JPH0458894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a polarization measuring device, and particularly to a device for measuring the polarization state of phase-aligned light such as laser light.

[Technical Background of the Invention and Problems Therewith] In a laser processing machine, it is most advantageous for processing when the laser light is circularly polarized, so it is necessary to monitor the polarization state of the irradiated laser light.
Therefore, in a CO ₂ laser processing machine with a wavelength of 10.6 μm, a zinc selenide (ZnSe) plate is placed in front of the laser beam at the Brillusta angle as a device to measure the polarization state of the CO ₂ laser beam, and the plate is The device was configured to measure the laser output of the transmitted laser light. Then, by rotating this ZnSe plate 360 degrees around the optical axis of the laser beam and measuring the laser output at each rotation angle, we can determine the polarization state of linearly polarized light, elliptically polarized light, circularly polarized light, etc. There is.

To explain in more detail, laser light is generally considered to be divided into a P component parallel to the incident plane and an S component perpendicular to the incident plane. In FIG. 7, the P component is incident on the incident surface H while vibrating in a direction parallel to the plane of the paper and shown as an arrow, while the S component is shown as ◯ in a direction perpendicular to the plane of the paper.

When such an incident laser beam enters a dielectric material such as ZnSe, the reflection of the P component becomes 0 at the incident angle φ at the Brillusta angle (φ = 68.5 for ZnSe).
There is. At this angle, as shown in FIG. 8, the reflected light consists of only the S component, and the transmitted light becomes light in which the S component is reduced by the amount of the reflected light compared to the incident light.

Therefore, as shown in Figure 9, ZnSe plate 1
If a plurality of layers are stacked and incident light is applied thereto, the transmitted light can be made into only P-component light.
This is because in each plate 1, only the S component of the incident light is sequentially reduced as reflected light, and finally the S component is removed and only the P component becomes transmitted light.

However, in the case of such a structure in which the plates 1 are stacked in multiple layers, the optical axis of the incident light and the optical axis of the transmitted light are deviated from each other. Therefore, as shown in Fig. 10, the ZnSe plates 1a are installed at the Brillusta angle, and the same number of ZnSe plates 1b are installed symmetrically for optical axis compensation, so that the transmitted light has the same optical axis as the incident light. A polarization measuring device called a polarizer is used.

In the conventional polarization measuring device shown in FIG. 10, the plates 1a and 1b rotate 360° around the optical axis C.
It is designed to be able to rotate and determine the polarization state by measuring changes in the intensity of transmitted light relative to incident light.

However, such conventional polarization measurement devices called polarizers use a large number of expensive ZnSe plates, making the cost extremely high.Also, cooling of the part that is hit by the reflected light is required, making the device large and bulky. When I changed my mind, a problem arose. Furthermore, the expensive ZnSe plates were difficult to handle, and when used as a polarization measurement device for laser beams in laser processing machines, there were problems in that they were difficult to use at work sites. Furthermore, this ZnSe plate would break if water droplets got on it, making it even more difficult to handle at the work site.

[Purpose of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and is a method for measuring the polarization of a laser beam of a laser processing machine without increasing the cost or increasing the size of the device. An object of the present invention is to provide a polarization measuring device that can be easily used even when used in the field.

[Summary of the Invention] The present invention includes a reflecting mirror that allows incident light to enter at a predetermined angle of incidence and reflects the reflected light, a rotating means that rotates the reflecting mirror around an optical axis, and a rotating means that controls the intensity of the reflected light of the reflecting mirror. A polarization measuring device comprising a measuring means for measuring the polarization state of incident light by measuring the intensity of the reflecting mirror which changes by rotating the reflecting mirror. .

[Embodiment of the invention] As shown in FIG.
If the P component Ap and S component As of the incident light are the P component Rp and S component As of the reflected light, and the refraction angle of the refracted light is x, then from Fresnel's equation, the amplitude reflectance of the P component and S component is becomes like the following formula.

Rp/Ap=tan(φ-x)/tan(φ-x)...(1) Rs/As=-sin(φ-x)/sin(φ+x)
...(2) Note that the refraction angle X value of a metal reflecting mirror differs depending on the wavelength of the light.

Since the energy reflectance is given as the square of the above equations (1) and (2), the incident light is 10.6 μm.
When it is a CO ₂ laser beam and the incident surface H is a copper reflector, the energy reflectance with respect to the incident angle is 3rd.
It will look like the graph in the figure. As can be seen from the graph in FIG. 3, there is a large difference in reflectance between the S component and the P component as the incident angle φ increases.

The embodiment of the present invention is characterized in that the degree of polarization is measured using the above difference. In other words, as shown in FIGS. 3 and 4, the incident angle φ=
At 80°, the P component is 90% reflected and the S component is approximately
It is 100% reflective, and there is a difference in reflectance. For this reason, the intensity of the light after reflection is lower than the intensity of the light before incidence. Therefore, by measuring the output of this reflected light, the polarization state of the incident light can be determined.

Basically, a single copper reflector 3 as shown in Figure 4 is used, and the polarization state can be determined by measuring the output after reflection, but in practice, Figure 5 shows As shown, multiple reflecting mirrors 3 are used,
The difference in reflectance between the S and P components is increased, and a mechanism for rotation with respect to the incident optical axis is provided. This is because when two reflecting mirrors 3 are used, the difference in reflectance is 10
% becomes 0.9×0.9=0.81, which is about 20
This is because the measurement accuracy can be improved since the difference is in percentages.

FIG. 1 shows a polarization measuring device according to an embodiment of the present invention, which utilizes the above principle. Two copper reflecting mirrors 3a and 3b are installed in the housing 5 at positions that give a predetermined angle of incidence, for example 80°, to the incident light. A thermocouple or other light intensity measuring means 7 is installed in front of the second reflecting mirror 3b in the traveling direction of the reflected light. The entire apparatus is set so that it can freely rotate 360° around the optical axis C by means of a rotation means (not shown), using a rotation axis 9 that coincides with the incident optical axis C.

The operation of the polarization measuring device having the above configuration will be explained next. As shown in FIG. 1, when the incident light on the first reflecting mirror 3a is elliptical polarized light with a ratio of 2 major axis and 1 minor axis, when it is rotated by α° around the optical axis C, The power change is shown in Figure 6. However, the reflectance of the P component of the incident light is 90%, and the S component is 100%.
%, and when reflected twice by the first and second reflecting mirrors 3a and 3b, the P component is reduced to about 80%.

Azimuth α=0° When the azimuth α of the reflecting mirrors 3a, 3b is 0° and coincides with the long axis of the incident light, this long axis is the P component and the two reflecting mirrors 3a, 3b Approximately 80% depending on
and input into the measuring means 7. The short axis is the S component, which is not reduced at all by the two reflecting mirrors 3a and 3b and enters the measuring means 7 as it is. Therefore, the intensity of the light detected by the measuring means 7 is (2×0.8)+1=2.6, which is 86.6% of the original intensity of the incident light 2+1=3.

Azimuth α=90° If the measuring device is rotated by 90° and the short axis of the incident light becomes parallel to the reflecting mirrors 3a and 3b, the short axis side becomes the P component and the long axis side becomes the S component. Therefore,
The intensity of the reflected light is 2+(1×0.8)=2.8, which is 90% of the intensity of the incident light.

Azimuth angle α = 180° If the device rotates further and the azimuth angle α becomes 180°, the long axis side becomes the P component again and the short axis side becomes the S component, so as when α = 0°, The reflected light intensity is 2
×0.8+1=2.6, which is 86.6 for the incident light intensity
%.

Azimuth angle α=270° In this case, as in the case of α=90°, the long axis side becomes the S component and the short axis side becomes the P component, and the laser output becomes 2.8.90% as shown in FIG.

If the device is thus rotated 360° with respect to the optical axis C and the change in the measurement output of the measuring means 7 at each angle is known, the polarization state of the incident light can be determined. In other words, in the case of elliptical polarization, a large decrease is seen at α = 0° and 180°, and α =
There is a small decrease at 90° and 270°, so
It can be recognized as elliptical polarized light.

In the case of circularly polarized light, as shown in FIG. 6, the reflected light output decreases at a constant rate no matter what the azimuth angle α is, indicating that the light is circularly polarized.

Furthermore, in the case of linearly polarized light, the reflected output is 80% at a constant azimuth angle, whereas at a position rotated by 90 degrees, the reflected output is 100%, indicating that it is linearly polarized light.

The present invention is not limited to this embodiment, but can be used in various optical machines that need to measure polarized light. Furthermore, the material of the reflecting mirror is not limited to copper, and any suitable material can be used as needed.

[Effects of the Invention] This invention allows incident light to enter at a predetermined angle of incidence, makes a reflecting mirror rotatable around the incident optical axis, and measures the intensity of the reflected light from the reflecting mirror. Compared to the conventional method of transmitting light through a plate that exhibits specific properties and measuring the polarization state based on changes in the intensity of the transmitted light, this method can reduce costs, and the reflecting mirror is equipped with a cooling means. Since this is not necessary, the entire device can be made smaller and simpler, and when used to measure the polarization of laser light from a laser processing device, it has the advantage of being able to be used even when brought into the field.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a diagram showing reflection and refraction of light, FIG. 3 is a characteristic diagram showing changes in light energy reflectance with respect to the angle of incidence, and FIG. Front view explaining the principle of the above embodiment, No. 5
The figure is a front view explaining the state of light reflection when two reflecting mirrors are used, Figure 6 is a characteristic diagram of the above embodiment, Figure 7 is a diagram showing the characteristics of light reflection and refraction, and Figure 8 is a characteristic diagram showing the change in light reflectance with respect to the incident angle,
FIG. 9 is a principle diagram of a conventional example, and FIG. 10 is a conventional diagram. 3, 3a, 3b...reflecting mirror, 5...housing, 7...measuring means, 9...rotation axis, C...optical axis.

Claims (1)

[Claims] 1. A reflecting mirror that allows incident light to enter at a predetermined angle of incidence and reflects the reflected light, a rotating means that rotates the reflecting mirror around an optical axis, and a measuring means that measures the intensity of the reflected light from the reflecting mirror. A polarization measuring device consisting of: