JP2011108867A - Output mirror monitor and laser oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an output mirror monitor capable of detecting the stain of an output mirror securely, and a laser oscillator using the output mirror monitor. <P>SOLUTION: Provided are a light source 5 that irradiates light of a different wavelength from that of the laser beam 4 to an output mirror 2 which reflects part of laser beams and passes part of the laser beams, and a control means 8 which has a photo diode 6 as a means of receiving reflected light 5b from the output mirror 2 out of light 5a emitted from the light source 5 and a photo diode 7 as a means of receiving transmitted light 5c that penetrates the output mirror 2 out of light 5a emitted from the light source 5, obtains the ratio of the received light intensity of the reflected light 5b and that of the transmitted light 5c, and compares the setting value with the obtained ratio. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an output mirror monitor for detecting the degree of contamination of an output mirror, and to a laser oscillator using the output mirror monitor.

  In recent years, among laser oscillators, for example, CO2 gas laser oscillators mounted on laser processing systems that perform thermal processing have been increasing in output.

  The output mirror of such a laser oscillator is a contact point between the laser oscillator and the processing system. When the output mirror is exposed to the processing dust generated from the workpiece and the dust adheres to the surface of the output mirror, the laser beam from the output mirror is transmitted. The absorption rate is increased, and the output mirror is damaged by the absorption heat of the laser beam.

  Therefore, measures have been taken to devise a structure that is difficult to get processed dust, but the contaminants cannot be completely blocked.

  Also in the laser oscillator, there is a possibility that contaminants are accumulated inside the long-term use and the contaminants adhere to the output mirror.

  Therefore, there is a demand for a function of monitoring the contamination status of the output mirror before it breaks.

  Such a conventional output mirror monitor applies light to the surface of the output mirror from the outside, and monitors the degree of contamination from the amount of reflected light (see, for example, Patent Document 1).

  FIG. 5 shows the conventional output mirror monitor.

  As shown in the figure, an output mirror 102 is attached to the holder 101. The output mirror 102 adjusts the attachment angle to the holder 101 so that a part of the laser beam is reflected to the laser resonator 103 and a part thereof is output as the laser beam 104.

  Further, in order to detect the state of the surface 105 of the output mirror 102, a light source 106 and a light receiver 107 arranged at a position where the light output from the light source 106 is reflected by the surface 105 are attached to the holder 101, respectively. .

  A comparator 108 for comparing with the set value is connected to the light receiver 107.

  The operation of the output mirror monitor configured as described above will be described.

  Light having a wavelength different from the laser oscillation wavelength is emitted from the light source 106, irradiated onto the surface 105 of the output mirror 102 at an incident angle of 30 degrees or less, and the reflected light is received by the light receiver 107. The signal detected by the light receiver 107 is compared with a set value by the comparator 108.

  The laser beam 104 oscillated by the laser resonator 103 is transmitted through the output mirror 102 and is output. However, when contaminants adhere to the surface 105 of the output mirror 102, a part of the laser beam 104 is absorbed and the output mirror 102 is absorbed. Increases the temperature of the output mirror 102 and induces breakage of the output mirror 102.

  When the light emitted from the light source 106 is reflected by the surface 105 of the output mirror 102, if a contaminant is attached, the amount of light incident on the light receiver 107 is reduced by being absorbed or scattered by the contaminant.

  Therefore, the signal from the light receiver 107 is compared with the set value by the comparator 108, and when it is determined that the set value is not reached, it is determined that the contaminant is attached, and the operation of the laser resonator 103 is stopped. .

  The above-described conventional output mirror monitor device has been described as monitoring the front surface 105, but there is also a device that monitors the back surface 109 of the output mirror 102.

US Pat. No. 7,193,700

  However, the conventional output mirror monitor has a problem that only information on one side of the output mirror 102 can be obtained. In order to solve this, it is necessary to provide a pair of light sources 106, a light receiver 107, and a comparator 108 on both sides of the output mirror.

  In addition, the pollutant is a substance that does not absorb or scatter with respect to the wavelength of the light source 106 even though it has absorption with respect to the wavelength of the laser oscillator 103 (such as an organic substance having a low optical density with visible light). In such a case, the output mirror 102 may be damaged without being detected.

  The present invention provides an output mirror monitor that reliably detects the degree of contamination of the output mirror, and a laser oscillator using the output mirror monitor.

  In order to solve the above problems, an output mirror monitor of the present invention includes a light source that reflects a part of laser light and irradiates light having a wavelength different from that of the laser light to an output mirror that passes a part of the output mirror. Means for receiving the reflected light from the output mirror, and means for receiving the transmitted light that passes through the output mirror among the light from the light source, and the received light intensity of the reflected light and the transmitted light Is provided with a control means for obtaining the ratio of the received light intensity and comparing the ratio with the set value.

  Now, as contamination of the output mirror proceeds, the temperature of the output mirror rises due to the absorption of laser light, so that the surface of the output mirror becomes convex, resulting in a convex lens with large aberrations. In addition, the refractive index increases as the temperature rises, so that the focal length of the lens is shortened, and the refractive index distribution due to the temperature gradient synergizes to increase the intensity of the central portion of the transmitted light. The intensity of the reflected light is lowered due to the convex reflecting surface. Therefore, by comparing the ratio with the set value, not only the front surface (or back surface) contaminant can be detected, but also the thermal lens condition of the output mirror can be detected, and the output mirror can be prevented from being damaged.

  In the above-described invention, a reflecting mirror is provided in at least one optical path from the light source to the means for receiving the reflected light or from the light source to the means for receiving the transmitted light, or the output from the light source. In the optical path to the mirror, a partial reflecting mirror is provided, and a light receiving means for monitoring the intensity of light emitted from the light source is provided. In front of the light receiving section of the means for receiving the reflected light or the means for receiving the transmitted light An opening with a limited size is provided, or the control means compares the received light intensity of the reflected light and the received light intensity of the transmitted light, and stops the discharge of the laser oscillator when the ratio becomes larger than the set value, The control means differentiates the ratio between the received light intensity of the reflected light and the received light intensity of the transmitted light, and is configured to operate the alarm means when the ratio and the differential value are larger than a set value. .

  As described above, the present invention not only detects the contaminants on the front surface (or the back surface) by comparing the received light intensity of the reflected light and the received light intensity of the transmitted light, but also detects the thermal lens of the output mirror, Damage to the output mirror can be prevented.

  In particular, since the rapid change is monitored using the differential of the ratio, the output mirror can be prevented from being broken.

Configuration diagram of Embodiment 1 of an output mirror monitor of the present invention used in a laser oscillator Configuration diagram of Embodiment 2 of output mirror monitor of the present invention used in a laser oscillator Configuration diagram of Embodiment 3 of output mirror monitor of the present invention used in a laser oscillator Explanatory drawing of the comparison signal in Embodiment 1-3 of the output mirror monitor of this invention Configuration of conventional output mirror monitor

  Hereinafter, embodiments for carrying out the present invention will be described with reference to FIGS. 1 to 4.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of an output mirror monitor according to Embodiment 1 of the present invention used in a laser oscillator.

  As shown in the figure, the holder 1 is equipped with an output mirror 2 made of ZnSe. The output mirror 2 adjusts the attachment angle to the holder 1 so that a part of the laser beam is reflected to the laser resonator 3 and a part of the laser beam is output as the laser beam 4.

  In this embodiment, a laser gas composed of CO2 gas as a main component and a mixture of nitrogen gas and helium gas is used as a laser medium, and an electrode (not shown) provided in a discharge tube (not shown) is supplied from a power source (not shown). Electric power is supplied to generate a discharge in the discharge tube, and high-speed electrons generated by the discharge excite nitrogen molecules to raise to a high energy level, and the excited nitrogen molecules collide with CO2 molecules. Totally reflecting mirrors that are excited by applying energy to CO2 molecules, raising energy levels, lowering energy levels of nitrogen molecules, and inversion-distributed CO2 molecules facing opposite ends of the discharge tube. (Not shown) is amplified in the laser resonator 3 by the output mirror 2 and stimulates and emits the laser beam, and the laser beam 4 is output from the output mirror 2 to the outside.

  A hole 3b is provided in the housing 3a of the laser resonator 3, and a light source 5 in which a collimator lens is incorporated in, for example, a semiconductor laser having a wavelength different from the wavelength 10600 nm of the laser light 4 is disposed.

  Also, a hole 3c is provided in the housing 3a of the laser resonator 3, and for example, a photodiode 6 is disposed as means for receiving the reflected light 5b reflected by the output mirror 2 out of the light 5a irradiated from the light source 5, In front of the light receiving portion of the photodiode 6, a mask 6a having an opening with a limited size is provided.

  Further, for example, a photodiode 7 is disposed outside the housing 3 a of the laser resonator 3 as means for receiving the transmitted light 5 c transmitted through the output mirror 2 out of the light 5 a emitted from the light source 5. A mask 7a having an opening with a limited size is also provided in front of the light receiving portion.

  The signals from the photodiodes 6 and 7 are connected so as to be input to the control means 8. After the control means 8 adjusts the output level to each of the photodiodes 6 and 7 with a preamplifier, the signal is digitally converted by an AD converter. It converts into a signal, divides, calculates a ratio, calculates | requires the ratio of the received light intensity of the reflected light 5b, and the received light intensity of the transmitted light 5c, It is set as the structure which compares a setting value and a ratio with a comparator, Alarm means (illustrated) Control the power supply so that the discharge to the discharge tube is stopped.

  As the alarm means, a commonly used red light or buzzer is used.

  FIG. 4 is an explanatory diagram of a ratio signal in which the calculation results of the control means 8 are displayed in analog form, with the horizontal axis indicating time and the vertical axis indicating the ratio obtained by dividing the transmitted light received output by the reflected light received output.

  The operation of the output mirror monitor configured as described above will be described.

  A part of the laser light amplified by the laser resonator 3 passes through the output mirror 2 and becomes laser light 4.

  This laser light 4 is absorbed according to the absorption rate of the output mirror 2 and converted into heat inside the output mirror 2.

  Even when the output mirror 2 is not contaminated, the output mirror 2 has an absorption rate of about 0.1%, and therefore the output mirror 2 has a heat input of about 4 W when outputting 4 KW of laser light 4.

  Therefore, the periphery of the output mirror 2 is cooled by a cooling mechanism (not shown).

  However, since it cannot be uniformly cooled and there is a distribution of heat input by the laser beam, an unavoidable temperature gradient occurs in the central portion and the peripheral portion, and the output mirror 2 is deformed by this temperature gradient.

  This deformation does not become a beautiful spherical surface, but the distortion at the center is large. Further, the resonator-side surface 9 on which the partial reflection film is formed and the output-side surface 10 on which the antireflection film is formed have different absorption rates of laser light on the surface, so that the front and back surfaces do not swell.

  When the output mirror 2 is contaminated with contaminants, the absorption increases further, and the temperature rise and temperature gradient become abrupt. When the temperature rise and the temperature gradient exceed the destruction threshold, the output mirror 2 is broken.

  As shown in FIG. 4, when laser oscillation is performed, the light reception output ratio increases. In the case of the output mirror 2 without contamination, it rises gently as shown by the curve 41 and stabilizes within one minute.

  However, as contamination progresses, the local portions of the resonator-side surface 9 and the output-side surface 10 of the output mirror 2 become convex, resulting in a convex lens with large aberration.

  In addition, the refractive index increases as the temperature rises, and the focal length of the lens is shortened. In addition, the refractive index distribution due to the temperature gradient synergizes to increase the central intensity of the transmitted light 5c.

  The intensity of the reflected light 5b is lowered due to the convex reflecting surface. Therefore, the difference is enlarged as shown by the curve 42. By setting a certain level as the set value, it is detected as an abnormality when the difference exceeds the set value, the alarm means is activated, and laser oscillation is stopped to prevent the output mirror 2 from being damaged.

  A curve 43 is a curve obtained when contamination occurs during operation and the output mirror 2 rapidly deteriorates.

  In this case, since it is necessary to stop laser oscillation urgently even if the level is equal to or less than the set value, a differentiation circuit is provided in the control means 8 so as to detect a sudden change.

  Since the differential coefficient is maximum at the start of laser oscillation, an excessive reaction occurs when only the differential coefficient is used as a criterion. For this reason, the alarm means is operated and the laser oscillation is stopped only when the ratio and the differential coefficient are multiplied by a coefficient and the value is a certain value or more.

  In FIG. 4, the curve shown by the broken line is an example of the calculation result obtained by adding the differential coefficients.

  As described above, according to the present embodiment, the light source 5 that irradiates light having a wavelength different from that of the laser light 4 onto the output mirror 2 that reflects a part of the laser light and passes the laser light. Photodiode 6 as means for receiving reflected light 5b from the output mirror 2 out of the light 5a, and photo as means for receiving transmitted light 5c that passes through the output mirror 2 out of light 5a from the light source 5 A control unit 8 is provided which includes a diode 7 and obtains a ratio between the received light intensity of the reflected light 5b and the received light intensity of the transmitted light 5c, and compares the ratio with the set value. The ratio of the light intensity and the transmitted light intensity is obtained to detect the thermal lens of the output mirror 2, and the risk is predicted for a sudden change in the intensity ratio by comparing the differential value with the set value, and laser oscillation Can be stopped Because, to prevent damage to the output mirror 2, it is possible to prevent destruction of the laser oscillator in advance.

  In addition, since the laser oscillator incorporating the output mirror monitor according to the present embodiment can prevent the output mirror 2 from being suddenly broken, contamination caused by ZnSe powder in the oscillator vacuum system, which occurs when the output mirror 2 is damaged, Secondary damage such as breakage due to sudden vacuum break of the vacuum circulation pump can be prevented.

  In the figure, even if the direction of the resonator side and the output side are switched, there is no influence on the function.

(Embodiment 2)
FIG. 2 is a diagram showing the configuration of the output mirror monitor according to the second embodiment of the present invention used in the laser oscillator.

  In addition, in this Embodiment, the same code | symbol is attached | subjected about the location similar to Embodiment 1, and detailed description is abbreviate | omitted.

  As shown in FIG. 2, in this embodiment, the light 5a of the light source 5 is not emitted from the resonator-side surface 9 as in the first embodiment, but the light 5a of the light source 5 is emitted from the output-side surface 10 side. I try to irradiate. Specifically, the position of the light source 5 is arranged at a position away from the housing 3a, and the reflecting mirror 11 is arranged in the optical path from the light source 5 to the output mirror 2 so that the overall length of the apparatus can be shortened. The light 5a is reflected in the direction of the output mirror 2.

  According to this difference in configuration, the photodiode 7 that receives the transmitted light 5c is disposed in the hole 3d of the housing 3a, while the photodiode 6 that receives the reflected light 5b is disposed at a position away from the housing 3a. ing.

  In addition, in the optical path of light reception to the photodiode 6, the reflecting mirror 12 is arranged, and the photodiode 6 is arranged so that the entire length of the apparatus can be shortened.

  As described above, the optical axes of the light 5a and the reflected light 5b from the light source 5 can be changed by the reflecting mirrors 11 and 12, the optical system can be laid out in the gap in the laser oscillator, and the size of the laser oscillator can be further increased. In addition, since the distance to the photodiode 6 can be increased, it is possible to be sensitive to changes in the shape of the convex surface and to improve detection sensitivity.

(Embodiment 3)
FIG. 3 is a diagram showing the configuration of the output mirror monitor according to the third embodiment of the present invention used in the laser oscillator.

  In the present embodiment, the same parts as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 3, in the present embodiment, the reflecting mirror 11 in the configuration of the second embodiment is changed to a partial reflecting mirror 13, and a photodiode is used as a light receiving means for receiving light transmitted through the partial reflecting mirror 13. 14 is different from that of the second embodiment.

  In this way, a part of the light 5 a emitted from the light source 5 is branched by the partial reflection mirror 13 and monitored by the photodiode 14, thereby making it possible to correct the detection accuracy of the apparatus due to the temporal change of the light source 5.

  As described above, according to the present embodiment, as a result of monitoring the light 5a from the light source 5 with the partial reflection mirror 13, the change over time of the detection system is corrected, and stable operation for a long period of time becomes possible.

  The output mirror monitor and laser oscillator according to the present invention can monitor the state of the thermal lens inside the output mirror, and can further predict the danger against a sudden change in the intensity ratio and stop the laser oscillation. It is industrially useful as an output mirror monitor and laser oscillator for monitoring and protecting a mirror.

DESCRIPTION OF SYMBOLS 2 Output mirror 3 Laser resonator 4 Laser light 5 Light source 5a Light 5b Reflected light 5c Transmitted light 6 Photodiode 6a Mask 7 Photodiode 7a Mask 8 Control means 11 Reflective mirror 12 Reflective mirror 13 Partial reflective mirror 14 Photodiode

Claims (7)

  A light source that reflects part of the laser light and irradiates light having a wavelength different from that of the laser light to an output mirror that passes through the part; and means for receiving reflected light from the output mirror among light from the light source; And means for receiving transmitted light that passes through the output mirror among the light from the light source, obtains a ratio between the received light intensity of the reflected light and the received light intensity of the transmitted light, and compares the set value with the ratio Output mirror monitor with control means.   2. The output mirror monitor according to claim 1, wherein a reflecting mirror is provided in at least one optical path from the light source to the means for receiving the reflected light or from the light source to the means for receiving the transmitted light.   The output mirror monitor according to claim 1, wherein a partial reflection mirror is provided in an optical path from the light source to the output mirror, and light receiving means for monitoring the intensity of light emitted from the light source is provided.   4. The output mirror monitor according to claim 1, wherein an opening having a limited size is provided in front of a light receiving portion of the means for receiving the reflected light or the means for receiving the transmitted light.   The output mirror according to any one of claims 1 to 4, wherein the control means compares the received light intensity of the reflected light and the received light intensity of the transmitted light, and stops the discharge of the laser oscillator when the ratio becomes larger than a set value. monitor.   6. The control unit according to claim 1, wherein the control unit differentiates a ratio between the received light intensity of the reflected light and the received light intensity of the transmitted light, and operates the alarm unit when the ratio and the differential value are larger than a set value. The output mirror monitor according to any one of the above.   A laser oscillator comprising the output mirror monitor according to any one of claims 1 to 6, wherein the output mirror monitor is disposed at one end of a laser resonator that excites a laser medium, reflects a part of the laser light, and transmits a part of the laser beam. .

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