JPH07209507A - Optical filter for laser beam - Google Patents

Abstract

PURPOSE:To obtain the optical filter of simple constitution for the laser beam which has a uniform light intensity distribution and generates a parallel laser beam having small variation in light quantity by operating a light transmission distribution for the uniform light intensity distribution from data on the uneven light intensity distribution that the parallel laser beam has. CONSTITUTION:This optical filter has a laser light source part 2, a projection lens 3 which converts an expanded laser beam into a parallel laser beam, and a photodetection lens 4 which converges the parallel laser beam. Further, the filter consists of a photodetecting element part 5 which senses the whole quantity of the laser beam converged by the photodetection lens 4, an optical filter 6 for the laser beam, and a controller 7. A body 8 to be measured is positioned within the effective measurement range width of the parallel laser beam formed between the projection lens 3 and photodetection lens 4. A signal based upon a decrease in the quantity of light corresponding to the shadow of the parallel laser beam cut off by the body 8 to be measured is received by the photodetecting element part 5 and the signal processing part of the controller 7 operates and displays the width of the measured body 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical filter for a laser beam, and a uniform light intensity distribution particularly required in a laser-based measuring device such as an outer shape (diameter) measuring device or a sensor using a parallel laser beam. The present invention relates to an optical filter for laser beam capable of forming a parallel laser beam.

[0002]

2. Description of the Related Art The cross-sectional beam shape of a laser beam varies from 1 mm or less to 30 mm due to differences in the resonator structure and the like.
There are a wide variety of types, including prismatic ones, which are selected according to the purpose of use such as measurement and detection. For example, when a pattern obtained by projecting a laser beam on a screen is viewed, a circular pattern, which is a basic mode, or a multimode having a complicated shape such as an elliptical shape or a donut shape is formed. Generally, the above-mentioned beam-shaped intensity distribution forms a Gaussian distribution, a two-dimensional asymmetric Gaussian distribution, or a distribution close thereto.
Such a laser beam is applied to various devices by bending, expanding, narrowing, shaking, or modulating the laser beam output from the laser oscillator.

An apparatus for converting a laser beam into a band-shaped parallel laser beam, positioning an object to be measured such as a wire rod or a bar within the area of the parallel laser beam, and measuring the outer shape and diameter of the object to be measured without contact. Is known. As a method for converting a laser beam into a parallel laser beam, for example, a galvanometer scanner, a polygon scanner, an acousto-optic effect means, etc. are used to shake the laser beam to form a parallel laser beam, and a scanning type of measuring an object to be measured. A measuring device is mentioned. Further, a beam expansion type measuring device for measuring an object to be measured by forming a parallel laser beam by expanding a laser beam using an optical lens such as a cylindrical lens or a collimator lens can be used.

[0004]

Such a measuring apparatus is affected by the optical intensity distribution of the laser beam itself for the above-mentioned reason, as well as the optical element, lens, aperture, etc. used. The light intensity distribution of the laser beam formed through them is further deviated. That is, the unevenness of the change in the light amount becomes large, and the difference in the light intensity between the central portion and the end portion in the width direction becomes large within the measurement region. Even when measuring the same object to be measured, if the measurement position changes, the measurement result by the light receiver in the device will be different, and there is a drawback that accurate measurement cannot be performed. In order to reduce such unevenness of light intensity change, it is necessary to always use the vicinity of the central portion in the width direction of the parallel laser beam, which has a relatively small difference in light intensity distribution, and to reduce the maximum width of the measured object. There was a limit.

By the way, in order to form a uniform parallel laser beam, the focal length of the lens is increased, the beam width is expanded, and only the beam near the center where the light intensity distribution is relatively uniform is used. There is known a method of forming a parallel laser beam having a uniform light intensity by cutting the area of (3) with an aperture or a shielding plate. However, the light intensity of the collimated laser beam formed is weak, so
The SN ratio decreases, and the resolution of the minimum measurement width of the measured object deteriorates. Therefore, the width of the parallel laser beam cannot be expanded and the effective width is limited.

In the apparatus having the above-mentioned structure, there is no apparatus in which the effective width of the parallel laser beam is 100 mm or more, and in any case, the apparatus having the width of 50 to 60 mm is the maximum.
Moreover, the size of the effective measured object is limited to a size considerably smaller than the maximum effective utilization width. The present invention has been made in view of the above problems, an optical element, a lens,
Has a uniform light intensity distribution with a simple configuration without changing the design or arrangement of the measuring device such as the aperture.
An object of the present invention is to provide an optical filter for a laser beam capable of forming a parallel laser beam with a small change in light amount.

[0007]

In order to solve the above-mentioned problems, an optical filter for a laser beam according to the present invention is characterized in that it has a light transmission distribution that is an inverse ratio to the light intensity distribution in the width direction of an input parallel laser beam. And in particular,
The laser beam output from the laser oscillator is converted by the conversion means into parallel parallel laser beams having a constant width, and the light corresponding to the light intensity distribution is made uniform so that the light intensity distribution in the width direction of the parallel laser beam becomes uniform. Data of transmission distribution is calculated, and a filter material that absorbs a laser beam is formed on a transparent or semitransparent substrate with a light transmission distribution based on the data. Further, the laser beam optical filter is formed by vapor-depositing or sputtering a metal thin film layer on a transparent or semitransparent substrate, or records the light intensity distribution of an incident parallel laser beam on a photographic film. It is characterized by being formed by.

[0008]

With the above structure, the optical filter for a laser beam of the present invention calculates the light transmission distribution for obtaining a uniform light intensity distribution from the data of the nonuniform light intensity distribution of the parallel laser beam. A filter material such as metal is formed in a thin film on a transparent or semi-transparent substrate by means such as vapor deposition. A parallel laser beam having a uniform intensity distribution can be obtained by arranging the laser beam optical filter thus formed in a laser utilizing measuring device or the like.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the drawings by taking as an example the case of being incorporated in a laser measuring apparatus. FIG. 1 shows an example of a laser-based measuring device using a strip-shaped parallel laser beam according to the present invention. The laser-based measuring device 1 mainly includes a laser light source unit 2 including a device for expanding a laser beam, a light projecting lens 3 for converting the expanded laser beam into a parallel laser beam, and a parallel laser beam for a light receiving element unit 5 described later. A light-receiving lens 4 for focusing, a light-receiving element portion 5 for sensing the total light amount of the laser beam focused by the light-receiving lens 4, an optical filter 6 for a laser beam, which will be described later, according to the present invention, located behind the light projecting lens 3, and a controller 7. It is composed of The controller 7 is composed of an internal oscillator that sends a signal to the laser light source unit 2, a signal processing unit that calculates a signal from the light receiving element, and a display unit that displays the measurement after the calculation to the user. The DUT 8 is positioned within the effective measurement range width D of the parallel laser beam formed between the light projecting lens 3 and the light receiving lens 4. The amount of light corresponding to the shadow of the parallel laser beam blocked by the DUT 8 decreases. The light-receiving element unit 5 receives a signal associated with a decrease in the amount of light, and the signal processing unit of the controller 7 calculates the width of the measured object and displays it on the display unit.

FIG. 2 shows a general light intensity distribution of a belt-shaped parallel laser beam output from the light projecting lens 3 within the one-dimensional effective utilization width D. As shown in the figure, in the width D direction, the central portion has the strongest light intensity (Imax), the light intensity decreases toward the end portions away from the central portion, and the light intensity becomes the lowest at both end portions (Imin). ). In this example, when the DUT of the same size is measured at different positions, the amount of light received by the light receiving element unit 5 differs due to the difference in the measurement position in the width direction. Further, when the measurement position is set at the central portion, the measured values do not have a proportional relationship depending on the size of the object to be measured, and accurate measurement cannot be expected.

In order to evaluate the above-mentioned uniformity of the light intensity distribution, as shown in FIG. 3, the light shield plate by the knife edge 9 is moved from one end of the parallel laser beam to the other end in the width direction. The uniformity of the light intensity distribution is evaluated by measuring the amount of light that reaches the light receiving element portion 5 without being cut by the knife edge 9 at each position.

FIG. 4 shows the measurement results showing the relationship between the light intensity and the effective utilization width obtained by the knife edge 9 of FIG. For a parallel laser beam with a uniform light intensity,
A straight line A is theoretically obtained. However, when the light intensity is not uniform as shown in FIG. 2, the curve B is obtained as a typical example. In order to stabilize the measured value, it is necessary to bring the curve B having a nonuniform light intensity close to the straight line A. That is, it is necessary to correct the light intensity distribution so that the light intensity always remains constant even if the measurement position of the object to be measured is changed.

In order to solve the above problems, an optical filter for a laser beam having a light transmission distribution with a concentration gradient is designed. As shown in FIG. 5, the light intensity distribution C before correction is measured, data inversely proportional to the light intensity distribution C is calculated, and the transmission distribution D is derived. The guided transmission distribution D is formed on the laser beam optical filter. The transmittance of a normal filter substrate is almost 100%. Therefore, the formed optical filter for laser beam has a transmittance of 1 near the end.
The transmittance becomes 00%, and the transmittance decreases toward the central portion. By correcting the light intensity by using the laser beam optical filter in the laser measuring apparatus of FIG. 1, a parallel laser beam having a finally uniform light intensity distribution is formed as shown in FIG. The optical filter for the laser beam is preferably arranged between the laser light source unit 2 and the DUT 8. In the example shown in FIG.
Although it is arranged immediately after, the position is not limited to this position, and the laser beam optical filter may be arranged at a position between the DUT 8 and the light receiving element section 5.

The laser beam optical filter 6 is a means such as vapor deposition or sputtering of a thin film layer of a metal such as iron or aluminum or a special alloy of several metals, or a synthetic resin on a transparent or translucent glass substrate. It is formed by. As the substrate material, synthetic resin such as transparent or translucent plastic can be used. In addition to the above, it is also possible to record the light intensity distribution on a photographic film, or to use a transparent or anti-transparent substrate coated with an organic dye as an optical filter.

The above-mentioned optical filter for laser beam is not limited to the use in the laser measuring device described in the above embodiment, but can be effectively used in other devices such as a sensor using a parallel laser beam. can do.

[0016]

INDUSTRIAL APPLICABILITY The present invention is a laser-based measuring device that uses a light source such as a parallel laser beam having a non-uniform light intensity distribution. The light transmission distribution, which is the reciprocal of the light intensity distribution data, is recorded on the filter substrate and corrected as an optical filter for the laser beam, so that the laser beam with uneven light intensity is converted into a laser beam with uniform light intensity. Can be converted. Further, it is possible to form a uniform light intensity distribution with almost no decrease in light intensity.

[0017]

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an embodiment according to the present invention.

FIG. 2 is a diagram showing a change in light intensity distribution within an effective width D according to a conventional example.

FIG. 3 is a diagram showing a method of evaluating a light intensity distribution.

FIG. 4 is a diagram showing measurement results by the evaluation method of FIG.

FIG. 5 is a diagram showing a non-uniform light intensity distribution and a light transmission distribution of an optical filter for a laser beam, which is the inverse of this distribution.

FIG. 6 is a diagram showing a light intensity distribution after correction by a laser beam optical filter.

[Explanation of symbols]

 1 Laser-based measuring device 2 Laser light source section 3 Light emitting lens 4 Light receiving lens 5 Light receiving element section 6 Optical filter for laser beam 7 Controller

Claims (4)

[Claims] 1. An optical filter for a laser beam, which has a light transmission distribution that is an inverse ratio to a light intensity distribution in the width direction of an input parallel laser beam. 2. A laser beam output from a laser oscillator is converted into a parallel laser beam having a constant width by a conversion means, and the light intensity is made uniform so that the light intensity distribution in the width direction of the parallel laser beam becomes uniform. An optical filter for a laser beam, characterized in that data of a light transmission distribution corresponding to the distribution is calculated, and a filter substance absorbing a laser beam is formed on the transparent or semitransparent substrate with a light transmission distribution based on the data. . 3. The laser beam optical filter comprises:
The optical filter for a laser beam according to claim 1 or 2, wherein a metal thin film layer is formed by vapor deposition or sputtering on a transparent or semitransparent substrate. 4. The laser beam optical filter comprises:
3. An optical filter for a laser beam according to claim 1, which is formed by recording a light intensity distribution of an incident parallel laser beam on a photographic film.