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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 24 — Nov. 24, 2008
  • pp: 19706–19711
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Laser micro/nano fabrication in glass with tunable-focus particle lens array

Z. B. Wang, Wei Guo, A. Pena, D. J. Whitehead, B. S. Luk’yanchuk, Lin. Li, Z. Liu, Y. Zhou, and M. H. Hong  »View Author Affiliations


Optics Express, Vol. 16, Issue 24, pp. 19706-19711 (2008)
http://dx.doi.org/10.1364/OE.16.019706


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Abstract

Based on medium-tuned optical field enhancement effect around a self-assembled particle-lens array (PLA) irradiated with a femtosecond (fs) laser source, we demonstrated that high-precision periodical array of micro/nano-structures can be readily fabricated on glass surface or inside glass in large areas in parallel without any cracks or debris. The technique has potential for rapid fabrication of three-dimensional structures in multiple layers inside glass.

© 2008 Optical Society of America

1. Introduction

Due to its outstanding mechanical, chemical and optical properties, glass has widespread applications in novel device packaging, optical communication and micro-technologies such as micro-optics and biomedical devices. In general, glass is hard, brittle and non-conducive. It is a high challenge to process glass by most conventional machining techniques. In recent years, laser microprocessing has arisen as an attractive approach in glass engineering. Before the availability of femtosecond (fs) laser, high power UV and CO2 lasers had been generally used for glass processing, since glass has very low linear absorption rate in the visible wavelength range. The mechanism of bulk damage by these lasers involves heating of conduction band electrons by the incident radiation and transferring of this energy to the lattice. Damage occurs via the conventional thermal process. The build up of heat-affected zone (HAZ) and thermal stress often lead to glass cracking, which greatly limits the applications.

2. Theory

Although it was discovered nearly a century ago, Mie theory continues to play a crucial role in describing the optical properties of small particles [10

10. G. Mie, “Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen,” Ann. Phys. (Leipzig) 25, 377–445 (1908). [CrossRef]

]. To illustrate the basic physics of focus tuning effect by a liquid medium, Mie theory modeling of optical near field around a single particle has been carried out. Figure 1 shows the Mie modeling results of the cross-sectional view of the normalized local field distribution (|E|2) underneath a single 5.0 µm particle in (a) air and (b) immersed in water medium, under an x-polarized plane wave excitation at 800 nm. As it can be seen in Fig. 1(a), the focus point of a 5.0 µm particle in air is located at position z/a=1.1, which is close (subwavelenth distance) to the particle surface. Such enhanced field was associated with optical cavity resonance inside transparent particles and can be thought as the inference of incident beam and evanescent waves presented in the vicinity regions of the particles [11

11. Z. B. Wang, Optical resonance and near field effects: small particles under laser irradiation, Normal, Ph.D thesis (National University of Singapore, Singapore, 2005).

], i.e., in the optical near-field region. As a near-field characteristics, the field enhancement within range from z/a=1.1 to z/a=2.2 in Fig. 1(a) decays almost exponentially. It means for efficient surface patterning the sample must be kept in near-field contact with particles. As such, PLA tends to be removed after single pulse irradiation due to substrate thermal expansion or ablative force. On the other hand, the focusing properties of particle changes dramatically when a surrounding medium is used. As it can be seen from Fig. 1(b), the presence of water medium greatly extends the focal length, from z/a=1.1 to z/a=2.7, as compared to Fig. 1(a). In this case, PLA tends to remain on surface after multiple laser shots. Meanwhile, the field enhancement decays from focus point much slowly compared with that in Fig. 1(a) for air medium, resulting in significant increase of the focus depth. It is beneficial for laser processing of materials in terms of fabricating higher-aspect-ratio structures into substrates with multiple shots, since more laser energy could be coupled into substrate when focus depth extends.

Fig. 1. Cross-sectional view of the normalized local field distribution (|E|2) underneath a single 5.0 µm particle in (a) air and (b) immersed in water medium. The incident laser (λ=800 nm) beam is linearly polarized along x-axis and propagates along z-axis.

Fig. 2. Cross-sectional view of normalized local field distribution (|E|2) underneath a hexagonal array of 5.0 µm particles deposited on Quartz substrate (a) in air and (b) immersed in water. The incident beam has a wavelength of 800 nm and is polarized along horizontal-direction. The refractive index of quartz and spheres are same as 1.45332, and 1.326 for water. (c) the electric field on substrate surface just under the particles.

3. Experimental

A 1.0-mm-thick fused silica was used as the sample in experiment. It was cleaned with warmed acetone in an ultrasonic bath for 10 min followed by rinsing in IPA and DI water for 5 min. It was then immersed in 30% Nitric acid solution for 24 hours to make the glass surface hydrophilic. The sample was finally re-rinsed with DI water and dried by pure N2 gas. The spherical silica particles (Bangs Laboratories) with diameter of 5.0 µm were applied on the quartz surface after the original suspension had been diluted with DI water. The substrate was kept still until all the water had been evaporated. As a result, a reasonable uniform monolayer hexagonal array in a area of ~0.5 cm2 was formed on the glass surface in our experiment. Before laser irradiation, the glass sample was fixed onto the bottom of a small glass vessel mounted on a three-axis stage. DI water was then added into the vessel to completely immerse the sample and the PLA.

A Ti: Sapphire regenerative amplifier system (Coherent Libra) was used as the light source (wavelength λ=800 nm, pulse duration τ=110 fs, maximum pulse energy 1.0 mJ and repetition rate variable from 1 to 1000 Hz). The nominal Gaussian beam diameter (1/e2, TEM00 mode, M2<1.5) at the laser exiting window is ~5 mm. The laser beam (linearly polarized) was incident normally on the sample surface without any focusing. The pulse energy was controlled by the Neutral Density Filters inserted in the optical path. The laser was operated in the manual mode and only a single pulse was used for each processing. The sample after processing was characterized by optical microscopy (OM) and atomic force microscopy (AFM; Vecco CP2).

Figure 3 shows the AFM images of hexagonal array of two different types of bumps formed on the quartz surface immersed inside water after a single fs laser pulse irradiation (central region of the Gaussian laser spot) at a pulse energy of 0.20 mJ (fluence:1.0 mJ/cm2) and 0.88 mJ (fluence:4.5 mJ/cm2) through self-assembled 5.0 µm PLA, respectively. As was shown in Fig. 2(b), the primary focus of water-immersed PLA is inside the glass bulk. In the fs time scale, the laser energy was simultaneously coupled into the glass bulk under PLA through nonlinear multiphoton absorption processes. Within each focal volume inside glass, the energy is highly confined and it pushes the matter into a state of extreme non-equilibrium. This can lead to material properties modification or the generation of micro-voids (micro-explosion) inside glass [19

19. Y. Hayasaki and D. Kawamura, “High-density bump formation on a glass surface using femtosecond laser processing in water,” Appl. Phys. A 87, 691–695 (2007). [CrossRef]

]. Through OM examination of samples processed at different laser energies, we confirmed that hexagonal array of patterns do exist inside glass as evidenced by the appearance of dark-contrast dot array inside glass. These in-bulk dark-contrast arrays were observed for all the samples including those processed at low pulse energies without visible patterns induced on the top surface. Ring-bumps were the first structures that can be seen on glass surface as field enhancement factor within the surface plane reaches some critical level (see Fig. 2(c)). Since there are no any field enhancements at particle-glass contacting points, the convex bumps in Fig. 3(b) can only be possible to be induced by the in-bulk micro-explosion process, which pushes the materials on the top of focal volume towards the top surface. This assumption was confirmed by different heights of convex-bumps observed at different laser energies. At a pulse energy of 0.88 mJ, the bump height is around 60 nm (Fig. 3(c)). There is no cracks and debris observed around these bumps. The roughness of the bump surface and original glass surface are almost same, indicating bumps were formed due to inner material expansion towards surface instead of violent ablation taking processing on surfaces. As a Gaussian beam was used in experiments, the bumps height are gradually decreasing toward the edges of laser spot. To improve the uniformity, a top-hat beam source should be applied. This can be done by inserting a homogenizer in the optical path. The fabricated high-quality convex-bumps are ideal for low flying height control in hard disk industry.

Fig. 3. Atomic Force Microscopy (AFM) images of hexagonal array of (a) ring-bumps and (b) convex bumps generated on quartz surface immersed inside water after a single femtosecond laser pulse irradiation at a pulse energy of 0.20 mJ and 0.88 mJ through a self-assembled 5.0 µm SiO2 particle array, respectively.

As a final note, the developed technique here is possible to be extended to generate multi-layers of hexagonal array inside transparent glass materials. The focus position for different layers can be easily and precisely controlled by a liquid medium with controllable refractive index. Furthermore, if an angular-incident laser beam is applied [20

20. W. Guo, Z. B. Wang, L. Li, D. J. Whitehead, B. S. Luk’yanchuk, and Z. Liu, “Near-field laser parallel nanofabrication of arbitrary-shaped patterns,” Appl. Phys. Lett. 90, 243101 (2007). [CrossRef]

], one can fabricate multi-layers of complex shaped patterns inside the glass bulk.

6. Summary

We have presented a simple and efficient technique to fabricate periodical micro/nano-structures array (hexagonal) on glass surface or inside glass. Due to the presence of water medium, the multiple focusing spots of the microsphere array illuminated by fs laser were tuned to positions beneath the surface, and focal length is greatly extended. Depending on the laser fluence, it has demonstrated that different micro/nano-structures such as nano-height ring-bumps and convex bumps can be fabricated on glass surface in large area without cracks and debris. We also discussed the possibility to extend present technique to fabricating multi-layered three dimensional micro/nano-structures inside the bulk.

Acknowledgments

This work was conducted by the Northwest Laser Engineering Consortium (NWLEC), funded by the Northwest Science Council of the United Kingdom (contract no: N0003200).

References and links

1.

H. R. Qiu, K. Miura, and K. Hirao, “Femtosecond laser-induced microfeatures in glasses and their applications,” J. Non-Cryst. Solids 354, 1100–1111 (2008). [CrossRef]

2.

S. Theppakuttai and S. Chen, “Nanoscale surface modification of glass using a 1064 nm pulsed laser,” Appl. Phys. Lett. 83, 758–760 (2003). [CrossRef]

3.

R. Piparia, E. W. Rothe, and R. J. Baird, “Nanobumps on silicon created with polystyrene spheres and 248 or 308 nm laser pulses,” Appl. Phys. Lett. 89, 223113.1–223113.3 (2006). [CrossRef]

4.

J.-I. Kato, N. Takeyasu, Y. Adachi, H.-B. Sun, and S. Kawata, “Multiple-spot parallel processing for laser micronanofabrication,” Appl. Phys. Lett. 86, 044102 (2005). [CrossRef]

5.

H. Yang, C. K. Chao, M. K. Wei, and C. P. Lin, “High fill-factor microlens array mold insert fabrication using a thermal reflow process,” J. Micromech. Microeng. 14, 1197–1204 (2004). [CrossRef]

6.

S. M. Huang, M. H. Hong, B. Lukiyanchuk, and T. C. Chong, “Nanostructures fabricated on metal surfaces assisted by laser with optical near-field effects,” Appl. Phys. A 77, 293–295 (2003).

7.

B. S. Luk’Yanchuk, Z. B. Wang, W. D. Song, and M. H. Hong, “Particle on surface: 3D-effects in dry laser cleaning,” Appl. Phys. A 79, 747–751 (2004). [CrossRef]

8.

Y. Zhou, M. H. Hong, J. Y. H. Fuh, L. Lu, B. S. Lukyanchuk, and Z. B. Wang, “Near-field enhanced femtosecond laser nano-drilling of glass substrate,” J. Alloys Compd. 449, 246–249 (2008). [CrossRef]

9.

Y. Zhou, M. H. Hong, J. Y. H. Fuh, L. Lu, B. S. Luk’yanchuk, Z. B. Wang, L. P. Shi, and T. C. Chong, “Direct femtosecond laser nanopatterning of glass substrate by particle-assisted near-field enhancement,” Appl. Phys. Lett. 88, 023110 (2006). [CrossRef]

10.

G. Mie, “Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen,” Ann. Phys. (Leipzig) 25, 377–445 (1908). [CrossRef]

11.

Z. B. Wang, Optical resonance and near field effects: small particles under laser irradiation, Normal, Ph.D thesis (National University of Singapore, Singapore, 2005).

12.

C. Hafner, The Generalized Multiple Multipole Technique for Computational Electromagnetics (Artech, Boston, 1990).

13.

W. H. Yang, G. C. Schatz, and R. P. Vanduyne, “Discrete Dipole Approximation for Calculating Extinction and Raman Intensities for Small Particles with Arbitrary Shapes,” J. Chem. Phys. 103, 869–875 (1995). [CrossRef]

14.

J. M. Jin, The Finite Element Method in Electromagnetics, 2nd ed., (John Wiley & Sons, New York, 2002).

15.

A. Taflove, Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed. (Artech House, 2005).

16.

T. Weiland, “Time Domain Electromagnetic Field Computation with Finite Difference Methods,” Int. J. Numer. Modelling 9, 295–319 (1996). [CrossRef]

17.

Computer Simulation Technology: CST Microwave Studio (http://www.cst.com); Remote license access provided by one of the author B.S. Lukiyanchuk in DSI, Singapore, (2007).

18.

Z. B. Wang, W. Guo, B. S. Luk’yanchuk, D. J. Whitehead, L. Li, and Z. Liu, “Optical Near-field Interaction between Neighboring Micro/Nano-particles,” J. Laser Micro/Nanoeng. 3, 14–18 (2008). [CrossRef]

19.

Y. Hayasaki and D. Kawamura, “High-density bump formation on a glass surface using femtosecond laser processing in water,” Appl. Phys. A 87, 691–695 (2007). [CrossRef]

20.

W. Guo, Z. B. Wang, L. Li, D. J. Whitehead, B. S. Luk’yanchuk, and Z. Liu, “Near-field laser parallel nanofabrication of arbitrary-shaped patterns,” Appl. Phys. Lett. 90, 243101 (2007). [CrossRef]

OCIS Codes
(220.4610) Optical design and fabrication : Optical fabrication
(350.3850) Other areas of optics : Materials processing

ToC Category:
Optical Design and Fabrication

History
Original Manuscript: July 22, 2008
Revised Manuscript: November 6, 2008
Manuscript Accepted: November 6, 2008
Published: November 13, 2008

Citation
Z. B. Wang, Wei Guo, A. Pena, D. J. Whitehead, B. S. Luk'yanchuk, Lin. Li, Z. Liu, Y. Zhou, and M. H. Hong, "Laser micro/nano fabrication in glass with tunable-focus particle lens array," Opt. Express 16, 19706-19711 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-24-19706


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References

  1. H. R. Qiu, K. Miura, and K. Hirao, "Femtosecond laser-induced microfeatures in glasses and their applications," J. Non-Cryst. Solids 354, 1100-1111 (2008). [CrossRef]
  2. S. Theppakuttai and S. Chen, "Nanoscale surface modification of glass using a 1064 nm pulsed laser," Appl. Phys. Lett. 83, 758-760 (2003). [CrossRef]
  3. R. Piparia, E. W. Rothe, and R. J. Baird, "Nanobumps on silicon created with polystyrene spheres and 248 or 308 nm laser pulses," Appl. Phys. Lett.  89, 223113.1-223113.3 (2006). [CrossRef]
  4. J.-I. Kato, N. Takeyasu, Y. Adachi, H.-B. Sun, and S. Kawata, "Multiple-spot parallel processing for laser micronanofabrication," Appl. Phys. Lett. 86, 044102 (2005). [CrossRef]
  5. H. Yang, C. K. Chao, M. K. Wei, and C. P. Lin, "High fill-factor microlens array mold insert fabrication using a thermal reflow process," J. Micromech. Microeng. 14, 1197-1204 (2004). [CrossRef]
  6. S. M. Huang, M. H. Hong, B. Lukiyanchuk, and T. C. Chong, "Nanostructures fabricated on metal surfaces assisted by laser with optical near-field effects," Appl. Phys. A 77, 293-295 (2003).
  7. B. S. Luk'Yanchuk, Z. B. Wang, W. D. Song, and M. H. Hong, "Particle on surface: 3D-effects in dry laser cleaning," Appl. Phys. A 79, 747-751 (2004). [CrossRef]
  8. Y. Zhou, M. H. Hong, J. Y. H. Fuh, L. Lu, B. S. Lukyanchuk, and Z. B. Wang, "Near-field enhanced femtosecond laser nano-drilling of glass substrate," J. Alloys Compd. 449, 246-249 (2008). [CrossRef]
  9. Y. Zhou, M. H. Hong, J. Y. H. Fuh, L. Lu, B. S. Luk'yanchuk, Z. B. Wang, L. P. Shi, and T. C. Chong, "Direct femtosecond laser nanopatterning of glass substrate by particle-assisted near-field enhancement," Appl. Phys. Lett. 88, 023110 (2006). [CrossRef]
  10. G. Mie, "Beiträge zur Optik trüber Medien, speziell kolloidaler Metallösungen," Ann. Phys. (Leipzig) 25, 377-445 (1908). [CrossRef]
  11. Z. B. Wang, Optical resonance and near field effects: small particles under laser irradiation, Normal, Ph.D thesis (National University of Singapore, Singapore, 2005).
  12. C. Hafner, The Generalized Multiple Multipole Technique for Computational Electromagnetics (Artech, Boston, 1990).
  13. W. H. Yang, G. C. Schatz, and R. P. Vanduyne, "Discrete Dipole Approximation for Calculating Extinction and Raman Intensities for Small Particles with Arbitrary Shapes," J. Chem. Phys. 103, 869-875 (1995). [CrossRef]
  14. J. M. Jin, The Finite Element Method in Electromagnetics, 2nd ed., (John Wiley & Sons, New York, 2002).
  15. A. Taflove, Computational Electrodynamics: The Finite-Difference Time-Domain Method, 3rd ed. (Artech House, 2005).
  16. T. Weiland, "Time Domain Electromagnetic Field Computation with Finite Difference Methods," Int. J. Numer. Model 9, 295-319 (1996). [CrossRef]
  17. Computer Simulation Technology: CST Microwave Studio (http://www.cst.com); Remote license access provided by one of the author B.S. Lukiyanchuk in DSI, Singapore, (2007).
  18. Z. B. Wang, W. Guo, B. S. Luk'yanchuk, D. J. Whitehead, L. Li, and Z. Liu, "Optical Near-field Interaction between Neighboring Micro/Nano-particles," J. Laser Micro/Nanoeng.  3, 14-18 (2008). [CrossRef]
  19. Y. Hayasaki and D. Kawamura, "High-density bump formation on a glass surface using femtosecond laser processing in water," Appl. Phys. A 87, 691-695 (2007). [CrossRef]
  20. W. Guo, Z. B. Wang, L. Li, D. J. Whitehead, B. S. Luk'yanchuk, and Z. Liu, "Near-field laser parallel nanofabrication of arbitrary-shaped patterns," Appl. Phys. Lett. 90, 243101 (2007). [CrossRef]

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