JPH0198946A - Light convergence optical system for optical measuring instrument - Google Patents

Abstract

PURPOSE:To set the converged spot diameter and spread angle of converged light at a convergence point optionally and relatively small by providing a 1st lens system, a pinhole, a 2nd lens system, and a stop. CONSTITUTION:This optical system consists of the condenser lens 3 which converges laser light emitted by an He-Ne laser 1, the pinhole 10 provided at the convergence point of the laser light converged through the condenser lens 3, the lens 5a which converges the laser light emitted from this pinhole 10 on a body to be measured, the convergence point 12 of the laser light converged by the lens 5a, and the stop 11 provided between the convergence point and lens 5a. Consequently, the spot diameter of irradiation light required for the accurate measurement of the optical measuring instrument is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a condensing optical system for an optical measuring instrument, and more particularly, it scans an object to be measured with a laser beam or the like, or A focusing optical system of an optical measuring instrument that obtains information about an object by moving the object with a fixed laser beam, etc., and detecting the level, directivity, etc. of reflected or transmitted light from the object. Regarding.

Examples of such optical measuring instruments include flaw inspection devices that utilize the fact that the reflectance and reflection direction of light irradiated onto an object differ depending on the presence or absence of flaws on the surface of the object, and flaw inspection devices that utilize refractive index distribution. 2. Description of the Related Art There are known refractive index distribution measuring devices that irradiate the side surface of a cylindrical object to be measured and determine the refractive distribution of the object based on the refraction angle of the transmitted light.

With these measurement devices, in order to obtain detailed information on the object to be measured, it is necessary to reduce the diameter of the condensed light spot irradiating the object to be measured. Therefore, in order to determine the internal refractive index distribution, it was necessary to reduce the spread angle of the irradiated light in addition to reducing the condensed spot diameter.

[Prior art]

FIG. 3 shows a typical example of a conventional lens flaw inspection device which is such an optical measuring device. In this Figure 3, He-N
The output light from the e-laser 1 is reflected by a mirror 2, focused by a condenser lens 3, transmitted through a half mirror 4, and then sent to a lens 5.
, a condensed spot is formed on the lens 8 to be tested by the mirror 7. The light flux that has passed through the test lens 8 is reflected by the retroreflective screen 9 and travels backward along the same optical path. This backward reflected light is branched by a half mirror 4 and enters a detector 6. In FIG. 3, the mirror 7 is rotatable, and by rotating the mirror 7, the laser spot is scanned on the lens 8 to be tested, and the reflected light on the retroreflection screen 9 is detected. 6 to check the condition of the lens 8 to be tested.

[Problems to be solved by the present invention]

The condensing optical system of the conventional optical measuring instrument shown in FIG. 3 has a configuration in which the condensed spot of the laser is imaged by a lens 5 on a lens 8, which is an object to be examined.

Therefore, in order to reduce the diameter of the focused spot by lens 5, it is necessary to reduce the imaging magnification of lens 5. In this case, the divergence angle of the focused light of lens 5 (indicated by θ in the figure) is ) becomes larger.

Furthermore, in order to reduce this divergence angle, it is necessary to increase the imaging magnification of the lens 5, and in this case, the focusing property deteriorates and it is not possible to reduce the condensed spot diameter. Therefore, there was a so-called trade-off.

In this way, it is not possible to simultaneously satisfy the two conditions necessary for accurate measurement with optical measuring instruments: reducing the focused spot diameter and reducing the divergence angle. Ta.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a condensing optical system in which the convergence spot diameter and divergence angle of converged light at a condensing point can be set arbitrarily and relatively small.

[Means for solving problems]

The condensing optical system for an optical measuring instrument according to the present invention condenses laser light emitted from a laser emitting device. a pinhole arranged at a point; a second lens system that projects an image of the transmitted-illuminated pinhole onto an object to be measured at a predetermined magnification; the second lens system and the second lens; The system is characterized by including a diaphragm provided between the system and the convergence point of the laser.

[Effect]

By having the above structure and providing a pinhole, it is possible not only to reduce the size of the light source, but also to provide a secondary light source with a relatively stable luminance distribution. It can prevent the light spot from spreading.

〔Example〕

Embodiments according to the present invention will be described below with reference to the drawings.

In the drawings, elements denoted by the same reference numerals have the same functions, and therefore, redundant explanation will be omitted.

FIG. 1 shows the configuration of a condensing optical system according to the present invention.

The focusing optical system shown in this figure includes a focusing lens 3 that focuses laser light emitted from a He-Ne laser 1, and a pinhole 10 provided at the focal point of the laser light focused by the focusing lens 3. A lens 5a that focuses the laser light emitted from the pinhole 10 toward the object to be measured, and a focal point 1 of the laser light focused by this lens 5a.
2, and an aperture 11 provided between the lens 5a and the lens 5a.

Here, the objective lens 3 functions similarly to the conventional lens shown in FIG. 3 described above. Next, the pinhole 10 is
A pinhole with a diameter of several μm is usually used.
Spatial filter used when creating holograms using laser light
) using the pinhole. By providing this pinhole and using the light transmitted through this pinhole as a secondary light source, it is possible not only to reduce the size of the light source, but also to remove spectral noise caused by temporal and spatial interference of laser light, and to compare It is possible to obtain a light source with a visually stabilized luminance distribution.

Further, the aperture 11 is provided at such a position for the purpose of limiting the divergence angle (indicated by θ in FIG. 1) of the laser beam focused toward the focal point 12 by the lens 5a. That is, by providing this aperture 11, the lens 5
The substantial aperture of a can be selected, and as a result, by reducing this aperture, the divergence angle θ of the convergent light to the focal point 12 can be reduced.

The object to be measured to be scanned with the focused laser beam is placed at the focusing point 12. In this configuration, if the spot diameter required for measurement is D and the pinhole diameter is d, then the magnification ratio of the lens 5a may be D/d. Here, it is preferable to use an objective lens in view of the resolution of this lens 5a. For example, when the value of D/d is 5, an objective lens having a magnification of 5 times is used as the lens 5a.

Using the condensing optical system with the above configuration, changes in the condensed spot diameter at the condensing point 12 were specifically measured depending on the presence or absence of a pinhole.

In this measurement, the lens 3 is an objective lens with a magnification of 10, the lens 5a is an objective lens with a magnification of 5, and the pinhole 1 is an objective lens with a magnification of 5.
A pinhole with a diameter of 1 μm was used as zero, and a detector with a fiber having a core of 10 μm in diameter was used as the measuring device.The tip of the fiber was scanned within plane 29 in Figure 1, and the intensity of the light was measured The distribution was measured and the focused spot diameter was measured. The results are shown in FIGS. 2(a) and 2(b).

Here, FIG. 2(a) shows the result when no pinhole is provided, and FIG. 2(b) shows the result when a pinhole is provided. In FIG. 2(a), the half-width of the focused spot is about 290 μm, and in FIG. 2(b), the half-width of the focused spot is about 17 μm.

As can be seen from this measurement result, when a pinhole is provided, a laser beam with a smaller focused spot diameter can be obtained.

Regarding the relationship between the aperture diameter of the diaphragm and the spread of the focused spot diameter, the position of Pρ′ shown in FIG.
Install the camera tube at a position closer to aperture 11 than Q, and
1 has a diameter of 2mm.

When the diameter of the spot was changed to 1.5 mm and then 1 mm, and the spread of the spot on the image pickup tube was measured, it was confirmed that the size of the aperture of the diaphragm 11 and the spread of the spot were directly proportional.

Furthermore, the present invention is not limited to the above embodiments, and various modifications may be made.

〔Effect of the invention〕

By configuring the present invention as described above, it is possible to reduce the spot diameter of the irradiated light, which is required for accurate measurement with an optical measuring instrument, and also to increase the spread angle without increasing the spot diameter. We have achieved a condensing optical system that can be made smaller.

Furthermore, as can be seen from the comparison between FIG. 2(a) and FIG. 2(b), it is possible to realize a condensing optical system that can also reduce variations in the amount of light depending on location due to speckle.

In particular, we provide an optimal light source for measuring instruments that enter focused light from the side of a cylindrical transparent body, such as an optical fiber base material, and determine the internal refractive index distribution of the cylindrical transparent body from the refraction angle of the transmitted light. We were able to create a condensing optical system that can do this.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a condensing optical system according to the present invention, FIG. 2 is a diagram showing measurement results using the condensing optical system according to an embodiment of the present invention, and FIG. 3 is a diagram showing a conventional condensing optical system. It is a block diagram of a system. 1... He-Ne laser, 3... Condensing lens, 5a
...Objective lens, 10...Pinhole, 11...
Aperture. Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] A condensing optical system for an optical measuring instrument, comprising: a first condensing optical system for condensing laser light emitted from a laser emitting device;
a lens system, a pinhole placed at the focal point of the laser focused by the first lens system, and projecting an image of the transmitted-illuminated pinhole onto the object to be measured at a predetermined magnification. 1. A condensing optical system for an optical measuring instrument, comprising: a second lens system; and an aperture provided between the second lens system and a laser converging point by the second lens system.