JPH05102560A - Laser device - Google Patents

Abstract

PURPOSE:To provide a laser device which is excellent in converging performance proper to laser machining performance and operates with high efficiency. CONSTITUTION:A laser device is provided with an output mirror having at least three stage reflectance where the laser device is equipped with an oscillator comprising at least more than one reflecting mirror having an output mirror 7 which extracts energy from a laser medium 2.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device having a resonator for taking out energy from a laser medium, and more particularly, the reflectance distribution of an output mirror which constitutes the resonator has a converging performance of output laser light. The present invention relates to an improved laser device.

[0002]

_2. Description of the Related Art A CO ₂ laser for high power processing is conventionally used as a laser device having a resonator for extracting a laser beam having a relatively good focusing performance from a laser medium having a large cross section (Fresnel number> 1). What is provided is generally constructed as shown in FIG. That is, a convex mirror 3 having a small diameter is provided at the right end across the rear mirror 1 and the laser medium 2 at the left end, and an annular coupling mirror 4 is provided immediately inside this, and an output window 5 is provided beside this coupling mirror 4. Is provided.
In the laser device having this resonator configuration, laser light 6 is obtained in which the power of the central portion where the focusing performance is determined by the curvature ratio (magnification ratio) of the rear mirror 1 and the convex mirror 3 (ring-shaped power distribution) is obtained. Be done.

[0003]

However, the above-mentioned conventional laser device has a problem that the oscillation efficiency of the laser decreases when the enlargement ratio is increased in order to improve the focusing performance. On the contrary, if the oscillation efficiency of the laser is increased, it is necessary to reduce the enlargement ratio, and as a result, the condensing performance is deteriorated even if the condensing optical system condenses the laser light. Especially, since the power of the central portion of the output laser light suddenly becomes 0, a large amount of power escapes to the outside (side lobe) of the area to be focused, and the laser processing performance is greatly reduced. It was

Therefore, the present invention has been made to solve the above-mentioned problems, and an object thereof is a laser device which has an excellent focusing performance suitable for laser processing performance and operates with high efficiency. To provide. [Constitution of Invention]

[0005]

In order to achieve the above object, the present invention provides a laser device having a resonator composed of at least one reflecting mirror having an output mirror for extracting energy from a laser medium. A laser device characterized in that the reflectance of the output mirror has at least three levels of reflectance.

[0006]

In the laser device of the present invention configured as described above, the output mirror is provided with a reflectance distribution so that the laser light is partially transmitted even from the central portion, and the transmittance changes in at least three stages. Therefore, an output laser beam having a gradual power distribution can be obtained, so that an efficient laser operation can be realized with excellent focusing performance.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. It should be noted that the same parts as those of the conventional type shown in FIG.

In this embodiment, as shown in FIG.
An output mirror 7 having a reflectance distribution of at least three stages is provided on the right side of the rear mirror 1 on the left end and the laser medium 2. The resonator configuration is an unstable configuration (magnification factor M), and one output mirror has a function of expanding the laser light inside the resonator and transmitting the light to the outside of the resonator, and has a gentle power distribution. Is obtained. Further, an aperture 9 for limiting the laser beam diameter is provided inside the resonator.
Although not shown here, one or more folding mirrors may be provided between the rear mirror 1 and the output mirror 7.

FIG. 2 shows the reflectance distribution of the output mirror 7 shown in FIG. The alternate long and short dash line represents the function expressed by the following equation (1), and the solid line represents the reflectance distribution in three steps, R ₁ , R ₂ , R
_With the reflectance of ₃ , R ₁ and R ₂ are approximated by the following formula (1) except for R ₃ which transmits almost 100% (reflects almost 0%). That is, the outer radius of the reflectance R ₁ is defined as w ₀ and the outer radius of the reflectance R ₂ is w _m, and in the following formula (1), when the radius r = w _{0/2, the} reflectance R = R ₁ is defined as the radius r. = (W _m +
It is approximated to satisfy the reflectance R = R ₂ when w ₀ ) / 2.

There are various other methods for approximating the following equation (1), such as the reflectance R ₁ when r = w ₀ and the reflectance R ₂ when r = w _m. I've only extended the example. Further, it is not always necessary to set the outer radius of the reflectance R ₂ to w _m .

As described above, the reason why the reflectance distribution is changed stepwise is that a large output laser has a high laser power, so that the output mirror of this embodiment having a transmission function continuously reflects a substance having low absorption. This is because it is difficult to change the rate distribution and to reduce the production cost. Also, the center of the output mirror is not necessarily r
It is not necessary to set = 0.

FIG. 3 shows an example of a coating method of the output mirror 7 having a three-step reflectance distribution (longitudinal drawing passing through the central axis of the output mirror). The reflectance distribution coating layer 11 is provided on the reflective surface side of the ZnSe base material 10, and the antireflection coating layer 12 is provided on the opposite surface side. The reflectance coating layer 11 is composed of ZnSe coating layers 13 and 14, non-reflection coating layers 15, 16 and 17, a reflectance R ₁ coating layer 18, and a reflectance R ₂ coating layer 19. The end portion 20 on the surface of the ZnSe base material 10 is not coated in order to enhance the cooling effect of the output mirror.

Here, the reflectance R ₁ coating layer 18,
The phase difference of the laser light reflected inside the resonator on both surfaces of the reflectance R ₂ coating layer 19 is π / 4 or less, and the phase difference of the laser light transmitted through the output mirror 7 is π /.
The thickness of each coating layer is set so as to be 4 or less (excluding the end portion 20). Here, the transmittance is almost 100
The reflectance distribution R of the circular output mirror excluding the percentage
(R) is R (r) = R ₀ exp (−2 (r / w _m ) ⁿ ) ... Consider the laser characteristics when it can be approximated to (1). Here, R ₀ ; reflectance of the center w _m ; diameter of reflectance of the reflecting mirror n; order r; distance from the center. 4 and 5 show the laser output and the laser focusing performance when the order n is a variable under the condition of the magnification ratio M. The conventional example is shown by a broken line in both figures, and the present embodiment is shown by a solid line. In the conventional example, the laser output is reasonably high, but the laser focusing performance is extremely low. Therefore, only 0.36 (arbitrary scale) is entered into the region useful for processing (the region excluding the side lobe region). However, in the case of the present embodiment, it is understood that the laser condensing performance is very excellent, and when the order n exceeds 7, the laser output also becomes higher than that of the conventional example. Even when the laser output is low (n = 2), the power in the region useful for processing is 0.48 (arbitrary scale), which is higher than that of the conventional example. Therefore, very good laser processing can be realized by using this embodiment.

The order of the laser power in the main lobe region and the side lobe region at the converging point obtained by adopting the unstable resonator configuration shown in FIG. 1 under the condition that the injection power into the laser medium is constant. Figure 6 shows the n dependence.
Shown in. The power entering the main lobe region is a little small when n is 5 or less, but the maximum is around n = 10, and then n
Gradually decreases with increasing. The power entering the side lobe region, which adversely affects processing, increases as the order n increases.

In order to realize excellent processing, the power is efficiently input to the main lobe region and the total laser power (= power obtained by subtracting the power entering the side lobe region from the power entering the main lobe region) is about 2. A minimum of / 3 must be in the main lobe area. Therefore,
The range of the order n may be set to 2 ≦ n ≦ 35.

As a result, a large amount of power can be concentrated in the main lobe region (hatched region) useful for laser processing in the intensity distribution of laser light at the focal point shown in FIG. Much power can be concentrated in the main lobe area (hatched area). The main lobe region is generally defined within the divergence angle of the first dark portion of the Airy disk at the focal point.

The present invention is not limited to the above-mentioned embodiment, and the reflectance of the output line may be three or more stages. Further, although the present embodiment is an example of a positive branch unstable resonator, a negative branch unstable resonator configuration may be used.

Further, due to the difference in the structure of the unstable resonator, the laser efficiency may be improved when the phases of the reflected light into the resonator are not all aligned but partially shifted. Even in such a case, by using an output mirror in which a part of the phases is shifted from the others, it is possible to realize a highly efficient laser device having an excellent focusing performance. When the reflectance is changed stepwise,
It suffices if the phases of the reflected light in some of the reflectance portions are shifted.

Further, in this embodiment, since the focusing characteristic can be freely changed by arbitrarily changing the phase of each reflectance portion, it is possible to create a focused laser distribution according to the laser processing application. is there.

[0020]

As described in detail above, according to the present invention,
It is possible to provide a laser device which has excellent focusing performance suitable for laser processing performance and operates with high efficiency.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing a reflectance distribution of an output mirror in one example of the present invention.

FIG. 3 is a vertical cross-sectional view showing coating of an output mirror in one embodiment of the present invention.

FIG. 4 is a graph showing laser outputs of an example of the present invention and a conventional example.

FIG. 5 is a graph showing laser converging performance of one example of the present invention and a conventional example.

FIG. 6 is a graph showing the dependence of the powers in the main lobe and side lobe regions on the order in one embodiment of the present invention.

FIG. 7 is a graph showing a laser intensity distribution at a focal point in one example of the present invention.

FIG. 8 is a schematic view showing a conventional laser device.

[Explanation of symbols]

1 ... Rear mirror, 2 ... Laser medium, 3 ... Output mirror, 8 ...
Laser light 11 ... Reflectance distribution coating layer, 12 ... Anti-reflection coating layer, 15 ... Anti-reflection coating layer, 18 ... Reflectance R ₁ coating layer, 19 ... Reflectance R ₂ coating layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Nishida, 2-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa, Ltd. Inside the Hamakawasaki Plant, Toshiba Corporation (72) Ken Sato, 2 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 in stock company Toshiba Hamakawasaki factory (72) Inventor Masao Takahashi Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 2 In-house stock company Toshiba Hamakawasaki (72) Inventor Sakae Ikuta Ukishima, Kawasaki-ku, Kawasaki-shi, Kanagawa Town No. 2 in stock company Toshiba Hamakawasaki factory (72) Inventor Toru Tamagawa No. 2 in Ukishima-cho Ukishima-cho, Kawasaki-ku, Kawasaki City, Kanagawa Stock company inside Toshiba Hamakawasaki factory

Claims (3)

[Claims] 1. A laser device including a resonator including at least one reflecting mirror having an output mirror for extracting energy from a laser medium, wherein the reflectance of the output mirror has at least three levels of reflectance. A laser device characterized by the above. 2. The reflectance distribution R (r) of the circular output mirror excluding the portion where the transmittance is almost 100% is R (r) = R ₀ exp (−2 (r / w _m ) ⁿ ), R ₀ ; reflectance of the center w _m ; diameter of reflectance of the reflecting mirror n; order r; distance from the center approximated by the following formula: A laser device according to claim 1. .. 3. A laser device including a resonator having at least one reflecting mirror having an output mirror for extracting energy from a laser medium, wherein the reflectance of the output mirror is at least three levels. And the reflectance distribution R (r) of the circular output mirror excluding the portion where the transmittance is almost 100% is R (r) = R ₀ exp (−2 (r / w _m ) ⁿ ), R ₀ ; reflectance of the center w _m ; diameter of reflectance of the reflecting mirror n; order r; distance from the center is approximated, and the order n is in the range of 2 ≦ n ≦ 35. Laser device.