Modification of dielectric surfaces with ultra-short laser pulses

doi:10.1016/S0169-4332(01)00675-4

Applied Surface Science

Volume 186, Issues 1–4, 28 January 2002, Pages 352-357

https://doi.org/10.1016/S0169-4332(01)00675-4 Get rights and content

Abstract

Crater morphology is investigated after femtosecond laser ablation of wide bandgap insulators (BaF₂ and CaF₂). Experiments performed at a weak laser ablation rate show a particular elastic, sound wave-like structure, frozen on the surface, with a periodicity in the order of some microns and a modulation depth up to 0.5 μm. When superimposed, a periodic fine structure (ripples) is generated, the origin of which cannot be explained in the classical ripple model. We observe a periodicity ranging from 100 to 500 nm, dependent on the laser intensity rather than on the laser wavelength. Based on our recent results, demonstrating an explosive surface decomposition, we assume self-organizing relaxation of a non-equilibrium surface to be responsible for the structures.

Introduction

Surface damage ablation with ultra short, sub-picosecond laser pulses has been investigated for intentional high-precision material processing [1], [2], and for the study of the dynamics in laser materials interaction [3], [4]. Considering laser ablation from transparent wide bandgap dielectrics, these investigations [5], [6], [7] have confirmed the mechanism previously proposed [8], [9], [10] that multiphoton surface ionization is followed by Coulomb explosion of positive ions from an electrostatically unstable surface. The competing model of surface super-heating resulting in phase explosion [11] does not seem to play an important role in this case, being considered to correspond only to strong absorption, e.g. in metals, semiconductors or at much higher intensities in insulators [12].

In this contribution, we demonstrate that the morphology of the irradiated surfaces yields valuable details concerning the microscopic mechanisms involved in laser ablation, in particular, femtosecond laser ablation.

For instance, it is well known that the periodic structures occur on the bottom of the sub picosecond ablated crater [13], [14]. They look very similar to those observed previously on various metals, semiconductors, and insulators upon irradiation ranging from CW to nanosecond pulses. In a classical model [15], these structures correspond to a non-uniform energy input into the sample, modulated by the interference between the incident wave and an induced (evanescent) surface wave.

Section snippets

Experiments

Our experiments were carried out on freshly cleaved single crystal slides of BaF₂ and CaF₂, under high vacuum (<10⁻⁷ mbar) and irradiated with ultra-short laser pulses provided by an amplified Ti:sapphire laser system, with 800 nm central wavelength and 1 kHz repetition rate. Pulse duration was 120 fs and pulse energy <0.5 mJ. Experiments were performed using p-polarized and s-polarized beams focused on the target by using single spherical quartz lenses $(f=+300 and +500 mm)$ . Additionally,

Results

We examined the ablated craters produced on BaF₂ (also in CaF₂) by ultra-short laser pulses with intensities of $1–12×10^{12} W/cm^{2}$ , applying several thousand laser pulses per spot (1000–10 000). At these intensities, the ablation rate was rather moderate, i.e. of about 5 nm/pulse at $0.8×10^{13} W/cm^{2}$ , as determined using white light interference microscopy.

We note that the crater morphology particularities observed in BaF₂ were relatively equivalent in CaF₂. Therefore, we proceed to expose our results

Discussion

From our previous studies [5], [6], we know that positive ions are emitted explosively with mean kinetic energies in the order of 100 eV. However, the energy distribution corresponds only to a surface temperature of 1 eV (10⁴ K), a typical value for plasma. As the origin for this difference between kinetic energy and temperature, Coulomb explosion after strong surface ionization was invoked. This means, that the laser input results first in an electrostatically highly unstable surface and then the

Acknowledgements

We would like to thank Prof. Dr. D. Linke for the opportunity to use his high resolution optical microscope, and W. Seifert, S. Pandelov, and T. Arguirov for their support with the electron microscopy.

References (20)

R. Stoian et al.
Nucl. Instr. B
(2000)
M. Henyk et al.
Appl. Surf. Sci.
(2000)
M. Henyk et al.
Appl. Surf. Sci.
(2000)
J.T. Dickinson et al.
Appl. Surf. Sci.
(1996)
D. Ashkenasi et al.
Nucl. Instrum. Meth. Phys. Res. B
(1997)
H. Varel et al.
Appl. Surf. Sci.
(1998)
R.J. Recknagel et al.
Opt. Commun.
(1998)
S. Küper et al.
Appl. Phys. Lett.
(1989)
W. Kautek et al.
Appl. Phys. Lett.
(1996)
J. Reif et al.
SPIE Proc. Ser.
(2000)

There are more references available in the full text version of this article.

Cited by (148)

Fabrication of printable nanograting using solution-based laser-induced periodic surface structure process
2021, Applied Surface Science
Laser-induced periodic surface structure (LIPSS) is of significant interest because it can be used to produce sub-wavelength structures through a simple laser patterning process. One of the main applications of LIPSS is color marking, which is due to diffraction from periodic grating structures. Such structural coloration is produced mainly by irradiating metal plates with femtosecond laser beams. However, when used with bulk materials, the unpatterned areas of the metal plate have undesirable properties, such as low transmittance, making it difficult to apply the LIPSS process. To overcome this problem, we propose herein a solution-based LIPSS process for fabricating printable nanogratings. The unique growth process of organometallic compounds allows gratings to form only in the desired area, leaving the surrounding unpatterned area to be easily cleaned using organic solvents. To form a periodic ripple structure, we apply specific processing parameters that enable the simultaneous growth and sintering of Ag nanoseeds. Given that the selective ripple patterns can be used in various applications, the proposed LIPSS process should be of significant practical use.
Polarization effect on hole evolution and periodic microstructures in femtosecond laser drilling of thermal barrier coated superalloys
2021, Applied Surface Science
A high-pulse-energy femtosecond pulsed Ti:sapphire laser was employed to perform laser drilling of 2.4-mm-thick thermal barrier coated In718. The influences of polarization on hole profile and morphology of periodic structures on the sidewall of drilled holes were explored. Based on Fresnel formula, combined with the effects of multiple reflections and energy-trapping, a comprehensive analysis of the effect of polarization on polarization removal was proposed. The microstructures on the sidewall of drilled holes for different layers under different polarizations were compared. The fabricated structures on the thermal barrier coating (TBC) layer showed a strong dependence on the polarization state of the laser beam. The structures with ball-like profile were generated under circular polarization while pine needle-like periodic structures were produced under linear polarization. However, for both the bond coat and substrate layers, the microstructures of the sidewall were independent of the polarization state of the laser beam. For TBC layer the interaction between the resonance of charge carriers and the second harmonic of the surface contributed to a corrugated structure in harmony with the polarization state. Thereinto, the charge carriers may remember the polarization state of the light beam and maintain this information because of the low mobility.
Femtosecond laser pulse ablation characteristics of polymer-derived SiAlCN ceramics
2020, Ceramics International
Citation Excerpt :
Moreover, molten material adhered to the margin of the circular lines (Fig. 1d), possibly indicating that the ablation of SiAlCN ceramics was related to melting. Except for the molten material, the laser-induced stripes, covered with nanoparticles, were observed at the bottom of the circle lines oriented in parallel to the moving direction of the laser; this observation could be mainly related to the polarization of the laser beam, the energy fluence and Neff [23–25]. Moreover, some cracks and irregular microstructures were observed at the bottom of the circle lines at low rotational speed of 800 rpm (Fig. 1e).
Polymer-derived ceramics (PDCs) are promising high-performance materials for various applications, yet their brittleness represents major drawback in their machining. Femtosecond laser pulse ablation is non-contact rapid processing method used in precision machining of PDCs. Herein, two laser parameters (laser energy fluence and rotational speed) were investigated to achieve laser–material interactions and machining characteristics via machine single circular lines, blind holes, and through-holes in polymer-derived SiAlCN ceramics. With the decrease in rotational speed, the morphology of single circular lines gradually roughened and heat-affected zone was produced. Varying ablation rates were obtained at different energy fluences. For blind holes, three different ablation regions were observed. As the energy fluence increased, blind holes gradually transformed into through-holes. Through-holes with near-cylindrical profiles and minimal collateral damage were obtained. Ablation debris deposited around through-holes were indicative of N release, breaking of Si–N and C–C bonds, and formation of SiO_x. Laser ablation of PDCs led to the formation of laser-induced surface structures, bubble pits, stripe structures, molten materials, and sphere-like particles.
Femtosecond laser-induced large area of periodic structures on chalcogenide glass via twice laser direct-writing scanning process
2020, Optics and Laser Technology
We presented a theoretical and experimental study for the evolution of femtosecond laser direct-writing induced large area of periodic surface structures on As₂S₃ glass. The laser direct-writing induced large area of low spatial frequency LIPSS (LSFL) structures can be fabricated with the overlap rate increases from 65% to 80%. The evolution process can be defined by the competition between the laser fluence and pulse overlap rate. What is more important is that, based on secondary femtosecond laser scanning process, the interaction between the initial LSFL structures induced by the first scanning and the laser pulse of the second scanning process can induce local field enhancement effect, which can directly split the surface periodic structures of LSFL. Such new subsequent high spatial frequency LIPSS (HSFL) fabrication process is quite different from the traditional multi-pulse induced HSFL and can be used to fabricate large-area HSFL structures.
Simultaneous nanopatterning and reduction of graphene oxide by femtosecond laser pulses
2018, Applied Surface Science
This paper presents a novel one-step method for the periodical nanopatterning and reduction of graphene oxide (GO). Self-organized periodic structures of reduced graphene oxide (rGO) appear on GO surfaces upon processing with a femtosecond laser at fluences slightly higher than the fluence needed for reduction of the GO. This indicates that the periodic pattern is formed either simultaneously with or due to the reduction of the GO. The laser-induced reduction of GO was identified by sheet resistance measurements, Raman and X-ray photoelectron spectroscopy. This fast and simple method to both reduce and periodically structure GO offers a variety of possible applications in printed and flexible electronics.
Femtosecond laser irradiation on Nd:YAG crystal: Surface ablation and high-spatial-frequency nanograting
2018, Applied Surface Science
In this work, we systematically study the surface modifications of femtosecond (fs) laser irradiated Nd:YAG crystal in stationary focusing case (i.e., the beam focused on the target in the steady focusing geometry) or dynamic scanning case (i.e., focused fs-laser beam scanning over the target material). Micro-sized structures (e.g. micro-craters or lines) are experimentally produced in a large scale of parameters in terms of pulse energy as well as (effective) pulse number. Surface ablation of Nd:YAG surface under both processing cases are investigated, involving the morphological evolution, parameter dependence, the ablation threshold fluences and the incubation factors. Meanwhile, under specific irradiation conditions, periodic surface structures with high-spatial-frequency (<λ/2) can be generated. The obtained period is as short as 157 nm in this work. Investigations on the evolution of nanograting formation and fluence dependence of period are performed. The experimental results obtained under different cases and the comparison between them reveal that incubation effect plays an important role not only in the ablation of Nd:YAG surface but also in the processes of nanograting formation.

View all citing articles on Scopus

View full text

Modification of dielectric surfaces with ultra-short laser pulses

Abstract

Introduction

Section snippets

Experiments

Results

Discussion

Acknowledgements

Nucl. Instr. B

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Surf. Sci.

Nucl. Instrum. Meth. Phys. Res. B

Appl. Surf. Sci.

Opt. Commun.

Appl. Phys. Lett.

Appl. Phys. Lett.

SPIE Proc. Ser.