reference surface are condensed to form two light spots, and the distance between the two light spots is predetermined. An alignment method for an interferometer, wherein at least one of the test light and the reference light is deflected so as to have a distance.