JPH06302900A - Optical system of laser resonator - Google Patents

Abstract

PURPOSE:To convert light of linear polarization into polarization in the optional direction by providing three sheets of mirrors directly behind an output mirror of a laser resonator for rotating the whole of a mirror system round a first incident beam as a center. CONSTITUTION:A face SIGMA including centers of three mirrors P, Q, R and incident light and outgoing light is made rotatable. When the face SIGMA is rotated by THETAto a polarized face of an incident beam (h), a polarized face of an outgoing beam rotates by 2THETA. When the face SIGMA is rotated, for instance, by 30 deg., the polarized face of the outgoing beam (n) rotates by 60 deg.. When the face SIGMA rotates by 22.5 deg., the polarized face of the outgoing beam (n) rotates by 45 deg., that is, an optional polarization direction can be provided. Thereby, in any case of the polarized face of the outgoing beam of a laser device, the polarized face of the beam at the time of hitting an object can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator (optical system mirror) for an industrial high power carbon dioxide laser processing machine. The carbon dioxide laser generates linearly polarized light, but depending on the purpose, the polarization direction can be changed to any direction, or when circularly polarized, the rotation direction can be changed to either left or right. The structure of the optical system.

[0002]

2. Description of the Related Art Thermal processing such as cutting, welding, and surface treatment of metals can be performed using an industrial high-power carbon dioxide laser beam. The carbon dioxide laser resonator generates linearly polarized light. Polarization is the direction of the electric field vector.
The direction of linearly polarized light of a carbon dioxide laser is conventionally the horizontal direction,
The mirror configuration in the resonator was taken to be in the vertical direction, or just in the direction between these two directions.

The laser light is composed of two mirror-like mirrors.
It is reciprocated between and amplified. However, if the polarizations are not the same, they do not amplify each other. The polarization of the amplified light is determined by the orientation of the mirror of the resonator. Therefore, the polarization of the light emitted from the laser is determined by the mirror direction of the resonator. Of the two mirrors that make up the laser resonator, the rear mirror that reflects 100% of the light is called the rear mirror. A mirror that has a reflectance of not 100% and emits a part of light to the outside will be referred to as an output mirror here. The present invention relates to an optical system provided between an output mirror and an object.

[0004]

When cutting an object with a carbon dioxide gas laser, there is a strong relationship between the polarization state of the laser beam and the cut surface state. Resonator output mirror
A linearly polarized beam emitted from the output side mirror) is guided to the object to be processed through a plurality of metal mirrors (which may be coated with a dielectric multilayer film) and a condenser lens, etc. Cut the symmetrical object by condensing at. However, the light of the carbon dioxide gas laser is linearly polarized. The cutting speed and the shape of the cutting opening differ depending on the relative relationship between the cutting direction and the polarization direction.

That is, the cutting situation is significantly different between the case where the polarization direction and the cutting direction are orthogonal to each other and the case where the polarization direction is parallel to the cutting direction. There are several reasons for this. When the object to be processed is metal, an eddy current flows in the direction of the electric field. That is, a current flows in the direction of polarization. When the cutting direction and the polarization direction are parallel, a current flows in the cutting direction, which heats the metal. In this case, the cut surface is the best. When the cutting direction and the polarization direction are orthogonal to each other, a current flows at right angles to the cutting direction. In this case, the cut surface expands, and the cut surface may have an irregular wave front.

[0006] This is one reason, but there is a stronger asymmetry that occurs in common whether the object is a metal or an insulator. It is the asymmetry of P and S polarization. P-polarized light is a beam whose electric field vector is parallel to a surface (tentatively called an optical surface) including an incident beam, a reflected beam and a refracted beam. The direction of the electric field is the polarization direction, which is called P-polarized light because it is parallel to the optical surface (PARALLEL). On the other hand, the polarization direction, that is, the direction of the electric field perpendicular to the optical surface (SENKRECHT) is called S-polarized light.

Generally, when light is obliquely incident on the surface of a certain material, the smaller the angle (incident angle) the beam makes with the surface, the smaller the light reflectance. The reflectance becomes the smallest in the case of vertical incidence. The reflectance increases as the beam is tilted. However, this change is different between S-polarized light and P-polarized light. In the case of S-polarized light, the reflectance monotonically increases as the incident angle increases. However, in the case of P-polarized light, the reflectance decreases once as the incident angle increases, becomes 0 at the Brewster angle, and increases sharply thereafter.

The reflectance of S-polarized light is always higher than that of P-polarized light. That is, P-polarized light has more absorption. When laser light is applied to an object to cut it, the material is melted by the energy of light to form a groove. The surface of the groove and the beam make an angle close to 90 °. Therefore, the reflectance is high.
Therefore, many components are multi-reflected and reach the bottom of the groove. However, the reflectance differs between P-polarized light and S-polarized light. Since P-polarized light has a lower reflectance, it is easily absorbed in the shallow portion of the groove.
Since the S-polarized light has a higher reflectance, the S-polarized light is reflected many times and reaches the depth of the groove.

Since the P-polarized light is absorbed at a shallow depth, the energy tends to concentrate at the shallow portion. The heat causes the groove wall portion to melt and the groove to expand. Since the S-polarized light goes to the back of the V groove, the groove does not spread, and the energy is likely to concentrate at one point. Depending on the application such as cutting, welding, heat treatment, etc.
The conditions differ depending on whether or not to reach deep inside.

In terms of cutting, it is desirable to use S-polarized light because the cut end is disturbed with P-polarized light. Here, S-polarized light and P-polarized light refer to the surface of the groove. From the cut locus, the case where the polarized light is parallel to the locus corresponds to the above-mentioned S-polarized light. When making a cut, it is desirable that the polarization be parallel to the locus. However, the laser device is fixed, and the locus of cutting is not constant. When cutting along a curve, the cutting direction changes. Therefore, the polarization plane of light cannot always be made parallel to the cutting locus.

Since it is linearly polarized light, such a problem occurs. If the laser light is circularly polarized light, the problem of disorder of the shape of the cut surface should be avoided. Based on this idea, currently, in a carbon dioxide processing machine, linearly polarized light is converted to circularly polarized light and then applied to an object. A 90 ° retardation mirror (commonly called a circular polarization mirror) is provided on one mirror during transmission to convert linearly polarized light into circularly polarized light. The 90 ° retardation mirror means that a dielectric multilayer film is formed on a metal substrate, and the film thickness and refractive index of the dielectric layer are 90 ° between reflected light of S-polarized light and P-polarized light.
This mirror is designed to generate a phase difference of.

Light is incident in the direction of 45 °, the reflection angle is also 45 °, and the optical path is bent 90 °. 9
The 0 ° delay means that the phase difference is 90 °. When circularly polarized light is thus used, the plane of polarization is rotated with time, so that the anisotropy is averaged with time. In this way, stable and good cutting quality independent of the cutting direction is obtained. This is the current situation.

The light emitted from the laser is linearly polarized light and
0 ° retardation mirror (also called circularly polarized mirror)
In contrast, the polarization direction must be at an angle of 45 ° with respect to the plane of incidence. The polarization direction of laser light is determined by the device. Depending on the layout of the laser device, a 90 ° retarder
The arrangement of the section mirror is also decided, and the polarization direction of the reflected light from now on is also decided. The degree of freedom in the arrangement of the optical system is limited. Also, it is not possible to create linearly polarized light polarized in any direction.

It has been described above that a circularly polarized beam is used for processing. The polarization direction rotates with time and the anisotropy is averaged with time. This looks good, but it's not. With the recent advancement in processing quality, it has been found that the rotation direction of circularly polarized light affects processing quality. In other words, even if it is called circularly polarized light, there are right-handed circularly polarized light and left-handed circularly polarized light. It was found that the processing quality differs between clockwise and counterclockwise. However, circularly polarized mirrors can be used to create circularly polarized light that rotates to the right or left, but cannot be freely switched between right and left. That is, the current laser resonator cannot control the rotation direction of the circularly polarized beam in the final state. The above is a disconnection story.

Welding using a laser will be described. Ray
In the welding process, the dependence of the beam on the polarization has not been considered as a problem so far. However, with the progress of welding technology, it has been reported that the polarization of laser light affects the penetration depth and the welding speed. These reports state that it is important to control the linearly polarized light in the direction along the processing locus. In other words, it should be S-polarized.

In the current commercially available lens, the plane of polarization of the linearly polarized light of the exit beam is fixed. Therefore, even in the case of welding, the polarization direction of the linearly polarized laser light cannot be controlled. If the welding direction is straight, the polarization direction and the welding locus can be made parallel. However, this is not possible if the welding trajectory is curved.

It is a first object of the present invention to provide an optical system capable of converting linearly polarized light generated from a carbon dioxide gas laser device into polarized light in an arbitrary direction. A second object is to provide an optical system capable of freely changing the rotation direction of circularly polarized light when the circularly polarized light is converted into circularly polarized light.

[0018]

According to the present invention, three mirrors are provided immediately after an output mirror of a laser resonator, and each mirror has incident light and reflected light in the same plane, and finally, An optical system is provided in which the reflected light is collinear with the first incident light and the entire mirror system is rotatable about the first incident beam.

A more detailed description will be given. FIG. 1 is a block diagram of the optical system of the present invention. Let the three mirrors be P, Q, and R. There are two mirrors P and R (herein referred to as the reference line s) on an extension of the path of the light emitted from the output mirror of the carbon dioxide laser. The second Mira-Q is off the reference line. The light emitted from the output mirror of the carbon dioxide laser is Mira P,
It is reflected in the order of Q and R. The incident light and the reflected light are all on the same plane. Let this surface be the Σ surface. In each mirror, the incident reflection points of the beam are A, B and C. Let the beam from the output mirror of the carbon dioxide laser be h.

This enters the first mirror and is reflected at the point A to become a beam k. This reaches the point B of the second mirror Q and is reflected to become a beam m. Beam m is the previous beam
It is on the same plane as h and k. This plane is called Σ. Therefore, the optical surface defined above is all mirrors.
It means that P, Q, and R are included in the Σ plane. The beam m is reflected at the point C of the third mirror R
It becomes m n. Beam n is collinear with the first beam h. This straight line will be referred to as a reference line s. Furthermore, the whole mirror system is made to rotate around the reference line s. That is, the Σ plane can rotate about the reference line s. This is the feature of the present invention.

The three points A, B and C may or may not form an isosceles triangle. For an isosceles triangle,
AB = BC, but if the base angle Ψ and the length AC of the base are determined, all other parameters are determined. Second Mira-Q
Becomes parallel to the reference line s. The tilt angle of the Mira-P with respect to the reference line s is Ψ / 2, and the tilt angle of the Mira-R is π-Ψ / 2.
Is. Low degree of freedom in design. However, in this case, the second mirror can be a circularly polarized mirror. that way,
The beams m and n can be circularly polarized. In the case of a circularly polarized mirror,
Since the incident light and the emitted light are orthogonal to each other, it is possible to replace only the second mirror with the circularly polarized mirror.

In the case of a scalene triangle, other parameters are not determined even if the base AC is determined, so that the degree of freedom in design is high. Mira-Q does not have to be parallel to the reference line,
It is not necessary for the tilt angles of P and R to complement each other. The first and third mirrors can be circularly polarized mirrors. Then, the beam n can be circularly polarized.

All three mirrors need to be perpendicular to the Σ plane. This is a condition that defines the direction of the mirror. This is the same as the condition that the final beam n is on the same straight line s as the incident beam h.

The mirrors P, Q, and
The inclination angles α, β and γ of R are defined as shown in FIG. α is the tilt angle of the mirror P with respect to the incident beam h. γ is the tilt angle of the mirror R with respect to the output beam n. β is a mirror
It is the tilt angle of Q to the right with respect to the reference line. in this case,
If α + β = γ, the beam n becomes parallel to the beam h.
In order to match the two, not only the direction of the mirror but also the position must be determined appropriately.

The mirror is made of a simple substance of metal or Si.
Alternatively, a multi-layered dielectric film may be formed on a metal to increase the reflectance.

[0026]

The present invention utilizes the phenomenon that the plane of polarization of light reflected by the mirror (the plane including the polarization direction and the traveling direction) touches the optical surface at the same angle on the opposite side. Suppose that the plane of polarization of the incident light is inclined by Θ with respect to the optical surface.
Let Φ be the angle that the plane of polarization of the reflected light makes with the optical surface. Although not exact, Φ is approximately equal to −Θ. This property is not always correct, unlike the geometrical optical law of reflection. However, it can be said that Φ is proportional to Θ and the constant of proportionality is negative, which is −1 to −infinity. Especially in the case of mirrors with high reflectance, the proportional constant is almost -1.
Is.

That is, the reflection by one mirror causes the plane of polarization to swing in the opposite direction with respect to the optical surface. If it is reflected by two mirrors continuously, the plane of polarization returns to the original. By doing so, the polarization plane of the initial light can be changed to the polarization plane of the opposite direction by causing reflection with an odd number of mirrors. Even if an odd number of mirrors have the same optical surface,
Since there is no constant term, the plane of polarization of the last light can be oriented in the opposite direction with respect to the plane of polarization of the first light.

The reason why the polarization plane touches the opposite side with respect to the optical surface will be described. The light obliquely incident on the mirror must be considered as S-polarized light and P-polarized light. FIG. 2 shows the electric field vector and magnetic field vector of incident, outgoing, and refracted light in the case of S-polarized light.

For S-polarized light, the electric field vector is perpendicular to the optical plane. Also called TE wave. This is because the electric field is perpendicular to the optical surface. Since the tangential components of the electric field and magnetic field are continuous at the boundary surface, the electric field of the reflected beam can be obtained. This is in the opposite direction of the incident electric field. Since the electric field is parallel to the boundary surface, the phase is inverted (shifted by 180 °) when entering the high refractive index medium from the low refractive index medium, as in the case of vertical incidence of light. That is, when the electric field direction of the incident light and 1, the electric field of the reflected light is -r _s. Here, r _s is the reflectance. The reflectance is low when the incident angle θ is small (normal incidence), and the reflectance monotonously increases as the incident angle increases. What is important is that in the case of S-polarized light, the electric field direction is always reversed in the reflected light.

FIG. 3 shows the electric field vector and magnetic field vector of incident and outgoing refracted light in the case of P-polarized light. In the case of P-polarized light, the electric field vector is included in the optical surface. Therefore, when the incident angle is θ, the electric field vector of P-polarized light makes an angle of θ with respect to the boundary surface. As long as the incident angle θ is small, the electric field of the reflected light is in the same direction as the electric field of the incident light. In the case of P-polarized light, the reflectance decreases as θ increases, and the reflectance decreases to 0 at the Brewster angle.
become. After this, the direction of the electric field becomes negative (the direction opposite to the electric field of the incident light), and the absolute value sharply increases. The Brewster angle can be defined when the mirror is a dielectric and the permittivity is a real number. Since there is a loss in the case of metal, the Brewster angle does not have a clear meaning, and the reflectance is 0 here.
It never becomes.

Further, even if it is a dielectric material, if it is made into a multilayer film, the Brewster angle becomes plural, and the clear meaning is lost. Therefore, there is no place where the reflectance becomes zero. However, the reflectance r _p of P-polarized light is generally smaller than the reflectance r _s of S-polarized light.

When the electric field of the incident light is E _i , the angle formed by the polarization plane with respect to the optical surface is Θ, so the electric field of the S-polarized component is E _i sin Θ. The electric field of the P-polarized component is E _i cos Θ. The electric field of the S-polarized component of the reflected light is −r _s E _i sin Θ. The electric field of the P-polarized component is r _p E _i cos Θ.

The angle made by the polarization plane of the reflected light with respect to the optical surface is Φ. Since tan Φ is equal to the ratio of the electric field of S polarization and the electric field of P polarization,

Tan Φ = −r _s E _i sin Θ / r _p E _i cos Θ = − (r _s / r _p ) tan Θ (1)

[0035] In general, r _s and r _p are not equal.
This ratio is often greater than 1. But high reflectivity mirror - If, because none close to 100% reflectance, r _s also r _p be close to one. Therefore, the high reflectance mirror
In the case of, r _s / r _p becomes almost 1. In this case, Φ is approximately equal to −θ. -Φ may be a little larger than Θ, but they are almost equal. FIG. 4 is a diagram schematically showing rotation of polarization planes of incident light and reflected light.

What has been described here is that the obliquely incident light is reflected by the mirror, so that the polarization planes are substantially opposite with respect to the optical plane. This is not the case in the geometrical optics truth, but in the case of a high reflectance mirror. Assuming that the absolute values of the reflectances of S-polarized light and P-polarized light are equal, Φ = −Θ.

Then, in the case of multiple reflection by m mirrors, the tilt angle Φ _{m of the} polarization plane with respect to the optical plane of the reflected light at the final mirror is

Φ _m = (-1) ^m Θ + Φ ₀ (2)

Can be written as Φ ₀ is the inclination of the plane of polarization of the final reflected light when Θ = 0. If the number of mirrors is even,

Φ _m = Θ + Φ ₀ (3)

It is FIG. 5 shows a case where the number of mirrors is even. This means that the polarization plane of the incident light and the polarization of the final reflected light have the same change. If the number of mirrors is odd, the result is as shown in FIG.

Φ _m = −Θ + Φ ₀ (4)

Further, if all the mirror optical surfaces are arranged so as to be included in the same surface, Φ ₀ becomes 0. In this case,

Φ _m = −Θ (5)

It becomes The present invention provides three mirrors in such an arrangement. Since m = 3, which is an odd number, this formula is obtained.

In the present invention, it is a condition for setting Φ ₀ = 0 that the incident light and the reflected light of the three mirrors are included in the same Σ plane. Assuming that (r _s / r _p ) in each mirror is 1, carbon dioxide gas
Assuming that the inclination of the plane of polarization of the beam h emitted from the output mirror with respect to the optical plane is Θ, the inclinations of the planes of polarization of the following three beams are as follows. Beam k is -Θ, beam m is + Θ,
The beam n is-?.

As described above, it has been explained that the polarization plane changes in the opposite direction by the odd number of mirrors. Bee from the output mirror
The beam h and the final beam n reflected by the three mirrors are on the same reference line s. This is necessary because the entire mirror unit rotates about the reference line s. When the unit consisting of three mirrors is rotated, if h and n are not on the same straight line, the position of the beam will change. Since the position of the beam n does not change even when the unit is rotated, h = n = s.

FIG. 10 shows the polarization direction .THETA. Of the incident laser beam and the polarization direction .THETA. Of the exit laser beam in the case of the three-mirror system. The combination of these three mirrors can rotate the polarization plane of the laser light at an arbitrary angle. This will be explained. As I said, rotating the plane of polarization of light is
A Faraday rotator element is a typical element. However, there is currently no crystal that transmits the light of carbon dioxide laser without loss and has the Faraday effect. In the present invention, the plane of polarization can be freely rotated instead of the Faraday element. This is the feature of the present invention.

In FIGS. 1 and 100, three mirrors are shown.
The centers of P, Q and R and the Σ plane including the incident light and the emitted light can be rotated. As can be seen from the above description, the angle formed by the incident light with the Σ plane is Θ, and the angle formed by the emitted light with the Σ plane is −Θ. That is, in FIG. 10, the z axis is taken as the traveling direction of light in the coordinate system on which the incident light is based, and the coordinate included in the Σ plane is y. The polarization direction of the incident light is y
It is the angle between the axis and the polarized light. The polarization direction of the emitted light is also the angle formed with the y axis.

The Σ plane is a plane including the z axis and the y axis. The reference line s is equal to the z axis. Since Φ = −Θ, the difference Δθ between the polarization directions of the emitted light and the incident light is the difference between the polarization angle of the emitted light and the polarization angle of the incident light.

ΔΘ = Φ−Θ = −2Θ (6)

What does this expression mean? This means that the polarization plane of the outgoing light is rotated by twice the angle Θ between the polarization plane of the incident beam h and the Σ plane. Up to now, the Σ plane was considered as the center, but conversely, it is assumed that the incident beam h is a fixed beam and the Σ plane rotates. If the Σ plane coincides with the polarization plane of the incident beam h, the polarization plane of the emission beam n also coincides with them. However, this means that when the Σ plane rotates by Θ with respect to the plane of polarization of the incident beam h, the plane of polarization of the outgoing beam rotates by 2Θ.

That is, it can be said that when the Σ plane is rotated, the polarization plane of the outgoing beam rotates in the same direction at twice the speed. For example, when the Σ plane is rotated by 30 °, the polarization plane of the outgoing beam n is rotated by 60 °. When the Σ plane is rotated by 22.5 °, the polarization plane of the outgoing beam n is rotated by 45 °. Σ
When the plane is rotated by 45 °, the plane of polarization of the exit beam n is 90 °.
° rotate. Since the rotation range of the plane of polarization is 180 °,
If the Σ plane can rotate 90 ° in one direction, the polarization plane of the outgoing beam can rotate 180 °. That is, an arbitrary polarization direction can be given.

The same thing can be expressed in various ways. For example, you could say: , The plane of polarization of the linearly polarized light h emitted from the output mirror is in the horizontal direction, and if this is desired to be the vertical direction, the plane of incidence of the mirror unit (Σ
The plane may be rotated about the reference line and inclined by 45 ° with respect to the horizontal direction (or the vertical direction). When the plane of polarization of the linearly polarized light emitted from the output mirror is + 45 ° with respect to the incident surface of the mirror unit, if this is set to -45 ° with respect to the incident surface after passing through the mirror unit, The incident surface (Σ surface) may be a vertical surface.

Alternatively, the following may be said. When it is desired to change the polarization plane of the outgoing beam by a certain angle χ with respect to the polarization plane of the incident beam, the mirror unit may be rotated by χ / 2 in the same direction. Since the mirror unit is rotated around the reference line, it is extremely easy as compared with the rotation of the polarization plane by a Faraday element or the like. Moreover, it is excellent and accurate.

The above is a case where all three mirrors are ordinary mirrors. In this case, the outgoing beam is also linearly polarized light. It is the first advantage of the present invention that the plane of polarization of this linearly polarized light can be freely rotated. But it doesn't stop there. The present invention has another significant effect. This is an action that cannot be obtained even with a Faraday element, and the uniqueness of the present invention strongly appears. It was described above that the linearly polarized light is changed to circularly polarized light by using the circularly polarized light mirror. Circularly polarized light should have no anisotropy no matter how it is cut, because the anisotropy is averaged over time.

However, it has recently been found that even with circularly polarized light, the rotation direction of the polarized light affects cutting.
Even if the circularly polarized light is used for circularly polarized light, the direction of rotation is determined as one direction, and it cannot be changed freely. However, in the present invention, the rotation direction of circularly polarized light can be freely changed to the right or left. This has not been possible in the past.

Any one of the three mirrors is replaced with a circular polarization mirror (also referred to as a 90 ° retardation mirror). The remaining mirrors are normal mirrors. In the case of a circularly polarized mirror, the incident light and the outgoing light form an angle of 90 °. This places restrictions on the arrangement of the mirror system. This is because the sum of the interior angles of the triangle is 180 °.

When the second mirror is a circularly polarized mirror,
As shown in FIG. 7, in the arrangement ABC of the mirror, the corner B is 9
It becomes 0 °. The sum of angles A and B may be 90 °. Figure 7
If the shape is an isosceles triangle, the symmetry is good. However, there is no need to make another isosceles triangle.

When the first mirror is a circularly polarized mirror, it is as shown in FIG. Beams h and k are orthogonal. Corner B and corner C
The sum may be 90 °. Circular polarization mirror for the third mirror
If so, it becomes as shown in FIG. The angle C is 90 °.

Any mirror may be used as the circularly polarized mirror. The linearly polarized beam is incident on the circularly polarized mirror, which must be incident such that the plane of polarization forms an angle of 45 ° with the optical surface. The circularly polarized mirror is to change the polarization state from linearly polarized light to circularly polarized light by giving a difference of 90 ° between the phases of S-polarized light and P-polarized light.

This principle will be described first. The angle formed by the plane of polarization of the incident beam and the optical plane of the circularly polarized mirror is Θ. When the electric field is E _i , the electric field E _s of the S-polarized component is E _i sin Θ. The P-polarized component electric field E _p is E _i cos Θ. This circularly polarized mirror is, for example, one in which the phase of S-polarized light is increased by 90 ° with respect to the phase of P-polarized light. Then,
The S-polarized component E _rs and the P-polarized component E _rp of the electric field of the outgoing beam
Is

E _rs = E _i sin Θ sin (ωt + 90) (7) E _rp = E _i cos Θ sin (ωt) (8)

However, sin (ωt + 90) = cos (ω
t),

E _rs = E _i sin Θ cos (ωt) (9) E _rp = E _i cos Θ sin (ωt) (10)

It becomes This means that the electric field of the emitted light draws an elliptical locus. That is, the exit beam is generally elliptically polarized. However, this is circularly polarized, especially at Θ = 45 °.

[0067] _{^{E rs 2 + E rp 2 =}} E i 2/2 (11) E rs = (E i / 2 1/2) cos (ωt) (12) E rp = (E i / 2 1/2) sin (Ωt) (13)

Moreover, this is a counterclockwise rotation when the axis of S-polarized light is the x-axis and the axis of P-polarized light is the y-axis. In other words, it is a left-handed circularly polarized light.

However, when Θ = −45 °, E _rs = − (E _i / 2 ^1/2 ) cos (ωt) (14) E _rp = (E _i / 2 ^1/2 ) sin (ωt) (15) )

As described above, the sign of S-polarized light is reversed. This exit beam is also circularly polarized. However, the rotation direction of polarized light is clockwise. In other words, it becomes clockwise circularly polarized light. From this, it becomes clear that the rotation direction of circularly polarized light can be changed to the right or left if Θ can be switched to plus 45 ° and minus 45 °.

According to the present invention, the mirror unit can be rotated around the reference line by an arbitrary angle. That is, the Σ plane can be rotated. Then, the polarization plane of the incident beam entering the circularly polarized mirror is set by setting the angle formed by the polarization plane of the first incident beam h entering the first mirror with the Σ plane to be + 45 ° or −45 °. ± 45 °
Can be switched to. This may be a little confusing, but it's understandable from what I've explained so far.

As shown in FIG. 8, the first mirror P is a circularly polarized mirror.
The case is simple. Polarization plane of beam h and Σ plane are +45
If the angle is °, the circularly polarized light created by P is counterclockwise. This is reflected by Q and turns clockwise. It is reflected by R and returns counterclockwise. Finally it is counterclockwise.

On the contrary, the polarization plane of the beam h is -45 ° with the Σ plane.
The circularly polarized light created by P is clockwise. This is reflected by Q and R, and finally becomes clockwise circularly polarized light. That is, with respect to the incident beam h from the laser, circularly polarized light becomes counterclockwise when the Σ plane is + 45 ° and clockwise when it is −45 °.

The same applies to the case where the second mirror Q is a circularly polarized mirror, but it will be described just in case. Also in this case, the plane of polarization of the incident beam h is set to ± 45 ° with respect to the Σ plane. When the polarization plane of the beam h is + 45 ° with respect to the Σ plane,
The mirror P has a plane of polarization of -45 °, and this enters the mirror Q, so that it becomes a clockwise circularly polarized light. Since this is reflected by R, it becomes a left-handed circularly polarized light. On the contrary, when the polarization plane of the beam h is -45 with respect to the Σ plane, it becomes a polarization plane of + 45 ° at the mirror P. Since this enters Mira-Q, it becomes a left-handed circularly polarized light. Since this is reflected by the mirror R, it becomes clockwise circularly polarized light. Also in this case, if the plane of polarization of the incident beam h is + 45 ° with respect to the Σ plane, the outgoing beam n turns counterclockwise,
At 45 °, the output beam n is clockwise.

After all, which mirror is a circularly polarized mirror is the same. If the beam h is + 45 ° with respect to the Σ plane, the output beam n is counterclockwise, and if it is -45 °, the output beam is n. It means that n is clockwise.

FIG. 11 shows the overall construction of the optical system of the present invention. The laser resonator 1 is a carbon dioxide gas laser, and has a mechanism for discharge-exciting carbon dioxide gas inside. Mirror is rear mirror
And the output mirror. The beam h emitted from the output mirror is linearly polarized light. This enters a reflective mirror unit 2 consisting of three mirrors P, Q and R. Here, the incident beam h is reflected and becomes beams k, m, and n. The final beam n is collinear with the incident beam h. This straight line is referred to as a reference line s. The reflection mirror unit 2 can rotate about the reference line s.

There is a unit rotation driver-3, which rotates the reflection mirror unit 2. The light emitted from the reflection mirror unit 2 passes through the transmission optical system 4, is focused by the condenser lens 5, and is applied to the object 6. This is cutting, welding,
It may be heat treatment.

In the case of cutting, it is desirable that the cutting locus and the plane of polarization of linearly polarized light are parallel. In this case, the reflection mirror unit 2 is appropriately rotated by the unit rotation driver-3 so that the plane of polarization of the object 6 coincides with the cutting direction. When the cutting direction changes, the reflecting mirror unit 2 is rotated by about half of the change angle in accordance with this, so that the cutting direction and the polarization plane can be always matched. This is effective not only when cutting along a straight track but also when cutting along a curved track. In this case, the reflection mirror unit 2 may be continuously rotated little by little at a speed which is about half the changing angular speed of the curve.

The above is the case of using linearly polarized light. When circularly polarized light is used, it becomes as follows. If left-handed circularly polarized light is required, the reflection mirror unit 2 is set so that the Σ plane of the reflection mirror unit 2 is −45 ° with respect to the beam h.
Rotate unit 2. If the clockwise circularly polarized light is required, the reflection mirror unit 2 is rotated so that the Σ surface of the reflection mirror unit 2 is + 45 ° with respect to the beam h. In this way, circularly polarized light having a desired rotation direction can be easily obtained. It is extremely simple and accurate because it does not require a magnetic field like a Faraday element.

The material of the mirror will be described. Since it receives the strong light of a carbon dioxide laser, it must have a high reflectance. It may be a water-cooled one using a metal or Si mirror. However, the reflectance may be insufficient with only metal or Si. Unless the reflectance is close to 1, the attenuation of the laser beam cannot be ignored and cooling of the mirror becomes difficult. In this case, a noble metal (gold, silver, etc.) coat is applied in the form of a mirror base, or a dielectric multilayer film coat is further applied. By doing so, it is possible to prevent a decrease in beam strength as much as possible. At the same time, the phase difference change due to the reflection (when the plane of polarization of the linearly polarized light incident on the mirror unit is not the same as or orthogonal to the plane of incidence of the mirror unit, the phase difference change occurs) can be minimized.

[0081]

EXAMPLE An Au-coated Si mirror having a shape of φ60-6t was prepared as three reflection mirrors. These mirrors were arranged such that the surface centers of the mirrors were located at the three vertices of an equilateral triangle. An indirect cooling structure was provided on the back side of each mirror.
This reflection mirror unit was attached to the emission port of a commercially available carbon dioxide gas laser resonator having an output of 2.5 kW. Then, the unit was rotated, and it was confirmed that the polarization plane of the output light was rotated.

Output beam by rotation of the reflection mirror unit
The rotation of the plane of polarization of the beam was confirmed by placing an infrared polarizer in the path of the emitted light. Infrared beam in the output beam
The laser beam transmitted through the riser is measured by a power meter. The polarization plane of the polarizer is rotated to find the direction in which the transmitted light becomes maximum. This is the polarization direction of the outgoing beam. In this way, the relationship between the polarization directions of the beams can be known. It was confirmed that the relationship between the rotation of the reflection mirror unit and the rotation of the polarization plane is as described above.

Rays by a reflection mirror in the mirror unit
The intensity decrease of the light was about 2%. In order to prevent a decrease in reflectance, a mirror having a low phase difference (Δ ≦ 1 °) and a high reflectance (R ≧ 99.6%) obtained by adding a (ThF ₄ / ZnSe) -based dielectric multilayer film to an Au coat mirror. The same experiment was performed with-. In this mirror system, the reduction in laser intensity was about 1%. An improvement was seen over the case of the Au Co-Tomylar system described above.

[0084]

According to the present invention, the plane of polarization can be rotated in any direction by rotating the reflection mirror unit 2. Whatever the plane of polarization of the output beam of the laser device, the plane of polarization of the beam when it hits the object can be controlled. That is, the arrangement of the optical system of the transmission system is not restricted by the direction of the polarization plane of the beam emitted from the laser resonator.

In the laser cutting process, the operation of reversing the direction of rotation of the polarization plane of the circularly polarized light beam is performed at 90 ° of the mirror unit.
It can be easily realized by rotation. This has not been possible in the past.

In the welding process, the operation of aligning the polarization planes of the linearly polarized beam on the welding process locus can be realized by rotating the mirror unit in conjunction with the inclination of the tangential direction on the processing locus. Is.

[Brief description of drawings]

FIG. 1 is a schematic view of a general reflection mirror unit showing the principle of the present invention.

FIG. 2 is a diagram showing directions of an electric field and a magnetic field of an incident beam, a reflection beam and a refraction beam in the case of S-polarized light.

FIG. 3 is a diagram showing directions of an electric field and a magnetic field of an incident beam, a reflection beam and a refraction beam in the case of P-polarized light.

FIG. 4 is a schematic perspective view for explaining that when the obliquely incident light is reflected by the mirror, the polarization plane of the outgoing beam is displaced in the opposite direction to the polarization plane of the incident beam.

FIG. 5 is an output beam when multiple reflections are performed by an even number of mirrors.
6 is a schematic view showing that the plane of polarization of the beam is displaced in the same direction as the plane of polarization of the incident beam. FIG.

FIG. 6 is an emission beam when multiple reflections are performed by an odd number of mirrors.
FIG. 3 is a schematic view showing that the plane of polarization of the beam is displaced in the opposite direction to the plane of polarization of the incident beam.

FIG. 7 is a schematic view of a laser and a mirror showing an example in which three mirrors are arranged so as to form an isosceles triangle whose second mirror is the apex.

FIG. 8 is a schematic view of a laser and a mirror showing an example in which three mirrors are arranged so as to form a right triangle in which the first mirror is a right angle.

FIG. 9 is a schematic view of a laser and a mirror showing an example in which three mirrors are arranged in a right triangle in which the third mirror is a right angle.

FIG. 10 is a reflection mirror unit composed of three mirrors according to the present invention, wherein the polarization plane of the incident beam is an optical plane (Σ plane).
FIG. 6 is a schematic perspective view showing that the polarization plane of the output beam forms −θ with respect to the optical surface when the angle θ is formed with respect to.

FIG. 11 is a schematic configuration diagram showing the overall configuration of a laser optical system of the present invention.

[Explanation of symbols]

 1 Laser Resonator 2 Reflection Mirror Unit 3 Unit Rotation Driver 4 Transmission Optical System 5 Condenser Lens 6 Object

Claims (5)

[Claims] 1. A laser resonator which includes an output mirror and a rear mirror and emits light from the output mirror, and a reflection mirror unit which is provided immediately after the output mirror and includes three mirrors P, Q and R. A laser resonator optical system for irradiating an object with light to perform processing such as cutting, welding, heat treatment, etc., wherein the mirror of the reflection mirror unit is designed to receive an incident beam h from the laser as a first beam. Mira
P, the second mirror Q and the third mirror R are sequentially reflected so that the reflected beam n of the third mirror is on the same straight line as the incident beam h, and this straight line is used as a reference. The laser resonator optical system is characterized in that the entire reflection mirror unit can be rotated at an arbitrary angle by a unit rotation driver as a line. 2. A laser resonator which includes an output mirror and a rear mirror and emits light from the output mirror, and a reflection mirror unit which is provided immediately after the output mirror and includes three mirrors P, Q and R. A laser resonator optical system for irradiating an object with light to perform processing such as cutting, welding, heat treatment, etc., wherein the mirrors P, Q, R of the reflecting mirror unit are appropriate points A inside thereof. B,
C is an isosceles triangle having B as its apex, and the incident beam h from the laser is sequentially at points A, B and C of the first mirror P, the second mirror Q and the third mirror R. It is reflected so that the reflection beam n of the third mirror is on the same straight line as the incident beam h, and with this straight line as a reference line, the entire reflection mirror unit is driven by the unit rotary driver. A laser resonator optical system characterized in that it can rotate at an arbitrary angle. 3. A laser resonator which includes an output mirror and a rear mirror and emits light from the output mirror, and a reflection mirror unit which is provided immediately after the output mirror and includes three mirrors P, Q and R. A laser resonator optical system for irradiating an object with light to perform processing such as cutting, welding, heat treatment, etc., wherein the mirrors P, Q, R of the reflecting mirror unit are appropriate points A inside thereof. B,
C is a right-angled isosceles triangle with B as its apex, the second mirror Q is a circularly polarized mirror, and the incident beam h from the laser is
The points A of the first mirror P, the second mirror Q, and the third mirror R,
The reflection beam n of the third mirror is sequentially reflected so that the reflection beam n of the third mirror is on the same straight line as the incident beam h, and with this straight line as a reference line, the entire reflection mirror unit is A laser resonator optical system characterized in that it can be rotated at an arbitrary angle by a unit rotation driver. 4. A laser resonator which includes an output mirror and a rear mirror and emits light from the output mirror, and a reflection mirror unit which is provided immediately after the output mirror and includes three mirrors P, Q and R. A laser resonator optical system for irradiating an object with light to perform processing such as cutting, welding, heat treatment, etc., wherein the mirrors P, Q, R of the reflecting mirror unit are appropriate points A inside thereof. B,
C is a right triangle whose apex is A, the first mirror P is a circularly polarized mirror, and the incident beam h from the laser is the first.
Points A, B and C of the mirror P, the second mirror Q and the third mirror R
So that the reflection beam n of the third mirror is on the same straight line as the incident beam h, and with this straight line as a reference line, the whole reflection mirror unit is a unit rotary driver. A laser resonator optical system characterized in that it can be rotated by an arbitrary angle by-. 5. A laser resonator which includes an output mirror and a rear mirror and emits light from the output mirror, and a reflection mirror unit which is provided immediately after the output mirror and includes three mirrors P, Q and R. A laser resonator optical system for irradiating an object with light to perform processing such as cutting, welding, and heat treatment, wherein the mirrors P, Q, and R of the reflection mirror unit are appropriate points A inside thereof. B,
C is a right triangle whose apex is C, the third mirror R is a circularly polarized mirror, and the incident beam h from the laser is the first.
Points A, B and C of the mirror P, the second mirror Q and the third mirror R
So that the reflection beam n of the third mirror is on the same straight line as the incident beam h, and with this straight line as a reference line, the whole reflection mirror unit is a unit rotary driver. A laser resonator optical system characterized in that it can be rotated by an arbitrary angle by-.