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Journal ArticleDOI

Ultrashort-pulse laser machining of dielectric materials

22 Apr 1999-Journal of Applied Physics (American Institute of Physics)-Vol. 85, Iss: 9, pp 6803-6810
TL;DR: In this article, the authors show that high precision machining of all dielectrics (oxides, fluorides, explosives, teeth, glasses, ceramics, SiC, etc.) with no thermal shock or distortion of the remaining material by this mechanism is described.
Abstract: There is a strong deviation from the usual τ1/2 scaling of laser damage fluence for pulses below 10 ps in dielectric materials. This behavior is a result of the transition from a thermally dominated damage mechanism to one dominated by plasma formation on a time scale too short for significant energy transfer to the lattice. This new mechanism of damage (material removal) is accompanied by a qualitative change in the morphology of the interaction site and essentially no collateral damage. High precision machining of all dielectrics (oxides, fluorides, explosives, teeth, glasses, ceramics, SiC, etc.) with no thermal shock or distortion of the remaining material by this mechanism is described.
Citations
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Book
12 Mar 2014
TL;DR: In this paper, the effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1).
Abstract: In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

1,539 citations

Journal ArticleDOI
TL;DR: In this paper, the mechanism of ablation of solids by intense femtosecond laser pulses is described in an explicit analytical form, and the formulas for ablation thresholds and ablation rates for metals and dielectrics, combining the laser and target parameters, are derived and compared to experimental data.
Abstract: The mechanism of ablation of solids by intense femtosecond laser pulses is described in an explicit analytical form. It is shown that at high intensities when the ionization of the target material is complete before the end of the pulse, the ablation mechanism is the same for both metals and dielectrics. The physics of this new ablation regime involves ion acceleration in the electrostatic field caused by charge separation created by energetic electrons escaping from the target. The formulas for ablation thresholds and ablation rates for metals and dielectrics, combining the laser and target parameters, are derived and compared to experimental data. The calculated dependence of the ablation thresholds on the pulse duration is in agreement with the experimental data in a femtosecond range, and it is linked to the dependence for nanosecond pulses.

749 citations

Journal ArticleDOI
16 Dec 2004-Nature
TL;DR: Femtosecond laser surgery is used for axotomy in the roundworm Caenorhabditis elegans and it is shown that axons functionally regenerate after the operation.
Abstract: Understanding how nerves regenerate is an important step towards developing treatments for human neurological disease, but investigation has so far been limited to complex organisms (mouse and zebrafish) in the absence of precision techniques for severing axons (axotomy). Here we use femtosecond laser surgery for axotomy in the roundworm Caenorhabditis elegans and show that these axons functionally regenerate after the operation. Application of this precise surgical technique should enable nerve regeneration to be studied in vivo in its most evolutionarily simple form.

584 citations

Journal ArticleDOI
TL;DR: In this paper, an experimentalist's point of view of the dynamics of H-2+ in an intense laser field is presented, which is interpreted in terms of bond-softening, vibrational trapping (bond-hardening), below-threshold dissociation and laser-induced alignment of the molecular axis.
Abstract: In the past decade, the understanding of the dynamics of small molecules in intense laser fields has advanced enormously. At the same time, the technology of ultra-short pulsed lasers has equally progressed to such an extent that femtosecond lasers are now widely available. This review is written from an experimentalist's point of view and begins by discussing the value of this research and defining the meaning of the word 'intense'. It continues with describing the Ti: sapphire laser, including topics such as pulse compression, chirped pulse amplification, optical parametric amplification, laser-pulse diagnostics and the absolute phase. Further aspects include focusing, the focal volume effect and space charge. The discussion of physics begins with the Keldysh parameter and the three regimes of ionization, i.e. multi-photon, tunnelling and over-the-barrier. Direct-double ionization (non-sequential ionization), high-harmonic generation, above-threshold ionization and attosecond pulses are briefly mentioned. Subsequently, a theoretical calculation, which solves the time-dependent Schrodinger equation, is compared with an experimental result. The dynamics of H-2(+) in an intense laser field is interpreted in terms of bond-softening, vibrational trapping (bond-hardening), below-threshold dissociation and laser-induced alignment of the molecular axis. The final section discusses the modified Franck-Condon principle, enhanced ionization at critical distances and Coulomb explosion of diatomic and triatomic molecules.

463 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compared the performance of the atomic spectrometric methods based on a number of figures of merit, including detection power, selectivity, multi-element capability, cost, applications, and "age" of the methods.
Abstract: The “super stars” of analytical atomic spectrometry are electrothermal atomization-atomic absorption spectrometry (ETA-AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Many other atomic spectrometric methods have been used to determine levels of elements present in solid, liquid and gaseous samples, but in most cases these other methods are inferior to the big three super star methods. The other atomic methods include glow discharge emission, absorption and mass spectrometric methods, laser excited fluorescence emission and ionization methods, and flame and microwave plasma emission and mass spectrometric methods. These “lesser” methods will be compared to the “super star” methods based on a number of figures of merit, including detection power, selectivity, multi-element capability, cost, applications, and “age” of the methods. The “age” of the method will be determined by a modification of the well-known Laitinen “Seven Ages of an Analytical Method” (H.A. Laitinen, Anal. Chem., 1973, 45, 2305). Calculations will show that certain methods are capable of single atom detection, including several atomic absorption methods, as well as laser atomic ionization and fluorescence methods. The comparison of methods will indicate why the “super stars” of atomic spectrometric methods will continue to retain their status and what must be done for the lesser atomic methods to approach “super star” status. Certainly most of the lesser atomic spectrometric methods will have a limited place in the analytical arena. Because of the wide current interest and research activity, special emphasis will be placed on the technique of laser induced breakdown spectrometry (LIBS). Its current status and future developments will therefore be reviewed.

402 citations

References
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01 Jan 1956

4,298 citations

01 Jan 1962

3,014 citations

01 Jan 1986
TL;DR: In this article, an expression for the probability of tunnel ionization in an alternating field, of a complex atom and of an atomic ion that are in an arbitrary state, was derived in the quasiclassical approximation n* $1.
Abstract: An expression is derived for the probability of tunnel ionization, in an alternating field, of a complex atom and of an atomic ion that are in an arbitrary state. The expression for the tunnel-ionization probability is obtained in the quasiclassical approximation n* $1. Expressions are also obtained for states with arbitrary values of I at arbitrary ellipticity of the radiation. A quasiclassical approximation yields results up to values n * ~ 1, with accuracy up to several percent.

1,504 citations

Journal ArticleDOI
TL;DR: A decreasing threshold fluence is found associated with a gradual transition from the long-pulse, thermally dominated regime to an ablative regime dominated by collisional and multiphoton ionization, and plasma formation.
Abstract: We report extensive laser-induced damage threshold measurements on dielectric materials at wavelengths of 1053 and 526 nm for pulse durations $\ensuremath{\tau}$ ranging from 140 fs to 1 ns. Qualitative differences in the morphology of damage and a departure from the diffusion-dominated ${\ensuremath{\tau}}^{\frac{1}{2}}$ scaling of the damage fluence indicate that damage occurs from ablation for $\ensuremath{\tau}l~10$ ps and from conventional melting, boiling, and fracture for $\ensuremath{\tau}g50$ ps. We find a decreasing threshold fluence associated with a gradual transition from the long-pulse, thermally dominated regime to an ablative regime dominated by collisional and multiphoton ionization, and plasma formation. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement with the experimental results.

1,435 citations

Book
01 Jan 1982
TL;DR: In this paper, the energy and momentum conservation of phonon-impurity coupling in the diamond lattice is discussed. But the authors do not consider the effect of photo-ionization on photo-deionization of a hydrogenic acceptor.
Abstract: Part 1 Band structure of semiconductors: the crystal Hamiltonian adiabatic approximation phonons the one-electron approximation Bloch functions nearly-free-electron model energy gaps spin-orbit coupling and orbital characteristics band structures chemical trends k.p perturbation and effective mass temperature dependence of energy gaps deformation potentials alloys. Part 2 Energy levels: the effective-mass approximation electron dynamics Zener-Bloch oscillations Landau levels plasma oscillations excitons hydrogenic impurities hydrogen molecule centres core effects deep-level impurities scattering states impurity bands. Part 3 Lattice scattering: general features energy and momentum conservation acoustic phonon scattering optical phonon scattering polar optical mode scattering piezoelectric scattering scattering-induced electron mass mobilities appendix - acoustic waves in the diamond lattice. Part 4 Impurity scattering: general features charged-impurity scattering neutral-impurity scattering central-cell contribution to charged-impurity scattering dipole scattering electron-hole scattering electron-electron scattering mobilities appendix - Debye screening length, average separation of impurities, alloy scattering. Part 5 Radiative transitions: transition rate photo-ionization and radiative capture cross-section wavefunctions direct interband transitions photo-deionization of a hydrogenic acceptor photo-ionization of a hydrogenic donor photo-ionization of quantum-defect impurities photo-ionization of deep-level impurities summary of photo-ionization cross-sections indirect transitions indirect interband transitions free-carrier absorption free-carrier scattering of light appendix - justification of effective-mass approximation in light scattering. Part 6 Non-radiative processes: electron-lattice coupling the configuration-co-ordinate diagram semi-classical thermal generation rate thermal broadening of radiative transitions thermal generation and capture rates electron-lattice coupling strengths selection rules for phonon-impurity coupling phonon-cascade capture the Auger effect impact ionization appendix - the multiphonon matrix element. Part 7 Quantum processes in a magnetic field: introduction collision-free situation collision-induced current scattering mechanisms transverse Shubnikov-de Haas oscillations longitudinal Shubnikov-de Haas oscillations magnetophenon oscillations. Part 8 Scattering in a degenerate gas: general equations elastic collisions acoustic phonon scattering energy relaxation time. Part 9 Dynamic screening: introduction polar optical modes plasma modes coupled modes the Lindhard dielectric function fluctuations screening regimes. Author index. Subject index.

1,259 citations