JP2800006B2 - Laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device having a function of adjusting a phase of a laser beam.

[Prior Art] FIG. 9 is a laser handbook (Laser Handbook 19).
FIG. 79 is an explanatory diagram showing an example of a conventional laser device having an unstable resonator described in North-Holland Publishing Company (P.3). In the figure, (1) is a collimating mirror composed of a concave mirror, (2) is an enlarged mirror composed of a convex mirror disposed opposite to the collimating mirror (1),
Both mirrors (1) and (2) are constituted by total reflection mirrors. (3) is a laser medium, which is a gas medium excited by electric discharge in the case of a gas laser such as a CO ₂ laser, and a glass medium excited by a flash lamp in the case of a solid laser such as a YAG laser. (4) is a wind mirror, (5) is a non-reflective coating film formed on the surface of the wind mirror (4), (6) is a box covering the periphery, (7) is a collimating mirror (1) and a magnifying mirror. A laser beam generated in the optical resonator constituted by (2) and (8) is a laser beam taken out from the periphery of the magnifying mirror (2).

Next, the operation will be described. Collimating mirror (1)
And the magnifying mirror (2) constitute a so-called unstable resonator. The laser beam (7) reflected and expanded by the magnifying mirror (2) is amplified by the laser medium (3) and the collimating mirror (1). As a result, the light is collimated into a parallel beam (7a), reflected on the magnifying mirror (2) and the peripheral portion of the magnifying mirror (2), and extracted outside from the window mirror (4) as a ring-shaped laser beam. Since the extracted ring-shaped laser beam (8) is obtained with almost the same phase, it is condensed by a lens or the like (not shown) to become a middle-high laser beam (8). It can be performed efficiently.

The degree of light collection is determined by the ratio of the inner diameter to the outer diameter (M value (Magnification) of the ring-shaped laser beam (8) to be extracted.
facter)) In conclusion, the larger the M value, that is, the more the beam is extracted in the middle, the better the focus. However, when the M value is increased, the oscillation efficiency is significantly deteriorated. Therefore, the upper limit of the M value that is practically used industrially is about 2.

In such a laser device, if the M value is increased to improve the light-collecting characteristics, the oscillation efficiency deteriorates. Therefore, in practice, the M value cannot be increased to near infinity where the maximum light-collecting performance can be obtained. There was a problem. In addition, since the window mirror (4) is non-uniformly heated by the ring-shaped laser beam (8), the phase distribution of the laser beam (8) passing through due to generation of non-uniform internal stress is broken, and the light-collecting performance is improved. And the like.

In order to solve such a problem, the applicant of the present invention applied for a laser device as shown in FIGS. 10 and 11 as Japanese Patent Application No. 61-291786.

In the figure, (4a) is a convex mirror which also serves as a wind mirror, and a convex portion (FIG. 10) or a concave portion (FIG. 11) is formed at a central portion of a surface facing the collimating mirror (1). (20) is a partially reflective coating film having a partial reflectance provided on the surface of the convex portion and the concave portion, and functions as a magnifying mirror. (5) is a non-reflective coating film formed on the periphery and the other side of the partially reflective coating film (20).

In the laser device configured as described above, the partially reflecting coating film (20) of the collimating mirror (1) and the convex mirror (4a) forms a so-called unstable resonator, and the partially reflecting coating of the convex mirror (4a). The laser beam (7) reflected and expanded by the film (20) is converted into a laser medium (3)
And is collimated into a parallel beam by the collimating mirror (1), and is extracted from the convex mirror (4a) to the outside as a laser beam (8). The laser beam (8) comprises a portion (70) passing through the partially reflective coating film (20) and a portion (71) passing through the non-reflective coating film (5). By the action of (40), it is extracted to the outside as a laser beam (8) having the same phase and a middle shape.

As described above, the laser beams (70) and (71) pass through the portions of the convex mirror (4a) on which the two types of coating films, the partially reflective coating film (20) and the non-reflective coating film (5), are applied. It is taken out. However, since the phase change given to the passing laser beam varies depending on the type of the coating film, if there is no step (40) and the thickness of the convex mirror (4a) is constant, the laser beams (70) and (71) Will produce a phase difference. The laser beams (70) and (71) having a phase difference may not be focused by a lens or the like, and cannot be efficiently laser-processed. In addition, the beam shape changes during transmission and becomes high on the condensing lens, and the lens is destroyed.

The laser device shown in FIGS. 10 and 11 is such that the convex mirror (4a) is provided with a step (40) to cancel such a phase difference, and the laser beams (70) and (71) pass through. Steps (40) are provided between the parts to change the thickness of each part. For example, if the phase given to the laser beam passing through the partially reflective coating film (20) on the inner surface of the convex mirror (4a) is advanced by δ from the phase given to the laser beam passing through the non-reflective coating film (5),
To correct this, a step (4) at the center of the convex mirror (4a)
The depth d of (0) is determined by (n-1) d / λ = δ. Here, n is the refractive index of the material of the convex mirror (4a), and λ is the wavelength of the laser beam.

[Problems to be Solved by the Invention] As described above, the laser device (FIGS. 10 and 11) described in Japanese Patent Application No. 61-291786 is a wind mirror (convex mirror).
Since the laser beam is made to have the same phase by providing a constant step, a laser beam having excellent light-collecting characteristics can be obtained without sacrificing the oscillation efficiency. However, since the refractive index of the window mirror changes when the temperature of the base material and the coating film rises due to absorption of the high-power laser beam, the depth of the step must be changed in order to correct this. Further, in forming a step in the wind mirror, diamond cutting or the like is used, but there is a problem that it is extremely expensive.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a laser device capable of freely adjusting the phase.

[Means for Solving the Problems] A laser device according to the present invention is a laser device for processing an object to be processed by a laser beam emitted from a laser resonator, wherein: a total reflection mirror having an opening in the center; A movable reflection mirror having the same optical axis as that of the total reflection mirror and movable in the optical axis direction, and reflected by the total reflection mirror and the movable reflection mirror. It is provided with phase adjusting means for adjusting the phase between the beams.

Further, in a laser device including a laser resonator having an enlarging mirror for reflecting and expanding a laser beam and a collimating mirror for turning a laser beam expanded by the enlarging mirror into a parallel beam, the collimating mirror has an opening at the center. And a movable reflection mirror provided behind the opening, having the same optical axis as the optical axis of the total reflection mirror, and movable in the optical axis direction. And a phase adjusting means for adjusting the phase between the laser beams reflected by the movable reflecting mirror.

Further, a phase changing means for periodically moving the movable reflecting mirror and changing the phase with time is provided.

[Operation] A reflecting mirror having a movable portion adjusts the phase difference between two laser beams reflected by the movable portion and its surrounding portion, and changes the phase difference of the laser beam with time.

[Embodiment of the Invention] FIG. 1 is an explanatory view showing an embodiment of the present invention. In the figure, (1) is a collimating mirror, (4b) is a convex window mirror, (5) is a non-reflective coating film, (20) is a partially reflecting coating film, and a collimating mirror (1) and a window mirror (4b). Partially reflective coating film (20)
Constitutes a so-called unstable resonator. (6) is a box covering the resonator, (7), (70) and (71) are laser beams in the resonator, and (8), (80) and (81) are extracted from the laser resonator to the outside. Laser beam. (10) is the laser beam (8) extracted from the wind mirror (4b).
0) and (81) are total reflection mirrors provided on the optical path, and (10a) is an opening provided at the center of the total reflection mirror (10).
(11) has a larger diameter than the opening (10a) of the total reflection mirror (10), has the same optical axis as the optical axis of the total reflection mirror (10), and is movable in the optical axis direction. A reflective movable reflecting mirror that has a clearance behind the opening (10a) of the total reflection mirror (10) and the total reflection mirror (10) as viewed from the incident laser beams (80) and (81). It is arranged so that it does not occur. (13) is a fixed part fixed to the total reflection mirror (10), (14) is a movable part linearly moving along the fixed part (13), and linearly moved by the fixed part (13) and the movable part (14). A mechanism (12) is configured, and a movable reflection mirror (11) is attached to the movable section (14). (15) is a condenser lens,
(16) is a workpiece. Reference numeral (21) denotes a transmission total reflection mirror provided in the optical path of the lens beams (80) and (81).

The operation of the present invention configured as described above will be described as follows.

The partially reflecting coating film (20) of the collimating mirror (1) and the convex window mirror (4b) forms a so-called unstable resonator, and is partially reflected by the partially reflecting coating film (20) and expanded. Beam (7) is
Amplified by the laser medium (3) and collimated into a parallel beam by the collimating mirror (1).
In this case, a part of the central laser beam (70) passes through the partially reflective coating film (20) to the outside of the laser beam (8).
0) and the surrounding laser beam (71)
Is extracted as a laser beam (81) to the outside through the anti-reflection coating film (5). Since the two laser beams (80) and (81) are emitted through different coating films on the surface of the wind mirror (4b), a phase difference generally occurs between the two.

To cancel this phase difference, for example, assuming that the phase of the laser beam (81) is ahead of the laser beam (80) by δ, the wavelength of the laser beam is set to λ. Only the propagation distance of the laser beam (81) is
The movable part (14) of the linear motion mechanism (12) is moved so as to be longer than the propagation distance of the movable reflection mirror (1).
Just move 1) forward. By the way, if the incident angles on the total reflection mirror (10) and the movable reflection mirror (11) are sufficiently small, the moving amount d of the movable reflection mirror (11) is Becomes In the initial state, the distance between the front surface of the total reflection mirror (10) and the surface of the movable reflection mirror (11) is set to an integral multiple of the wavelength λ.

Next, when the phase of the laser beam (80) is ahead of the phase of the laser beam (81) by δ, the movable reflection mirror (11) may be retracted by d in reverse to the previous case. The laser beam (8), which has been made equal in phase in this manner, is condensed to a remarkably middle and high level by the condensing lens (15), whereby the workpiece (16) can be laser-processed.

In the above embodiment, the total reflection mirror (1
0) and the case where the movable reflection mirror (11) is provided outside the resonator, but as shown in FIG. 2, the total reflection mirror (10) has the same optical axis as the total reflection mirror (10). The movable reflection mirror (11) having the optical axis described above and movable in the optical axis direction may be provided in the resonator as one of the resonator mirrors.

In the embodiment of FIG. 1, the case of an unstable resonator having a plurality of optical paths in the resonator has been described. However, the present invention is not limited to this. For example, as shown in FIG. , Collimating mirror (1) and partially reflecting mirror (4
c) may be used. In this case, generally, the phase on the peripheral side is delayed and the light-collecting performance is deteriorated, but this can be corrected by retracting the movable reflection mirror (11) of the total reflection mirror (10).

FIG. 4 is an explanatory view showing still another embodiment of the present invention. In this embodiment, the phase of the laser beam extracted from the laser device is changed over time to control the focused beam pattern. The same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. (1
8) is a telescopic element such as a piezo element attached to the movable part (14) of the linear motion mechanism (12), and (19) is a power supply for exciting the telescopic element (18). is there. Is excited by the power supply (19) and vibrates back and forth.

In the present embodiment configured as described above, the laser beam (8
0) and (81) are reflected on the surfaces of the total reflection mirror (10) and the movable reflection mirror (11), respectively.
Is vibrated back and forth by the expansion and contraction element (18), so that an optical path difference is periodically generated between the two due to a change in the optical path length. Therefore, between the two laser beams (80) and (81), A phase difference occurs periodically. The laser beams (80) and (81) having a phase difference are combined to form a laser beam (8) having a phase distribution, which is further condensed by a condensing lens (15), and is condensed by a laser beam on a workpiece (16). Perform processing.

FIG. 5 (a). FIG. 5B is a diagram showing an example of a pattern when the synchronous phase change of the laser beam in the embodiment of FIG. 4 is large. FIG. 5 (a) shows a laser beam (8
1) shows a beam intensity distribution when a laser beam (8) having a phase shifted by 180 ° from that of (80) is condensed.
FIG. 6B shows a beam intensity distribution when the laser beams (81) and (80) have the same phase. From this figure, by periodically changing the phase difference from -180 ° to 0 °,
The on-axis intensity of the laser beam shows a very large change,
It is understood that pulsed laser processing can be performed by using this laser beam. The amount of movement d of the movable reflecting mirror (11) required to provide a phase difference between −180 ° and 0 ° is λ with a wavelength, and the incident angle on the movable reflecting mirror (11) is sufficiently small. In this case, taking a CO ₂ laser as an example, λ = 1
Since it is 0.6 μm, d = 2.65 μm, which is small, and therefore, a stretching element such as a piezo element (17)
The number 1 that cannot be realized with a CO ₂ laser oscillator
Repetitive pulse processing at 00 KHz or more, for example, processing for generating fine irregularities on the surface of an iron plate can be performed at an extremely high speed.

Next, an embodiment in which the phase is adjusted to extend the depth of focus will be described. Curves A, B, and C in FIG. 6 indicate that the phase differences between the laser beams (80) and (81) shown in FIG.
FIG. 7 shows the change of the on-axis intensity before and after the focus at + 60 °, and FIG. 7 shows the change of the average on-axis intensity when the phase control is oscillated within ± 60 ° within one cycle. From FIGS. 6 and 7, it can be seen that by periodically performing the phase control, a laser beam having a very deep focal depth, in which the on-axis intensity hardly changes before and after focusing, can be obtained. By using such a laser beam, cutting of a thick plate and deep penetration processing can be easily realized.

In the embodiment of FIG. 4, the case where the total reflection mirror (10) for adjusting the phase and the movable reflection mirror (11) are arranged outside the laser resonator has been described. However, the embodiment shown in FIG. As in the case, it may be arranged in the resonator as one of the mirrors of the laser resonator.

Further, in the embodiment of FIG. 4 described above, a laser resonator having a plurality of optical paths in the resonator has been described as an example, but the present invention is not limited to this, and the present invention is not limited to this. As in the case described above, the present invention can be applied to a laser device having a stable resonator including a collimating mirror (1) and a partial reflection mirror (4c).

FIG. 8 shows a case in which a Gaussian beam mode is generated by the above-mentioned stable resonator and condensed without giving a phase difference (curve A in FIG. 8). It shows a focused beam intensity distribution when a phase difference of 180 ° is given (curve B in the figure). Also in this case, it is understood that the pulse processing can be performed by changing the phase difference over time by changing the phase difference over time by changing the phase difference.

[Effects of the Invention] As is clear from the above description, according to the present invention, the equal phase of the laser beam is adjusted to have the same optical axis as the optical axis of the total reflection mirror at the center of the total reflection mirror, Since this is performed by a movable reflection mirror composed of a total reflection mirror movably provided in the direction of the optical axis, even if the phase of the laser beam to be made equal in phase changes due to a change in the temperature of the window mirror, for example, it is quickly responded to this. And the phase can be adjusted accurately. In addition, the present invention is configured to change the phase distribution in the cross section of the laser beam with time. Laser processing can be performed, and by performing phase control periodically, a laser beam having an extremely deep depth of focus can be obtained. Further, since the present invention is arranged such that the movable reflecting mirror having a larger diameter than the opening is arranged behind the opening of the total reflecting mirror, a gap may be generated between the movable reflecting mirror and the total reflecting mirror. No loss of laser beam output. It can also be easily manufactured industrially.

[Brief description of the drawings]

FIGS. 1, 2, and 3 are explanatory diagrams each showing an embodiment of the present invention, FIG. 4 is an explanatory diagram showing another embodiment of the present invention, and FIGS. 4 is a diagram showing the beam intensity distribution of the embodiment, FIG. 6 is a diagram showing the depth of focus due to the phase difference, and FIG. 7 is a phase control of ± 60 ° within one cycle.
FIG. 8 is a diagram showing a change in average on-axis intensity when the vibration is changed in FIG. 8. FIG. 8 is a diagram showing a beam intensity distribution when the embodiment of FIG. FIG. 1 is an explanatory diagram showing an example of a conventional laser device, and FIGS. 10 and 11 are explanatory diagrams showing an example of a laser device according to the application of the present applicant. In the figure, 1 is a collimating mirror, 4b is a wind mirror, 4c is a partially reflecting mirror, 5 is a non-reflective coating film,
7, 70, 71, 8, 80, 81 are laser beams, 10 is a total reflection mirror, 1
0a is an opening, 11 is a movable reflection mirror, 12 is a linear motion mechanism,
Reference numeral 18 denotes a stretching element, 19 a power source, and 20 a partially reflective coating film. The same reference numerals in the drawings indicate the same or corresponding parts.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 26/00-26/18 G02B 27/50

Claims (3)

(57) [Claims] 1. A laser apparatus for processing an object to be processed by a laser beam emitted from a laser resonator, comprising: a total reflection mirror having an opening in the center; and a light of the total reflection mirror provided behind the opening. A movable reflecting mirror having the same optical axis as the axis and movable in the optical axis direction, comprising a phase adjusting means for adjusting a phase between laser beams reflected by the total reflecting mirror and the movable reflecting mirror; A laser device. 2. A laser apparatus comprising: a laser resonator having a magnifying mirror for reflecting and expanding a laser beam; and a collimating mirror for converting a laser beam expanded by the magnifying mirror into a parallel beam. A total reflection mirror having an opening, and a movable reflection mirror provided behind the opening, having the same optical axis as the optical axis of the total reflection mirror, and movable in the optical axis direction, A laser device comprising: a phase adjusting unit that adjusts a phase between laser beams reflected by a total reflection mirror and the movable reflection mirror. 3. The movable reflecting mirror is periodically moved,
The laser device according to claim 1 or 2, further comprising a phase changing means for changing a phase with time.