JPS5935003B2 - optical equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical device for processing a light beam.

Laser light is characterized by having much higher straightness than normal light.

That is, in FIG. 1, the angle θ at which the laser beam 2 emitted from the laser oscillator 1 spreads is called the beam spread angle.
-In the case of single transverse mode oscillation in Ne lasers, low-output YAG lasers, etc., it is about 1 to 2 rad,
Even in multi-mode oscillation, 2-3 rad, high output YA
Even in the case of a G laser, it is approximately 10 to 15 mrad or less, which is extremely small. However, even with such a small divergence angle, the following difficulties arise when using the laser beam to take advantage of its characteristics. In other words, there are cases where laser light is focused on a minute spot for the purpose of detecting or processing minute parts, and in this case, the diameter of the focused spot is the product of the focal length f of the focusing lens and the beam divergence angle f・θ is given by

When focusing with a lens with a focal length of 5 mm, the diameter is 5 to 10 μmφ for single mode, and 10 to 25 μmφ for multimode.
, it is difficult to obtain a condensing diameter smaller than 50 to 75 μmφ with a high-power YAG laser. To solve this problem, a beam expander is usually used to obtain a small beam divergence angle. This is shown in Figure 2. In a beam expander, two lenses with different magnifications are installed with a common focal point and optical axis. That is, in FIG. 2, a condensing lens 3 with a focal length f1 and a collimating lens 4 with a focal length F2 are installed with the optical axis 5 and focal point 6 in common. Generally it is 11 x F2.
Let F2/f1=m. When the incident beam 7 parallel to the optical axis enters the condenser lens 3, it is focused at a focal point 6 on the optical axis,
The output beam 8 passes through the collimating lens 4 and becomes parallel again.
becomes. Based on the similarity relationship, the diameter d1 of the incident beam and the diameter of the output beam have the relationship expressed by equation (1).

Therefore, the beam diameter was expanded m times by the beam expander. The effective apertures of the condensing lens 3 and the collimating lens 4 must be larger than each of Dl and d2.
FIG. 3 shows how the beam divergence angle changes depending on the beam expander. Incident beam 7
Parallel beam Al, all whose beam divergence angle is θ
Assume that the angle formed by the parallel beams Bl and bll is θ1. By the condenser lens 3, the parallel beam Al, a'1 is condensed at a point A on the focal plane, and the parallel beam B1, b', is condensed at a point B on the focal plane. The distance between AB is equal to f1θ1, which is the spot diameter at the focal plane. The light rays condensed at A become parallel beams A2, al2 by the collimating lens 4, and the light rays condensed at B become parallel beams B2, b'2 by the collimating lens 4. Angle θ2 between parallel beam 4 A2ja and parallel beam 4 B2Sb'2
Since is the beam divergence angle of the output beam 8, it becomes 2..., and the beam divergence angle is reduced to 1/m.

From (1) and (4), D2θ22d1θ11111111
8(5).

That is, when the beam spread angle is reduced to 1/m by the beam expander, the beam diameter is multiplied by m, and the product of these remains unchanged. Using such a beam expander can reduce the beam divergence angle, but
Since the beam diameter becomes large, problems occur with optical elements, detection systems, etc. In other words, regarding the F number of the lens (D is the effective aperture of the lens, f is the focal length), there are theoretical and technical restrictions on the F number, and it is difficult to make it smaller than 0.8 to 1.0. .

Furthermore, D cannot be made very large due to restrictions on optical materials and the like. Furthermore, such a lens with a large aperture and a small focal length has the disadvantage that it is difficult to manufacture and expensive. Now, if we assume that the aperture of the condenser lens is D and is equal to the beam diameter, then the spot diameter will be.

Since F has a lower limit, if F is set to the lower limit (approximately 0.8), the spot diameter cannot be reduced unless dθ. As is clear from equation (5), it is not possible to reduce dθ by using a beam expander, so the spot diameter cannot be reduced thereby. Of course, it is possible to reduce dθ by cutting the beam with an aperture plate smaller than the beam diameter and extracting a portion of the beam, but it is clear that this will lead to a corresponding decrease in power. As an example, when the beam spread angle of a high power multi-mode YAG laser with a beam spread angle of 10 mrad and a beam diameter of 5 mm is reduced to 1 mrad by a beam expander, the beam diameter becomes 50 mm.

The effective aperture of the lens to condense this light is 50m1Lφ
Then FO. In the case of 8, the focal length f is 40 mm, and the condensing diameter is 40 μmφ. In the case where the beam expander does not pass through the lens, the effective aperture of the lens is 5mmφ and the FO. 8, the focal length is 4TLT
Since it is 1 L, the condensing spot diameter is also 40 μmφ. (10 mrad×4×40 μm) Therefore, it is not possible to reduce the diameter of the condensing spot by passing the beam through a beam expander. As described above, in the conventional technology, it is necessary to increase the beam diameter in order to reduce the beam divergence angle without reducing the power of the optical beam, which leads to technical difficulties and has the disadvantage that the equipment becomes expensive. It was hot. Another problem was that even if a beam expander was used, the spot diameter could not be made smaller. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide an optical device that reduces the product of the divergence angle θ of a light beam and the beam diameter d without reducing the power of the light beam. The objective is to reduce the diameter of the converging spot when condensing light.

The present invention will be specifically described below based on embodiments shown in the drawings.

FIG. 4 shows an outline of the apparatus according to the present invention. It is assumed that the incident laser beam 9 is linearly polarized in a direction parallel to the plane of the paper by a Brieuster window of a laser oscillator or the like. The right half beam Bc of the incident beam 9 is connected to the 1/2 wavelength plate 1
0. The beam that passes through this becomes linearly polarized light perpendicular to the plane of the paper. This light is reflected by a reflecting mirror 11 and enters a polarizing beam splitter 12 . The polarizing beam splitter is made of birefringent crystals such as calcite or quartz cut and polished into triangular prisms, ABD and BCD, and pasted together to form a rectangular parallelepiped ABCD. Vertical linearly polarized light is on the bonding surface BD
It has the property of being reflected. In this case, the transmittance of linearly polarized light parallel to the paper surface and the reflectance of linearly polarized light perpendicular to the paper surface are approximately 100%, and the reflectance of linearly polarized light parallel to the paper surface and the transmittance of linearly polarized light perpendicular to the paper surface are approximately 0%. % is technically possible, and those with such transmittance and reflectance shall be adopted. After passing through the 1/2 wavelength plate 10, the beam reflected by the reflecting mirror 11 and perpendicular to the plane of the paper enters the CD surface of the polarizing beam splitter 12 perpendicularly and is reflected by the bonding surface BD. , beams a' and B7 are emitted.

Further, the left half Ab of the incident beam passes through the polarizing beam splitter 1 and is taken out as a beam A7b/. As a result, the output beam 8 has a width that is 1/2 of the width of the input beam 9.
was gotten. FIG. 5 is a cross-sectional view of the incident beam and the output beam. The cross section of the incident beam is a circle PQRS centered at O.
It is.

The right half of the incident beam PO is
RS is moved to the position of KQLO and the left half of the incident beam POR
Partially overlaps with Q. In this way, an output beam cross section PKLR having a width of 1/2 of the original incident beam diameter is obtained. In the systems shown in FIGS. 4 and 5, the output beam has a nearly rectangular cross section. Furthermore, the intensity distribution of the emitted beam is largely different from the intensity distribution of the original laser beam near Q and O in FIG. Therefore, an embodiment will be described in which an emitted beam having a high intensity distribution at the center and a square cross section is formed. FIG. 6 is a diagram showing a cross section of a laser beam. The square ABCD circumscribing the circle 13 of the cross section of the incident beam is divided into six pieces vertically and horizontally into small square blocks. mth horizontally from the left, vertically nth from the top
Let the number of the th block be M, n. In the optical apparatus shown in FIG. 4, the polarizing beam splitter 12 is connected to the reflecting mirror 1
It is clear that two non-adjacent beams can be superimposed by moving them away from 1 to the left. Therefore, in FIG. 6, using this method, the beam of the 12th block is transferred to the 22nd block, the beam of the 13th block is transferred to the 33rd block, and so on. Inside the EFGH of FIG. 6 is a cross-section of the output beam, each block of which is marked with the number of the block transferred by the optical system. As a result of such a shift, the block of the beam with a high intensity distribution at the center is shifted, and the resulting output beam becomes a square beam with a high intensity distribution at the center. 7, 8, and 9, when the beam emitted from the laser oscillator 1 is immediately focused by the objective lens 14, the beam spread angle is reduced by the beam expander 15, and then the objective lens 14 is focused. This figure shows a comparison between the case where the beam diameter is reduced using the optical device 16 according to the present invention after passing through the beam expander 15, and then the beam is focused. The beam divergence angle of laser oscillator 1 is 5mrad, the F number of all lenses is 1, and the beam diameter entering the first optical system is 5m1.
If Lφ is assumed, the focal length of the objective lens 14 in FIG. 7 is 5.
mT! L, and the diameter of the spotter 7 is 25 μmφ. In FIG. 8, the magnification of the beam expander, that is, the ratio of the focal lengths of the collimating lens and the focusing lens is assumed to be 1.4. The divergence angle of the beam passing through this is 5mrad/1.
4=3.57mrad. Beam diameter is 5×1.4=
7mTILφ. Since the objective lens 14 has a focal length of 7 mm, the diameter of the condensing spotter 7 is 3 mm.
57 mrad×7 mT1L=25 μmφ, which is the same as in the case of FIG. In FIG. 9, the beam emitted from the beam expander 1 is made incident on the optical device 16 according to the present invention. This device 16 is designed to obtain an emitted beam having a substantially circular cross section by the method described in FIG. The diameter of the output beam is approximately 1/V2 (1/1.4 times) the diameter of the input beam.

Therefore, the diameter of the emitted beam is 7 mm/1.4=5 mmμ. Also, the beam divergence angle remains the same as before entering the optical device 16, which is 3.57 mrad. Therefore, the focal length of the objective lens 14 is 5 mm, and the diameter of the condensing spot 17 is 5 mTIL x 3.57 mrad - 17.85 μmφ.
becomes. Therefore, 1/ of the spot diameter in Figures 7 and 8
This means that a spot diameter 1.4 times smaller was obtained by the optical system shown in FIG. As explained above, according to the present invention, it is possible to obtain a device that reduces the beam diameter without reducing the power of the light beam, and as a result, the product of the beam diameter and the beam divergence angle can be reduced, so that it can be focused by a lens. The diameter of the condensing spot when emitting light can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating the divergence angle of a laser beam emitted from a laser oscillator, FIG. 2 is a diagram illustrating a beam expander 1, and FIG. 3 is an explanatory diagram illustrating a decrease in the beam divergence angle due to the beam expander 1, FIG. 4 is a schematic configuration diagram showing an optical device according to the present invention, FIG. 5 is a diagram showing a cross section of a beam entering the optical device of FIG. 4 and a cross section of a beam exiting from the optical device, and FIG. Cross-sectional views of the input and output beams to illustrate how to repeatedly use an optical device to create a beam with a high power density in the center and a square cross section. Figure 8 shows the case where the light is focused immediately by the beam expander and then the objective lens, and Figure 9 shows the case where the light is focused through the beam expander and the optical device according to the present invention. FIG. Explanation of symbols, 1... Laser oscillator, 3...
...Condensing lens, 4...Collimating lens, 1
0...1/2 wavelength plate, 11...Reflector, 12...Polarized beam splitter, 14...
... Condensing lens, 15 ... Beam expander 16 ... Optical device.

Claims (1)

[Claims] 1. A polarizing beam splitter, which includes a half-wave plate as a component, makes a part of a linearly polarized light beam incident on the polarizing beam splitter, transmits or reflects it, and transmits the other part of the light beam. After passing through a 1/2 wavelength plate and changing its polarization direction by 90°, the light is guided and incident on a polarizing beam splitter, where it is reflected or transmitted, and is combined with the transmitted beam to form the original beam. An optical device characterized in that the diameter of a light beam is reduced and extracted without increasing the beam divergence angle of the light beam. 2. Divide the cross section of a linearly polarized light beam into a large number of small areas, and use a number of optical devices consisting of the polarizing beam splitter and 1/2 wavelength plate to separate the light beam from one section into a light beam from another section. Claim 1 is characterized in that the cross-sectional area of the entire light beam is reduced by superimposing the light beam on the light beam, and the cross-sectional power density distribution of the light beam is changed to a predetermined distribution before being extracted. optical device. 3 A beam expander is provided to expand the aperture of the light beam and change it into a linearly polarized light beam, and the beam expander divides the cross section of the linearly polarized light beam into a plurality of small areas, and a portion of the light beam is A half-wave plate that transmits the light and changes its polarization direction by 90 degrees, and the other part of the light beam and the part of the light beam that has been polarized by the half-wave plate are made incident and reflected or transmitted. An optical device consisting of a polarizing beam splitter for combining is provided, and the diameter of the light beam is made to be the same as or smaller than that before entering the beam, and the beam divergence angle is made to be the same as or smaller than that before entering. Featured optical device.