Daniela Dufft

Bio: Daniela Dufft is an academic researcher. The author has contributed to research in topics: Femtosecond & Laser. The author has an hindex of 2, co-authored 4 publications receiving 341 citations.

Femtosecond laser-induced periodic surface structures revisited: A comparative study on ZnO

Abstract: Laser-induced periodic surface structures (LIPSS) (ripples) with different spatial characteristics have been observed after irradiation of single-crystalline zinc oxide surfaces with multiple linearly polarized femtosecond pulses (150–200 fs, 800 nm) in air. For normal incident laser radiation, low spatial frequency LIPSS (LSFL) with a period (630–730 nm) close to the wavelength and an orientation perpendicular to the laser polarization have been found in the fluence range between ∼0.7 and ∼0.8 J/cm2 and predominantly for pulse numbers up to N=100. For lower fluences (0.5–0.7 J/cm2), a sharp transition from the LSFL features toward the formation of high spatial frequency LIPSS (HSFL) appears at any given pulse number below N=100. The HSFL are always parallel to the LSFL, exhibit spatial periods between 200 and 280 nm, and completely substitute the LSFL for pulse numbers N>100. Additionally, the influence of the angle of incidence has been studied experimentally for both LIPSS types revealing a different b...

Femtosecond-laser-induced quasiperiodic nanostructures on TiO2 surfaces

Abstract: High-spatial frequency, quasiperiodic structures (HSFL, Nanoripples) of 170 nm feature size were induced in rutile-type titanium dioxide surfaces by focused 150 fs Ti:sapphire laser pulses at wavelengths around 800 nm. The ripple formation is distinctly visible for numbers of pulses of N=100–1000. At lower number of pulses (N=10), a significant surface roughening appears instead of ripples which is characterized by randomly meandering nanostructures. These observations confirm an essential contribution of early stage irregular material modifications to the dynamics of quasiperiodic ripple formation. The threshold fluence for ripple generation is estimated on the basis of the conventional theory of laser-induced surface structuring. The decrease in the threshold fluence from 0.34 to 0.24 J/cm2, as it was found for an increase in the number of pulses from N=100 to N=1000, is attributed to a damage accumulation effect. Nanostructuring of spatially extended regions was enabled by utilizing a controlled sample...

Mechanisms of femtosecond-laser induced surface structuring of zinc oxide crystals

Abstract: The formation of laser-induced periodic surface structures (LIPSS, ripples) was studied since four decades for a variety of materials including semiconductors. Recently, it was demonstrated that even a structuring of materials with high-energetic band edges like ZnO is enabled by highly intense femtosecond laser pulses at center wavelengths of 800 nm and pulse durations between 10 fs and 200 fs [1–3]. Because of its transparence and biocompatibility, ZnO is of increasing interest for UV optoelectronics, photovoltaics, spintronics and biosensors. Although the LIPSS phenomenon is well-known for a long time, the discussion about the relevant mechanisms is still controversial. Usually, the formation of periodic ripples is explained by the interference of a scattered surface electromagnetic wave with the incident laser pulse. For high intensity ultrashort laser pulses, however, the laser-material interaction is rather complex because of contributions from nonlinear optical excitation pathways. Here, we report on recent investigations on LIPSS formation in single-crystalline ZnO with two distinct types of ripple structures characterized by lower and higher spatial frequency LIPSS. The results are interpreted in frame of a simple Drude-model including a nonlinear process at the irradiated surface. On the basis of this approach it can be well understood that high frequency ripples are only observed with sub-picosecond laser pulses for a below band-gap excitation of dielectrics and semiconductors.

Femtosecond-laser induced sub-200 nm structures in TiO 2

Abstract: Sub-wavelength periodic surface structures in titanium dioxide with periods of 170 and 90 nm were generated with 150 fs pulses at 800 and 400 nm, respectively. Formation mechanisms and conditions for large-area patterning are discussed.

Direct femtosecond laser surface nano/microstructuring and its applications

Abstract: This paper reviews a new field of direct femtosecond laser surface nano/microstructuring and its applications. Over the past few years, direct femtosecond laser surface processing has distinguished itself from other conventional laser ablation methods and become one of the best ways to create surface structures at nano- and micro-scales on metals and semiconductors due to its flexibility, simplicity, and controllability in creating various types of nano/microstructures that are suitable for a wide range of applications. Significant advancements were made recently in applying this technique to altering optical properties of metals and semiconductors. As a result, highly absorptive metals and semiconductors were created, dubbed as the “black metals” and “black silicon”. Furthermore, various colors other than black have been created through structural coloring on metals. Direct femtosecond laser processing is also capable of producing novel materials with wetting properties ranging from superhydrophilic to superhydrophobic. In the extreme case, superwicking materials were created that can make liquids run vertically uphill against the gravity over an extended surface area. Though impressive scientific achievements have been made so far, direct femtosecond laser processing is still a young research field and many exciting findings are expected to emerge on its horizon.

Femtosecond laser-induced periodic surface structures

Abstract: The formation of laser-induced periodic surface structures (LIPSS) in different materials (metals, semiconductors, and dielectrics) upon irradiation with linearly polarized fs-laser pulses (τ ∼ 30–150 fs, λ ∼ 800 nm) in air environment is studied experimentally and theoretically. In metals, predominantly low-spatial-frequency-LIPSS with periods close to the laser wavelength λ are observed perpendicular to the polarization. Under specific irradiation conditions, high-spatial-frequency-LIPSS with sub-100-nm spatial periods (∼λ/10) can be generated. For semiconductors, the impact of transient changes of the optical properties to the LIPSS periods is analyzed theoretically and experimentally. In dielectrics, the importance of transient excitation stages in the LIPSS formation is demonstrated experimentally using (multiple) double-fs-laser-pulse irradiation sequences. A characteristic decrease of the LIPSS periods is observed for double-pulse delays of less than 2 ps.

Laser-Induced Periodic Surface Structures— A Scientific Evergreen

Abstract: Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon and can be generated on almost any material upon irradiation with linearly polarized radiation. With the availability of ultrashort laser pulses, LIPSS have gained an increasing attraction during the past decade, since these structures can be generated in a simple single-step process, which allows a surface nanostructuring for tailoring optical, mechanical, and chemical surface properties. In this study, the current state in the field of LIPSS is reviewed. Their formation mechanisms are analyzed in ultrafast time-resolved scattering, diffraction, and polarization constrained double-pulse experiments. These experiments allow us to address the question whether the LIPSS are seeded via ultrafast energy deposition mechanisms acting during the absorption of optical radiation or via self-organization after the irradiation process. Relevant control parameters of LIPSS are identified, and technological applications featuring surface functionalization in the fields of optics, fluidics, medicine, and tribology are discussed.

On the role of surface plasmon polaritons in the formation of laser-induced periodic surface structures upon irradiation of silicon by femtosecond-laser pulses

Abstract: The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSSs) on single-crystalline silicon upon irradiation with single or multiple femtosecond-laser pulses (pulse duration τ=130 fs and central wavelength λ=800 nm) in air is studied experimentally and theoretically. In our theoretical approach, we model the LIPSS formation by combining the generally accepted first-principles theory of Sipe and co-workers with a Drude model in order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma. Our results are capable to explain quantitatively the spatial periods of the LIPSSs being somewhat smaller than the laser wavelength, their orientation perpendicular to the laser beam polarization, and their characteristic fluence dependence. Moreover, evidence is presented that surface plasmon polaritons play a dominant role during the initial stage of near-wavelength-sized periodic surface structures in fem...

Pulse number dependence of laser-induced periodic surface structures for femtosecond laser irradiation of silicon

Abstract: The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSS) on single-crystalline silicon upon irradiation with single (N=1) and multiple (N≤1000) linearly polarized femtosecond (fs) laser pulses (pulse duration τ=130 fs, central wavelength λ=800 nm) in air is studied experimentally. Scanning electron microscopy (SEM) and optical microscopy are used for imaging of the ablated surface morphologies, both revealing LIPSS with periodicities close to the laser wavelength and an orientation always perpendicular to the polarization of the fs-laser beam. It is experimentally demonstrated that these LIPSS can be formed in silicon upon irradiation by single fs-laser pulses—a result that is additionally supported by a recent theoretical model. Two-dimensional Fourier transforms of the SEM images allow the detailed analysis of the distribution of the spatial frequencies of the LIPSS and indicate, at a fixed peak fluence, a monotonous decrease in their mean spatial period between ∼770 nm...