Filtern
Erscheinungsjahr
- 2010 (21) (entfernen)
Dokumenttyp
- Vortrag (8)
- Zeitschriftenartikel (6)
- Posterpräsentation (4)
- Beitrag zu einem Tagungsband (3)
Schlagworte
- Femtosecond laser ablation (6)
- Dielectrics (2)
- Semiconductor (2)
- Silicon (2)
- Coherent scattering (1)
- Damage threshold (1)
- Drude model (1)
- Elemental semiconductors (1)
- Fourier transforms (1)
- Free electron lasers (1)
- Fused silica (1)
- Heat affected zone (1)
- Indium phosphide (1)
- Laser beam effects (1)
- Laser damage (1)
- Laser safety (1)
- Laser-induced periodic surface structures (1)
- Optical breakdown (1)
- Optical microscopy (1)
- Photoelektron spectroscopy (1)
- Plasma formation (1)
- Polarisation (1)
- Polaritons (1)
- Polymer (1)
- Reflectivity measurements (1)
- Sapphire (1)
- Scanning Auger electron microscopy (1)
- Scanning electron microscopy (1)
- Scanning force microscopy (1)
- Surface morphology (1)
- Surface plasmons (1)
- TeO2 (1)
- Time-resolved coherent XUV scattering (1)
- Time-resolved measurements (1)
- Time-resolved microscopy (1)
- Time-resolved reflectivity measurements (1)
- Titanium nitride (1)
- Transmission measurements (1)
- Ultrashort laser pulses (1)
- X-ray (1)
Eingeladener Vortrag
- nein (8)
Short-pulse laser induced melting and ablation studied with time-resolved coherent XUV scattering
(2010)
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 (N = 1) and 560 nm (N
= 1000). The characteristic decrease in the LIPSS period is caused by a feedback-mechanism acting
upon excitation of surface plasmon polaritons at the rough silicon surface which is developing under
the action of multiple pulses into a periodically corrugated surface.
Femtosecond (fs) laser pulse ablation (pulse duration of 150 fs, wavelength of 775 nm, repetition rate of 1 kHz) of single-crystalline TeO2 surfaces was performed in air using the direct focusing technique. The lateral and vertical dimensions of laser ablated craters as well as the laser damage thresholds were evaluated for different pulse numbers applied to the same spot. The joint observation using optical microscopy, atomic force microscopy and scanning electron microscopy revealed the surface morphology of the ablated craters and also showed that the ablation threshold depends significantly on the number of laser pulses applied to the same spot due to incubation effects. The incubation effects change the absorption processes involved in fs-laser ablation of the transparent material from multiphoton absorption to a single-photon absorption. These results are discussed on the basis of recent models of the interaction of fs-laser pulses with dielectrics.
Structural and morphological modifikation of crystalline silicon induced femtosecond laser pulses
(2010)
A new approach is presented to quantify the so-called "heat affected zone" (HAZ) during
femtosecond laser pulse processing. Ablation of titanium nitride (TiN) thin films (~3 μm
thickness) by multiple femtosecond laser pulses (τ=130 fs, λ=800 nm) in air environment was
studied by means of two different surface analytical methods both being sensitive to chemical
alterations at the surface. Scanning Auger electron microscopy was applied for a visualization of the
spatial distribution of specific elements (Ti, O) within the laser-modified areas. The chemical state
of the irradiated surface was revealed by complementary x-ray photoelectron spectroscopy. Both
methods were used for a depth-profiling chemical analysis (tracking the elements Ti, N, O, and C)
using an Ar-ion beam for surface sputtering. In a narrow laser fluence range slightly below the
ablation threshold of TiN significant superficial oxidation can be observed leading to the formation
of substoichiometric TiO2-x. At fluences above the ablation threshold, an increased titanium
concentration is observed within the entire ablation craters. Following upon sputter removal the
elemental distribution into the depth of the nonablated material, the results allow an estimation of
the heat-affected zone for femtosecond laser ablation in air environment. According to our analyses,
the HAZ extends up to a few hundreds of nanometers into the nonablated material.
Near-IR femtosecond ( τ = 150 fs, λ = 775 nm, repetition rate 1 kHz) and VUV nanosecond (τ = 20 ns, λ = 157 nm, repetition rate 1 to 5 Hz) laser pulse ablation of single-crystalline TeO2 (c-TeO2, grown by the balance controlled Czochalski growth method) surfaces was performed in air using the direct focusing technique. The multi-method characterization using optical microscopy, atomic force microscopy and scanning electron microscopy revealed the surface morphology of the ablated craters. This allowed us to characterize precisely the lateral and vertical dimensions of the laser-ablated craters for different laser pulse energies and pulse numbers at each spot. Based on the obtained information, we quantitatively determined the ablation threshold fluence for the fs laser irradiation when different pulse numbers were applied to the same spot by using two independent extrapolation techniques. We found that in case of NIR femtosecond laser pulse irradiation, the ablation threshold significantly depends on the number of laser pulses applied to the same spot indicating that incubation effects play an important role in this material. In case of VUV ns laser pulses, the ablation rate is significantly higher due to the high photon energy and the predominantly linear absorption in the material. These results are discussed on the basis of recent models of the interaction of laser pulses with dielectrics.