JPH01209332A - Interference measuring apparatus - Google Patents

Abstract

PURPOSE:To always obtain a good interference fringe having a high contrast, by inserting an afocal lens system in a reference beam path. CONSTITUTION:The beam emitted from a beam source 21 such as He-Ne laser is split into a reference beam path 41 and a body beam path 42 by a beam splitter 23A. The beam passing through the body beam path 42 is allowed to pass through an objective lens 27 and a lens 28 to be inspected to form the image of the pupil surface of the lens 28 to be inspected on an image forming surface 31 through an image forming lens 29. An afocal lens system 43 is inserted on the way of the reference beam path 41 and the beam passing therethrough is allowed to meet with the body beam path 42 through a beam splitter 24B. Parallel beam wherein the ratio of the emitting beam diameter and incident beam diameter of parallel incident beam is changed by the afocal lens system 43 is emitted. By this method, the unbalance of the quantity of beam generated by changing the diameter of the lens to be inspected or the number of apertures can be simply corrected and a good interference fringe having a high contrast can be observed.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an interferometer, a so-called interferometer, for measuring the optical performance of an optical component such as a lens from the distortion of its transmitted wavefront. In particular, the present invention relates to an interference measurement device useful for measuring the optical performance of microlenses with a diameter of several millimeters or less.

[Prior art] For evaluating the optical performance of optical components such as lenses and mirrors,
Interference measurement technology has been developed for a long time, and various interference i91 determination devices and interferometers are commercially available and widely used.

FIG. 2 shows an example of such a conventional interference measurement device. In the figure, 1 is a He-Ne laser, 2 is a beam expander, and the laser beam, which is made into a parallel beam by the beam expander 2, is sent to a Matsuhatsu Ender interferometer, which is composed of beam splitters 3, 4 and mirrors 5, 6. incident on . An objective lens 7 and a test lens 8 are placed on one optical path, and both lenses are arranged so that the light beam transmitted through the test lens 8 becomes a substantially parallel light beam again. An imaging lens 9 is placed after the beam splitter 4, and forms an image of the pupil plane of the test lens 8 on an imaging plane 10. At this time, by aligning the direction of the light flux passing through the reference optical path 11 and the direction of the light flux in the object optical path 12 after passing through the test lens 8,
An interference pattern of the transmitted wavefront of the test lens 8 is obtained.

FIG. 3 shows an example of the resulting interference pattern.

If the test lens has good optical properties, the
) is obtained, and if there is an aberration in the lens, an interference pattern that is distorted according to the amount of aberration is obtained, as shown in FIG. 3(b). Therefore, by inputting the interference pattern thus obtained using, for example, a CCD camera, A/D converting the image, and performing computer processing, it is possible to stabilize the aberration level of the lens under test.

[Problems to be Solved by the Invention] However, in the conventional interferometric measurement device, the diameter of the light flux passing through the reference optical path 11 is fixed.
When the light intensity per unit cross-sectional area of the light flux after passing through the test lens 8 changes depending on the size of the lens diameter and NA (numerical aperture), the light intensity ratio of the light flux passing through the two optical paths 11 and 12 changes. However, if the balance between the two is poor, the contrast of the interference fringes will drop significantly.

In such a case, it is also possible to insert an optical attenuator into the reference optical path 11 or the object optical path 12 to reduce the amount of light beam with the stronger light intensity and adjust the balance. In such a method, the total amount of light of the object light and the reference destination decreases, so when measuring a minute lens, an insufficient amount of light as a whole becomes a problem.

[Means for Solving the Problems] The device of the present invention that solves the above problems converts the light emitted from the light source into a substantially parallel beam, and then divides the light into a reference optical path and an object optical path. In the interference measurement device, a light-transmitting object is disposed, and the light beam passing through the object is merged with the light beam passing through the reference optical path in the same direction, thereby causing interference. A lens system with a single aperture is placed in the reference optical path, so that the diameter of the light beam passing through the reference optical path can be adjusted by the lens system.

[Function] According to the above device, the unbalance between the sight of the object light and the reference light caused by changing the lens diameter, NA, etc. of the test lens can be corrected by adjusting the reference light beam diameter using an afocal lens system in the reference light path. can be easily corrected.

[Implementation example] An embodiment of the present invention will be described below with reference to FIG.

The apparatus shown in FIG. 1 is based on a Matsuhatsu Ender type interferometer, in which light emitted from a light source 21 such as a HeNe laser is made into a parallel beam by a beam expander 22, and sent to a reference optical path 41 by a beam splitter 23A.
and an object optical path 42.

The light flux passing through the object optical path 42 is reflected by the mirror 25A and then enters the subject lens 28 via the objective lens 27.

The subject lens 28 by passing through both lenses 27 and 28.
The light after passing through becomes a parallel beam of light, and the beam splitter 24
Transmit B.

An imaging lens 29 is placed behind the beam splitter 24B, and forms an image of the pupil plane of the subject lens 28 on an imaging plane 31.

On the other hand, an afocal lens system 43 is inserted in the middle of the reference optical path 41, and the light beam passing through this lens system 43 is reflected by a mirror 25B, as in the conventional device, and then passes through a beam splitter 24B to an object. It joins the optical path 42.

The afocal lens system 43 is an optical system that emits a parallel incident light beam as a parallel light beam, and its magnification, that is, the ratio of the diameter of the emitted light beam to the diameter of the incident light beam, is variable or at least one or more. The afocal lens system can be inserted into the reference optical path, and the diameter of the reference beam can be changed in stages.

For example, when measuring two types of subject lenses with the same NA and different lens diameters, the light intensity per unit cross-sectional area of the light beam after passing through the subject lens 28 is
is roughly inversely proportional to the square of the lens diameter.

On the other hand, since the light intensity per unit cross-sectional area of the reference target is approximately inversely proportional to the square of the magnification of the afocal lens system 43, it is necessary to set the By inserting an afocal lens system 43 with a certain magnification, it is possible to balance the light intensity of the object light and the reference destination.

The measurement of the lens has been described above, but in addition to the lens as the test object 28, the apparatus of the present invention can also measure the refractive index distribution of the waveguide cross section by measuring the transmitted wavefront of a slice sample of the leading waveguide. Generally, it can be widely applied to the evaluation of micro optical elements. In such a case, the objective lens 27 in FIG. 1 may be omitted. Also, as a light source,
A solid light source such as a semiconductor laser may also be used.

Further, although the description has been made based on a Matsuhatsu Ender type interferometer, it is also possible to apply it to other types of interferometers.

[Effects of the Invention] According to the present invention, by inserting an afocal lens system into the reference optical path, it is possible to eliminate the imbalance between the light intensity of the object light and the reference light, which is caused by changing the lens diameter, NA, etc. of the test lens. It can be corrected with a simple configuration, and good interference fringes with high contrast can always be observed.

Particularly when measuring the interference of the transmitted wavefront of a lens with a small lens diameter, as the lens diameter becomes smaller, conventional interferometers use only a small portion of the reference beam, so the reference beam is However, according to the present invention, the reference beam can be narrowed down according to the lens diameter, so a sufficient amount of light can be obtained and the difference between the object beam and the reference beam can be The amount of light can be balanced and good interference fringes can be observed.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an embodiment of the present invention, Fig. 2 is a plan view showing a conventional interference measurement device, and Figs. 3 (a) and (b) are diagrams showing examples of interference patterns. . 21...Light source 22...Beam expander 23A, 24B...Beam splitter 2
5A, 2B... Mirror 28... Subject lens 29... Imaging lens 31... Imaging surface 41... Reference optical path 42 ...Object optical path 43...Afocal lens system

Claims (1)

[Claims] After the light emitted from the light source is made into a substantially parallel beam, it is divided into two into a reference optical path and an object optical path, a translucent object is placed in the middle of the object optical path, and the beam after passing through the object is In an interference measurement device that generates interference by merging light fluxes passing through a reference optical path in the same direction, an afocal lens system is placed in the reference optical path to measure the diameter of the light flux passing through the reference optical path. An interference measuring device characterized by being adjustable with a lens system.