Range Of Laser Pulse Durations Research Articles

Laser-induced ablation of tantalum in a wide range of pulse durations

We present data and analysis of the laser-induced ablation of pure tantalum (Ta, Z=73). We have identified different physical regimes using a wide range of laser pulse durations. A comparison of the influence of strongly varying laser pulse parameters on high-Z materials is presented. The crater depth caused by three different laser systems of pulse duration {varDelta }tau _1=5,mathrm {ns} and wavelength lambda _1=1064,mathrm {nm}, {varDelta }tau _2=35,mathrm {ps}, lambda _2=355,mathrm {nm} and {varDelta }tau _3=8.5,mathrm {fs}, lambda _3=790,mathrm {nm} are analyzed via confocal microscopy as a function of laser fluence and intensity. The minimum laser fluence needed for ablation, called threshold fluence, decreases with shorter pulse duration from 1.10,mathrm {J/cm}^2 for the nanosecond laser to 0.17,mathrm {J/cm}^2 for the femtosecond laser.

On the pulsed laser ablation of polycrystalline cubic boron nitride—Influence of pulse duration and material properties on ablation characteristics

Polycrystalline cubic boron nitride (PCBN) is widely used in industry as a cutting tool material for the machining of hardened steels, cast iron, or nickel-based super alloys. For the generation of geometrical features on such cutting tools, laser ablation is a novel and promising technology, which offers wear-free processing, high automation potential, and geometrical flexibility. In this study, the ablation mechanisms are experimentally investigated for a wide range of laser pulse durations (fs–ns regime), and the effects on ablation depth, ablation efficiency, and surface roughness are investigated. It is shown that melting and recrystallization of binder material when processing with nanosecond pulse duration leads to a reduction of the ablation efficiency and reduced surface quality. These defects can be avoided by using a shorter pulse duration (picosecond and femtosecond). The highest ablation efficiency is achieved for femtosecond laser ablation. Moreover, fs-laser processing shows beneficial behavior in the ablation of coarse-grained PCBN grades, where grain excavation due to binder removal is prevented and the resulting surface roughness is significantly decreased compared to ns-laser processing.

Influence of pulsed laser ablation on the surface integrity of PCBN cutting tool materials

Polycrystalline cubic boron nitride (PCBN) is widely used in industry as a cutting tool material for the machining of hardened steels, cast, or nickel-based super alloys. For the generation of geometrical features of such tools, laser ablation is a novel and promising technology, which offers wear-free processing, high automation potential, and geometrical flexibility. In this study, the ablation mechanism is experimentally investigated for a wide range of laser pulse durations (fs-ns regime) and laser-induced effects on the surface properties are presented. It could be shown by using Raman spectroscopy that laser-induced transformations of cubic boron nitride to the hexagonal lattice structure (hBN) or boron oxide (B2O3) are strongly determined by the single pulse and areal fluence of the laser source. Furthermore, a pulse duration of few picoseconds or below reduces the thermally induced phase transformations. Moreover, it was shown that the use of ns-laser leads to significant melting and recrystallization processes of the binder material, which reduces surface hardness. This mechanism was not found for the use of fs- and ps-laser sources.

Magnetic-field-induced enhancement of atomic stabilization in intense high-frequency laser fields

The role of the magnetic-field component of the laser pulse on the phenomenon of atomic stabilization is investigated in an ab initio study. This is achieved by solving the time-dependent Schr\"odinger equation for the laser-atom interaction beyond the dipole approximation. The system under study is atomic hydrogen and the atom is assumed to be irradiated by an intense xuv laser light pulse of varying intensity and duration. We consider two different photon energies, $\ensuremath{\hbar}\ensuremath{\omega}=54$ and 95 eV. The main finding is that there exists a range of laser pulse durations lasting for a few tens of field cycles where the atomic stabilization effect is enhanced due to the magnetic-field component. This is a rather surprising result that contradicts earlier statements made in the few-cycle pulse regime, where it has been shown that the magnetic field has a destructive effect in that the degree of stabilization is suppressed. It is further found that in the long-pulse limit the ionization probabilities obtained when illuminating the target with dipole and nondipole fields eventually coincide, meaning that the magnetic-field component of the laser field finally loses its significance in the context of atomic stabilization. It is also found that within the window of enhanced stabilization, the surplus population is distributed among excited bound states rather than in the initial ground state.

Thermomechanical effect of pulse-periodic laser radiation on cartilaginous and eye tissues

This paper is devoted to theoretical and experimental studies into the thermomechanical action of laser radiation on biological tissues. The thermal stresses and strains developing in biological tissues under the effect of pulse-periodic laser radiation are theoretically modeled for a wide range of laser pulse durations. The models constructed allow one to calculate the magnitude of pressures developing in cartilaginous and eye tissues exposed to laser radiation and predict the evolution of cavitation phenomena occurring therein. The calculation results agree well with experimental data on the growth of pressure and deformations, as well as the dynamics of formation of gas bubbles, in the laser-affected tissues. Experiments on the effect of laser radiation on the trabecular region of the eye in minipigs demonstrated that there existed optimal laser irradiation regimens causing a substantial increase in the hydraulic permeability of the radiation-exposed tissue, which can be used to develop a novel glaucoma treatment method.

Flexible CO2 laser system for fundamental research related to an extreme ultraviolet lithography source

A CO(2) laser system with flexible parameters was developed for fundamental research related to an extreme ultraviolet (EUV) lithography source. The laser is a master oscillator and power amplifier (MOPA) system, consisting of a master oscillator, an externally triggered plasma switch, a preamplifier, a main amplifier, and electronic synchronization units. The laser pulse duration can be varied easily from 10 to 110 ns, with a constant peak power for pulse durations from 25 to 110 ns. The MOPA laser system can also be operated in dual-oscillator mode to produce laser pulse with pulse duration as long as 200 ns and a train of laser pulses with flexible interval. The divergence of the laser beam is 1.3 times the diffraction limit. The laser intensity on the target surface can be up to 8x10(10) W/cm(2). Utilizing this CO(2) MOPA laser system, high conversion efficiency from laser to in-band (2% bandwidth) 13.5 nm EUV emission has been demonstrated over a wide range of laser pulse durations.

Microscopic analysis of the laser-induced femtosecond graphitization of diamond

We present a theoretical study of ultrafast phase transitions induced by femtosecond laser pulses of arbitrary form. Molecular-dynamics simulations on time dependent potential-energy surfaces derived from a microscopic Hamiltonian are performed. Applying this method to diamond, we show that a nonequilibrium transition to graphite takes place for a wide range of laser pulse durations and intensities. This ultrafast transition $(\ensuremath{\sim}100 \mathrm{fs})$ is driven by the suppression of the diamond minimum in the potential-energy surface of the laser excited system.

Characteristics of the absorption of high-intensity infrared radiation by molecules (review)

A review is given of the mechanisms of excitation of the vibrational levels of polyatomic molecules over a broad range of laser pulse durations. The part played by the rotational structure of the levels in compensating for the anhannonicity of the molecular vibrations is indicated. The theoretical conclusions are compared with the existing experimental results for SF6 and BCl3, molecules. The future trends of research on multiphoton excitation of molecules by high-intensity infrared radiation are outlined.