Showing papers by "Arkadi Rosenfeld published in 2003"

Fundamentals and advantages of ultrafast micro structuring of transparent materials

Abstract: Experimental investigations using femtosecond and picosecond laser pulses at 800 nm illuminate the distinctions between the dynamics and nature of ultrafast processing of dielectrics compared with semiconductors and metals. Dielectric materials are strongly charged at the surface on the sub-ps time scale and undergo an impulsive Coulomb explosion prior to thermal ablation. Provided the laser pulse width remains in the ps or sub-ps time domain, this effect can be exploited for processing. In the case of thermal ablation alone, the high localization of energy accompanied by ultrafast laser micro-structuring is of great advantage also for high quality processing of thin metallic or semiconducting layers, in which the surface charge is effectively quenched.

Temporal pulse manipulation and ion generation in ultrafast laser ablation of silicon

Abstract: The possibility of phase manipulation and temporal tailoring of ultrashort laser pulses provides new opportunities for optimal processing of materials. An experimental demonstration of the technique that shows the possibility to design excitation sequences tailored with respect to the material response is presented, laying the groundwork for adaptive optimization in material structuring. The technique is particularly suitable to generate controllable ion beams by ultrafast laser ablation. Silicon samples irradiated with multiple laser pulses separated by the phase-transformation time show increased ion emission efficiency with different energetic signatures correlated to a cleaner aspect of the laser-induced structures on the surface.

Dynamic temporal pulse shaping in advanced ultrafast laser material processing

Abstract: Phase-manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectrics, allowing to adapt the laser energy delivery rate to the material properties for optimal processing. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.

Ultrafast laser material processing using dynamic temporal pulse shaping

Abstract: Phase manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectric materials, allowing to adapt the energy delivery rate to the material properties for optimal processing quality. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.

Ultrashort laser pulse processing of wave guides for medical applications

Abstract: The availability of ultra short (ps and sub-ps) pulsed lasers has stimulated a growing interest in exploiting the enhanced flexibility of femtosecond and/or picosecond laser technology for micro-machining. The high peak powers available at relatively low single pulse energies potentially allow for a precise localization of photon energy, either on the surface or inside (transparent) materials. Three dimensional micro structuring of bulk transparent media without any sign of mechanical cracking has been demonstrated. In this study, the potential of ultra short laser processing was used to modify the cladding-core interface in normal fused silica wave guides. The idea behind this technique is to enforce a local mismatch for total reflection at the interface at minimal mechanic stress. The laser-induced modifications were studied in dependence of pulse width, focal alignment, single pulse energy and pulse overlap. Micro traces with a thickness between 3 and 8 μm were generated with a spacing of 10 μm in the sub-surface region using sub-ps and ps laser pulses at a wavelength of 800 nm. The optical leakage enforced by a micro spiral pattern is significant and can be utilized for medical applications or potentially also for telecommunications and fiber laser technology.

Microstructuring of an optical waveguide for producing functional optical elements

Abstract: The invention relates to a method for microstructuring an optical waveguide having a first cross-sectional region with a first refractive index, a second cross-sectional region with a second refractive index, and a boundary region in the transition from the first to the second cross-sectional region, in which the optical waveguide is exposed to laser radiation in the form of at least one ultra-short single pulse or a sequence of pulses with a defined energy input, whereby the radiant exposure takes place in such a manner that a modification of at least one optical property of the optical waveguide takes place at at least one defined portion of the boundary region.

Advanced ultrafast laser material processing using temporal pulse shaping

Abstract: Phase manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectric materials, allowing to adapt the laser light to the material properties for optimal processing quality. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. Loss and cooling mechanisms in the electron population, surface charging, as well as the strength of the electron-phonon interactions control the effectiveness of the energy deposition into the lattice. Knowledge of the response times of materials establishes a guideline for using temporally shaped pulses or pulse trains in order to optimize the structuring process with respect to efficient material removal and reduction of the residual damage. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show, that this can result in lower stress, cleaner structures, and allow for a material-dependent optimization process.

Temporal pulse shaping and optimization in ultrafast laser ablation of materials

Abstract: Dielectric materials exposed to ultrashort laser radiation have shown individualized reaction pathways to accommodate the sudden energy input, depending on the efficiency of the free electron generation and on the ability to release the electronic energy into the lattice. Electronic loss mechanisms, the efficiency of surface charging, as well as the strength of the electron-phonon interaction control the effectiveness of the energy deposition into the lattice. The electrostatic surface break-up is a fast, subpicosecond process, while thermal mechanisms start to dominate on a longer, picosecond time scale given by the electron-lattice equilibration and phase transformation time. From this perspective, phase-manipulated ultrafast laser pulses and temporally tailored pulse trains with THz repetition rates are promising new tools for quality micromachining of brittle dielectrics, permitting to adapt the laser energy delivery rate to the material intrinsic properties and forecasting a material-dependent optimization process.

Temporal Pulse Shaping and Optimization in Ultrafast Laser Ablation of Materials

Abstract: The possibility of phase manipulation and temporal tailoring of ultrashort laser pulses enables new opportunities for optimal processing of materials. Phase-manipulated ultrafast laser pulses allow adapting the laser energy delivery rate to the material properties for optimal processing laying the groundwork for adaptive optimization in materials structuring. Different materials respond with specific reaction pathways to the sudden energy input depending on the efficiency of electron generation and on the ability to release the energy into the lattice. The sequential energy delivery with judiciously chosen pulse trains may induce softening of the material during the initial steps of excitation and change the energy coupling for the subsequent steps. We show that this can result in lower stress, cleaner structures, and allow for a materialdependent optimization process.