JP2009094161A - Laser oscillator equipped with apertures - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser oscillator equipped with an aperture structure for solving the problem occurring from the displacement of the laser optical axis etc. though it has a simple and inexpensive structure. <P>SOLUTION: Guard apertures 41-43 are arranged to protect mode limiting apertures. The inside diameter of each guard aperture is set up to be somewhat larger than that of the mode limiting apertures between which the guard apertures are arranged. In this case, a path 36 is interrupted by the guard apertures 41 and 43, and the ambient light which does not belong to a desired laser profile 35 reaching the mode limiting apertures 31 and 34 is reduced. Even if the optical axis is displaced as shown in Fig.3, the heat production at the apertures 31 and 34 is reduced so that the melting breakage of the apertures scarcely occurs. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-power laser oscillator using a fluid or a solid as a medium.

  In general, a laser oscillator such as an axial flow gas laser oscillator is used for laser processing such as cutting and welding. In recent years, laser oscillators tend to have a higher output for improving cutting performance. However, in a laser oscillator having a higher output, amplified natural light (ASE) is likely to be generated, so that the beam quality generally decreases. . In order to solve the above-described problems, there is a method of providing an aperture in the resonator.

  FIG. 1 is a diagram showing an example of a schematic configuration of a conventional axial flow type gas laser oscillation device. Electrodes 2 and 3 are provided around the discharge tube 1 made of a dielectric material such as glass. A power source 4 is connected to the electrodes 2 and 3. At both ends of the discharge space 5 including the laser medium sandwiched between the electrodes 2 and 3, a rear mirror 6 that is a substantially total reflection mirror and an output mirror 7 that is a partial reflection mirror are arranged oppositely to form an optical resonator. ing. A laser beam 8 is output from the output mirror 7.

  The laser gas circulates in the laser gas flow path 10 at a pressure of about 13 to 27 kPa according to the arrow 9. Heat exchangers 11 and 12 are provided in the gas laser flow path 10 and serve to lower the temperature of the laser gas whose temperature has been raised by the discharge in the discharge space 5 and the operation of the blower 13. A gas flow of about 100 m / sec is obtained in the discharge space 5 by the blower 13. The laser gas flow path 10 and the discharge tube 1 are connected by a laser gas introduction part 14.

  The above is the configuration of the conventional gas laser oscillation apparatus. Next, the operation thereof will be described. The laser gas sent out from the blower 13 passes through the laser gas flow path 10 and is introduced into the discharge tube 1 from the laser gas introduction unit 14. In this state, a discharge is generated in the discharge space 5 from the electrodes 2 and 3 connected to the power source 4. The laser gas in the discharge space 5 is excited by obtaining this discharge energy, and the excited laser gas is in a resonance state by an optical resonator formed by the rear mirror 6 and the output mirror 7, and the laser beam 8 is emitted from the output mirror 7. Is output. This laser beam 8 is used for applications such as laser processing represented by cutting and welding.

  In many cases, an aperture for limiting the oscillation mode of the laser beam is provided in the discharge tube of the laser oscillation device as described above. For example, Patent Document 1 discloses a gas laser oscillator in which a plurality of knife-edge shaped apertures are provided in accordance with the beam profile in the resonator.

  Various developments and improvements have been made to the configuration related to the aperture. For example, Patent Document 2 discloses an alignment apparatus that measures the temperature of an aperture with a sensor and determines the deviation of the laser optical axis from the temperature rise of the aperture. Patent Document 3 discloses a laser oscillator in which apertures are provided on both sides of a beam waist to reduce inconvenient diffracted light. Further, Patent Document 4 discloses an apparatus for providing a plurality of light detection plates on an aperture base and measuring the temperature rise of the light detection plate so as to know the direction and degree of deviation of the laser beam axis with respect to the aperture. Has been.

JP-A-6-350166 JP 2001-53370 A JP 2006-196827 A Japanese Patent Laid-Open No. 11-274614

  The aperture provided in the laser resonator can easily control the characteristics of the laser beam by limiting the beam diameter for laser oscillation. However, in the case of a high-power, high-power laser, the laser light is amplified even in a laser medium blocked by the aperture and becomes a thermal load on the aperture. Therefore, a plurality of apertures are provided in the resonator, but in a state where the optical axis is adjusted, a design is made so that the thermal load on the aperture does not become excessive. That is, in a general laser oscillator, an aperture having an inner diameter matching a desired beam propagation shape at each position in the discharge tube is disposed at each position, and is limited by being absorbed or scattered by each aperture in the operating state. There is no significant difference in laser energy.

  However, at the adjustment stage, due to the deviation of the optical axis, the amplification of the laser beam is not suppressed by a plurality of apertures intended for the design, and there is an optical path that propagates in the medium for a relatively long distance. May destroy the aperture. Even during operation, the optical axis may shift for some reason, and the same situation may occur. Further, the laser beam may be reflected outside the oscillator and return to the oscillator. In this case, the returned light does not accurately follow the original laser beam path, but may be amplified by the laser medium inside the oscillator, resulting in an unexpectedly high energy density. Such return laser light from the outside of the oscillator may destroy the aperture.

  In addition, it is advantageous to increase the mode selectivity of the laser that the inner diameter portion of the aperture has a sharp edge shape like a knife edge, but in the case of a high-power laser, the heat load on each aperture is large. As a result, the portion of the aperture inner diameter that blocks the laser beam is exposed to a significant temperature rise, which may result in damage to the aperture. Although there is a technique for detecting and correcting the deviation of the laser optical axis as described above, a detecting means and a correcting means for that purpose are required, and the whole apparatus tends to be increased in size and cost.

  Accordingly, the present invention provides a laser oscillator having an aperture structure that solves problems caused by deviation of the laser optical axis, etc., while having a simple and inexpensive configuration.

  In order to achieve the above object, the invention according to claim 1 is a mode restriction in which laser oscillation is performed between reflecting mirrors facing each other with a laser medium interposed therebetween, and the diameter of the laser beam is limited by blocking the periphery of the laser optical axis. There is provided a laser oscillator having an aperture for use, wherein a guard aperture is provided which has an inner diameter larger than the inner diameter of the mode limiting aperture and protects the mode limiting aperture.

  According to a second aspect of the present invention, in the laser oscillator according to the first aspect of the present invention, the laser oscillator includes a plurality of mode limiting apertures having the same inner diameter arranged along an optical path, and the plurality of mode limiting apertures In the meantime, a laser oscillator having an inner diameter larger than the inner diameter of the mode limiting aperture and provided with a guard aperture for protecting at least one of the plurality of mode limiting apertures is provided.

  According to a third aspect of the present invention, in the laser oscillator according to the first aspect, the laser oscillator includes a plurality of mode limiting apertures having the same inner diameter arranged along an optical path, and the plurality of mode limiting apertures There is provided a laser oscillator provided with a guard aperture that is adjacent to at least one and has a diameter larger than the mode limiting aperture and protects the mode limiting aperture.

  According to a fourth aspect of the present invention, in the laser oscillator according to the first aspect, a plurality of mode limiting apertures having an inner diameter corresponding to the propagation shape of the outer peripheral portion of the laser beam arranged along the optical path are provided. A laser having an inner diameter larger than an inner diameter of the mode limiting aperture between the plurality of mode limiting apertures and protecting at least one of the plurality of mode limiting apertures Provide an oscillator.

  According to a fifth aspect of the present invention, in the laser oscillator according to the first aspect, a plurality of mode limiting apertures having an inner diameter corresponding to the propagation shape of the outer peripheral portion of the laser beam arranged along the optical path are provided. There is provided a laser oscillator provided with a guard aperture that is adjacent to at least one of the plurality of mode limiting apertures and has a larger diameter than the mode limiting aperture and protects the mode limiting aperture.

  A sixth aspect of the present invention provides the laser oscillator according to any one of the first to fifth aspects, wherein the mode limiting aperture is provided with a mode limiting aperture adjacent to the reflecting mirror. To do.

  When the optical axis of the laser beam is shifted due to adjustment of the optical axis, etc., the light diffracted by the mode limiting aperture increases in intensity while propagating in the resonator over a relatively long distance. According to the present invention, since the guard aperture having an inner diameter larger than the inner diameter of the mode limiting aperture is provided, a part of the light is blocked by the guard aperture, so that the amount incident on the mode limiting aperture is reduced. The mode limiting aperture is protected. In particular, in an oscillator having a large laser oscillation gain per optical path, a laser beam that oscillates naturally appears even in a laser medium sandwiched between the apertures. However, the guard aperture has an effect of suppressing such undesirable oscillation. is there. On the other hand, when the laser oscillator is correctly adjusted in the optical axis, the guard aperture is only irradiated with slightly diffracted laser light.

  According to the present invention, a preferred embodiment is provided for each of a plurality of mode limiting apertures having the same inner diameter and an inner diameter corresponding to the outer shape of a desired laser beam profile.

  In addition, by providing a guard aperture adjacent to the mode limiting aperture, the portion behind the guard aperture other than the portion close to the inner diameter of the mode limiting aperture does not oscillate due to the laser medium, so there is no laser beam. Will not win. Therefore, the heat load on the mode limiting aperture is significantly suppressed.

  Even when the guard aperture is disposed adjacent to the reflecting mirror, a part of the light reaching the reflecting mirror is blocked, so that there is an effect of suppressing undesirable oscillation.

  FIG. 2 is a diagram showing a conventional example of the optical system of the gas laser oscillation device shown in FIG. Here, in order to help understanding, in particular, only components that contribute to laser oscillation are extracted and shown. In the illustrated example, a rear mirror 6 and an output mirror 7 constitute a laser resonator, and discharge tubes 21 to 26 including a laser gas serving as a laser medium are arranged between the rear mirror 6 and the output mirror 7. Laser gas is excited to discharge. In the case of a so-called long resonator, the direction of the laser beam may be reversed by a folding mirror to reduce the size of the oscillator, but here it is illustrated as being arranged in series for the sake of clarity.

  In the example of FIG. 2, four apertures 31 to 34 are arranged so as to follow the propagation shape of the outer peripheral portion of the laser beam 35, and each aperture restricts the outer peripheral portion of the laser beam 35. Limited. However, even at a place deviating from the place where the intensity of the laser beam is high, such as point p, a certain amount of laser oscillation occurs if it is inside the laser medium. This is caused by the diffracted light generated in the inner diameter portion of the aperture, that is, the knife edge portion, or it oscillates naturally in the longitudinal direction of the laser medium. Generally, a high-power laser has a high gain. This is what happens.

  The laser light that does not fit in the desired laser beam path 35 emitted in this way is eventually irradiated onto the aperture and reflected and absorbed. For example, the path 36 shown in FIG. 2 corresponds to this. For this reason, the aperture is heated during laser oscillation. Further, this heat generation of the aperture can occur even when the laser optical axis is accurately adjusted.

  By the way, the optical axis of the laser may be tilted as shown in FIG. 3 due to a laser adjustment operation or an unintended failure. In this case, the laser beam profile is defined by, for example, paths 37 and 38, and the portions where the laser light contacts the aperture are only a part of the apertures 31 and 34 indicated by reference numerals 31a and 34a. Then, in the region immediately outside the portions 31a and 34a, there is nothing to block the laser beam over a distance substantially equal to the resonator length, and therefore, a considerably strong laser beam is emitted in these portions, and the aperture portion 31a. And 34a. As a result, these parts are heated strongly and in some cases are melted and broken.

  Therefore, in the present invention, as in the first embodiment shown in FIG. 4, guard apertures 41 to 43 for protecting the mode limiting aperture are arranged. The inner diameter of each guard aperture is set to be somewhat larger than the inner diameter of the mode limiting aperture that sandwiches the guard aperture. In this case, the above-described path 36 is blocked by the guard apertures 41 and 43, and ambient light that does not belong to the desired laser profile 35 reaching the mode limiting apertures 31 and 34 is attenuated. Even when the optical axis is deviated as shown in FIG. 3, the apertures 31 and 34 generate less heat, and the aperture is less likely to melt.

  In the second embodiment shown in FIG. 5, guard apertures 51 to 56 are arranged adjacent to the mode limiting apertures 31 to 34. The inner diameter of each guard aperture is set somewhat larger than the inner diameter of the adjacent mode limiting aperture. When the guard apertures 51 to 56 are not used, as shown in FIG. 2, the aperture 31 is irradiated with a wide range of ambient light. In this embodiment, the exposed portion of each mode limiting aperture is Since it is limited to an extremely narrow portion in the vicinity of the inner diameter portion, heat generation of the mode limiting aperture itself is extremely small.

  In the two embodiments described above, the laser profile 35 is illustrated as having a beam waist near the center of the optical path, but generally the propagation shape of the laser light is as shown in the laser profile 35 'shown in FIG. It is close to parallel lines (cylindrical when viewed three-dimensionally). Under such circumstances, in a commercially available laser oscillation device, it is not economical to configure the aperture diameter in strict accordance with the propagation shape of the laser beam, and therefore, all the apertures are often configured to have the same inner diameter. 6 and 7 show a laser oscillator having apertures 31 'to 34' having the same inner diameter and apertures 41 'to 43' and 51 'to 56' substantially similar to those of the first and second embodiments described above, respectively. An applied example is shown.

  The guard aperture is not necessarily provided between the mode limiting apertures. For example, the guard aperture is provided adjacent to or close to the output mirror 7 or the rear mirror 6 like the guard apertures 61 and 62 shown in FIG. You can also. According to such a configuration, part of the light reaching the rear mirror or the output mirror is blocked, so that an effect of suppressing undesirable oscillation can be obtained.

  The use of the guard aperture according to the present invention reduces the thermal load on the mode limiting aperture and eliminates special design considerations such as the use of special materials such as water cooling of the aperture and ceramic. Further, since the heat generated by the mode limiting aperture causes the thermal distortion of the resonator, the effect of reducing this is useful in constructing a stable laser oscillator. Furthermore, by configuring the guard aperture in the downstream portion of the discharge tube where the temperature becomes high, the heat generated by the aperture can be concentrated in the heat generating portion of the resonator and can be cooled intensively and effectively. This is an important technique for obtaining a thermally stable resonator.

  The gas laser has been described above. However, in the case of a solid-state laser, it can be easily understood that the same effect can be obtained by using the discharge tube of FIGS. 4 to 8 as a laser medium.

It is a figure which shows schematic structure of the principal part of a general laser oscillator. It is a figure which shows an example of the laser beam path | route in a prior art example. It is a figure which shows the other example of the laser beam path | route in a prior art example. It is a figure showing a 1st embodiment of a laser oscillator concerning the present invention. It is a figure which shows 2nd Embodiment of the laser oscillator based on this invention. It is a figure which shows the form which applied 1st Embodiment when the aperture for mode restrictions has the same internal diameter. It is a figure which shows the form which applied 2nd Embodiment when the aperture for mode restrictions has the same internal diameter. It is a figure which shows the example which made the guard aperture adjoin to a reflective mirror.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge tube 6 Rear mirror 7 Output mirror 21-26 Discharge tube 31-34 Mode restriction aperture 35 Laser beam profile 41-43, 51-56, 61, 62 Guard aperture

Claims (6)

A laser oscillator in which a laser is oscillated between reflecting mirrors facing each other with a laser medium interposed therebetween, and a mode limiting aperture is provided to block the periphery of the laser optical axis and limit the diameter of the laser beam,
A laser oscillator having a larger inner diameter than the inner diameter of the mode limiting aperture and provided with a guard aperture for protecting the mode limiting aperture. Having a plurality of same-diameter mode limiting apertures arranged along the optical path;
The guard aperture for protecting at least one of the plurality of mode limiting apertures is provided between the plurality of mode limiting apertures and having an inner diameter larger than the inner diameter of the mode limiting aperture. The laser oscillator described. Having a plurality of same-diameter mode limiting apertures arranged along the optical path;
2. The laser oscillator according to claim 1, further comprising a guard aperture that is adjacent to at least one of the plurality of mode limiting apertures and has a larger diameter than the mode limiting aperture and protects the mode limiting aperture. A plurality of mode limiting apertures having an inner diameter corresponding to the propagation shape of the outer peripheral portion of the laser beam, arranged along the optical path;
The guard aperture for protecting at least one of the plurality of mode limiting apertures is provided between the plurality of mode limiting apertures and having an inner diameter larger than the inner diameter of the mode limiting aperture. The laser oscillator described. A plurality of mode limiting apertures having an inner diameter corresponding to the propagation shape of the outer peripheral portion of the laser beam, arranged along the optical path;
2. The laser oscillator according to claim 1, further comprising a guard aperture that is adjacent to at least one of the plurality of mode limiting apertures and has a larger diameter than the mode limiting aperture and protects the mode limiting aperture.   The laser oscillator according to claim 1, wherein the mode limiting aperture is provided with a mode limiting aperture adjacent to the reflecting mirror.

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