Abstract:
A laser apparatus which has a laser resonator  2  for emitting a laser beam  8 , an optical fiber  23 , on which the laser beam  8  transmitted from the laser resonator  2  through a beam transmission optical path is made incident, for transmitting the laser beam  8  to a workpiece, a measurement and adjustment jig  44  for measuring laser beam output of an annular pattern occurring in the periphery of a beam pattern of the laser beam  8  emitted from the optical fiber  23 , and a fiber incidence section  22  for adjusting incidence of the laser beam  8  on the optical fiber  23  based on output from the measurement and adjustment jig  44.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a laser apparatus and in particular to fiber adjustment of the laser apparatus. 
     A solid-state laser apparatus will be discussed as an example of the laser apparatus. 
     FIG. 10 is a schematic diagram to show an oscillator head and a laser beam path of a solid-state laser apparatus in a related art. Numeral  1  denotes an oscillator head, numeral  2  denotes a resonator, numeral  3  denotes a partial reflecting mirror, numeral  4  denotes a total reflecting mirror, numeral  5  denotes an excitation light source, numeral  6  denotes a solid-state component of an excitation medium, numeral  7  denotes a cavity (box) containing the excitation light source  5  and the solid-state component  6 , numeral  8  denotes a laser beam emitted from the resonator  2 , numeral  9  denotes a magnifying lens, numeral  10  denotes a collimating lens, numeral  11  denotes a beam shutter, numeral  12  denotes a reflecting mirror, numeral  14  denotes a damper, numeral  20  denotes a condensing lens, numeral  21  denotes a fiber holder, numeral  22  denotes a fiber incidence section having the condensing lens  20  and the fiber holder  21 , numeral  23  denotes an optical fiber, numeral  24  denotes a machining head, and numerals  25   a  and  25   b  denote machining lenses. 
     The operation of the described solid-state laser apparatus is as follows: In the laser apparatus in FIG. 10, the solid-state component  6  is excited by excitation light of the excitation light source  5  and the partial reflecting mirror  3  and the total reflecting mirror  4  placed so as to sandwich the solid-state component  6  cause lasing to occur. The laser beam  8  emitted from the resonator  2  is widened after passing through the magnifying lens  9  and becomes a collimated beam after passing through the collimating lens  10 , and the collimated laser beam is incident on the fiber incidence section  22 . 
     The beam shutter  11  is placed between the collimating lens  10  and the fiber incidence section  22 , so that the laser beam  8  can be shut off when it is not wanted to emit the laser beam  8  to the outside of the laser oscillator. The beam shutter  11  consists of the reflecting mirror  12  for reflecting the laser beam  8  and the damper  14  for absorbing the laser beam  8  and converting it into heat. The reflecting mirror  12  is movable. When the reflecting mirror  12  is at a position A, the laser beam  8  passes through the beam shutter  11 ; when the reflecting mirror  12  is at a position B, the laser beam  8 ,is reflected on the reflecting mirror  12  to the damper  14 . The surface of the damper  14  is formed of a laser beam absorber for converting energy of the laser beam  8  into heat. Although not shown, the damper  14  is water-cooled for releasing the amount of heat absorbed. 
     The collimated laser beam  8  incident on the fiber incidence section  22  is gathered by the condensing lens  20  in the fiber incident section, and is incident on an end face  23   i  of the optical fiber  23  held by the fiber holder  21 , and propagates in the optical fiber  23 . adjustment in an optical axis direction to match the optical axis direction position of the focus of the gathered laser beam  8  with the optical fiber incidence end  23   i , and the fiber holder  21  is made movable for adjustment in a direction perpendicular to the optical axis to match the focus position with the center of the plane of the optical fiber incidence end  23   i.    
     The laser beam  8  passing through the optical fiber  23  is emitted from an emission end  23   o  of the optical fiber  23  connected to the machining head  24 . The laser beam  8  guided into the machining head  24  is gathered by the condensing lenses  25   a  and  25   b  and is used for machining, etc. 
     The fiber incidence section  22  is adjusted seeing the characteristic of the laser beam  8  emitted from the emission end  23   o  of the optical fiber  23 . 
     Generally, in the solid-state laseroscillator, the light quantity of the excitation light source  5  is changed to change oscillation output. That is, the heat energy given to the solid-state component  6  is changed and by extension optical heat distortion of the solid-state component  6  itself changes. Specifically, the solid-state component  6  is cooled from the periphery, thus the temperature of the center becomes higher than that of the periphery and the solid-state component  6  has remarkably a nature like a convex lens; the strength degree of the convex lens changes. In this kind of solid-state laser oscillator, the characteristic of the solid-state component  6  in the resonator as the lens changes, thus if the strength of the excitation light source  5 , namely, output of the laser beam  8  is changed, the propagation characteristic of the laser beam  8  emitted from the resonator  2  changes and consequently the optimum adjustment value of the fiber incidence section  22  changes. 
     Therefore, to make the above-described adjustment, it is necessary to cause 500-W lasing to occur to machine in 500 W in a laser oscillator of output equivalent used for actual machining, for example, rated output 500-W output; otherwise, the propagation characteristic of the laser beam  8  at the adjustment time differs largely from that at the actual machining time, and the reliability of the adjustment itself is impaired. 
     The above-described adjustment is made finally with the laser beam  8  of machining output of high output. When adjustment to the fiber incidence section  22  differs largely from the optimum position, if the laser beam  8  of high output is made incident on the fiber incidence section  22  suddenly, there is a possibility that the optical fiber  23  and any other part will be damaged. Then, the fiber incidence section  22  is adjusted in such low output as not to damage the optical fiber  23  or any other part and while output is increased gradually, adjustment of the fiber incidence section  22  is repeated. Finally, the adjustment is made in actual machining output, then is completed. 
     FIG. 11 shows a solid-state laser apparatus as an example of a laser apparatus in another related art. The laser apparatus differs from that previously described with reference to FIG. 10 in beam shutter section structure. In the laser apparatus shown in FIG. 11, numeral  30  denotes a beam absorber and numeral  31  denotes a reflecting mirror. The reflecting mirror  31  has a little, for example, 0.2% passing characteristic, namely, reflects most of an incident laser beam  8  and allows some output to pass through. The laser beam  8  passing through is absorbed in the beam absorber  30 . The beam absorber  30  acts as a laser beam shield. It is placed so that the beam absorber  30  can be removed from the rear of the reflecting mirror  30 , so that the laser beam  8  passing through the reflecting mirror  31  can be made incident on a fiber incidence section  22  as required. 
     The operation of the laser apparatus shown in FIG. 11 is as follows: To adjust an optical path in an oscillator shown in FIG. 11, the beam shutter is closed, namely, the reflecting mirror  31  is set to a position of B and the beam absorber  30  is removed, then the laser oscillator is made to laser in output equivalent to that at the actual machining time, for example, 500 W. Then, the laser beam  8  reflected on the reflecting mirror  31  is absorbed in a damper  14  and a laser beam of small output passing through the reflecting mirror, in the example, 500 W×0.2%=1 W is emitted from an oscillator exit, namely, a condensing lens  20 . At this time, input to a solid-state component  6  is equivalent to that at the actual machining time, thus optical heat distortion of the solid-state component  6  is equivalent to that at the actual machining time and therefore the propagation characteristic of the laser beam  8  emitted from a resonator is equivalent to that at the actual machining time. 
     At this time, the propagation characteristic of the laser beam  8  passing through the reflecting mirror  31  is equivalent to that at the actual machining time. Moreover, output of the laser beam  8  passing through the reflecting mirror  31  is small. Thus, if the laser beam is made incident on an incidence end  23   i  of an optical fiber  23  in an entirely unadjusted state, there is not a fear of damaging the optical fiber  23 , etc. 
     Therefore, if an adjustment is made to the fiber incidence section  22  in the state, it can be made in a state equal to that at the actual machining time with respect to optical heat distortion of the solid-state component  6  from the beginning, eliminating the need for making intricate adjustment to the laser apparatus shown in FIG. 10 in such a manner that first a rough adjustment is made in such small output as not to damage the optical fiber  23 , etc., then while adjustment output is increased gradually, adjustment is repeated more than once and finally, full-scale adjustment is made in actual machining output; the fiber incidence section  22  can be adjusted easily in a short time. 
     That is, in the solid-state laser apparatus previously described with reference to FIG. 11, the effect of the optical heat distortion of the solid-state component itself little introduces a problem. 
     After the termination of the adjustment, the beam absorber  30  is restored to the former position. 
     In the solid-state laser apparatuses as previously described with reference to FIGS. 10 and 11, hitherto, GI-type optical fibers have been often used. However, in recent years, SI-type optical fibers have been used increasingly in place of the GI-type optical fibers. The SI-type optical fiber has the advantage that the optical damage threshold can be increased about double digits as compared with the GI-type optical fiber, so that the demand for the SI-type optical fibers grows with high output of recent laser apparatuses. 
     When the optical fiber is an Si-type optical fiber, namely, is a fiber such that it has a refractive index changing stepwise on the boundary between the fiber core and clad, if all laser beam is incident on the fiber core at the fiber incidence end, total incident beam is transmitted in the core. In many cases, the incident beam diameter at the fiber incidence end is about 90% of the core diameter or less and allows the total incident beam to be incident on the core in the range thereof. 
     On the other hand, if a part of the laser beam cannot enter the fiber core because the optical axis shifts at the fiber incidence end or for any other reason, clad propagation in the fiber occurs. 
     Thus, if the SI-type optical fiber is used, the fiber incidence section  22  is adjusted while whether or not the above-mentioned clad propagation occurs is determined. That is, the fiber incidence section  22  is adjusted while the laser beam strength distribution after fiber emission is checked. To check the laser beam strength distribution, for example, a laser power meter  40  is placed at a position at a proper distance L from the fiber emission end  23   o , a laser beam after fiber emission is applied to the laser power meter  40 , and a beam pattern on the laser power meter  40  is observed with an IR scope for visualizing an invisible laser beam or the like, as shown in FIG.  12 . 
     FIGS. 13A and 13B show observed beam patterns after fiber emission. When a total incident laser beam propagates in the core, a circular pattern  50   a  results as shown in FIG.  13 A. On the other hand, if clad propagation occurs because of an adjustment failure, the brightness of the circular pattern  50   a  at the center, namely, the beam strength lessens and an annular pattern  50   b  appears on the outer periphery of the circular pattern  50   a , forming a double circle pattern, as shown in FIG.  13 B. The double circle pattern also occurs if an adjustment difference occurs in any direction from the optimum adjustment value. 
     The fiber incidence section  22  is adjusted so that the observed beam patterns after fiber emission becomes a circular pattern as shown in FIG.  13 A. The optimum adjustment value in output at the adjustment time lies in an intermediate of the adjustment values for causing a double circle pattern to appear (two in one direction). 
     As described above, in the laser oscillators in the related arts, if the SI-type optical fiber is used, to adjust the fiber incidence section at the maintenance time, etc., appropriate measurement and adjustment means are not available and the fiber incidence section is adjusted based on a determination made by a visual inspection of an actual beam after fiber emission. Thus, it is necessary to repeat an adjustment while output is increased gradually; it takes time. A skill is required to determine the optimum adjustment value by a visual inspection. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a laser apparatus for making it possible to make a precise and objective optical path adjustment and fiber incidence section adjustment easily in a short time if an SI-type optical fiber is used as an optical fiber. 
     According to the invention, there is provided a laser apparatus comprising a laser resonator for emitting a laser beam, an optical fiber, on which the laser beam transmitted from the laser resonator through a beam transmission optical path is made incident, for transmitting the laser beam to a workpiece, laser beam output measurement means for measuring laser beam output of an annular pattern occurring in the periphery of a beam pattern of the laser beam emitted from the optical fiber, and fiber incidence adjustment means for adjusting incidence of the laser beam on the optical fiber based on output from the laser beam output measurement means. 
     The laser beam output measurement means comprises an aperture member having an opening for allowing the annular pattern occurring in the periphery of the beam pattern of the laser beam to pass through and a power meter for measuring laser beam output of the laser beam passing through the opening. 
     The opening of the aperture member is placed at a position corresponding to the NA value of the optical fiber used. 
     The laser beam output measurement means comprises a first aperture member having a first opening for allowing the annular pattern occurring in the periphery of the beam pattern of the laser beam to pass through, a second aperture member having a second opening for allowing a circular pattern occurring in the center of the beam pattern to pass through, and a power meter for measuring laser beam output of the laser beam passing through the first or second opening. 
     The laser beam output measurement means has the first and second aperture members that can be replaced together with hold members. 
     The laser beam output measurement means comprises a first aperture member having a first opening for allowing the annular pattern occurring in the periphery of the beam pattern of the laser beam to pass through and a second opening for allowing a circular pattern occurring in the center of the beam pattern to pass through, the first and second openings being switched exclusively for use, and a power meter for measuring laser beam output of the laser beam passing through the first or second opening. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic diagram to show the configuration of a solid-state laser apparatus according to a first embodiment of the invention; 
     FIG. 2 is a schematic diagram to show the configuration of a measurement and adjustment jig according to the first embodiment of the invention; 
     FIG. 3 is a drawing to show the relationship between the adjustment position of a fiber incidence section with the measurement and adjustment jig shown in FIG.  2  and the indication value of a power meter; 
     FIG. 4 is a schematic diagram to show the configuration of another measurement and adjustment jig according to the first embodiment of the invention; 
     FIG. 5 is a drawing to show the relationship between the adjustment position of a fiber incidence section with the measurement and adjustment jig shown in FIG.  4  and the indication value of a power meter; 
     FIG. 6 is a schematic diagram to show the configuration of a measurement and adjustment jig according to a second embodiment of the invention; 
     FIG. 7 is a schematic diagram to show the configuration of a measurement and adjustment jig according to a third embodiment of the invention; 
     FIG. 8 is a drawing to show the structure of an aperture according to the embodiment of the invention; 
     FIG. 9 is a schematic representation to show a part of a laser beam path; 
     FIG. 10 is a schematic diagram to show the configuration of a solid-state laser apparatus in a related art; 
     FIG. 11 is a schematic diagram to show the configuration of a solid-state laser apparatus in another related art; 
     FIG. 12 is a schematic representation to show a strength distribution check method of a beam after fiber emission in the solid-state laser apparatuses in the related arts; and 
     FIGS. 13A and 13B are drawings to show beam patterns after fiber emission. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A laser oscillator according to a first embodiment of the invention will be discussed with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram to show the configuration of a solid-state laser apparatus according to the first embodiment of the invention and FIG. 2 is a schematic diagram to show the configuration of an adjustment jig. 
     The laser apparatus shown in FIG. 1 differs from the laser apparatus in the related art previously described with reference to FIG. 11 in the structure of emission end  23   o  of optical fiber  23 . This structure will be discussed. Other parts of the laser apparatus in FIG. 1 are similar to those of the laser apparatus in FIG.  11 . In FIG. 1, parts denoted by reference numerals  1  to  10 ,  14 ,  20  to  23 ,  23   i ,  23   o ,  30 , and  31  are identical with or similar to those denoted by the same reference numerals in FIG.  11  and therefore will not be discussed again. 
     In FIG. 1, numeral  44  denotes a measurement and adjustment jig as laser beam output measurement means. To make a position adjustment to a fiber incidence section  22  as fiber incidence adjustment means, namely, a movable condensing lens  20  and a fiber holder  21 , the measurement and adjustment jig  44  is connected to the fiber emission end  23   o . In the measurement and adjustment jig  44  shown in FIGS. 1 and 2, numeral  51  denotes an aperture, numeral  52  denotes a power meter, and numeral  53  denotes a display section. 
     FIG. 2 shows an aperture  51   a  for determining whether or not clad propagation occurs to adjust the fiber incidence section  22  if an SI-type optical fiber is used. The aperture  51   a  in FIG. 2 is placed at a laser beam measurement position and has an opening set at a position through which an outer ring-like laser beam of a double circle pattern occurring if clad propagation occurs passes at the aperture position, and output of a laser beam passing through the opening of the aperture  51   a  is measured with the power meter  52  and is displayed on the display section  53 . 
     The operation is as follows: In FIG. 2, a laser beam emitted from the output end  23   o  of the optical fiber  23  propagates while it is spread as shown. If clad propagation occurs because of a fiber adjustment failure, output of an outer ring-like laser beam of a double circle pattern is elevated, the percentage of the laser beam passing through the aperture  51   a  increases, and a detection value of the power meter  52  becomes large. As the adjustment becomes better, the percentage of the laser beam passing through the aperture  51   a  becomes relatively smaller and the detection value of the power meter  52  becomes smaller. 
     FIG. 3 shows the relationship between the adjustment position of the fiber incidence section  22  and the output value detected by the power meter  52 . As shown here, the fiber incidence section  22  is adjusted to the position where the detection value of the power meter  52  reaches the minimum, whereby the fiber incidence section  22  can be adjusted to a good condition. The power meter  52  is capable of converting laser beam output into an electric signal and therefore in the laser apparatus according to the embodiment, the adjustment state of the fiber incidence section  22  is monitored as an electric signal. 
     FIG. 4 shows a measurement and adjustment jig comprising an aperture different from that shown in FIG.  2 . Unlike the measurement and adjustment jig shown in FIG. 2, an aperture  51   b  has an opening placed at the center of a laser beam with the inner diameter of the opening set smaller than the laser beam diameter at the aperture position, and output of the laser beam passing through the opening is measured with a power meter  52 . If adjustment to the fiber incidence section  22  becomes a failure and clad propagation occurs, the percentage of the laser beam passing through the opening of the aperture  51   b  becomes small and the detection value of the power meter  52  becomes small. If adjustment to the fiber incidence section  22  is good, the percentage of the laser beam passing through the opening of the aperture  51   b  becomes relatively large and the detection value of the power meter  52  becomes large. 
     FIG. 5 shows the relationship between the adjustment position of the fiber incidence section and the output value detected by the power meter. As shown here, the fiber incidence section is adjusted so that the detection value of the power meter  52  reaches the maximum, whereby the fiber incidence section can be adjusted to a good condition. The power meter is capable of converting laser beam output into an electric signal; in the embodiment, the adjustment state of the fiber incidence section  22  is monitored as an electric signal. 
     However, in the adjustment method with the measurement and adjustment jig shown in FIG. 4, the output value of the power meter  52  changes only a little until clad propagation occurs; it is difficult to detect the optimum value. Therefore, the adjustment method is suitable to coarse adjustment for adjusting the fiber incidence section  22  to a position not causing clad propagation to occur as the stage preceding execution of the adjustment method with the measurement and adjustment jig shown in FIG.  2 . 
     As compared with the adjustment with the measurement and adjustment jig shown in FIG. 4, the measurement and adjustment jig shown in FIG. 2 makes it possible to facilitate adjustment to t he optimum value. However, if a large shift from the optimum adjustment position occurs as shown in FIG. 3, the output value of the power meter  52  becomes small, thus there is a possibility that adjustment may become impossible. Therefore, adjustments with the measurement and adjustment jigs shown in FIGS. 2 and 4 are made properly, whereby a more precise adjustment can be made in a short time. 
     The aperture  51   a  shown in FIG. 2 has the opening set at a position through which an outer ring-like laser beam of a double circle pattern occurring if clad propagation occurs passes at the aperture position; the outer ring of the double circle pattern appears at a position determined based on NA of a fiber. For example, to use a fiber with NA=0.2, the outer ring occurs at the position of divergence angle (½ angle) tan θ=0.2. Therefore, placing the aperture  51   a  at a position corresponding to the position of NA is the best and the aperture  51   a  is configured so. 
     Second Embodiment 
     FIG. 6 is a schematic diagram to show the configuration of an adjustment jig  44  according to a second embodiment of the invention. In the adjustment jig  44  shown in FIG. 6, apertures are fixed to detachable trays, so that apertures  51   a  and  51   b  described in the first embodiment are replaced together with trays  55   a  and  55   b , whereby the apertures  51   a  and  51   b  can be easily replaced. According to this structure, two steps of adjustments to a fiber incidence section  22 , namely, a coarse adjustment using the aperture  51   a  and an optimum value adjustment using the aperture  51   b  can be made easily. 
     Third Embodiment 
     In the second embodiment, the apertures  51  can be replaced. As shown in FIG. 7, one aperture  51   c  may have an opening  61  that can be switched to a laser beam center position a corresponding to the aperture  51   a  and a position b corresponding to the aperture  51   b  through which an outer ring-like laser beam of a double circle pattern occurring if clad propagation occurs passes. To change the opening position, for example, a screw  60  may be used to move the opening  61  of the aperture  51   c  to the positions a and b. 
     An example of the shape of the aperture  51   a  will be discussed with reference to FIG.  8 . The aperture  51   a  has a roughly annular opening  61   a  joined to the outer periphery by two bridges  62 . This roughly annular opening  61   a  makes it possible to detect an annular laser beam occurring when clad propagation occurs over almost full circumference, and a sensible adjustment can be made. In FIG. 8, the two bridges  62  are provided, but any number of bridges may be placed if a roughly annular opening is provided; a similar advantage can be provided. 
     The beam shutter  11  placed between the collimating lens  10  and the fiber incidence section  22  is provided with the reflecting mirror  31  for reflecting most of the laser beam  8  and allowing a part thereof to pass through. When the laser beam passes through the reflecting lens  31 , a parallel shift in the laser beam path occurs as shown in FIG.  9 . The parallel shift amount grows as the incidence angle of the laser beam  8  on the reflecting mirror  31  grows. If the parallel shift amount grows, a shift from the actual beam directly reaching the condensing lens  20  not via the reflecting mirror  31  also grows, and a shift from the adjustment position based on the laser beam passing through the reflecting mirror  31  also grows. In practical use, if the incidence angle of the laser beam  8  on the reflecting mirror  31  is 15 deg or less, an adjustment can be made substantially with no problem and it can be acknowledged that the parallel shift lies in a range with no problem in practical use. 
     From the above-described viewpoint, the incidence angle may be small, but if it is made too small, the necessary space for the whole laser apparatus including the damper becomes large, impairing the practical use. Therefore, it is practical to configure the laser apparatus so as to set the incidence angle of the laser beam on the reflecting mirror in the range of 8 deg to 15 deg. 
     As described throughout the specification, according to the invention, there can be provided a laser apparatus (good in maintenance) for making it possible to make a precise, easy, and objective adjustment to a fiber incidence section of a laser oscillator independent of the experience of each adjustment worker, if an SI-type optical fiber is used as an optical fiber.