JP3491464B2 - Laser beam divergence angle measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a divergence angle of a laser beam (hereinafter, abbreviated as beam divergence angle), which is one of the characteristics of a laser beam.

[0002]

2. Description of the Related Art The beam divergence angle is one of the important items when evaluating the characteristics of a laser device. That is, the beam divergence angle is a factor that determines the optical transmission system and the spot diameter of the focused beam in the laser processing apparatus. As a method of measuring the beam divergence angle, there is a method of collecting the beam and obtaining it from the spot diameter. In this method, a laser beam emitted from a laser oscillator is condensed by a lens having a focal length f, and a beam diameter d at a focal position is measured to calculate a beam divergence angle θ, where θ = d / f. Calculate by formula.

FIG. 11 is a conceptual diagram of a beam divergence angle measuring device. This beam divergence angle measuring device includes a beam splitter 27, a measuring lens 17, and a CCD camera 18. The measurement of the beam divergence angle is performed by injecting the measured laser beam 30 into the measured laser beam inlet 28 of the beam divergence measuring device 15 and tens of mW by the beam splitter 27.
The light is dimmed to some extent and enters the measuring lens 17. The remaining laser beam is emitted from the measured laser beam outlet 29 to the measuring device 15
Released out of. The incident beam is condensed by the measuring lens 17, and is radiated to the CCD camera 18 arranged so that the position of the focal length f of the measuring lens 17 becomes the light receiving surface, and the signal thereof is image processing device 19. To obtain the beam divergence. If the intensity of light applied to the CCD camera 18 is too high, the attenuator 31 adjusts the intensity.

In this measurement, the lens 17 for measurement satisfies the conditions that it has little aberration, the focal length of the lens is accurately grasped, and the resolution is suitable for the beam divergence angle measuring device. It is necessary to select. In particular, the focal length of the lens may be about 1% around, depending on the manufacturing accuracy, so it is necessary to accurately know the focal position due to individual differences in the lens.

An example of a method for measuring the focal length of a lens is shown in FIG.
Shown in 12. In this example, the illumination light 20 emitted from the light source is passed through a double slit 21 which is precisely processed at intervals h to generate two light beams, which are then incident on a lens 22 to be measured. The light that has passed through the lens 22 to be measured is detected as two lines of light by the collimator lens 24 having a focal length of f _c and the measuring scale 25 using the autocollimator 23. At this time,
The position of the double slit 21 is the measurement scale 25 and the eyepiece lens 26.
In the measuring unit configured by, the two light flux images are arranged at positions in focus. In this measuring device, if the distance between the double slits 21 is h, the distance between the two light beams on the measuring scale 25 is x, and the focal length of the collimator lens 24 is f _c , the focal length f _t of the lens 22 to be measured is It is given by f _t = f _c × (h / x).

However, in this method, the double slit 21
Is an extremely difficult task because it is very difficult to focus the images of the two light fluxes in the measuring section, which is an operation for accurately arranging the image at the focal position of the lens 22 to be measured.

[0007]

As described above, in the prior art, it is difficult to accurately grasp the focal position of the lens, and the beam divergence angle measuring device for measuring the beam divergence angle must be calibrated. It can't be done easily.
The focal length of the lens may change about 1% due to manufacturing accuracy. However, in order to accurately grasp the focal length, it is necessary to have a lens focal length measuring device as shown in FIG. Even if the focal length of the lens is accurately grasped, it is impossible to accurately determine the position of the detection surface of the CCD camera because the beam waist and the focal length are different.

According to the results of experiments conducted by the inventor who investigated the influence of the deviation from the focal length on the beam divergence measuring device, for example, an aplanatic lens having a focal length of 120 mm was used in the beam divergence measuring device. , Divergence angle is 30mrad
When measuring the YAG laser beam of, the front and rear are 1 mm (1% of the focal length) with respect to the focal length equivalent position of the lens used.
It was found that the measurement value of the beam divergence angle was deviated by 5% when measured at the (weakly) shifted position. That is, a deviation of 1% from the focal position is 5% in the measured value of the beam divergence angle.
It means that it appears as an error of.

An object of the present invention is to eliminate the need for a device for accurately ascertaining the focal length as described above, and further, C
The difficulty of positioning the CD camera can be eliminated,
It is an object of the present invention to provide a beam divergence angle measuring device that can be easily calibrated.

[0010]

In order to solve such a problem, according to the present invention, a diverging beam reference light generating means for generating a plurality of reference beams having mutually known angles, and the reference beam are measured. A value W / f obtained by dividing the distance W between the means for entering the lens for use and the reference beam and the position where the reference beam is focused by the measuring lens by the focal length f.
However, it is provided with a means for adjusting the distance between the measuring lens and a means for measuring the distance W between the focused laser beams so as to coincide with the above α.

Injecting a reference beam with a known angle α,
Since the position of the measuring lens is adjusted while measuring W so that W / f becomes equal to α, the adjustment work becomes very easy and the accuracy becomes high. Further, in the present invention, a means for measuring the angle between the divided laser beams is provided, and the angle between the divided laser beams can be accurately grasped.

As means for splitting the laser beam, one surface has a flat surface, and the opposite surface opposite to that surface has a flat surface.
Equipped with an optical element having a valley shape or a roof shape, which is composed of angled two-sided, multi-sided or conical surfaces,
The laser beam can be split with a simple configuration. Furthermore, by centering the laser beam on the bottom of the troughs or the apex of the roof of these elements, there is no significant imbalance in the intensity between the split beams.

It is essential that the laser beam to be incident is incident within the effective incident diameter D of the measuring lens. Therefore, the angle α between the reference beams is equal to the effective incident diameter D of the measuring lens. The optical element or the like is selected so that the angle is 2 tan ⁻¹ (D / 2l) or less, which is determined by the distance 1 from the starting point of the reference laser beam to the measuring lens.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a beam divergence angle measuring device according to the present invention will be described with reference to FIG. Figure 1
FIG. 3 is a conceptual diagram showing a configuration of a beam divergence angle measuring device according to the present invention. This beam divergence measuring device 15 has
In addition to the conventional beam divergence measuring device, the divergent beam reference light generating means used to calibrate the device and the divergent beam reference light emitted by the diverging beam reference light (hereinafter referred to as reference light (Referred to as split beams) and means for measuring the angle between the split beams and means for making reference light incident on the measuring lens 17 to calibrate the apparatus.

The conventional beam divergence measuring device has a laser beam entrance to be measured as described in the section of the prior art.
Measuring laser beam 30 incident from 28
A beam splitter 27 that splits the beam to the side and a beam emitted from the laser beam outlet 29 to be measured, a measuring lens 17, an attenuator 31 for adjusting the amount of light, and a CCD camera 18 that is movable in the optical axis direction. , An image processing device 19 for calculating the beam divergence angle by arithmetically processing the output of the CCD camera 18.

Since the method of measuring the beam divergence angle of the laser beam 30 to be measured is the same as that described in the section of the prior art, it is omitted here and the calibration of the apparatus will be mainly described. A laser beam 4 emitted from the laser device 3 is divided by a diverging beam reference light generating means (which will be referred to as a reference light generating unit in the drawing, and hereinafter referred to as a reference light generating unit) 7 with a predetermined angle. Beam 5 is split into reflection mirrors 16a and 16
It is bent twice by b, enters the measuring lens 17, is condensed, and irradiates the light receiving surface of the CCD camera 18. The information received by the light receiving surface is analyzed by the image processing device 19. For example, in the case of a two-split beam, the image processing device 19 displays information on two condensed lights. The distance between the peak positions of these two pieces of information corresponds to d of "θ = d / f" (d is the diameter of the focused beam and f is the focal length of the measuring lens), which is a basic expression expressing the beam divergence angle. To do. Since the incident split beams 5 have a known angle α between them, the CCD camera 18 is set so that the instruction of the image processing device 19 coincides with α.
CCD camera by adjusting the position of
The focal position of the measuring lens 17 can be matched with the light receiving surface of 18, and the beam divergence angle measuring device 15 can be calibrated.

The angle between the split beams 5 of the reference light is measured by
This is carried out by removing the reflection mirror 16b, moving the reference light straight, irradiating the screen 6, and measuring the distance between the irradiation positions of the divided beams by the CCD camera 8 and the TV monitor 9. FIG. 2 is a conceptual diagram for explaining the measurement of the angle between the split beams 5, which is the reflection mirrors 16a and 16a in FIG.
It is a straight line without b, and the corresponding parts are designated by the same reference numerals as in FIG.

The angle α between the split beams 5 is measured by measuring the distance H between the split beams 5 irradiated on the screen 6 provided at a position separated by a distance L from the branch point of the split beams 5, Ask by. α = 2 × tan ⁻¹ [H / (2 × L)] In this measurement, the screen has a grid and T
When the grid and the split beams 5 are displayed on the V screen at the same time, it becomes easy to measure the interval H between the split beams 5.

Examples will be described below. [First Embodiment] The first embodiment corresponds to claim 2 and will be described with reference to FIGS. 3 and 5. FIG. 3 is a cross-sectional view showing the structure of the valley optical element 1 that divides the laser beam 4 in the reference light generator 7, and FIG. 5 shows that the reference light generator 7 including the valley optical element 1 divides the laser beam 4. It is a conceptual diagram which shows the state which generated 5.

The trough type optical element 1 has a trough shape in which one surface is a flat surface and the opposite surfaces are two surfaces inclined by an angle θ _{V with} respect to the above-mentioned flat surface. Light incident on the optical element 1 as shown in FIG. 3 has an incident angle on the optical element 1 of θ ₁ , a refractive index of the optical element 1 of n ₂ , and a surrounding refractive index of n ₂ .
_{When set to 1} , the light is emitted in the direction of the angle θ _x1 as shown in the figure. The angle θ _{x1 in} this case is

[0021]

[ _Equation 1] θ _x1 = sin ^-1 {(n ₂ / n ₁ ) × sin [sin ^-1 (n ₁ sin
obtained by _{θ 1 / n 2) + θ} V]} -θ V. When the laser beam 4 is incident by aligning the center of the laser beam 4 with the bottom 101 of the valley of the valley type optical element 1, as shown in FIG.
It is split into split beams 5 with an angle α between 51 and a balanced light intensity.

In FIGS. 3 and 5, an example in which the laser beam 4 is divided into two by the dihedral optical element 1 has been shown. However, if a multifaceted one or a one having a conical surface is used, it is multidivided. It can be a beam or a circular beam. Since it is difficult to process the valley bottom part of the valley type optical element, it is often manufactured by laminating a plurality of symmetrical shaped elements (two in a two-sided shape).

[Second Embodiment] The second embodiment corresponds to claim 4 and will be described with reference to FIGS. 4 and 6. FIG. 4 is a cross-sectional view showing the structure of the roof-type optical element 2 that divides the laser beam 4 in the reference light generator 7.
FIG. 6 is a conceptual diagram showing a state in which the reference light generator 7 including the roof-type optical element 2 generates the split beam 5.

The roof type optical element 2 has a flat surface on one side,
The opposite surface facing each other has a roof shape having two surfaces inclined at an angle θ _R with respect to the plane. The light incident on the optical element 2 as shown in FIG.
_When the refractive index of the optical element 2 is ₁ , the refractive index of the optical element 2 is n ₂ , and the refractive index of the surroundings is n ₁ , the light is emitted in the direction of the angle θ _x2 as shown in the figure. The angle θ _{x2 in} this case is

[0025]

[ _Equation 2] θ _x2 = θ _R − sin ⁻¹ {(n ₂ / n ₁ ) × sin [θ _R − s
in ⁻¹ (n ₁ sin θ ₁ / n ₂ )]}. The top 20 of the roof of this roof-type optical element 2
When the laser beam 4 is incident with the center part of the laser beam 4 aligned with 1, as shown in FIG. 6, there is an angle α between the directions 51 of the maximum intensity of the light amount, and the light amount is balanced in the vertical direction. It is divided into beams 5.

Although FIGS. 4 and 6 show an example in which the laser beam is divided into two parts by the two-sided roof type optical element 2, the multi-particulation can be performed by using a multi-sided one or one having a conical surface. Alternatively, it can be a circular beam. In Figure 7 (a), 2
A perspective view of the planar roof-type optical element 2a is shown in FIG. 7 (b).
A perspective view of a four-sided roof-type optical element 2b is shown. In the case of the four-sided shape, the beam is divided into the upper, lower, left and right sides, so that there is an advantage that the calibration in both directions can be performed simultaneously.

In the above two embodiments, the laser beam 4
Although the case where the laser beam 4 is incident from the plane side of the optical element is shown, a split beam can be obtained even if the incident surface and the emission surface of the laser beam 4 of the optical element are opposite. Although not shown in the drawing, in this state, in the case of the valley type optical element, the light is emitted in the state as shown in FIG. 6, and in the case of the roof type optical element, the light is emitted in the state of FIG.

Further, by arranging a plurality of optical elements in multiple stages, the angle between the divided beams can be changed. When the elements in the state of FIG. 5 are arranged, the angles approximately add and increase. When the element in the state of FIG. 5 and the element in the state of FIG. 6 are arranged side by side, they cancel each other and the angle becomes smaller. In the case of the above-mentioned optical element, the branch point of the split beam 5 is displaced from the bottom 101 of the valley of the element or the apex 201 of the roof, and the distance L to the screen used to obtain the angle α is Care must be taken when determining the value.

In the case of the valley type optical element 1, as shown in FIG. 5, the branch point of the split beam 5 (the laser beam branch point 102 in the figure) is located on the incident side by l ₁ from the bottom 101 of the valley. Deviated. In the case of the roof type optical element 2, as shown in FIG. 6, the branch point of the split beam 5 (in the figure, the branch point 202 of the laser beam) is shifted from the apex 201 of the roof portion to the emitting side by l ₂ . . This shift can be obtained from the position of the maximum intensity portion of the laser beam and α.

[Third Embodiment] FIG. 8 is a conceptual diagram showing a reference light generator in a third embodiment. This embodiment corresponds to claim 1 and comprises two laser devices 3a and 3b and four reflection mirrors 10a, 10b, 10c and 10d, one laser device and two laser devices. 1 with a reflective mirror
By making one beam and adjusting the angle of the reflecting mirror, the angle between both beams is adjusted. Therefore, in this case, although it is not a split beam in a strict sense, it is referred to as a split beam 5 in the drawing in order to match with other examples.

[Fourth Embodiment] FIG. 9 is a conceptual diagram showing a reference light generator in a fourth embodiment. This embodiment also corresponds to claim 1, in which the laser beam 4 of one laser device 3 is divided into two by the beam splitter 11.
The angle between the split beams 5 is adjusted by the reflecting mirrors 10a, 10b, 10c, 10d and 10e.

[Fifth Embodiment] FIG. 10 is a conceptual diagram showing a reference light generator in a fifth embodiment. This embodiment also corresponds to claim 1, and the laser beam 4 of one laser device 3 is divided into two by the beam splitter 11.
A split beam is generated by a set of condenser lens 12, optical fiber 13 and collimator lens 14.

The split beam of the reference light generated in this way cannot be accurately calibrated unless it is incident within the effective incident diameter D of the measuring lens. Therefore, the angle α between the divided beams needs to be α ≦ 2 tan ⁻¹ (D / 2l), where l is the distance from the branch point, which is the starting point of the divided beam 5, to the measuring lens.

[0034]

As described above, according to the present invention, in addition to the conventional beam divergence measuring device, the reference light generating section, the means for measuring the angle between the split beams generated therein, and the reference. A means for calibrating the device by making light incident on the measuring lens is provided, and the device is calibrated in order to calibrate the device by measuring the known angle between the split beams of the reference light, thereby calibrating the device. It will be easier and more accurate.

A valley type optical element or a roof type optical element is used for the reference light generating section for generating the reference light, so that the structure of the apparatus is simplified and the stability against vibration is increased. Further, the angle between the split beams can be easily changed by using the optical elements in multiple stages. Further, since the angle between the divided beams can be obtained by calculating the branch point of the divided beams, the measurement and the calculation can be easily performed. In particular,
Measurement is easy when using a screen with grid scales.

As described above, by using this beam divergence measuring apparatus, the user can calibrate it. As an example of this, the inventor has adopted Y as a laser device.
An AG laser is used, two types of roof-type optical elements are used for the reference light generation part, a graph paper is placed at a position about 1 m away from the branch point of the split laser beam, and the back side of the graph paper is divided using a CCD camera. The distance between the beams was measured, the angle between the split beams was determined, and the device was calibrated using the three types of reference light thus generated. In each case, the distance between the measuring lens and the CCD camera was It became the same. Thus, the calibration of the device is easy and accurate.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the configuration of a laser beam divergence angle measuring device according to the present invention.

FIG. 2 is a conceptual diagram for explaining measurement of an angle between split beams generated by a reference light generation unit.

FIG. 3 is a cross-sectional view of a valley optical element for generating a split laser beam.

FIG. 4 is a sectional view of a roof-type optical element for generating a split laser beam.

FIG. 5 is a conceptual diagram showing a state in which a split laser beam is generated by a valley optical element.

FIG. 6 is a conceptual diagram showing a state in which a split laser beam is generated by a roof type optical element.

FIG. 7A is a perspective view of a two-sided roof-type optical element. (B) Perspective view of a four-sided roof-type optical element

FIG. 8 is a conceptual diagram showing a generation state of a split laser beam using a reflection mirror.

FIG. 9 is a conceptual diagram showing a generation state of a split laser beam using a beam splitter and a reflection mirror.

FIG. 10 is a conceptual diagram showing a generation state of a split laser beam using a beam splitter and an optical fiber.

FIG. 11 is a conceptual diagram showing a configuration of a conventional laser beam divergence angle measuring device.

FIG. 12 is a conceptual diagram showing the configuration of a focal length measuring device.

[Explanation of symbols]

1 Valley type optical element 2 Roof type optical element 2a Two-sided roof type optical element 2b Four-sided roof type optical element 3 Laser device 3a Laser device 1 3b laser device 2 4 laser beam 5 split beams 51 direction of maximum intensity of split beam 6 screens 7 Reference light generator 8, 18 CCD camera 9 TV monitor 10, 10a, 10b, 10c, 10d, 10e Reflective mirror 11 Beam splitter 12 Condensing lens 13 optical fiber 14 Collimating lens 15 Laser beam divergence measuring device 16a, 16b Reflective mirror 17 Measuring lens 18 CCD camera 19 Image processor 20 illumination light 21 double slit 22 Lens to be measured 23 Auto Collimator 24 collimator lens 25 measuring scale 26 eyepiece 27 Beam splitter 28 Measured laser beam entrance 29 Laser beam outlet to be measured 30 Measured laser beam 31 Attenuator 51 Direction of maximum intensity 101 Bottom of valley 102 Laser beam branch point 201 Roof top 202 Laser beam branch point

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Claims (6)

(57) [Claims] 1. A laser beam to be measured is condensed by a measuring lens having a focal length f, a diameter d of the laser beam at the focal position is measured, and a divergence angle θ is measured as θ = d / f. Laser beam divergence angle measuring device, laser beam generating means, divergent beam reference light generating means for dividing the laser beam to generate a plurality of reference laser beams having angles with each other, and measuring the angle α between the reference laser beams Means, a means for injecting the reference laser beam into the measuring lens, a means for measuring the distance W between the laser beams focused by the measuring lens into which the reference laser beam is incident, and W divided by the focal length f. A means for adjusting the distance between the measuring lens and a means for measuring the distance W between the focused laser beams so that the value W / f matches the above α. Laser beam divergence angle measuring device according to symptoms. 2. The divergent beam reference light generating means has a valley shape having a flat surface on one surface and an angled two surface, a polyhedral surface or a conical surface on the opposite surface facing the surface. The laser beam divergence angle measuring apparatus according to claim 1, further comprising an optical element having the same. 3. The laser beam generating means and the optical element are arranged such that the center of the laser beam emitted by the laser beam generating means hits the bottom of the valley portion of the optical element having the valley shape. The laser beam divergence angle measuring device according to claim 2. 4. A diverging beam reference light generating means has a roof-like shape having a flat surface on one surface and an angled two-sided surface, a multi-sided surface or a conical surface on the opposite surface facing the surface. An optical element having
The laser beam divergence angle measuring device according to. 5. The laser beam generating means and the optical element are arranged so that the center of the laser beam emitted by the laser beam generating means hits the apex of the roof of the optical element having the roof shape. The laser beam divergence angle measuring device according to claim 4, which is characterized in that. 6. The angle α between the reference laser beams is determined by the effective incident diameter D of the measuring lens and the distance l from the starting point of the reference laser beam to the measuring lens, 2 tan ⁻¹ (D / 2l ) The laser beam divergence angle measuring device according to any one of claims 1 to 5, wherein: