- Email: [email protected]
Investigations on the laser cutting of LiNbO3
Journal Pre-proof Investigations on the laser cutting of LiNbO3 Wenyan Gao, Mingwei Lei, Benhai Li, Guang Li, Kai Li, Qiaoling Feng, Junlong Wang
PII:
S0030-4026(19)31406-8
DOI:
https://doi.org/10.1016/j.ijleo.2019.163508
Reference:
IJLEO 163508
To appear in:
Optik
Received Date:
10 June 2019
Revised Date:
23 September 2019
Accepted Date:
1 October 2019
Please cite this article as: Gao W, Lei M, Li B, Li G, Li K, Feng Q, Wang J, Investigations on the laser cutting of LiNbO3 , Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163508 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Investigations on the laser cutting of LiNbO3 Wenyan Gao, Mingwei Lei, Benhai Li, Guang Li, Kai Li, Qiaoling Feng, Junlong Wang* Beijing Institute of Aerospace Control Devices, Beijing 100094, China
*
Corresponding Author: Junlong Wang
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Email address: [email protected]
address: Building 3, Room 416, No.1, Feng Ying Dong Road, Haidian District, Beijing, 100094, China
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Tel.: +86-010-88104337
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Fax: +86-010-88104338
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Abstract
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In this work, we study the precision cutting technology of LiNbO3 which is belonged to brittle materials and difficult to machine. By using a femtosecond laser,
ur
we explore the influence of wavelengths on the cutting quality, the surface and cross-section morphology of the specimens were examined by optical microscopy and
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white light interferometer, the size of the slit width and cutting chipping, roughness have been measured. Subsequently, two optimization processing solutions have been designed to cut LiNbO3 with high quality and high reproducibility, the thermal effect and chipping have been reduced obviously. At last, the complete cut through the plate of LiNbO3 has been achieved.
Keywords Laser cutting; Femtosecond laser; Thermal influence; LiNbO3
1. Introduction High quality cutting of brittle transparent materials are essential for the manufacture of products including semiconductor, integrated electronics and displays,
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which has attracted much attention [1-3]. Traditionally, wheel cutter or diamond
tool-based scoring and break methods usually create poor near surface finish with microcracks leading to reduced product life. Post processing such as grinding and
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polishing are required to achieve smooth surfaces.
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Advanced cutting methods such as water jet cutting, hot air jet cutting, and laser cutting have been developed and used for decades [4-7]. Water jet cutting creates no
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heat affected zones due to the flowing water, but the use of abrasive materials, water
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and water jet nozzles increase the production cost. Smoother cut could be obtained by using the hot air jet-based cutting, but the limitation of this technique is that a scratch
ur
at the edge of the glass is required to initiate the crack propagation. Laser based cutting can be applied to generate a groove at a depth of one third to
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one half of the glass sheet thickness, then a braking force is applied to break the glass along the groove. Due to the non-contact and non-consumable features, laser cutting has been extensively studied [8-12]. Especially, with the developing of the picosecond and femtosecond pulsed lasers, the ultrafast laser cutting has been used for precision cutting of brittle transparent materials as it has high peak power and low heat affected
zone. L.Rapp et al. [13] studied the effects of the polarization, crystalline axes and scanning direction on the cleaving of crystalline materials with femtosecond lasers. When the scanning is operated along one of the directions of the crystalline axes with a polarization orthogonal to it, a single crack is formed along the scanning direction. The control on the crack formation enabled processing a fracture planed, used for
ro of
sapphire separation. It opens the route for high speed processing and separation of sapphire substrates. M. K. Bhuyan et al. [14] demonstrated high-speed cutting of
homogeneous and inhomogeneous glasses such as tempered glasses along straight
-p
trajectory using single-pass, and single-shot configuration. They identified and solved
re
some general issues of micromachining of transparent materials irrespective of their homogeneity using Bessel beams. K. Mishchik et al. [15] investigated the bulk
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processing of soda-lime and other silicate multicomponent glasses by means of
na
femtosecond laser pulses with spatial non-diffracting Bessel beam profiles, they found that the focusing geometry and the use of bursts of femtosecond-pulse play a key role
ur
in depositing the laser energy in the glass with controllable efficiency. Sanguk Park et al. [16] cut chemically strengthened glass using femtosecond laser pulses and induce
Jo
sub-surface cracks below the glass surface by nonlinear multiphoton absorption and subsequent creation of tensile residual stresses upon re-solidification. They completed line cutting and the cutting plane maintains a mirror-like surface quality without significant heat-affected zones or micro-cracks. Our current work is focused on the precision cutting technology of LiNbO3 which
has high resistance to thermal and mechanical shocks due to the inhomogeneous material properties. The influence of wavelengths on the cutting quality has been explored, the surface morphology of the specimens were examined by optical microscopy, the size of the slit width and cutting chipping have been measured. Subsequently, two optimization processing solutions have been designed to cut LiNbO3 with high quality and high reproducibility, the thermal effect and chipping
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have been reduced obviously. At last, the complete cut through the plate of LiNbO3 has been achieved. These results represent a significant advancement in the field of precision cutting of technologically important transparent materials.
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2. Experimental details
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The cutting substrate material in this research is LiNbO3 with dimensions of 30mm × 10mm × 1mm, the surface of the plate was rinsed with alcohol to get rid of the
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impurity. The sample’s relative position was varied using an X-Y-Z motorized
na
translation stage assembly associated with EZCAD software. The experiments were performed using PHAROS femtosecond laser systems (Light
ur
Conversion) emitting Gaussian laser which generates pulses of τ = 290 fs and a raw beam diameter 4.6mm of was attenuated with neutral density filters and a polarization
Jo
attenuator. Under the scanning Galvanometer (Scanlab), laser beam passed through a F-theta lens with focal length 80mm, which focus the laser beam to be a spot with diameter 20μm at 1/e2 of the maximum beam intensity. The max average power is 20W when the laser wavelength is 1030nm. The experiment is conducted under normal atmospheric conditions, the process
parameters are determined after preliminary experiments, which are optimized for cutting and split with better quality and visual appearance. The parameters are briefly summarized in Table 1, the scanning speed is 500mm/s which is considering energy efficiency, processing efficiency and cutting performance. After the experiments, the surface and cross-section morphology of the specimens were examined by OLYMPUS optical microscopy, the size of the slit width and
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cutting chipping has been measured. And the roughness of cutting cross-section is measured by ZYGO white light interferometer. 3. Results and discussion
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3.1 Morphology of the cutting samples
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Fig.1 Optical surface micrographs of No.1 sample
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Fig.2 Optical cross-section micrographs of No.1 sample Femtosecond laser cutting is described as cold processing, but in the
-p
high-frequency ablation cutting, the thermal effect still exists and affects the cutting
quality seriously. Fig.1 shows the cutting morphology of the No. 1 sample. During the
re
laser cutting of LiNbO3 at a wavelength of 1030 nm, a large number of white smoke
lP
and debris were generated at the process position. As seen from the figure, the width of the cutting slit is uneven. Fig.2 is the cross-section profile diagram of No.1 sample
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after the split along the slit, it can be seen that, due to the large heat effect, there is no obvious boundary between the cut area and the uncut area, and the material separation
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is mainly based on the thermal stress expansion.
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Fig.3 Optical surface micrographs of No.2 sample
Fig.4 Optical cross-section micrographs of No.2 sample
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Subsequently, cutting was performed using a 515 nm wavelength laser to obtain No. 2 sample. For laser processing materials, Short wavelength has greater absorption and
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less thermal effects than long wavelength. Therefore, as can be seen in Fig.3, the consistency of the slit width is improved, the slit is straightened. In Fig.4, it can be clearly distinguished that the left part is the cutting area, and the right side is the splitting area, and the cutting ratio is 220:1018. Meanwhile, the wavelength of laser is reduced to 343nm further, the cutting quality of the front and the cross section have
been significantly improved. The cutting ratio is 495:1012, the width of the cutting
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slit is around 123μm, and the chipping is less than 40μm.
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Fig.5 Optical surface micrographs of No.3 sample
Fig.6 Optical cross-section micrographs of No.3 sample
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3.3 Improvement of the cutting quality By reducing the laser wavelength, the energy utilization rate is increased and the
thermal influence is reduced during the Femtosecond laser cutting. However, the cutting quality is not meet the final requirements of LiNbO3 cutting. In order to further improve the cutting quality, two optimization methods were designed. Fig.7
exhibits the schematic view of the first device, in which the plate of LiNbO3 is placed on the carbon steel columns and fixed attracted by magnets. Considering the high reflection and heat conduction characteristics of the aluminum alloy material, the plate is supported by the aluminum alloy cone columns, which is applied to reduce the negative influence of the support column on the cutting quality. Besides, the N2 gas
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has been used for cooling the processing position and blowing off the residue.
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Fig.7 Schematic diagram of optimized experimental device
Fig.8 Physical diagram of optimized experimental device
Fig.8 is the physical diagram of experimental device. Using this device, the No.4 sample was obtained, and the process parameters are set corresponding to the ones of No.3 sample. As shown in Fig.9, the cutting quality of LiNbO3 was obviously
improved, there is no residue, the width of the cutting slit is around 105μm, and the chipping is less than 20μm. Fig.10 shows the cross-section shape of No.4 sample with a cutting ratio of 646:1016, it makes the separation process after laser cutting easy. The reason for the results above is that: by the using of magnet, the plate has been fixed and avoids being blown away by N2 gas and causing the cutting deviation; by
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helpful to further cutting and quality improvement.
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blowing N2 gas, it takes away the heat and debris during the cutting process, which is
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Fig.9 Optical surface micrographs of No.4 sample
Fig.10 Optical cross-section micrographs of No.4 sample
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Fig.11 Schematic diagram of optimized experimental device
Fig.12 Physical diagram of optimized experimental device
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In addition, a water-cooling solution is also designed, as seen from Fig.11. There is flowing water filled under the upper surface of the plate, the water flows to remove
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the heat and cut debris during the laser processing. Using the experimental device as
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shown in Fig.12, the No.5 sample was obtained. Fig.13 illustrates the surface micrographs of this sample, the width of the cutting slit is about 95μm, and the chipping is less than 5μm. Fig.14 shows the cross-section shape of No.5 sample, the cutting ratio is 778:1002, the force applied to separate the plate in No.5 sample is the smallest in all the samples. The reason for the phenomena above is that, the flowing water is conducive to uniform cooling, so that the heat affected zone and the cutting
residue are minimized during the cutting process, it is beneficial to improve the cutting quality obviously. At the same time, it must be noted that the water surface cannot exceed the plate surface, otherwise the laser beam energy will be attenuated
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sharply and the cutting depth will be reduced significantly.
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Fig.13 Optical surface micrographs of No.5 sample
Fig.14 Optical cross-section micrographs of No.5 sample
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Fig.15 Comparison of complete cutting morphology under two methods
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At last, by applying the optimization methods, controlling focus position and
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increasing the number of cutting passes from 150 to 300, we have achieved the complete cut through the plate of LiNbO3. It is worth noting that both methods are
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helpful to improve the complete cutting quality. The samples are dangling, which prevents the influence of thermal accumulation from the substrate on the morphology
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and quality of the bottom of the plate. Fig.15 is the morphology comparison of
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LiNbO3 cutting under two methods. Under the condition of gas cooling, the slit width is much larger (128μm), at the same time, the carbonization phenomenon exists in the cross section obviously; while in the water-cooling solution, the slit width is 100μm, the cutting profile is relatively smooth with no carbonization, and the roughness of which is about 2μm, as shown in Fig.16. Therefore, the cutting quality in the water-cooling solution is much more advantageous and meets the product
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requirements of LiNbO3.
Fig.16 Roughness measurement of the cutting cross-section in the water-cooling solution
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4. Conclusions
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Based on the above-mentioned discussion, it is found that, optimizing the process parameters and reducing the wavelength of the laser are helpful to improve the cutting
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quality of LiNbO3, but for more precise cutting requirements, two effective solutions
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have been achieved. One is based on air cooling, the width of the cutting slit is around 105μm, the chipping is less than 20μm, and the cutting ratio is 646:1016; another is
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based on water cooling, the width of the cutting slit is around 95μm, the chipping is less than 5μm, and the cutting ratio is 778:1002. Both methods have reduced thermal
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effect during femtosecond laser cutting and effectively improved the cutting quality. At last, by controlling focus position and increasing the number of cutting passes, we have achieved the complete cut through the plate of LiNbO3. The cutting quality in the water-cooling method is much more advantageous and meets the product requirements of LiNbO3.
Acknowledgments This research has been supported by the National Key R&D Program of China (2017YFB1104604, 2016YFB1102503)
References
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[1]A. R. Collins, G. M. O’Connor, Mechanically inspired laser scribing of thin flexible glass, Opt. Lett., 40 (2015) 4811-4814.
[2]Ueda T., Yamada K., Oiso K., Hosokawa A., Thermal Stress Cleaving of Brittle Materials by Laser Beam, CIRP Annals, 51 (2002) 149-152.
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[3]Lumley R., Controlled separation of brittle materials using a laser, Am. Ceram. Soc. Bull, 48 (1969) 850-854.
lP
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[4]Prakash E., Sadashivappa K., Joseph V., Singaperumal M., Nonconventional cutting of plate glass using hot air jet: experimental studies, Mechatronics, 11 (2001) 595-615. [5]Dudutis J., GeČys P., RaČiukaitis G., Non-ideal axicon-generated Bessel beam application for intra-volume glass modification, Optics Express, 24 (2016) 28433.
ur
na
[6]Ahmed F., Lee M., Sekita H., Sumiyoshi T., Kamata M., Display glasscutting by femtosecond laser induced single shot periodic void array, Applied Physics A, 93 (2008) 189-192.
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[7]Strigin M., Chudinov A., Cutting of glass by picosecond laser radiation, Optics Communications, 106 (1994) 223-226. [8]Varel H., Ashkenasi D., Rosenfeld A., Wähmer M., Campbell E., Micromachining of quartz with ultrashort laser pulses, Applied Physics A: Materials Science & Processing, 65 (1997) 367-373. [9]Wang Y., Yan S., Friberg A., Kuebel D., Visser T., Electromagnetic diffraction theory of refractive axicon lenses, Journal of the Optical Society of America A, 34 (2017) 1201. [10]Yuan F., Johnson J., Allred D., Todd R., Waterjet cutting of cross-linked glass,
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 13 (1995) 136-139. [11]Zhou M., Ngoi B., Yusoff M., Wang X., Tool wear and surface finish in diamond cutting of optical glass, Journal of Materials Processing Technology, 174 (2006) 29-33. [12]M. K. Bhuyan, O. Jedrkiewicz, V. Sabonis, M. Mikutis, S. Recchia, A. Aprea, M. Bollani, and P. Di Trapani, High-speed laser-assisted cutting of strong transparent materials using picosecond Bessel beams, Appl. Phys. A, 120 (2015) 443-446.
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[13]L. Rapp, R. Meyer, L. Furfaro, C. Billet, R. Giust, F.Courvoisier, High speed cleaving of crystals with ultrafast Bessel beams, Optics Express, 8 (2017) 9312-9317. [14]M. K. Bhuyan, O. Jedrkiewicz, V. Sabonis, M. Mikutis, S. Recchia, A. Aprea, M. Bollani, P. Di Trapani, High-speed laser-assisted cutting of strong transparent materials using picosecond Bessel beams, Appl. Phys. A, 120 (2015) 443-446.
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-p
[15]K. Mishchik, R. Beuton, O. Dematteo Caulier, S.Skupin, B. Chimier, G. Duchateau, B. Chassagne, R.Kling, C. HÖnninger, E. Mottay, J. Lopez, Improved laser glass cutting by spatio-temporal control of energy deposition using bursts of femtosecond pulses, Optics Express, 25 (2017) 33271-33282.
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ur
na
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[16]Sanguk Park, Yunseok Kim, Joonho You, Seung-Woo Kim, Damage-free cutting of chemically strengthened glass by creation of sub-surface cracks using femtosecond laser pulses, CIRP Annals - Manufacturing Technology 66 (2017) 535-538.
Figure captions:
Fig.1 Optical surface micrographs of No.1 sample Fig.2 Optical cross-section micrographs of No.1 sample Fig.3 Optical surface micrographs of No.2 sample Fig.4 Optical cross-section micrographs of No.2 sample
Fig.6 Optical cross-section micrographs of No.3 sample
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Fig.5 Optical surface micrographs of No.3 sample
Fig.7 Schematic diagram of optimized experimental device
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Fig.8 Physical diagram of optimized experimental device Fig.9 Optical surface micrographs of No.4 sample
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Fig.10 Optical cross-section micrographs of No.4 sample
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Fig.11 Schematic diagram of optimized experimental device Fig.12 Physical diagram of optimized experimental device
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Fig.13 Optical surface micrographs of No.5 sample Fig.14 Optical cross-section micrographs of No.5 sample
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Fig.15 Comparison of complete cutting morphology under two methods
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Fig.16 Roughness measurement of the cutting cross-section in the water-cooling solution
Table captions:
1
2
3
4
5
Laser power (W)
15
7.8
3.8
3.8
3.8
Wavelength (nm)
1030
515
343
343
343
Repetition frequency (kHz)
50
50
50
50
50
Scanning speed (mm/s)
500
500
500
500
500
Width of cutting track (μm)
80
80
80
80
80
20
20
20
20
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No.
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Table 1 Experimental parameters
Spacing of each laser scanning
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path in cutting track (μm) 150
Method
Normal
150
150
150
150
Normal
Normal
Optimization
Optimization
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Cutting times
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20
PII:
S0030-4026(19)31406-8
DOI:
https://doi.org/10.1016/j.ijleo.2019.163508
Reference:
IJLEO 163508
To appear in:
Optik
Received Date:
10 June 2019
Revised Date:
23 September 2019
Accepted Date:
1 October 2019
Please cite this article as: Gao W, Lei M, Li B, Li G, Li K, Feng Q, Wang J, Investigations on the laser cutting of LiNbO3 , Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163508 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Investigations on the laser cutting of LiNbO3 Wenyan Gao, Mingwei Lei, Benhai Li, Guang Li, Kai Li, Qiaoling Feng, Junlong Wang* Beijing Institute of Aerospace Control Devices, Beijing 100094, China
*
Corresponding Author: Junlong Wang
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Email address: [email protected]
address: Building 3, Room 416, No.1, Feng Ying Dong Road, Haidian District, Beijing, 100094, China
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Tel.: +86-010-88104337
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Fax: +86-010-88104338
lP
Abstract
na
In this work, we study the precision cutting technology of LiNbO3 which is belonged to brittle materials and difficult to machine. By using a femtosecond laser,
ur
we explore the influence of wavelengths on the cutting quality, the surface and cross-section morphology of the specimens were examined by optical microscopy and
Jo
white light interferometer, the size of the slit width and cutting chipping, roughness have been measured. Subsequently, two optimization processing solutions have been designed to cut LiNbO3 with high quality and high reproducibility, the thermal effect and chipping have been reduced obviously. At last, the complete cut through the plate of LiNbO3 has been achieved.
Keywords Laser cutting; Femtosecond laser; Thermal influence; LiNbO3
1. Introduction High quality cutting of brittle transparent materials are essential for the manufacture of products including semiconductor, integrated electronics and displays,
ro of
which has attracted much attention [1-3]. Traditionally, wheel cutter or diamond
tool-based scoring and break methods usually create poor near surface finish with microcracks leading to reduced product life. Post processing such as grinding and
-p
polishing are required to achieve smooth surfaces.
re
Advanced cutting methods such as water jet cutting, hot air jet cutting, and laser cutting have been developed and used for decades [4-7]. Water jet cutting creates no
lP
heat affected zones due to the flowing water, but the use of abrasive materials, water
na
and water jet nozzles increase the production cost. Smoother cut could be obtained by using the hot air jet-based cutting, but the limitation of this technique is that a scratch
ur
at the edge of the glass is required to initiate the crack propagation. Laser based cutting can be applied to generate a groove at a depth of one third to
Jo
one half of the glass sheet thickness, then a braking force is applied to break the glass along the groove. Due to the non-contact and non-consumable features, laser cutting has been extensively studied [8-12]. Especially, with the developing of the picosecond and femtosecond pulsed lasers, the ultrafast laser cutting has been used for precision cutting of brittle transparent materials as it has high peak power and low heat affected
zone. L.Rapp et al. [13] studied the effects of the polarization, crystalline axes and scanning direction on the cleaving of crystalline materials with femtosecond lasers. When the scanning is operated along one of the directions of the crystalline axes with a polarization orthogonal to it, a single crack is formed along the scanning direction. The control on the crack formation enabled processing a fracture planed, used for
ro of
sapphire separation. It opens the route for high speed processing and separation of sapphire substrates. M. K. Bhuyan et al. [14] demonstrated high-speed cutting of
homogeneous and inhomogeneous glasses such as tempered glasses along straight
-p
trajectory using single-pass, and single-shot configuration. They identified and solved
re
some general issues of micromachining of transparent materials irrespective of their homogeneity using Bessel beams. K. Mishchik et al. [15] investigated the bulk
lP
processing of soda-lime and other silicate multicomponent glasses by means of
na
femtosecond laser pulses with spatial non-diffracting Bessel beam profiles, they found that the focusing geometry and the use of bursts of femtosecond-pulse play a key role
ur
in depositing the laser energy in the glass with controllable efficiency. Sanguk Park et al. [16] cut chemically strengthened glass using femtosecond laser pulses and induce
Jo
sub-surface cracks below the glass surface by nonlinear multiphoton absorption and subsequent creation of tensile residual stresses upon re-solidification. They completed line cutting and the cutting plane maintains a mirror-like surface quality without significant heat-affected zones or micro-cracks. Our current work is focused on the precision cutting technology of LiNbO3 which
has high resistance to thermal and mechanical shocks due to the inhomogeneous material properties. The influence of wavelengths on the cutting quality has been explored, the surface morphology of the specimens were examined by optical microscopy, the size of the slit width and cutting chipping have been measured. Subsequently, two optimization processing solutions have been designed to cut LiNbO3 with high quality and high reproducibility, the thermal effect and chipping
ro of
have been reduced obviously. At last, the complete cut through the plate of LiNbO3 has been achieved. These results represent a significant advancement in the field of precision cutting of technologically important transparent materials.
-p
2. Experimental details
re
The cutting substrate material in this research is LiNbO3 with dimensions of 30mm × 10mm × 1mm, the surface of the plate was rinsed with alcohol to get rid of the
lP
impurity. The sample’s relative position was varied using an X-Y-Z motorized
na
translation stage assembly associated with EZCAD software. The experiments were performed using PHAROS femtosecond laser systems (Light
ur
Conversion) emitting Gaussian laser which generates pulses of τ = 290 fs and a raw beam diameter 4.6mm of was attenuated with neutral density filters and a polarization
Jo
attenuator. Under the scanning Galvanometer (Scanlab), laser beam passed through a F-theta lens with focal length 80mm, which focus the laser beam to be a spot with diameter 20μm at 1/e2 of the maximum beam intensity. The max average power is 20W when the laser wavelength is 1030nm. The experiment is conducted under normal atmospheric conditions, the process
parameters are determined after preliminary experiments, which are optimized for cutting and split with better quality and visual appearance. The parameters are briefly summarized in Table 1, the scanning speed is 500mm/s which is considering energy efficiency, processing efficiency and cutting performance. After the experiments, the surface and cross-section morphology of the specimens were examined by OLYMPUS optical microscopy, the size of the slit width and
ro of
cutting chipping has been measured. And the roughness of cutting cross-section is measured by ZYGO white light interferometer. 3. Results and discussion
ur
na
lP
re
-p
3.1 Morphology of the cutting samples
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Fig.1 Optical surface micrographs of No.1 sample
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Fig.2 Optical cross-section micrographs of No.1 sample Femtosecond laser cutting is described as cold processing, but in the
-p
high-frequency ablation cutting, the thermal effect still exists and affects the cutting
quality seriously. Fig.1 shows the cutting morphology of the No. 1 sample. During the
re
laser cutting of LiNbO3 at a wavelength of 1030 nm, a large number of white smoke
lP
and debris were generated at the process position. As seen from the figure, the width of the cutting slit is uneven. Fig.2 is the cross-section profile diagram of No.1 sample
na
after the split along the slit, it can be seen that, due to the large heat effect, there is no obvious boundary between the cut area and the uncut area, and the material separation
Jo
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is mainly based on the thermal stress expansion.
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na
lP
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Fig.3 Optical surface micrographs of No.2 sample
Fig.4 Optical cross-section micrographs of No.2 sample
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Subsequently, cutting was performed using a 515 nm wavelength laser to obtain No. 2 sample. For laser processing materials, Short wavelength has greater absorption and
Jo
less thermal effects than long wavelength. Therefore, as can be seen in Fig.3, the consistency of the slit width is improved, the slit is straightened. In Fig.4, it can be clearly distinguished that the left part is the cutting area, and the right side is the splitting area, and the cutting ratio is 220:1018. Meanwhile, the wavelength of laser is reduced to 343nm further, the cutting quality of the front and the cross section have
been significantly improved. The cutting ratio is 495:1012, the width of the cutting
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slit is around 123μm, and the chipping is less than 40μm.
ur
na
lP
re
-p
Fig.5 Optical surface micrographs of No.3 sample
Fig.6 Optical cross-section micrographs of No.3 sample
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3.3 Improvement of the cutting quality By reducing the laser wavelength, the energy utilization rate is increased and the
thermal influence is reduced during the Femtosecond laser cutting. However, the cutting quality is not meet the final requirements of LiNbO3 cutting. In order to further improve the cutting quality, two optimization methods were designed. Fig.7
exhibits the schematic view of the first device, in which the plate of LiNbO3 is placed on the carbon steel columns and fixed attracted by magnets. Considering the high reflection and heat conduction characteristics of the aluminum alloy material, the plate is supported by the aluminum alloy cone columns, which is applied to reduce the negative influence of the support column on the cutting quality. Besides, the N2 gas
re
-p
ro of
has been used for cooling the processing position and blowing off the residue.
Jo
ur
na
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Fig.7 Schematic diagram of optimized experimental device
Fig.8 Physical diagram of optimized experimental device
Fig.8 is the physical diagram of experimental device. Using this device, the No.4 sample was obtained, and the process parameters are set corresponding to the ones of No.3 sample. As shown in Fig.9, the cutting quality of LiNbO3 was obviously
improved, there is no residue, the width of the cutting slit is around 105μm, and the chipping is less than 20μm. Fig.10 shows the cross-section shape of No.4 sample with a cutting ratio of 646:1016, it makes the separation process after laser cutting easy. The reason for the results above is that: by the using of magnet, the plate has been fixed and avoids being blown away by N2 gas and causing the cutting deviation; by
lP
re
-p
helpful to further cutting and quality improvement.
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blowing N2 gas, it takes away the heat and debris during the cutting process, which is
Jo
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Fig.9 Optical surface micrographs of No.4 sample
Fig.10 Optical cross-section micrographs of No.4 sample
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Fig.11 Schematic diagram of optimized experimental device
Fig.12 Physical diagram of optimized experimental device
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In addition, a water-cooling solution is also designed, as seen from Fig.11. There is flowing water filled under the upper surface of the plate, the water flows to remove
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the heat and cut debris during the laser processing. Using the experimental device as
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shown in Fig.12, the No.5 sample was obtained. Fig.13 illustrates the surface micrographs of this sample, the width of the cutting slit is about 95μm, and the chipping is less than 5μm. Fig.14 shows the cross-section shape of No.5 sample, the cutting ratio is 778:1002, the force applied to separate the plate in No.5 sample is the smallest in all the samples. The reason for the phenomena above is that, the flowing water is conducive to uniform cooling, so that the heat affected zone and the cutting
residue are minimized during the cutting process, it is beneficial to improve the cutting quality obviously. At the same time, it must be noted that the water surface cannot exceed the plate surface, otherwise the laser beam energy will be attenuated
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sharply and the cutting depth will be reduced significantly.
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Fig.13 Optical surface micrographs of No.5 sample
Fig.14 Optical cross-section micrographs of No.5 sample
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Fig.15 Comparison of complete cutting morphology under two methods
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At last, by applying the optimization methods, controlling focus position and
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increasing the number of cutting passes from 150 to 300, we have achieved the complete cut through the plate of LiNbO3. It is worth noting that both methods are
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helpful to improve the complete cutting quality. The samples are dangling, which prevents the influence of thermal accumulation from the substrate on the morphology
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and quality of the bottom of the plate. Fig.15 is the morphology comparison of
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LiNbO3 cutting under two methods. Under the condition of gas cooling, the slit width is much larger (128μm), at the same time, the carbonization phenomenon exists in the cross section obviously; while in the water-cooling solution, the slit width is 100μm, the cutting profile is relatively smooth with no carbonization, and the roughness of which is about 2μm, as shown in Fig.16. Therefore, the cutting quality in the water-cooling solution is much more advantageous and meets the product
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requirements of LiNbO3.
Fig.16 Roughness measurement of the cutting cross-section in the water-cooling solution
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4. Conclusions
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Based on the above-mentioned discussion, it is found that, optimizing the process parameters and reducing the wavelength of the laser are helpful to improve the cutting
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quality of LiNbO3, but for more precise cutting requirements, two effective solutions
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have been achieved. One is based on air cooling, the width of the cutting slit is around 105μm, the chipping is less than 20μm, and the cutting ratio is 646:1016; another is
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based on water cooling, the width of the cutting slit is around 95μm, the chipping is less than 5μm, and the cutting ratio is 778:1002. Both methods have reduced thermal
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effect during femtosecond laser cutting and effectively improved the cutting quality. At last, by controlling focus position and increasing the number of cutting passes, we have achieved the complete cut through the plate of LiNbO3. The cutting quality in the water-cooling method is much more advantageous and meets the product requirements of LiNbO3.
Acknowledgments This research has been supported by the National Key R&D Program of China (2017YFB1104604, 2016YFB1102503)
References
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[1]A. R. Collins, G. M. O’Connor, Mechanically inspired laser scribing of thin flexible glass, Opt. Lett., 40 (2015) 4811-4814.
[2]Ueda T., Yamada K., Oiso K., Hosokawa A., Thermal Stress Cleaving of Brittle Materials by Laser Beam, CIRP Annals, 51 (2002) 149-152.
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[3]Lumley R., Controlled separation of brittle materials using a laser, Am. Ceram. Soc. Bull, 48 (1969) 850-854.
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[4]Prakash E., Sadashivappa K., Joseph V., Singaperumal M., Nonconventional cutting of plate glass using hot air jet: experimental studies, Mechatronics, 11 (2001) 595-615. [5]Dudutis J., GeČys P., RaČiukaitis G., Non-ideal axicon-generated Bessel beam application for intra-volume glass modification, Optics Express, 24 (2016) 28433.
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[6]Ahmed F., Lee M., Sekita H., Sumiyoshi T., Kamata M., Display glasscutting by femtosecond laser induced single shot periodic void array, Applied Physics A, 93 (2008) 189-192.
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[7]Strigin M., Chudinov A., Cutting of glass by picosecond laser radiation, Optics Communications, 106 (1994) 223-226. [8]Varel H., Ashkenasi D., Rosenfeld A., Wähmer M., Campbell E., Micromachining of quartz with ultrashort laser pulses, Applied Physics A: Materials Science & Processing, 65 (1997) 367-373. [9]Wang Y., Yan S., Friberg A., Kuebel D., Visser T., Electromagnetic diffraction theory of refractive axicon lenses, Journal of the Optical Society of America A, 34 (2017) 1201. [10]Yuan F., Johnson J., Allred D., Todd R., Waterjet cutting of cross-linked glass,
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 13 (1995) 136-139. [11]Zhou M., Ngoi B., Yusoff M., Wang X., Tool wear and surface finish in diamond cutting of optical glass, Journal of Materials Processing Technology, 174 (2006) 29-33. [12]M. K. Bhuyan, O. Jedrkiewicz, V. Sabonis, M. Mikutis, S. Recchia, A. Aprea, M. Bollani, and P. Di Trapani, High-speed laser-assisted cutting of strong transparent materials using picosecond Bessel beams, Appl. Phys. A, 120 (2015) 443-446.
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[13]L. Rapp, R. Meyer, L. Furfaro, C. Billet, R. Giust, F.Courvoisier, High speed cleaving of crystals with ultrafast Bessel beams, Optics Express, 8 (2017) 9312-9317. [14]M. K. Bhuyan, O. Jedrkiewicz, V. Sabonis, M. Mikutis, S. Recchia, A. Aprea, M. Bollani, P. Di Trapani, High-speed laser-assisted cutting of strong transparent materials using picosecond Bessel beams, Appl. Phys. A, 120 (2015) 443-446.
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[15]K. Mishchik, R. Beuton, O. Dematteo Caulier, S.Skupin, B. Chimier, G. Duchateau, B. Chassagne, R.Kling, C. HÖnninger, E. Mottay, J. Lopez, Improved laser glass cutting by spatio-temporal control of energy deposition using bursts of femtosecond pulses, Optics Express, 25 (2017) 33271-33282.
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[16]Sanguk Park, Yunseok Kim, Joonho You, Seung-Woo Kim, Damage-free cutting of chemically strengthened glass by creation of sub-surface cracks using femtosecond laser pulses, CIRP Annals - Manufacturing Technology 66 (2017) 535-538.
Figure captions:
Fig.1 Optical surface micrographs of No.1 sample Fig.2 Optical cross-section micrographs of No.1 sample Fig.3 Optical surface micrographs of No.2 sample Fig.4 Optical cross-section micrographs of No.2 sample
Fig.6 Optical cross-section micrographs of No.3 sample
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Fig.5 Optical surface micrographs of No.3 sample
Fig.7 Schematic diagram of optimized experimental device
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Fig.8 Physical diagram of optimized experimental device Fig.9 Optical surface micrographs of No.4 sample
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Fig.10 Optical cross-section micrographs of No.4 sample
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Fig.11 Schematic diagram of optimized experimental device Fig.12 Physical diagram of optimized experimental device
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Fig.13 Optical surface micrographs of No.5 sample Fig.14 Optical cross-section micrographs of No.5 sample
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Fig.15 Comparison of complete cutting morphology under two methods
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Fig.16 Roughness measurement of the cutting cross-section in the water-cooling solution
Table captions:
1
2
3
4
5
Laser power (W)
15
7.8
3.8
3.8
3.8
Wavelength (nm)
1030
515
343
343
343
Repetition frequency (kHz)
50
50
50
50
50
Scanning speed (mm/s)
500
500
500
500
500
Width of cutting track (μm)
80
80
80
80
80
20
20
20
20
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No.
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Table 1 Experimental parameters
Spacing of each laser scanning
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path in cutting track (μm) 150
Method
Normal
150
150
150
150
Normal
Normal
Optimization
Optimization
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Cutting times
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20