Abstract

A customized UV nanosecond pulsed laser system has been developed for the fast generation of tamper-proof security markings on the surface of metals, such as stainless steel, nickel, brass, and nickel-chromium (Inconel) alloys. The markings in the form of reflective phase holographic structures are generated using a laser microsculpting process that involves laser-induced local melting and vaporization of the metal surface. The holographic structures are formed from an array of optically-smooth craters whose depth can be controlled with ± 25nm accuracy. In contrast to conventional security markings, e.g., engraved serial numbers, etched part numbers and embossed polymer holographic stickers, which are only attached to the metal products as an adhesive tape, the phase holographic structures are robust to local damage (e.g. scratches) and resistant to tampering because they are generated directly on the metal surface. This paper describes a novel laser-based process for security marking of high-value metal goods, investigates the optical performance of the holographic structures, and demonstrates their application to watches.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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References

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  3. N. B. Dahotre and S. P. Harimkar, “Laser marking and engraving,” in Laser Fabrication and Machining of Materials (Springer, 2008), pp. 277–280.
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    [Crossref]
  5. L. Sobotova and P. Demec, “Laser marking of metal materials,” MM Sci. J. 12, 808–812 (2015).
  6. A. Han and D. Gubencu, “Analysis of the laser marking technologies,” Nonconventional Technol. Rev. 4, 17–22 (2008).
  7. “Detailed descriptions of holographic products,” retrieved 9th November 2016, http://www.holography.ch/Detailed%20Descriptions%20of%20Holographic%20Products.pdf .
  8. L. Li, “Technology designed to combat fakes in the global supply chain,” Bus. Horiz. 56(2), 167–177 (2013).
    [Crossref]
  9. B. Dusser, Z. Sagan, H. Soder, N. Faure, J. P. Colombier, M. Jourlin, and E. Audouard, “Controlled nanostructrures formation by ultra fast laser pulses for color marking,” Opt. Express 18(3), 2913–2924 (2010).
    [Crossref] [PubMed]
  10. K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
    [Crossref]
  11. T. Murphy, P. Harrison, and S. Norman, “Black anneal marking with pulsed fiber lasers,” Proc. SPIE 9657, 96570I (2015).
    [Crossref]
  12. K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
    [Crossref]
  13. N. J. Weston, D. P. Hand, S. Giet, and M. Ardron, “A method of forming an optical device,” WO/2012/038707 (29 March 2012).
  14. B. Wang and L. Gallais, “A theoretical investigation of the laser damage threshold of metal multi-dielectric mirrors for high power ultrashort applications,” Opt. Express 21(12), 14698–14711 (2013).
    [Crossref] [PubMed]
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  16. M. S. Brown and C. B. Arnold, “Fundamentals of laser-material interaction and application to multiscale surface modification,” in Laser Precision Microfabrication, K. Sugioka, M. Meunier, A. Pique, eds. (Springer, 2010), pp. 91–120.
  17. K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
    [Crossref]
  18. K. Wissenbach, “Surface Treatment,” in Tailored Light 2: Laser Application Technology, R. Poprawe, ed. (Springer Berlin Heidelberg, Berlin, Heidelberg, 2011), pp. 173–239.
  19. N. Eustathopoulos, B. Drevet, and E. Ricci, “Temperature coefficient of surface tension for pure liquid metals,” J. Cryst. Growth 191(1-2), 268–274 (1998).
    [Crossref]
  20. I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
    [Crossref] [PubMed]
  21. C. R. Heiple and J. R. Roper, “Mechanism for minor element effect on GTA fusion zone geometry,” Weld. J. 61, 97–102 (1982).
  22. B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
    [Crossref]
  23. K. L. Wlodarczyk, N. J. Weston, M. Ardron, and D. P. Hand, “Direct CO2 laser-based generation of holographic structures on the surface of glass,” Opt. Express 24(2), 1447–1462 (2016).
    [Crossref] [PubMed]

2016 (1)

2015 (3)

L. Sobotova and P. Demec, “Laser marking of metal materials,” MM Sci. J. 12, 808–812 (2015).

T. Murphy, P. Harrison, and S. Norman, “Black anneal marking with pulsed fiber lasers,” Proc. SPIE 9657, 96570I (2015).
[Crossref]

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

2013 (3)

B. Wang and L. Gallais, “A theoretical investigation of the laser damage threshold of metal multi-dielectric mirrors for high power ultrashort applications,” Opt. Express 21(12), 14698–14711 (2013).
[Crossref] [PubMed]

L. Li, “Technology designed to combat fakes in the global supply chain,” Bus. Horiz. 56(2), 167–177 (2013).
[Crossref]

K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
[Crossref]

2011 (1)

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

2010 (2)

B. Dusser, Z. Sagan, H. Soder, N. Faure, J. P. Colombier, M. Jourlin, and E. Audouard, “Controlled nanostructrures formation by ultra fast laser pulses for color marking,” Opt. Express 18(3), 2913–2924 (2010).
[Crossref] [PubMed]

I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
[Crossref] [PubMed]

2008 (1)

A. Han and D. Gubencu, “Analysis of the laser marking technologies,” Nonconventional Technol. Rev. 4, 17–22 (2008).

2006 (1)

B. Gu, “Review - 40 years of laser-marking - industrial applications,” Proc. SPIE 6106, 610601 (2006).
[Crossref]

1998 (1)

N. Eustathopoulos, B. Drevet, and E. Ricci, “Temperature coefficient of surface tension for pure liquid metals,” J. Cryst. Growth 191(1-2), 268–274 (1998).
[Crossref]

1982 (2)

C. R. Heiple and J. R. Roper, “Mechanism for minor element effect on GTA fusion zone geometry,” Weld. J. 61, 97–102 (1982).

B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
[Crossref]

Ardron, M.

K. L. Wlodarczyk, N. J. Weston, M. Ardron, and D. P. Hand, “Direct CO2 laser-based generation of holographic structures on the surface of glass,” Opt. Express 24(2), 1447–1462 (2016).
[Crossref] [PubMed]

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

Audouard, E.

Bryant, J. W.

B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
[Crossref]

Colombier, J. P.

Demec, P.

L. Sobotova and P. Demec, “Laser marking of metal materials,” MM Sci. J. 12, 808–812 (2015).

Drevet, B.

N. Eustathopoulos, B. Drevet, and E. Ricci, “Temperature coefficient of surface tension for pure liquid metals,” J. Cryst. Growth 191(1-2), 268–274 (1998).
[Crossref]

Dunn, A.

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

Dusser, B.

Egry, I.

I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
[Crossref] [PubMed]

Eustathopoulos, N.

N. Eustathopoulos, B. Drevet, and E. Ricci, “Temperature coefficient of surface tension for pure liquid metals,” J. Cryst. Growth 191(1-2), 268–274 (1998).
[Crossref]

Faure, N.

Gallais, L.

Gu, B.

B. Gu, “Review - 40 years of laser-marking - industrial applications,” Proc. SPIE 6106, 610601 (2006).
[Crossref]

Gubencu, D.

A. Han and D. Gubencu, “Analysis of the laser marking technologies,” Nonconventional Technol. Rev. 4, 17–22 (2008).

Han, A.

A. Han and D. Gubencu, “Analysis of the laser marking technologies,” Nonconventional Technol. Rev. 4, 17–22 (2008).

Hand, D. P.

K. L. Wlodarczyk, N. J. Weston, M. Ardron, and D. P. Hand, “Direct CO2 laser-based generation of holographic structures on the surface of glass,” Opt. Express 24(2), 1447–1462 (2016).
[Crossref] [PubMed]

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
[Crossref]

Harrison, P.

T. Murphy, P. Harrison, and S. Norman, “Black anneal marking with pulsed fiber lasers,” Proc. SPIE 9657, 96570I (2015).
[Crossref]

Heiple, C. R.

C. R. Heiple and J. R. Roper, “Mechanism for minor element effect on GTA fusion zone geometry,” Weld. J. 61, 97–102 (1982).

Hondros, E. D.

B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
[Crossref]

Jourlin, M.

Kaakkunen, J. J. J.

K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
[Crossref]

Keene, B. J.

B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
[Crossref]

Kidd, M. D.

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

Leitz, K.-H.

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

Li, L.

L. Li, “Technology designed to combat fakes in the global supply chain,” Bus. Horiz. 56(2), 167–177 (2013).
[Crossref]

Mills, K. C.

B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
[Crossref]

Murphy, T.

T. Murphy, P. Harrison, and S. Norman, “Black anneal marking with pulsed fiber lasers,” Proc. SPIE 9657, 96570I (2015).
[Crossref]

Norman, S.

T. Murphy, P. Harrison, and S. Norman, “Black anneal marking with pulsed fiber lasers,” Proc. SPIE 9657, 96570I (2015).
[Crossref]

Novakovic, R.

I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
[Crossref] [PubMed]

Otto, A.

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

Ozawa, S.

I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
[Crossref] [PubMed]

Redlingshöfer, B.

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

Reg, Y.

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

Ricci, E.

I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
[Crossref] [PubMed]

N. Eustathopoulos, B. Drevet, and E. Ricci, “Temperature coefficient of surface tension for pure liquid metals,” J. Cryst. Growth 191(1-2), 268–274 (1998).
[Crossref]

Roper, J. R.

C. R. Heiple and J. R. Roper, “Mechanism for minor element effect on GTA fusion zone geometry,” Weld. J. 61, 97–102 (1982).

Sagan, Z.

Schmidt, M.

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

Sobotova, L.

L. Sobotova and P. Demec, “Laser marking of metal materials,” MM Sci. J. 12, 808–812 (2015).

Soder, H.

Vahimaa, P.

K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
[Crossref]

Waddie, A. J.

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

Wang, B.

Weston, N. J.

K. L. Wlodarczyk, N. J. Weston, M. Ardron, and D. P. Hand, “Direct CO2 laser-based generation of holographic structures on the surface of glass,” Opt. Express 24(2), 1447–1462 (2016).
[Crossref] [PubMed]

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

Wlodarczyk, K. L.

K. L. Wlodarczyk, N. J. Weston, M. Ardron, and D. P. Hand, “Direct CO2 laser-based generation of holographic structures on the surface of glass,” Opt. Express 24(2), 1447–1462 (2016).
[Crossref] [PubMed]

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
[Crossref]

Adv. Colloid Interface Sci. (1)

I. Egry, E. Ricci, R. Novakovic, and S. Ozawa, “Surface tension of liquid metals and alloys--recent developments,” Adv. Colloid Interface Sci. 159(2), 198–212 (2010).
[Crossref] [PubMed]

Appl. Phys A-Mater (1)

K. L. Wlodarczyk, J. J. J. Kaakkunen, P. Vahimaa, and D. P. Hand, “Efficient speckle-free laser marking using a spatial light modulator,” Appl. Phys A-Mater 116(1), 111–118 (2013).
[Crossref]

Bus. Horiz. (1)

L. Li, “Technology designed to combat fakes in the global supply chain,” Bus. Horiz. 56(2), 167–177 (2013).
[Crossref]

Can. Metall. Q. (1)

B. J. Keene, K. C. Mills, J. W. Bryant, and E. D. Hondros, “Effects of Interaction Between Surface Active Elements on the Surface Tension of Iron,” Can. Metall. Q. 21(4), 393–403 (1982).
[Crossref]

J. Cryst. Growth (1)

N. Eustathopoulos, B. Drevet, and E. Ricci, “Temperature coefficient of surface tension for pure liquid metals,” J. Cryst. Growth 191(1-2), 268–274 (1998).
[Crossref]

J. Mater. Process. Technol. (1)

K. L. Wlodarczyk, M. Ardron, A. J. Waddie, A. Dunn, M. D. Kidd, N. J. Weston, and D. P. Hand, “Laser microsculpting for the generation of robust diffractive security markings on the surface of metals,” J. Mater. Process. Technol. 222, 206–218 (2015).
[Crossref]

MM Sci. J. (1)

L. Sobotova and P. Demec, “Laser marking of metal materials,” MM Sci. J. 12, 808–812 (2015).

Nonconventional Technol. Rev. (1)

A. Han and D. Gubencu, “Analysis of the laser marking technologies,” Nonconventional Technol. Rev. 4, 17–22 (2008).

Opt. Express (3)

Phys. Procedia (1)

K.-H. Leitz, B. Redlingshöfer, Y. Reg, A. Otto, and M. Schmidt, “Metal Ablation with Short and Ultrashort Laser Pulses,” Phys. Procedia 12, 230–238 (2011).
[Crossref]

Proc. SPIE (2)

T. Murphy, P. Harrison, and S. Norman, “Black anneal marking with pulsed fiber lasers,” Proc. SPIE 9657, 96570I (2015).
[Crossref]

B. Gu, “Review - 40 years of laser-marking - industrial applications,” Proc. SPIE 6106, 610601 (2006).
[Crossref]

Weld. J. (1)

C. R. Heiple and J. R. Roper, “Mechanism for minor element effect on GTA fusion zone geometry,” Weld. J. 61, 97–102 (1982).

Other (8)

N. J. Weston, D. P. Hand, S. Giet, and M. Ardron, “A method of forming an optical device,” WO/2012/038707 (29 March 2012).

K. Wissenbach, “Surface Treatment,” in Tailored Light 2: Laser Application Technology, R. Poprawe, ed. (Springer Berlin Heidelberg, Berlin, Heidelberg, 2011), pp. 173–239.

N. B. Dahotre and S. P. Harimkar, “Absorption of laser radiation,” in Laser Fabrication and Machining of Materials (Springer, 2008), pp. 34–39.

M. S. Brown and C. B. Arnold, “Fundamentals of laser-material interaction and application to multiscale surface modification,” in Laser Precision Microfabrication, K. Sugioka, M. Meunier, A. Pique, eds. (Springer, 2010), pp. 91–120.

“Detailed descriptions of holographic products,” retrieved 9th November 2016, http://www.holography.ch/Detailed%20Descriptions%20of%20Holographic%20Products.pdf .

“A serious problem for everyone,” retrieved 8th November 2016, http://ec.europa.eu/taxation_customs/business/customs-controls/counterfeit-piracy-other-ipr-violations/a-serious-problem-everyone_en .

W. M. Steen and J. Mazumder, “Laser Surface Treatment,” in Laser Material Processing, 4th ed. (Springer, 2010), pp. 339–340.

N. B. Dahotre and S. P. Harimkar, “Laser marking and engraving,” in Laser Fabrication and Machining of Materials (Springer, 2008), pp. 277–280.

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Figures (21)

Fig. 1
Fig. 1 Setup used for reading the laser-generated holographic structures and measuring their optical performance.
Fig. 2
Fig. 2 Diffractive images generated by a binary laser-generated hologram: a) the whole image projected onto the screen, b) the target image projected while using Mask 1, and c) the undiffracted 0th order beam projected while using Mask 2.
Fig. 3
Fig. 3 An example of the calibration map.
Fig. 4
Fig. 4 Schematic cross-sections of LISDs observed on the metal samples.
Fig. 5
Fig. 5 Example of the LISDs generated on stainless steel. The deformations were generated by single laser pulses with: a) EP = 1.4 × ETH, b) EP = 3.6 × ETH, c) EP = 4.3 × ETH, d) EP = 6.6 × ETH.
Fig. 6
Fig. 6 Example of the LISDs generated on brass. The deformations were generated by single laser pulses with: a) EP = 1.05 × ETH, b) EP = 1.2 × ETH, c) EP = 1.6 × ETH, d) EP = 1.9 × ETH.
Fig. 7
Fig. 7 Example of the LISDs generated on Inconel®X750. The deformations were generated by single laser pulses with: a) EP = 1.1 × ETH, b) EP = 1.5 × ETH, c) EP = 2.3 × ETH, d) EP = 3.4 × ETH.
Fig. 8
Fig. 8 Example of the LISDs generated on Inconel®718. The deformations were generated by single laser pulses with: a) EP = 1.1 × ETH, b) EP = 2.9 × ETH, c) EP = 3.4 × ETH, d) EP = 3.8 × ETH.
Fig. 9
Fig. 9 Example of the LISDs generated on Inconel®625. The deformations were generated by single laser pulses with: a) EP = 1.2 × ETH, b) EP = 2.0 × ETH, c) EP = 3.6 × ETH, d) EP = 4.1 × ETH.
Fig. 10
Fig. 10 Example of the LISDs generated on nickel. The deformations were generated by single laser pulses with: a) EP = 1.1 × ETH, b) EP = 1.9 × ETH, c) EP = 2.5 × ETH, d) EP = 4.4 × ETH.
Fig. 11
Fig. 11 Diffractive images generated by the holographic structures that were performed on: a) moderately-polished and b) highly-polished metal surface.
Fig. 12
Fig. 12 Reflectivity of the laser-generated binary holographic structures as a function of: a) depth and b) PV of the hologram individual elements (craters). The craters were spaced by a 10.5μm distance.
Fig. 13
Fig. 13 Diffraction efficiency of the binary holographic structures as a function of: a) depth and b) PV of the hologram individual elements (craters). The craters were spaced by a 10.5μm distance.
Fig. 14
Fig. 14 Illustration of: a) mismatch and b) ‘ideal’ match between the separation distance between adjacent craters (d) and their effective diameter (φEFF).
Fig. 15
Fig. 15 Reflectivity of the binary holographic structures vs. a) depth and b) PV of the craters. Results are presented for different separation distances between the craters (d = 7.1μm, 7.9μm, and 9.5μm).
Fig. 16
Fig. 16 The fraction of the incident power within the undiffracted 0th order beam measured for the binary holographic structures with different separation distances between the craters (d = 7.1μm, 7.9μm, and 9.5μm).
Fig. 17
Fig. 17 Diffraction efficiency of the binary holographic structures vs. a) depth and b) PV of the craters. Results are presented for different separation distances between the craters (d = 7.1μm, 7.9μm, and 9.5μm).
Fig. 18
Fig. 18 Diffractive image generated by: a) two-level (binary) and b) three-level holographic structure.
Fig. 19
Fig. 19 a) Watch back cover with the embedded structure containing four different binary holograms (placed next to each other in a 2 × 2 array); b) diffractive images generated by these holograms.
Fig. 20
Fig. 20 Watch back cover with the embedded holographic structure that displays the serial number.
Fig. 21
Fig. 21 a) Scratched watch back cover containing the holographic structure from Fig. 19, b) diffractive images generated by the holograms.

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