JP2821507B2 - Interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention measures or measures the surface shape or the like of a test object such as a lens using an interferometer using light wave interferometry and a laser interferometer. Also, the present invention relates to an interferometer for measuring interference fringes.

[Background of the Invention]

The use of the interferometry to measure the surface shape or the like of a test object such as a lens has an advantage that measurement can be performed without directly contacting the surface of the test object. As interferometers, for example, Twyman Green type, Fizeau type, Mach-Zehnder type interferometers and hologram interferometers of each type are introduced, and these interferometers are also provided as measuring devices on the market.

The interferometer provided on the market is a unit in which the optical elements that compose the interferometer are fixed in a single housing, and the interferometer unit is used to stably maintain the relative position of each optical element. The thing is a general form. However, the interference measurement of the test object requires that the relative distance between the interferometer unit and the test object in the direction of the test optical axis be movable and fixed. The interferometer generally provided is one in which an interferometer unit is fixed, and a test object is mounted on a movable table, and is moved and fixed in a direction of a test optical axis. Micron-order positioning and movement amount measurement can be performed. In addition, there is an example in which a test object is movable in a test optical axis direction using a linear bearing or an air slide. In this case, due to the size and weight of the test object, the moving means of the test object is separate from the interferometer unit. Although sometimes used, the length measurement system is separate from the interferometer unit.

FIG. 6 shows an interferometer described in JIS B-7433-1989. On the left is a Fizeau-type interferometer unit 90, and a laser beam from a laser light source 91 is provided. The test light beam L is emitted from the Fizeau reference lens 92 through the Fizeau-type optical element and projected onto the test object 93.
Behind the test object 93, there is a distance measuring mechanism 96 using a laser interferometer.The test object 93 is fixed on a gantry 95 and moves on a bench 94 along the test optical axis. The movement amount is monitored by the distance measuring mechanism 96. Since the distance measuring mechanism 96 measures the length from behind the test object 93, it is extremely difficult to incorporate it into the main unit of the interferometer. Absent. In addition, the above interferometer measures the measurement environment at 23 ° C ±
Although the measurement accuracy is set to 0.2 to 1 μm at 1 ° C., when the test light beam L and the length measuring optical path by the distance measuring mechanism 96 are long, it is difficult to maintain the accuracy, and basically, an error is likely to occur. It is arranged.

For example, if the temperature rises during the measurement, the interference type unit and the moving rail are separate bodies, so the position of the test object with respect to the interferometer body changes in the direction away from the main body due to thermal expansion of the mechanical parts. Since the mechanical thermal expansion also occurs in the length measurement optical path of the test object, the length measurement value becomes longer. Moreover, these fluctuations depend on the distance to be measured and the distance to be measured, and thus do not quantitatively match. That is, there is a disadvantage that the relative distance fluctuation between the interferometer and the test object due to the change of the measurement environment and the fluctuation of the measured value occur completely independently of each other and do not complement each other. Further, it is not easy to move and fix the test object with respect to the interferometer main body with a distance accuracy of 1 μm or less, and some kind of moving and fixing mechanism needs to be devised.

[Object of the invention]

The present invention, in addition to the function of observing and measuring the interference of the test surface that the interferometer has, makes it possible to simultaneously accurately measure the relative distance information between the interferometer and the test object, and as a whole It is an object of the present invention to provide an interferometer in which a measurement system is reduced in size and weight and workability is improved.

[Configuration of the invention]

The above object is to share a laser light source and a laser light source of an interferometer for interference observation, and to set a test optical axis of the interferometer for interference observation and a measurement optical axis of the laser interferometer parallel and in the same direction. Is achieved by an interferometer.

In the above invention, it is a preferred embodiment that the interferometer components other than the test object and the laser interferometer components except the length measuring mirror or prism are provided in the same unit.

〔Example〕

FIG. 1 (a) is a configuration diagram showing an embodiment of the present invention, and shows an interferometer comprising an interferometer unit 100 using a Fizeau interferometer 110. FIG. However, the type of the interferometer used in the present invention is not limited at all. The Fizeau interferometer 110 includes, for example, a laser light source 111 such as a He-Ne laser or a semiconductor laser, a condenser lens 116 for condensing the laser light from the laser light source 111, and an interference placed at the focal point of the condenser lens 116. A half mirror 118 for fringe observation, a collimator lens 112 that converts laser light into parallel light, and a fizer reference lens 113 having a reference surface 113a,
An interference fringe generated by interference between the reference light reflected from the reference surface 113a of the reference lens 113 and the test light reflected from the test surface 131a of the test object 131 passes through the half mirror 118 and the imaging lens 151. For example, an image can be picked up by an image pickup device 152 including a CCD image pickup device, and the image can be displayed on a television 150 as a display unit.

The interferometer optical element except for the test object 131 is fixed on one rigid substrate 101 or on the back surface thereof to constitute the interferometer unit 100, and the rigid substrate 101 is provided in a rigid box-shaped casting block. And a so-called shell structure.

The present invention provides an interferometer element of a laser interferometer 120 excluding a length measuring mirror or a length measuring prism in the interferometer unit 100, and a laser light source of the laser interferometer 120 is used for the laser interferometer 110. This is used in common with the laser light source 111 and uses a frequency stable laser. For this reason, in this embodiment, a half mirror 119 and a mirror 124 are provided on the rigid substrate 101 immediately before the laser light source 111 of the laser interferometer 110, and the laser light is divided and guided to the laser interferometer 120. On the rigid substrate 101, a beam shaper 121, a length measuring receiver 122, and a length measuring interference prism 123 (a fixed mirror in the case of a differential type) are fixedly provided.

After the optical axis to be measured of the interferometer 110 provided in the same interferometer unit 100 and the measuring optical axis of the laser interferometer 120 are adjusted to be parallel and in the same direction, these optical elements are fixed. In the case, a small displacement does not occur during the measurement in the housing.

On the other hand, the test object 131 and the length measuring mirror (or prism) 132 are mounted on a gantry 130, and the test object 131 and the length measuring mirror 132 are located directly opposite to the test optical axis and the length measuring optical axis, respectively. The gantry 130 can be moved on the bench 140 in parallel with the optical axis. The measurement of the test surface 131a of the test object 131 is performed by moving the gantry 130 while observing the television 150, and measuring the position where the interference fringe is observed by the interferometer 110 on the screen of the television 150 by the laser interferometer 120. Done by lengthening.

As is apparent from the above description, even if the relative position between the interferometer unit 100 and the test object 131 fluctuates due to environmental changes, the distance of the test surface in the test light, Since the distances are substantially equal, the distance to the surface to be inspected can be accurately measured.

Especially for optical surfaces where distance accuracy is strict,
By selecting and setting the position of 132 and the length measuring interference prism 123, the measured light path length at the center of the test surface 131a and the measured light path length are set to be approximately the same distance, and even if there is a distance difference, within ± 20 mm By doing so, the influence on the environmental change can be almost eliminated, and the effect of the optical arrangement of the present invention is greatly recognized. In addition, since a frequency-stabilized laser is used as the shared laser light source 111, the visibility of interference fringes is good, and stable length measurement accuracy can be obtained.

In addition, by incorporating the optical system of the laser interferometer 120 into the interferometer unit 100, the measurement light for measuring the relative distance between the interferometer main body 110 and the test surface 131a is parallel to the test optical axis and the same. Since the laser light source 111 is shared, the interference measuring device can be efficiently reduced in size as a whole system.

In the above description, the observation of the interference fringes by the interferometer 110 is performed using the imaging lens 151, the imaging device 152, and the television 150. However, an observation screen is provided, and the interference fringes are projected thereon. It is also done. When the television 150 or the like is used, there is an advantage that the length measured by the laser interferometer 120 can also be displayed.

FIG. 1 (b) is a configuration diagram showing an interferometer unit 100A which is an embodiment using a Twyman-Green interferometer 110A as an interferometer, and the same parts as the interferometer unit 100 in FIG. 1 (a) are the same. Reference numerals are used, and duplicated portions of the detailed description will be omitted. In this embodiment, the Fizeau reference lens 113
A condenser mirror 115 is provided instead of the collimator lens 112. A half mirror 114 inclined by 45 ° with respect to the optical axis, a reference mirror 117, and a condenser lens 15 are provided between the collimator lens 112 and the condenser lens 115.
Three are provided. The laser light emitted from the laser light source 111, which is a common light source, becomes parallel light by the collimator lens 112, passes through the half mirror 114, becomes the test light, and is reflected by the test surface 131a after being condensed by the condensing lens 115. The light is again reflected by the half mirror 114 via the condenser lens 115 and collected by the condenser lens 153. On the other hand, the laser light reflected by the half mirror 114 is reflected by the reference mirror 117, passes through the half mirror 114, and becomes reference light. The test light and the reference light are both condensed by the condenser lens 153 to generate interference fringes. The interference fringe is an imaging lens
The image is projected on the television 150 via the image pickup device 152.

FIG. 1C is a configuration diagram showing an interferometer unit 100B which is an embodiment using a Fizeau hologram interferometer 110B as an interferometer. In the figure, the same parts as those in FIGS. 1A and 1B are denoted by the same reference numerals, and 130 is a hologram provided interchangeably. The laser light emitted from the common laser light source 111 and converted into parallel light through the half mirror 119, the condenser lens 116, and the collimator lens 112 is condensed by the Fizeau reference lens 113 to become test light, and the test object The Fizeau reference lens 1 is reflected by the 131 test surface 131a again.
Hologram 1 after being reflected by half mirror 114 after 13
Reach 30. On the other hand, the reference surface 113 of the Fizeau reference lens 113
The reference light reflected by a is reflected by the half mirror 114, reaches the hologram 130, and is diffracted. The zero-order light of the test light passing through the hologram 130 and the first-order diffracted light of the reference light diffracted by the hologram 130 interfere with each other to generate interference fringes. This interference fringe is imaged by the imaging device 152 via the imaging lens 151 and
It is projected on 150. By selecting the hologram 130, interference measurement can be performed on the test surface 131a having various aspherical shapes.

FIG. 2 shows an embodiment in which the above-mentioned interferometer unit 100, 100A or 100B is made movable, a test object 131 and a length measuring mirror (prism) 132 are fixedly mounted on a substrate 130, and the test optical axis is horizontal. .

The test object 131 includes a mold for optical surface molding in addition to a normal prism or an optical element such as a lens, and has a large variation of 1 to 150 mm in diameter and 0.5 to 20 kg in weight. The specimen 13 with such a large difference
It is not easy to move, fix and position with high precision with respect to 1.

The embodiment shown in FIG.
1 is fixed, and the interferometer unit 10 of a certain size and weight
0,100A or 100B is attached to the gantry 210, moving and fixing on the bench 220, and incorporating a mechanism for positioning,
As compared with the embodiment of FIG.
Can be positioned.

Further, in the embodiment shown in FIG. 2, since the number of movable / fixed axes of the jigs for fixing the test object 131 is reduced by one, the error factor is reduced, and the weight and rigidity are not restricted. The accuracy of the test object holding member for moving and fixing the test object can be easily improved.

In the embodiment shown in FIG. 3, the linear movable direction of the interferometer units 100, (100A, 100B) in the embodiment shown in FIG. 2 is vertical. A moving rail 312 is provided on a column 311 that stands upright with respect to the fixed base 310, and a gantry 210 to which the interferometer units 100 and (100A, 100B) are fixed is vertically movable along the moving rail 312. The gantry 210 has an interferometer unit 100, (100A,
By providing the counter balance 314 substantially equal to the weight of the interferometer unit 100, (100B), the operation of moving and fixing the interferometer units 100, (100A, 100B) is facilitated.

In the embodiment shown in FIG. 3, there is no need to hold the test object 131, and it is sufficient only to place the test object 131 on the stage of the fixed base 310, so that the workability of the interference measurement is remarkably improved. In addition, since interference fringe measurement can be performed with reference to the installation surface of the test object 131,
For example, it is possible to easily perform interference measurement and comparison of a test object using a flange portion or the like as a reference surface, which has been conventionally difficult. Further, since the unit weight is actually zero by providing the counter balance 314, the moving rail 312 and the gantry 210
By using an air slide between them, the straightness in the moving direction of the unit is remarkably improved, and stick-slip or the like does not occur. According to the study of the prototype by the present inventor, it is not difficult to suppress the straightness to 1 μm or less by using the air slide, and the vibration accompanying the slide is also reduced.
10 μm or less, and the flatness of the stage of the test object is 1 μm.
m or less, and the verticality can be reduced to 2 ″ or less, and highly accurate measurement can be performed.

According to the study of the prototype by the inventor, it was not difficult to suppress the straightness to 1 μm or less by using an air slide, and the vibration accompanying the slide was 10 μm or less. Can be set to 1 μm or less and the verticality can be set to 2 ″ or less, so that highly accurate measurement can be performed.

FIG. 4 shows an embodiment of an interferometer in which the above data is obtained. The interferometer units 100, (100A, 100B) are moved up and down and stopped by an electric motor 401. is there. The ball screw 402 directly connected to the electric motor 401 is rotated by the rotation of the electric motor 401.
With the rotation of the ball screw 402, the interferometer units 100 and (100
A, 100B) is an air slide 4 that moves up and down along the cylindrical bar 403
Up and down and stop are performed with 04 as a guide. In the present embodiment, a pulse motor is used as the electric motor 401, and the electric motor 401 is configured to rotate via the motor driver 406 according to the number of pulses from the pulse generator 405 generated by manual input.

The embodiment shown in FIG. 5 uses a servo motor as the electric motor 401A, and uses a differential amplifier based on the length measured by the laser interferometer 120 housed in the interferometer unit 100, (100A, 100B). A feedback circuit including 501 is provided, and a feedback system of the relative position is applied to the electric motor 401A to realize a completely closed unit movement / stop and positioning system. As a result, the measured values are monitored one by one and the units 100, (10
0A, 100B) and the work of adjusting the relative distance between the test object 131 and the test object 131 are not required.
By simply setting 1, by inputting the target in conjunction with the personal computer 502, the differential amplifier 501 feeds back the measured value with respect to the target value, and the measurement process itself can be automated. The inventor measured the interferometer units 100 and (100) stably with an accuracy of ± 10 nm when measured by the apparatus of the embodiment shown in FIG.
A, 100B) and the test object 131 could be maintained at a relative distance.

In the foregoing, various embodiments and effects obtained by unitizing the components of the interferometer and incorporating the laser interferometer therein have been described.

Next, an example in which phase interference fringe measurement is performed using the above-described interference measurement device will be described. This is achieved by inputting a plurality of interference fringe images while changing the phase of the interference fringes to a dedicated image processing device or personal computer by finely moving the relative distance between the unit and the test object by about 1 μm by a servomotor.
From the measured value of the laser interferometer at that time, when the interference fringe intensity of each pixel is In = Asin (θ + 4π · φn / λ) + d, the phase angle θ of the pixel can be measured extremely accurately. Based on the phase angle θ of each pixel, the test object is highly accurate (λ
/ 1000).

Here, In is the intensity of a pixel in the interference screen captured at the nth position, A is the amplitude of the interference fringe intensity change, φn is the amount of fine movement (length measurement) at that time, d is the intensity of the background, and θ is the intensity of the pixel to be obtained. In the initial phase, usually 4 screens of φn are set to λ / 8
By taking the interference fringe intensity at each pixel of I ₁ ~I _4, Is used to calculate the initial position θ.

As described above, the interferometer according to the present invention, in which a plurality of interference fringe screens having different phases can be input to the image processing apparatus by slightly feeding the linear movable portion of the unit, can perform the phase interference method. The mathematical expressions including the post-processing and the processing are measured and evaluated by an ordinary method such as a 4-bucket method or a 5-bucket method. In the interferometer of the present invention, which enables fine movement and allows the amount of fine movement (length measurement) to be measured with high accuracy, as described above, without using a fine movement device using a piezo element conventionally used for phase fringe measurement. A lot of added value can be obtained.

〔The invention's effect〕

According to the present invention, as described above, the interferometer components other than the test object are unitized, and a laser interferometer is incorporated in this unit, and the laser light source of the interferometer and the interferometer is used. Since it is shared, in addition to the function of observing and measuring the interference of the test surface that the interferometer has, it is possible to accurately and simultaneously measure the relative distance information between the interferometer and the test object, and as a whole Measurement system is small and lightweight,
The cost has been reduced due to the reduction in the number of active optical components, and the reliability and workability of easy maintenance have been improved. In addition, since a frequency-stabilized laser is used as the shared laser light source, the coherent length is long, the visibility (contrast) of the observed interference fringes is good, and an interferometer that provides stable length measurement accuracy is provided. It was decided to be.

[Brief description of the drawings]

FIGS. 1 (a), (b) and (c), FIGS. 2, 3 and 4
FIG. 5 and FIG. 5 are configuration diagrams showing an embodiment of the present invention, and FIG. 6 is a configuration diagram of a conventional interferometer. 100,100A, 100B ... Interferometer unit 110,110A, 110B ... Interferometer 111 ... Laser light source 112 ... Collimator lens 113 ... Fizeau reference lens 115 ... Condenser lens 120 ... Laser interferometer 123 …… Measurement interference prisms 130,210 …… Base, 131 ………………………………………………………………………………………………………………………………………………………………………………………………………. …… Counter balance 401,401A …… Drive motor

Claims (2)

(57) [Claims] 1. A laser light source of an interferometer for interference observation and a laser light source of a laser interferometer are shared, and a test optical axis of the interferometer for interference observation and a measuring optical axis of the laser interferometer are measured. Characterized in that they are arranged in parallel and in the same direction. 2. The apparatus according to claim 1, wherein the interferometer components other than the test object and the laser interferometer components other than the length measuring mirror or prism are provided in the same unit. Interferometer.