LASER POWER MONITORING DEVICE AND LASER POWER MONITORING METHOD

A right angle reflection prism includes first and second surfaces that form a right angle, and a third surface connected to the first and second surfaces. The right angle reflection prism causes a laser beam, which is made incident on the first surface and with which a material to be processed is irradiated, to be totally reflected by the third surface so as to be emitted from the second surface. A sensor detects a power of a laser beam that has passed through the third surface.

TECHNICAL FIELD

The present disclosure relates to a laser power monitoring device and a laser power monitoring method for monitoring a power of a laser beam that is emitted from a laser beam source and with which a material to be processed is irradiated.

BACKGROUND ART

There exists a laser processing machine that bends, with a bend mirror, a laser beam emitted from a laser beam source and irradiates a material to be processed with the laser beam to weld or cut the material to be processed. Patent Literatures 1 and 2 describe monitoring of a power of a laser beam by detecting, with a sensor, a slight laser beam that has passed through a bend mirror.

CITATION LIST

Patent Literature

SUMMARY

In the laser power monitoring device as described in Patent Literature 1 and 2, a dichroic mirror that reflects a laser beam of a specific wavelength may be used as the bend mirror. The dichroic mirror is arranged at an angle of 45 degrees with respect to an optical axis of the laser beam. A dielectric multilayer film is formed on a reflecting surface of the dichroic mirror, and the dielectric multilayer film reflects the laser beam of a specific wavelength.

The laser beam includes a P wave and an S wave as polarization components. The polarization ratio, which is the ratio of the amount of the P wave to the amount of the S wave, changes due to the temperature environment and the like of an oscillator included in the laser beam source. When the polarization ratio of the laser beam changes, the reflectance, transmittance, or reflection band of the laser beam made incident at 45 degrees in the dielectric multilayer film changes. Therefore, the power of the laser beam that passes through the dichroic mirror and is made incident on the sensor changes. In other words, in the laser power monitoring device, which is used for a laser processing machine using the dichroic mirror as the bend mirror and is configured to detect, with the sensor, the laser beam that has passed through the dichroic mirror, it is not possible to monitor the power of the laser beam in a stable manner because the polarization ratio of the P wave to the S wave of the laser beam changes.

An object of one or more embodiments is to provide a laser power monitoring device and a laser power monitoring method capable of, even if the polarization ratio of the P wave to the S wave of a laser beam changes, stably monitoring a power of the laser beam with reduced influence of the change.

According to a first aspect of the one or more embodiments, a laser power monitoring device is provided, which includes a right angle reflection prism including first and second surfaces that form a right angle, and a third surface connected to the first and second surfaces, a laser beam for irradiation of a material to be processed being incident on the first surface, and being totally reflected by the third surface so as to be emitted from the second surface, and a sensor configured to detect a power of a laser beam that has passed through the third surface.

According to a second aspect of the one or more embodiments, a laser power monitoring method is provided, which includes causing a laser beam for irradiation of a material to be processed to be made incident on a first surface of a right angle reflection prism including the first surface and a second surface that form a right angle, and a third surface connected to the first and second surfaces, causing the laser beam made incident on the first surface to be totally reflected by the third surface so as to be emitted from the second surface, and detecting, by a sensor, a power of a laser beam that has passed through the third surface.

According to the laser power monitoring device and the laser power monitoring method of the one or more embodiments, even if the polarization ratio of the P wave to the S wave of the laser beam changes, it is possible to stably monitor the power of the laser beam with reduced influence of the change.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a laser power monitoring device and a laser power monitoring method of respective embodiments will be described with reference to the attached drawings. First, the problems of a laser power monitoring device of a comparative example shown inFIG.7will be described in detail.

InFIG.7, a laser beam source1emits a divergent laser beam. The laser beam source1is provided with a sensor1S for detecting a power of the emitted laser beam. A collimating lens2converts the divergent laser beam made incident thereon into a collimated beam and emits the collimated beam. A dichroic mirror3is arranged in a state of being tilted by 45 degrees with respect to an optical axis of the collimated beam. A dielectric multilayer film is formed on an incident surface (a reflecting surface)3aof the laser beam of the dichroic mirror3. The laser beam made incident on the incident surface3aof the dichroic mirror3is reflected by the incident surface3aand is made incident on a focusing lens4. The focusing lens4focuses the incident laser beam and irradiates a material to be processed W, which is a sheet metal, with the focused laser beam.

The laser beam source1, the collimating lens2, the dichroic mirror3, and the focusing lens4constitute a laser processing machine that irradiates the material to be processed W with the laser beam to weld or cut the material to be processed W.

Of the laser beam made incident on the dichroic mirror3, a slight laser beam indicated by the alternate long and short dash line passes through the dichroic mirror3and is made incident on a sensor5. The sensor5generates a voltage value corresponding to a power of the incident laser beam. By monitoring the voltage value generated by the sensor5, it is possible to monitor the power of the laser beam with which the laser processing machine irradiates the material to be processed W.

FIG.8shows an example of measurement results obtained by measuring powers of P waves and S waves of the laser beam made incident on the dichroic mirror3for a predetermined measurement time (here, 3600 seconds).FIG.8shows the results in which the laser beam, when a laser output of the laser beam source1is changed to 700 W, 400 W, and 100 W, is split into the P wave and the S wave with a polarized beam splitter and then the powers of the P wave and the S wave are measured for a predetermined time. InFIG.8, the solid line indicates the power of the P wave and the broken line indicates the power of the S wave. FromFIG.8, it can be seen that the polarization ratio between the P wave and the S wave fluctuates greatly at 700 W and 400 W. Note that when the laser beam is made incident on the dielectric multilayer film at 45 degrees, the power of the P wave detected by the sensor5is higher than the power of the S wave because the P wave has a lower reflectance than the S wave.

FIG.9shows voltage values (detected voltage values) generated by the sensor1S and the sensor5, respectively, for a predetermined measurement time (3600 seconds) when the laser output of the laser beam source1is 700 W. As shown inFIG.9, the voltage value generated by the sensor1S is substantially constant. In other words, the power of the laser beam emitted by the laser beam source1is controlled to be substantially constant.

However, the voltage value generated by the sensor5fluctuates greatly. This is because the polarization ratio of the P wave to the S wave fluctuates greatly as described above. As shown inFIG.8, since the power of the P wave is unstable, the unstable P wave exercises a great influence on the voltage value generated by the sensor5. In the example shown inFIG.9, the voltage value generated by the sensor5fluctuates by about 8%. Therefore, it can be seen that if the laser power is monitored by the sensor5, which detects the power of the laser beam that has passed through the dichroic mirror3, stable monitoring is not possible due to the fluctuation of the polarization ratio.

First to fourth embodiments described below reduce the above problems and realize stable monitoring of the power of the laser beam even if the polarization ratio of the P wave to the S wave fluctuates.

First Embodiment

FIG.1shows a laser power monitoring device and a laser power monitoring method according to the first embodiment. The first embodiment shows a basic configuration for stably monitoring a power of a laser beam, which is common to the first to fourth embodiments.

InFIG.1, a laser beam source11emits a divergent laser beam. The laser beam source11is provided with a sensor11S for detecting a power of the emitted laser beam. The laser beam source11is, for example, a fiber laser oscillator. The laser beam source11may be any laser oscillator. A collimating lens12converts the divergent laser beam made incident thereon into a collimated beam and emits the collimated beam. The laser beam of the collimated beam is made incident on a right angle reflection prism13.

Anti-reflection coating (AR coating) is applied to two surfaces13aand13b(first and second surfaces) of the right angle reflection prism13, the surfaces13aand13bforming a right angle. The anti-reflection coating is set to have properties corresponding to the operating frequency band of the laser beam so that reflection of the laser beam within the operating frequency band is prevented. The anti-reflection coating is not applied to a surface13c(a third surface) of the right angle reflection prism13connected to the surfaces13aand13b.

The laser beam emitted from the collimating lens12is made incident on the surface13aof the right angle reflection prism13and reaches the surface13c. If the laser beam is made incident on the surface13cat an angle larger than the critical angle, the laser beam is totally reflected by the surface13cand is emitted from the surface13b. Note that when the right angle reflection prism13is made of synthetic quartz having a refractive index of 1.458, it is possible to calculate the critical angle θr to be about 43.3 degrees from sin θr=1/1.458. If the incident angle, which is formed by the direction orthogonal to the surface13cand the incident direction of the laser beam, is larger than the critical angle θr, the laser beam is totally reflected.

The laser beam emitted from the surface13bof the right angle reflection prism13is made incident on a focusing lens14. The focusing lens14focuses the incident laser beam and irradiates the material to be processed W with the focused laser beam.

The laser beam source11, the collimating lens12, the right angle reflection prism13, and the focusing lens14constitute a laser processing machine that irradiates the material to be processed W with the laser beam to weld or cut the material to be processed W.

Of the laser beam made incident on the surface13cof the right angle reflection prism13, a slight laser beam (a leaked beam) indicated by the alternate long and short dash line passes through the surface13cand is made incident on a sensor15. The sensor15generates a voltage value corresponding to a power of the incident laser beam. One example of the sensor15is a photodiode. The photodiode may be a PIN photodiode. The sensor15may be any sensor that detects the power of the incident laser beam, and is not limited to the photodiode. By monitoring the voltage value generated by the sensor15, it is possible to monitor the power of the laser beam with which the laser processing machine irradiates the material to be processed W.

FIG.2Ashows a voltage value (a detected voltage value) generated by the sensor11S for a predetermined measurement time (here, 3600 seconds) when the laser output of the laser beam source11is 700 W.FIG.2Bshows a voltage value (a detected voltage value) generated by the sensor15for the measurement time. As shown inFIG.2A, the voltage value generated by the sensor11S is substantially constant. In other words, the power of the laser beam emitted by the laser beam source11is controlled to be substantially constant.

As shown inFIG.2B, the voltage value generated by the sensor15hardly fluctuates and is substantially constant. In the example shown inFIG.2B, the voltage value generated by the sensor15fluctuates only by about 1.86%. This is because, in the laser power monitoring device of the first embodiment, the sensor15does not detect the power of the laser beam that has passed through the dichroic mirror3, but detects the power of the laser beam that has passed through the surface13cthat totally reflects the laser beam of the right angle reflection prism13.

Since the right angle reflection prism13does not include the dielectric multilayer film on the surface13C, even if the polarization ratio of the P wave to the S wave of the laser beam changes, there is no change in the reflectance, transmittance, or reflection band of the laser beam, which is caused by the presence of the dielectric multilayer film. Therefore, according to the laser power monitoring device and the laser power monitoring method of the first embodiment, even if the polarization ratio of the P wave to the S wave of the laser beam changes, it is possible to reduce (or eliminate) the influence, and stable monitoring of the laser power is made possible.

Second Embodiment

A laser power monitoring device of the second embodiment shown inFIG.3is provided with two right angle reflection prisms. A laser power monitoring method of the second embodiment detects powers of laser beams that have passed through the surfaces totally reflecting the laser beam in the two right angle reflection prisms, respectively. InFIG.3, the same parts as those inFIG.1are denoted by the same reference numerals, and the description thereof will be omitted.

InFIG.3, the laser beam emitted from the collimating lens12is made incident on a right angle reflection prism131(a first right angle reflection prism). Surfaces131a,131b, and131cof the right angle reflection prism131correspond to the surfaces13a,13b, and13cof the right angle reflection prism13ofFIG.1, respectively. The laser beam, which is totally reflected by the surface131cof the right angle reflection prism131and is emitted from the surface131b, is made incident on a right angle reflection prism132(a second right angle reflection prism).

Of the laser beams made incident on the surface131cof the right angle reflection prism131, a slight laser beam indicated by the alternate long and short dash line passes through the surface131cand is made incident on a sensor151(a first sensor). The sensor151generates a voltage value corresponding to a power of the incident laser beam.

Surfaces132a,132b, and132cof the right angle reflection prism132correspond to the surfaces13a,13b, and13cof the right angle reflection prism13of FIG.1, respectively. The laser beam, which is totally reflected by the surface132cof the right angle reflection prism132and is emitted from the surface132b, is made incident on the focusing lens14. The focusing lens14focuses the incident laser beam and irradiates the material to be processed W, which is not shown inFIG.3, with the focused laser beam.

Of the laser beams made incident on the surface132cof the right angle reflection prism132, a slight laser beam indicated by the alternate long and short dash line passes through the surface132cand is made incident on a sensor152(a second sensor). The sensor152generates a voltage value corresponding to a power of the incident laser beam.

The laser beam source11, the collimating lens12, the right angle reflection prism131, the right angle reflection prism132, and the focusing lens14constitute a laser processing machine that irradiates the material to be processed W with the laser beam to weld or cut the material to be processed W.

According to the laser power monitoring device and the laser power monitoring method of the second embodiment, in addition to the same effect as that of the first embodiment, it is possible to monitor, with the two sensors151and152, the power of the laser beam with which the laser processing machine irradiates the material to be processed W.

FIG.4shows voltage values (detected voltage values) generated by the sensors151and152, respectively. The voltage value generated by the sensor151fluctuates by about 1.5%, and the fluctuation of the voltage value generated by the sensor152can also be maintained to the same degree. It is also possible to configure the laser power monitoring device to include three or more right angle reflection prisms.

Third Embodiment

A laser power monitoring device and a laser power monitoring method of the third embodiment shown inFIG.5are configured to split a laser beam into a P wave and an S wave, convert the P wave and the S wave into circularly polarized beams to be totally reflected by two right angle reflection prisms, and detect powers of the circularly polarized beams with two sensors. InFIG.5, the same parts as those inFIG.1are denoted by the same reference numerals, and the description thereof will be omitted.

InFIG.5, the laser beam emitted from the laser beam source11includes a linearly polarized P wave and a linearly polarized S wave. The laser beam emitted from the laser beam source11is made incident on a polarized beam splitter21(a first polarized beam splitter). The polarized beam splitter21is configured by joining a prism211and a prism212at a joint surface213. The joint surface213is provided with a dielectric multilayer film that transmits the P wave and reflects the S wave. The P wave passes through the joint surface213and is made incident on a ¼ wavelength plate22(a first ¼ wavelength plate). The S wave is reflected by a surface214of the prism212and made incident on a ¼ wavelength plate23(a second ¼ wavelength plate).

The ¼ wavelength plate22converts the linearly polarized P wave made incident thereon into a first circularly polarized beam. The ¼ wavelength plate23converts the linearly polarized S wave made incident thereon into a second circularly polarized beam. The first circularly polarized beam is made incident on a right angle reflection prism133(a first right angle reflection prism). The second circularly polarized beam is made incident on a right angle reflection prism134(a second right angle reflection prism). Surfaces133a,133b, and133cof the right angle reflection prism133correspond to the surfaces13a,13b, and13cof the right angle reflection prism13ofFIG.1, respectively. Surfaces134a,134b, and134cof the right angle reflection prism134correspond to the surfaces13a,13b, and13cof the right angle reflection prism13ofFIG.1, respectively.

The first circularly polarized beam made incident on the surface133aof the right angle reflection prism133is totally reflected by the surface133c, is emitted from the surface133b, and is made incident on a ¼ wavelength plate24. The second circularly polarized beam made incident on the surface134aof the right angle reflection prism134is totally reflected by the surface134c, is emitted from the surface134b, and is made incident on a ¼ wavelength plate25.

The ¼ wavelength plate24converts the first circularly polarized beam made incident thereon into a linearly polarized S wave. The ¼ wavelength plate25converts the second circularly polarized beam made incident thereon into a linearly polarized P wave. The linearly polarized P wave and the linearly polarized S wave are made incident on a polarized beam splitter26. The polarized beam splitter26is configured by joining a prism261and a prism262at a joint surface263. The joint surface263is provided with a dielectric multilayer film that transmits the P wave and reflects the S wave. The P wave passes through the joint surface263, and the S wave is reflected by a surface264of the prism262and the joint surface263. As a result, the linearly polarized P wave and the linearly polarized S wave are combined to be emitted from the polarized beam splitter26.

The laser beam including the linearly polarized P wave and the linearly polarized S wave emitted from the polarized beam splitter26is made incident on the focusing lens14. The focusing lens14focuses the incident laser beam and irradiates the material to be processed W with the focused laser beam.

The laser beam source11, the collimating lens12, the polarized beam splitter21, the ¼ wavelength plates22and23, the right angle reflection prisms133and134, the ¼ wavelength plates24and25, the polarized beam splitter26, and the focusing lens14constitute a laser processing machine that irradiates the material to be processed W with the laser beam to weld or cut the material to be processed W.

Of the first circularly polarized beam made incident on the surface133cof the right angle reflection prism133, a slight circularly polarized beam indicated by the alternate long and short dash line passes through the surface133cand is made incident on a sensor153. The sensor153generates a voltage value corresponding to a power of the incident circularly polarized beam. Of the second circularly polarized beam made incident on the surface134cof the right angle reflection prism134, a slight circularly polarized beam indicated by the alternate long and short dash line passes through the surface134cand is made incident on a sensor154. The sensor154generates a voltage value corresponding to a power of the incident circularly polarized beam.

In the laser power monitoring device and the laser power monitoring method of the third embodiment, the linearly polarized P wave and the linearly polarized S wave are converted into the circularly polarized beams, and the circularly polarized beams are totally reflected by the right angle reflection prisms133and134. Compared with the case in which the linearly polarized P wave and the linearly polarized S wave are totally reflected by the right angle reflection prisms133and134, in the case in which the circularly polarized beams are totally reflected by the right angle reflection prisms133and134, a gap, which is caused by a difference in the polarization direction at the time of totally reflecting the polarization components, is less likely to be generated.

In the third embodiment, the polarization ratio may change slightly when splitting into the P wave and the S wave is performed by the polarized beam splitter21. However, since the circularly polarized beams are totally reflected by the right angle reflection prisms133and134, the change in the polarization ratio is not so problematic as compared with the configuration in which the circularly polarized beam is reflected by the dichroic mirror.

In the third embodiment, when the polarization ratio of the P wave to the S wave changes, the voltage values generated by the sensors153and154fluctuate. Therefore, a value obtained by averaging the voltage values of the sensors153and154may be monitored.

Fourth Embodiment

A laser power monitoring device and a laser power monitoring method of the fourth embodiment shown inFIG.6are configured to split a laser beam into a P wave and an S wave, convert the P wave and the S wave into circularly polarized beams to be totally reflected by two right angle reflection prisms, return the circularly polarized beams to a linearly polarized beam, and detect a combined power of the P wave and the S wave with one sensor. InFIG.6, the same parts as those inFIG.5are denoted by the same reference numerals, and the description thereof will be omitted.

InFIG.6, of the first circularly polarized beam, a slight circularly polarized beam indicated by the alternate long and short dash line that has passed through the surface133cof the right angle reflection prism133is made incident on a ¼ wavelength plate27(a third ¼ wavelength plate). The ¼ wavelength plate27converts the circularly polarized beam made incident thereon into a linearly polarized S wave. The linearly polarized S wave is made incident on a polarized beam splitter29(a second polarized beam splitter). Of the second circularly polarized beam, a slight circularly polarized beam indicated by the alternate long and short dash line that has passed through the surface134cof the right angle reflection prism134is made incident on a ¼ wavelength plate28(a fourth ¼ wavelength plate). The ¼ wavelength plate28converts the circularly polarized beam made incident thereon into a linearly polarized P wave. The linearly polarized P wave is made incident on the polarized beam splitter29.

The polarized beam splitter29is configured by joining a prism291and a prism292at a joint surface293. The joint surface293is provided with a dielectric multilayer film that transmits the P wave and reflects the S wave. The P wave passes through the joint surface293, and the S wave is reflected by a surface294of the prism292and the joint surface293. As a result, the linearly polarized P wave and the linearly polarized S wave are combined and emitted from the polarized beam splitter29. The laser beam obtained by combining the linearly polarized P wave and the linearly polarized S wave emitted from the polarized beam splitter29is made incident on a sensor155. The sensor155generates a voltage value corresponding to a power of the incident laser beam.

In the same manner as the third embodiment, in the fourth embodiment as well, the polarization ratio may change slightly when splitting into the P wave and the S wave is performed by the polarized beam splitter21. However, in the laser power monitoring device and the laser power monitoring method of the fourth embodiment, the linearly polarized P wave and the linearly polarized S wave are combined by the polarized beam splitter29, and the power of the combined laser beam is detected by the sensor155. Therefore, even if the polarization ratio of the P wave to the S wave changes, the power of the combined laser beam will not change. As a result, it is possible to detect the power of the laser beam accurately.

In the fourth embodiment, it is possible to detect the power of the laser beam with the one sensor155.

The present invention is not limited to the first to fourth embodiments described above, and various modifications can be made without departing from the summary of the present invention. Any method can be used for specifically monitoring the powers of the laser beams detected by the sensors15,151to155.

The present application claims the priority based on Japanese Patent Application No. 2020-055949 filed with the Japan Patent Office on Mar. 26, 2020, and all the disclosure contents thereof are incorporated herein by reference.