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Laser cutting profile characterization using dynamic speckle method
Optik 124 (2013) 324–326
Contents lists available at SciVerse ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Laser cutting profile characterization using dynamic speckle method Xin-zhong Li a,c,∗ , Yu-ping Tai b , Zhao-gang Nie d , Li-ping Zhang a,c a
School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003, China School of Chemical Engineering and Pharmaceutics, Henan University of Science and Technology, Luoyang 471003, China c Luoyang Key Laboratory of Photoelectric Functional Materials, Luoyang 471003, China d Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore b
a r t i c l e
i n f o
Article history: Received 2 August 2011 Accepted 28 November 2011
Keywords: Dynamic speckle Laser cutting Profile characterization
a b s t r a c t Dynamic speckle method was employed to characterize the profile quality of the aluminum plate in process of laser cutting. Speckle contrast as an indicator was used to study the relation of the distance between the focusing lens and the sample and the focus length. Experimental results show that this method is effective to characterize the laser cutting profile quality. © 2012 Elsevier GmbH. All rights reserved.
With the laser technology development, many laser systems were used in industrial productions, such as laser cutting, drilling, and welding and so on. In laser cutting, the cutting profile quality is very important, and usually decides the working parameters of the laser cutting systems [1–3]. In our case, we proposed a novel inspection method to characterize the cutting profile quality in situ by using dynamic speckle method. This method can characterize the cutting profile roughness simply and fast. When a laser beam illuminates the cutting profile, laser speckle is generated in the reflective optical field. The speckle patterns carry the information of the illuminated surface. For non-Gaussian speckle field speckle contrast is weaker for small particles than for big ones. Speckle contrast (K) is defined the ratio of the standard deviation s and the mean local spatial speckle intensity fluctuations I, which is expressed as K=
s I
(1)
Therefore, we can obtain the cutting profile quality by analyzing the speckle patterns. In speckle theory, the speckle contrast is proportional to the surface roughness [4,5]. So, in our case, we use the speckle contrast as an indicator to characterize the cutting profile roughness in laser processing. In our experiments, the laser system is a Q-switched Nd:YAG laser, with an power of 50 W, repetition frequency of 1 kHz,
∗ Corresponding author at: School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003, China. E-mail address: [email protected] (X.-z. Li). 0030-4026/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijleo.2011.11.099
wavelength of 1064 nm. The sample is a 1-mm thick aluminum plate. The focal length of the focusing lens is 50 mm. A He–Ne laser with the wavelength of 632.8 nm is used as the testing laser. In our case, when the ratio of the distance d between the focusing lens and the sample and the focus length f was changed, we studied the cutting profile roughness using dynamic speckle method. The range of the ratio d/f changes from 0.90 to 1.10 by an interval of 0.01. Fig. 1(a) and (c) shows the SEM images of two cutting profiles of the ratio of 0.90 and 0.94, respectively. Fig. 1(b) and (d) are their corresponding AFM images. We can see that the cutting profile roughness of ratio 0.90 is higher than that of the ratio 0.94. As a contrast, we register the speckle patterns sequences of each ratio values. Fig. 2 illustrates the speckle images of ratio 0.90, 0.93, 0.95, 0.98, 1.0 and 1.1 from (a) to (f), respectively. These speckle images demonstrate explicitly that the speckle contrast becomes lower firstly and then higher, which corresponds that the cutting profile roughness has the same changing process. The detailed change of speckle contrast values versus the ratio d/f is presented in Fig. 3, from which we can see that the contrast values are as a quadratic function of the ratio d/f, approximately. Correspondingly, with increasing of the ratio d/f, the cutting profile roughness decreased firstly, then increased. The optimal ratio value is 0.95. This result is consistent with the previous studies [2,3]. In conclusion, we have shown a novel method to characterize the cutting profile quality by using dynamic speckle techniques. All results prove that this method can inspect the cutting profile quality quickly and effectively.
X.-z. Li et al. / Optik 124 (2013) 324–326
Fig. 1. The SEM (a and c) and AFM (b and d) images of two different cutting profile.
Fig. 2. (a–f) Speckle patterns of different ratio d/f.
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X.-z. Li et al. / Optik 124 (2013) 324–326
Acknowledgements This work was supported by the International Cooperation Foundation of Science & Technology of Henan Province (no. 104300510065) and the Foundation of Henan University of Science and Technology (no. 2009CZ0009 and SY0910020). References [1] S. Muto, K. Tei, T. Fujioka, Laser cutting for thick concrete by multi-pass technique, Chin. Opt. Lett. 5 (s1) (2007) 39–41. [2] X.C. Wang, H.Y. Zheng, P.L. Chu, et al., High quality femtosecond laser cutting of alumina substrates, Opt. Lasers Eng. 48 (6) (2010) 657–663. [3] A. Riveiro, F. Quintero, F. Lusquinos, et al., Parametric investigation of CO2 laser cutting of 2024-T3 alloy, J. Mater. Process. Technol. 210 (9) (2010) 1138–1152. [4] J.W. Goodman, Dependence of image speckle contrast on surface-roughness, Opt. Commun. 14 (3) (1975) 324–327. [5] P. Zakharov, A.C. Völker, M.T. Wyss, et al., Dynamic laser speckle imaging of cerebral blood flow, Opt. Express 17 (16) (2009) 13904–13917. Fig. 3. Speckle contrast values vs. d/f.
Contents lists available at SciVerse ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Laser cutting profile characterization using dynamic speckle method Xin-zhong Li a,c,∗ , Yu-ping Tai b , Zhao-gang Nie d , Li-ping Zhang a,c a
School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003, China School of Chemical Engineering and Pharmaceutics, Henan University of Science and Technology, Luoyang 471003, China c Luoyang Key Laboratory of Photoelectric Functional Materials, Luoyang 471003, China d Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore b
a r t i c l e
i n f o
Article history: Received 2 August 2011 Accepted 28 November 2011
Keywords: Dynamic speckle Laser cutting Profile characterization
a b s t r a c t Dynamic speckle method was employed to characterize the profile quality of the aluminum plate in process of laser cutting. Speckle contrast as an indicator was used to study the relation of the distance between the focusing lens and the sample and the focus length. Experimental results show that this method is effective to characterize the laser cutting profile quality. © 2012 Elsevier GmbH. All rights reserved.
With the laser technology development, many laser systems were used in industrial productions, such as laser cutting, drilling, and welding and so on. In laser cutting, the cutting profile quality is very important, and usually decides the working parameters of the laser cutting systems [1–3]. In our case, we proposed a novel inspection method to characterize the cutting profile quality in situ by using dynamic speckle method. This method can characterize the cutting profile roughness simply and fast. When a laser beam illuminates the cutting profile, laser speckle is generated in the reflective optical field. The speckle patterns carry the information of the illuminated surface. For non-Gaussian speckle field speckle contrast is weaker for small particles than for big ones. Speckle contrast (K) is defined the ratio of the standard deviation s and the mean local spatial speckle intensity fluctuations I, which is expressed as K=
s I
(1)
Therefore, we can obtain the cutting profile quality by analyzing the speckle patterns. In speckle theory, the speckle contrast is proportional to the surface roughness [4,5]. So, in our case, we use the speckle contrast as an indicator to characterize the cutting profile roughness in laser processing. In our experiments, the laser system is a Q-switched Nd:YAG laser, with an power of 50 W, repetition frequency of 1 kHz,
∗ Corresponding author at: School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003, China. E-mail address: [email protected] (X.-z. Li). 0030-4026/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijleo.2011.11.099
wavelength of 1064 nm. The sample is a 1-mm thick aluminum plate. The focal length of the focusing lens is 50 mm. A He–Ne laser with the wavelength of 632.8 nm is used as the testing laser. In our case, when the ratio of the distance d between the focusing lens and the sample and the focus length f was changed, we studied the cutting profile roughness using dynamic speckle method. The range of the ratio d/f changes from 0.90 to 1.10 by an interval of 0.01. Fig. 1(a) and (c) shows the SEM images of two cutting profiles of the ratio of 0.90 and 0.94, respectively. Fig. 1(b) and (d) are their corresponding AFM images. We can see that the cutting profile roughness of ratio 0.90 is higher than that of the ratio 0.94. As a contrast, we register the speckle patterns sequences of each ratio values. Fig. 2 illustrates the speckle images of ratio 0.90, 0.93, 0.95, 0.98, 1.0 and 1.1 from (a) to (f), respectively. These speckle images demonstrate explicitly that the speckle contrast becomes lower firstly and then higher, which corresponds that the cutting profile roughness has the same changing process. The detailed change of speckle contrast values versus the ratio d/f is presented in Fig. 3, from which we can see that the contrast values are as a quadratic function of the ratio d/f, approximately. Correspondingly, with increasing of the ratio d/f, the cutting profile roughness decreased firstly, then increased. The optimal ratio value is 0.95. This result is consistent with the previous studies [2,3]. In conclusion, we have shown a novel method to characterize the cutting profile quality by using dynamic speckle techniques. All results prove that this method can inspect the cutting profile quality quickly and effectively.
X.-z. Li et al. / Optik 124 (2013) 324–326
Fig. 1. The SEM (a and c) and AFM (b and d) images of two different cutting profile.
Fig. 2. (a–f) Speckle patterns of different ratio d/f.
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X.-z. Li et al. / Optik 124 (2013) 324–326
Acknowledgements This work was supported by the International Cooperation Foundation of Science & Technology of Henan Province (no. 104300510065) and the Foundation of Henan University of Science and Technology (no. 2009CZ0009 and SY0910020). References [1] S. Muto, K. Tei, T. Fujioka, Laser cutting for thick concrete by multi-pass technique, Chin. Opt. Lett. 5 (s1) (2007) 39–41. [2] X.C. Wang, H.Y. Zheng, P.L. Chu, et al., High quality femtosecond laser cutting of alumina substrates, Opt. Lasers Eng. 48 (6) (2010) 657–663. [3] A. Riveiro, F. Quintero, F. Lusquinos, et al., Parametric investigation of CO2 laser cutting of 2024-T3 alloy, J. Mater. Process. Technol. 210 (9) (2010) 1138–1152. [4] J.W. Goodman, Dependence of image speckle contrast on surface-roughness, Opt. Commun. 14 (3) (1975) 324–327. [5] P. Zakharov, A.C. Völker, M.T. Wyss, et al., Dynamic laser speckle imaging of cerebral blood flow, Opt. Express 17 (16) (2009) 13904–13917. Fig. 3. Speckle contrast values vs. d/f.