Arkadi Rosenfeld

Femtosecond laser-induced periodic surface structures

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.

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

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...

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

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...

Surface damage threshold and structuring of dielectrics using femtosecond laser pulses: the role of incubation

Abstract We present results on the surface damage threshold of a-SiO2 and YLF after single and multiple laser pulse irradiation at a pulse duration of 100 fs and radiation wavelength of 800 nm. The surface damage threshold drops dramatically after the first laser shots until reaching an almost constant level. The threshold reduction at low shot numbers is attributed to laser induced defect formation. This has important consequences for applications, such as laser machining and the lifetime of optical components. As an example of relevance to applications, we discuss the generation of high quality micro pockets in a-SiO2 and YLF.

Laser ablation of dielectrics with temporally shaped femtosecond pulses

A significant improvement in the quality of ultrafast laser microstructuring of dielectrics is demonstrated by using temporally shaped pulse trains with subpicosecond separation. The sequential energy delivery induces a material softening during the initial steps of excitation changing the energy coupling for the subsequent steps. This leads to lower stress, cleaner structures, and provides a material-dependent optimization process.

Femtosecond laser-induced periodic surface structures on silica

The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences (τ = 150 fs pulse duration, λ = 800 nm center wavelength, temporal pulse separation Δt < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL)] with different spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the “dynamics” of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier...

Laser-Induced Periodic Surface Structures— A Scientific Evergreen

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.

Laser-induced damage in SiO2 and CaF2 with picosecond and femtosecond laser pulses

Single- and multiple-shot damage thresholds and plasma-emission thresholds for fused silica and CaF2 are reported for 790 nm photons as a function of laser pulse width (190 fs – 4.5 ps). The results are compared with single-shot plasma-emission measurements [1] and with multiple-shot damage measurements [2]. Both the damage threshold and the plasma-emission threshold are shown to decrease with decreasing pulse width over the entire pulse-width range investigated.

APPLICATION OF SELF-FOCUSING OF PS LASER PULSES FOR THREE-DIMENSIONAL MICROSTRUCTURING OF TRANSPARENT MATERIALS

Self-focusing of ps laser pulses (λ=790 nm) due to the nonlinear Kerr effect is shown to provide an easy and flexible method for producing bulk structures with dimensions on the order of 10 μm without damaging the entrance or exit surfaces of the material. The depth at which damage occurs can be controlled by adjusting either the pulse energy or pulse length. A study of the dependence of structure depth on the square root of the laser power for a given pulse length provides a straightforward method for determining the nonlinear index of refraction (Kerr coefficient), n2.

Dynamic ultrafast laser spatial tailoring for parallel micromachining of photonic devices in transparent materials.

Femtosecond laser processing of bulk transparent materials can generate localized positive changes of the refractive index. Thus, by translation of the laser spot, light-guiding structures are achievable in three dimensions. Increasing the number of laser processing spots can consequently reduce the machining effort. In this paper, we report on a procedure of dynamic ultrafast laser beam spatial tailoring for parallel photoinscription of photonic functions. Multispot operation is achieved by spatially modulating the wavefront of the beam with a time-evolutive periodical binary phase mask. The parallel longitudinal writing of multiple waveguides is demonstrated in fused silica. Using this technique, light dividers in three dimensions and wavelength-division demultiplexing (WDD) devices relying on evanescent wave coupling are demonstrated.