Mechanisms of ultrafast laser-induced deep-subwavelength gratings on graphite and diamond

Min Huang, Fuli Zhao, Ya Cheng, Ningsheg Xu, and Zhizhan Xu

Phys. Rev. B 79, 125436 – Published 30 March 2009

Abstract

Deep-subwavelength gratings with periodicities of 170, 120, and 70 nm can be observed on highly oriented pyrolytic graphite irradiated by a femtosecond (fs) laser at 800 nm. Under picosecond laser irradiation, such gratings likewise can be produced. Interestingly, the 170-nm grating is also observed on single-crystal diamond irradiated by the 800-nm fs laser. In our opinion, the optical properties of the high-excited state of material surface play a key role for the formation of the deep-subwavelength gratings. The numerical simulations of the graphite deep-subwavelength grating at normal and high-excited states confirm that in the groove the light intensity can be extraordinarily enhanced via cavity-mode excitation in the condition of transverse-magnetic wave irradiation with near-ablation-threshold fluences. This field enhancement of polarization sensitiveness in deep-subwavelength apertures acts as an important feedback mechanism for the growth and polarization dependence of the deep-subwavelength gratings. In addition, we suggest that surface plasmons are responsible for the formation of seed deep-subwavelength apertures with a particular periodicity and the initial polarization dependence. Finally, we propose that the nanoscale Coulomb explosion occurring in the groove is responsible for the ultrafast nonthermal ablation mechanism.

Received 18 December 2008

DOI:https://doi.org/10.1103/PhysRevB.79.125436

Authors & Affiliations

Min Huang^1,*, Fuli Zhao¹, Ya Cheng², Ningsheg Xu¹, and Zhizhan Xu^2,†

¹State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, China
²State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800, China

^*syshm@163.com
^†zzxu@mail.shcnc.ac.cn

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Issue

Vol. 79, Iss. 12 — 15 March 2009

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Images

Figure 1
SEM images of graphite surface irradiated by 800-nm fs laser with a fluence of $0.17 J / {cm}^{2}$ and different pulse numbers. (a) 3000 pulses. Double arrow: the polarization of incident laser. Circles: the low-lying regions with ridges broken off. (b) 1000 pulses. Arrow I: a ridge with a length of about $8 μ m$ partially broken off its original location. Arrow II: the original location of the ridge. Arrow III: a thin sheet. (c) $100 000$ pulses. Arrow I, II, and III denote nanogratings with periodicities of 70, 120, and 170 nm, respectively. (d) $10 000$ pulses. The fine nanograting of 120 nm independently appears in the classic ripple areas.Reuse & Permissions
Figure 2
Nanograting characteristics of graphite surface irradiated by lasers with different pulse durations and wavelengths. (a) SEM image of graphite surface irradiated by 532-nm ps laser with 2000 pulses at a fluence of $46 J / {cm}^{2}$ . Area I and II show nanogratings with periodicities of 130 and 80 nm, respectively. (b) SEM image of graphite surface irradiated by 400-nm fs laser with $50 000$ pulses. (c) SEM image of graphite surface irradiated by 1300-nm ps laser with 300 pulses. (d) The relationship between the laser wavelength and the periodicity of coarse nanograting.Reuse & Permissions
Figure 3
SEM images of diamond surface irradiated by 800-nm fs laser with different fluences and pulse numbers. (a) 3000 pulses at a fluence of $1.9 J / {cm}^{2}$ . At the brim, the nanograting with a periodicity of 170 nm appears in accurate order. (b) 8000 pulses at a fluence of $2.8 J / {cm}^{2}$ . The nanogratings at the wall and the brim of the crater with periodicities of 190 and 170 nm, respectively, are both highly regular.Reuse & Permissions
Figure 4
(Color online) Simulations of the optical properties of the nanograting induced by 800-nm fs laser at normal and high-excited states. (a) A schematic view of the nanograting under study with the definition of different parameters involved. The diagonal areas I and II denote the groove and ridge areas for the average enhancement calculation, respectively. The field amplitude distributions under different irradiation conditions in one period (periodic boundary condition): (b) the $E_{x}$ at the high-excited state with 800-nm TM wave; (c) the $E_{y}$ at the high-excited state with 800-nm TE wave; (d) the $E_{x}$ at the normal state with 800-nm TM wave; (e) the $E_{x}$ at the high-excited state with 200-nm TM wave; (f) the $E_{x}$ at the high-excited state with 2000-nm TM wave; and (g) the $E_{z}$ at the high-excited state with 800-nm TM wave.Reuse & Permissions
Figure 5
(Color online) The average absolute (a) and relative (b) enhancements of $E_{x}$ field in the groove for the normal and high-excited states in the wavelength range from ultraviolet to near infrared in the TM wave case.Reuse & Permissions
Figure 6
(Color online) A schematic picture of CE occurring in the groove irradiated by ultrafast laser with the fluence near the ablation threshold.Reuse & Permissions

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