High-power Short-pulse Laser Research Articles

Phase rotation scheme of the ions accelerated by an intense femtosecond Laser

A phase rotation scheme is investigated for the ion beam that is emitted from foil target irradiated by a high power (100 TW) short-pulse (20 fs) laser. By application of an RF electric field synchronized with the laser pulse, the ion beams in the energy range of ± 5% is expected to be compressed into the range within (1% of our goal. Assumed parameters are 144 MHz for RF frequency and 280 kV RF amplitude for C with center energy of 2 MeV/u using ±π/4 RF phase range. We think that a quarter wave resonator with double-gaps is a good candidate for the RF-cavity. The gap length is 2 cm.

Weibel instability of relativistic electron flows in a laser produced plasma

The strong flows of relativistic electrons, encountered in high power short pulse laser plasma interaction, have the potential to drive Weibel instability producing short wavelength magnetic fields. The presence of a Langmuir wave couples the Weibel instability to two electrostatic wave sidebands. The density perturbations due to the sidebands couple with the oscillatory electron velocity due to the pump to produce a current that enhances the growth rate of Weibel instability. The thermal spread of the energetic (drifting) electrons, however, reduces the growth rate.

High-power short-pulse laser heating of low dimensional structures: a hyperbolic heat conduction study using TLM

Radiation from high-power fast-pulsed lasers is being used in the engineering and the investigation of low-dimensional semiconductor structures and devices. In all laser involved processes, heat is supplied to the material in very small localised areas at ultra-fast rates and is believed to obey the hyperbolic heat conduction. A Transmission Line Matrix (TLM) solution is developed to account for the heat wave propagation in the low dimensional thin film. A good agreement is found between the TLM and analytical results. The present results also show that pulsed laser thermal waves can be used in the analysis of subsurface properties such as defects, thickness distribution and the thermal nature of interfaces.

X ray laser spectroscopy at the ESR: a proposed novel tool for the investigation of exotic isotopes

Novel X-ray laser sources driven by short-pulse high power lasers can provide intense beams of radiation at fixed energy. In combination with the Doppler-tuning possible at the ESR storage ring, this can be utilized for precision spectroscopy of highly charged ions. The sensitivity should be sufficient to apply this technique to lithium-like radioactive ions.

Fast laser heating of electrons as a source of ion-acoustic oscillations

It is shown that heating of electrons due to the inverse bremsstrahlung absorption of high-power short-pulse laser radiation results in parametric generation of ion-acoustic waves. Dependences of the generation efficiency on the laser pulse duration and intensity are derived. The range of wave numbers where the amplitude of the ion-acoustic oscillations increases by more than an order of magnitude is determined.

Filamentation of ultrashort pulse laser beams resulting from their propagation over long distances in air

The propagation of high-power short-pulse laser beams over considerable distances in air is studied both experimentally and via numerical simulations. Filaments are formed after 5–10 m and their propagation over distances in excess of 200 m is reported for the first time. The lateral dimensions of the filaments are found to range from about 100 μm to a few millimeters in diameter. The early values of plasma electron density have been inferred to be a few times 1016 cm−3 using longitudinal spectral interferometry. For 500 fs pulses and a wavelength of 1053 nm, the energy in the filament can be quite high initially (∼8 mJ) and is found to stabilize at about 1.5–2 mJ, after about 35 m. A simple model based on the nonlinear Schrödinger equation coupled to a multiphoton ionization law appears to describe several experimental results quite well.

Laser-driven plasma-based accelerators: Wakefield excitation, channel guiding, and laser triggered particle injection

Plasma-based accelerators are discussed in which high-power short pulse lasers are the power source, suitably tailored plasma structures provide guiding of the laser beam and support large accelerating gradients, and an optical scheme is used to produce time-synchronized ultrashort electron bunches. From scaling laws laser requirements are obtained for development of compact high-energy accelerators. Simulation results of laser guiding and wakefield excitation in plasma channels, as well as laser-based injection of particles into a plasma wake, are presented. Details of the experimental program at Lawrence Berkeley National Laboratory on laser guiding, laser wakefield-based accelerators, and laser triggered injection are given.

Analysis of the kinetic equation for mass transport induced by short laser pulses

The interaction between high-power short-pulse laser radiation and a metal target is considered. An analysis is made of the transport of material atoms from the surface layer into the bulk of a semi-infinite sample under the action of the stress field of a plane shock wave and a temperature gradient. The results of numerical calculations for a laser power density of 109 W/cm2 and a pulse length of 30 ns show good agreement with the results of earlier experiments.

Penetration depth of Ultrapulse carbon dioxide laser in human skin.

Recent technological advances have dramatically increased the use of lasers in skin resurfacing. The first high-power short-pulse laser, Ultrapulse, has found extensive use in dermatology and plastic surgery for skin resurfacing. Reports for penetration depth are at best anecdotal. To our knowledge this is the first report of histological effects of the Ultrapulse in human skin. To determine the effect of single and repeated (two or three) Ultrapulse laser impacts on volar forearm skin. The volar surface of the arm in four patients received in adjacent areas either one, two, or three pulses, after anesthesia. The treated areas were immediately biopsied, hematoxylin & eosin prepared, and examined. Increasing the number of passes correlates with increased depth of penetration and thermal ablation. No significant propagation of destructive thermal energy to adjacent tissue was noted. One impact at the tested parameters ablated most of the epidermis. Two impacts superimposed ablated the entire epidermis and the superficial papillary dermis. Three superimposed impacts penetrated to the reticular dermis.

Optical ablation by high-power short-pulse lasers

Laser-induced damage threshold measurements were performed on homogeneous and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations τ ranging from 140 fs to 1 ns. Gold coatings were found, both experimentally and theoretically, to be limited to 0.6 J/cm2 in the subpicosecond range for 1053-nm pulses. In dielectrics, we find qualitative differences in the morphology of damage and a departure from the diffusion-dominated τ1/2 scaling that indicate that damage results from plasma formation and ablation for τ ≤ 10 ps and from conventional heating and melting for τ > 50 ps. A theoretical model based on electron production by multiphoton ionization, joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulse-width and the wavelength scaling of experimental results.

Multispectral tissue characterization with time-resolved detection of diffusely scattered white light

A novel technique for the noninvasive measurement of tissue optical properties simultaneously at all visible and near-infrared wavelengths is presented. The technique is based on the time-resolved detection of multicolor diffusely scattered light. Short pulses of white light are produced by using self-phase modulation by focusing the light from a short-pulsed high-power laser into a cuvette filled with water. After spectral dispersion in a polychromator and temporal dispersion in a streak tube, a two-dimensional CCD camera was used as a detector, with one dimension used for time resolution and the other one for wavelength separation.

A high-power short-pulse laser diode for waveguide second harmonic generation

This paper describes successful development of a high-power short-pulse i.r. laser diode, together with numerical analyses giving a clear understanding of the operation. The novel aspect of the present laser diode is that a saturable absorber is incorporated for gain switching into the buried-twin-ridge substrate (BTRS) structure which allows a high-stability fundamental spatial mode operation. Peak powers as high as 1.23 W and pulse widths as narrow as 34.1 ps have been obtained in an efficient gain-switching operation with the high mode stability. The experimental observations are well-explicable by the numerical analyses in substantial respects. We also report picosecond-pulse blue-light generation which has been attained by applying the frequency doubling technique to the above laser in a LiNbO 3 waveguide.

高出力短パルスレーザ照射によるクラスタの生成

高出力短パルスレーザ照射によるクラスタの生成

Theoretical analysis of a Brillouin switch for amplifier decoupling and prepulse suppression in short-pulse high-power laser systems

A switch suited for high-power amplifier chains emitting nanosecond pulses is theoretically investigated. It is based on a two-step Brillouin backscattering process. Gases like N2 or SF6 at high pressure are used as the scattering medium. The transmission efficiency is about 50%. The limitation is mainly due to gas breakdown. The capability for amplifier decoupling and prepulse suppression is excellent. Strong pulse steepening favors the generation of ultra-short laser pulses.

The analysis of the RF response of a solid wire excited by a focused laser beam

The solution is presented for the current excited on a solid cylindrical wire with a flat endcap which is excited by a short current filament oriented parallel to the wire axis and located on or near the endcap surface. This wire/source geometry has become of interest as a result of experimental findings in which transient source filaments have been excited on metal targets due to the incidence of a high-power short-pulse laser beam. Steady-state solutions are developed which show the basic characteristics of the responses and their dependence on critical wire and source parameters. Transient responses also are presented and shown to exhibit excellent agreement with measured results.