The present invention relates in general to laser-machining and laser processing methods and apparatus. The invention relates in particular to laser-machining methods in which a laser beam for effecting the machining is modulated by an acousto-optic modulator (AOM).
One commonly used laser-machining (laser-processing) method involves modulating a continuous wave (CW) or pulsed laser-beam using an AOM. Radiation used for the machining is admitted to a workpiece via the AOM at one angle of incidence thereon for effecting the machining, and directed away from the workpiece via the AOM at another angle of incidence thereon during a pause in the machining.
Traditionally, the beam is admitted to the workpiece by the AOM by diffracting the beam at a first-order diffraction angle (direction) of the AOM, and directed away from the workpiece by transmitting the laser-beam through the AOM at a zero-order incidence angle (direction) of the AOM. More recently, however, it has been found advantageous to use the zero-order transmission of the AOM to admit the laser-beam to the workpiece, and the first-order diffraction to direct the laser-beam away from the workpiece.
This latter method is preferred for laser-beams having a relatively broad spectral content, such as beams from carbon monoxide (CO) lasers, as no dispersion of the laser-beam occurs on zero-order transmission. This avoids a need to provide means to correct dispersion before delivering the laser-beam to the workpiece for the machining or processing. A method in which machining is effected by a first order AOM-diffracted beam is described in U.S. Pre-grant Publication No. 20150083698, assigned to the assignee of the present invention, and the complete disclosure of which is hereby incorporated herein by reference. A method in which machining is effected by a zero-order AOM-transmitted beam is described in U.S. Pre-grant Publication No. 20170050266, assigned to the assignee of the present invention, and the complete disclosure of which is also hereby incorporated herein by reference.
Laser-beams used in AOM-modulated laser processing methods are typically plane-polarized, and diffraction by an AOM is polarization sensitive. It has been found in cases where diffraction by the AOM is used to direct a laser-beam away from a workpiece that there is some “leakage” of laser-radiation along the zero-order transmission direction. This has been found to be as much as about 2% of the incident laser-radiation. The leakage can be due to deviation from exact plane-polarization of the laser-beam or by slight misalignment of the polarization-plane with the AOM.
In many applications, such a leakage may be below a threshold value at which a workpiece could be altered or damaged in some way and can accordingly be ignored. In some sensitive applications, however, or in an application where the leakage may strike repeatedly on a workpiece at the same spot, the threshold could be exceeded with negative consequences. There is a need to reduce such leakage, preferably by about an order of magnitude.
In one aspect, a method in accordance with the present invention for delivering a beam of laser-radiation to a workpiece for processing the workpiece, comprises delivering the beam of laser radiation to an acousto-optic modulator (AOM). The beam is then transmitted through the AOM first and second times, in respectively first and second zero-order directions of the AOM, at respectively first and second separate locations thereon, before delivering the beam of radiation to the workpiece.
The method is applicable to modulating a CW beam for proving a train of laser pulses on the workpiece, or to modulating a beam of laser pulses for temporally shaping the laser pulses.
Turning now to the drawings wherein like features are designated be like reference numerals,
AOM 16 is activated by an acoustic wave delivered to the AOM in a direction indicated by arrow A when it is required to interrupt passage of the laser beam to a workpiece not shown. Activation of AOMs is well known in the art to which the present invention pertains. A detailed description of such activation is not necessary for understanding principles of the present invention, and, accordingly, is not presented herein.
Beam 14 is first incident on AOM 16 (at a location B thereon) at an angle θB which is the first order diffraction angle of the AOM when the AOM is activated. When AOM 16 is not activated, beam 14 is transmitted through the AOM along a zero-order direction, i.e., the beam is not diffracted by the AOM, and leaves the AOM at the incidence angle θB. Preferably beam 14 is polarized in a direction indicated by double arrow P, parallel to the plane of incidence of beam 14 on the AOM, for minimizing reflection losses on transmission. The first-transmitted beam 14 is directed by a reflector 18 arranged such that beam 14 is again incident on AOM 16 (at a location C thereon) at angle θB and is transmitted a second time through the AOM along a zero-order direction. Twice-transmitted beam 14 is then directed by a reflector 26 past the AOM toward the workpiece. Those familiar with the art will recognize that beam 14 may be incident on beam-directing, beam-shaping or focusing optics before actually being incident on the workpiece.
When it is desired to interrupt passage of beam 14 to the workpiece, AOM 16 is activated by the acoustic wave and the AOM becomes essentially a diffraction grating. At the first incidence of beam 14 on the AOM, a substantial portion of the beam is diffracted along a first diffraction order direction of the AOM as indicated by dashed line 18 is captured by a beam-trap (beam-dump) 20. As the diffraction process is less than 100% efficient, there will be some “leakage” of laser-radiation along the zero-order transmission direction. This can be as much as about 2% of the incident laser-radiation as discussed above.
The leaked radiation proceeds along the beam-14 path and, with AOM still active, the leaked radiation is diffracted again by the AOM in a first diffraction order direction of the AOM as indicated by dashed line 22. The leaked radiation is captured by another beam-dump 22. Again, because of a less than 100% diffraction efficiency, the will be some leakage of leaked radiation long the transmission direction, but this will have less than 0.2% of radiation power first incident on the AOM.
Those skilled in the art will recognize from the description presented above that the present invention could be used with any wavelength of laser-radiation for which AOMs are available. Those skilled in art the will also recognize that the invention may be used with lasers delivering either continuous wave (CW) or pulsed radiation. Further, while in the embodiments of the present invention described above, first and second zero-order passes through the AOM take place in opposite (forward and reverse) directions, a suitable arrangement of reflector could be used to cause the first and second zero-order passes to occur in the same direction.
In summary, the present invention is described in terms of preferred embodiments. The invention, however, is not limited to the embodiments described and depicted herein. Rather, the invention is limited only by the claims appended hereto.
This application claims the priority of U.S. Provisional Application No. 62/367,581, filed Jul. 27, 2016, assigned to the assignee of the present invention, and the complete disclosure of which is hereby incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
3935419 | Lambert et al. | Jan 1976 | A |
4380694 | Dyson | Apr 1983 | A |
5051558 | Sukhman | Sep 1991 | A |
6052216 | Rolfe et al. | Apr 2000 | A |
6563845 | Kumkar | May 2003 | B2 |
6576869 | Gower et al. | Jun 2003 | B1 |
6618070 | Fischer et al. | Sep 2003 | B2 |
6697408 | Kennedy et al. | Feb 2004 | B2 |
6784399 | Dunsky et al. | Aug 2004 | B2 |
6826204 | Kennedy et al. | Nov 2004 | B2 |
7019891 | Johnson | Mar 2006 | B2 |
7039079 | Seguin et al. | May 2006 | B2 |
7058093 | Kennedy et al. | Jun 2006 | B2 |
7113529 | Seguin et al. | Sep 2006 | B2 |
7375819 | Courville et al. | May 2008 | B2 |
7453918 | Laughman et al. | Nov 2008 | B2 |
7508850 | Newman et al. | Mar 2009 | B2 |
7675673 | Mueller | Mar 2010 | B2 |
7756186 | Chenausky et al. | Jul 2010 | B2 |
7817685 | Osako et al. | Oct 2010 | B2 |
7903699 | Seguin et al. | Mar 2011 | B2 |
8050306 | Seguin et al. | Nov 2011 | B2 |
9012851 | Scherer et al. | Apr 2015 | B2 |
9414498 | Hua et al. | Aug 2016 | B2 |
20020048075 | Kumkar | Apr 2002 | A1 |
20040222197 | Hiramatsu | Nov 2004 | A1 |
20070215575 | Gu et al. | Sep 2007 | A1 |
20070280310 | Muenter | Dec 2007 | A1 |
20100193481 | Osako | Aug 2010 | A1 |
20100301023 | Unrath | Dec 2010 | A1 |
20110259860 | Bass et al. | Oct 2011 | A1 |
20120138586 | Webster et al. | Jun 2012 | A1 |
20130154159 | Noel et al. | Jun 2013 | A1 |
20140185119 | Staver | Jul 2014 | A1 |
20140231085 | Zediker et al. | Aug 2014 | A1 |
20140352358 | Washko, Jr. et al. | Dec 2014 | A1 |
20150083698 | Hua et al. | Mar 2015 | A1 |
20170050266 | Mueller et al. | Feb 2017 | A1 |
Number | Date | Country |
---|---|---|
2338201 | Dec 1999 | GB |
200052520 | Sep 2000 | WO |
2005121889 | Dec 2005 | WO |
Entry |
---|
Chang et al., “Design of a Double-Pass Shear Mode Acousto-Optic Modulator”, Review of Scientific Instruments, vol. 79, No. 033104, 2008, pp. 033104-1-033104-5. |
Donley et al., “Double-Pass Acousto-Optic Modulator System”, Review of Scientific Instruments, vol. 76, No. 063112, 2005, pp. 063112-1-063112-6. |
Decision to Grant received for European Patent Application No. 14762188.2, dated Nov. 6, 2017, 2 pages. |
Intention to Grant received for European Patent Application No. 14762188.2, dated May 9, 2017, 8 pages. |
Intention to Grant received for European Patent Application No. 14762188.2, dated Oct. 24, 2017, 6 pages. |
International Search Report and Written Opinion received for PCT Application No. PCT/US2016/043627, dated Oct. 20, 2016, 16 pages. |
International Search Report and Written Opinion Received for PCT Application No. PCT/US2017/042084, dated Oct. 25, 2017, 10 pages. |
International Preliminary Report on Patentability received for PCT Patent Application No. PCT/US2014/053129, dated Mar. 31, 2016, 6 pages. |
International Search Report and Written Opinion received for PCT Patent Application No. PCT/US2014/053129 dated Mar. 19, 2015, 10 pages. |
Non-Final Office Action received for U.S. Appl. No. 14/830,050, dated Jul. 7, 2017, 9 pages. |
Notice of Allowance received for U.S. Appl. No. 14/033,246, dated Apr. 18, 2016, 7 pages. |
Notice of Allowance received for U.S. Appl. No. 14/830,050, dated Nov. 24, 2017, 7 pages. |
Non-Final Office Action received for U.S. Appl. No. 14/033,246, dated Sep. 17, 2015, 9 pages. |
Number | Date | Country | |
---|---|---|---|
20180031948 A1 | Feb 2018 | US |
Number | Date | Country | |
---|---|---|---|
62367581 | Jul 2016 | US |