High-intensity Femtosecond Laser Research Articles

Spectroscopic study of gold nanoparticle formation through high intensity laser irradiation of solution

A spectroscopic study of the gold nanoparticle (NP) formation by high-intensity femtosecond laser irradiation of a gold ion solution was reported. The effect of varying energy density of the laser on the formation of gold NPs was also investigated. The surface plasmon resonance (SPR) peak of the gold nanocolloid in real-time UV-visible absorption spectra during laser irradiation showed a distinctive progress; the SPR absorption peak intensity increased after a certain irradiation time, reached a maximum and then gradually decreased. During this absorption variation, at the same time, the peak wavelength changed from 530 to 507 nm. According to an empirical equation derived from a large volume of experimental data, the estimated mean size of the gold NPs varied from 43.4 to 3.2 nm during the laser irradiation. The mean size of gold NPs formed at specific irradiation times by transmission electron microscopy showed the similar trend as that obtained in the spectroscopic analysis. From these observations, the formation mechanism of gold NPs during laser irradiation was considered to have two steps. The first is a reduction of gold ions by reactive species produced through a non-linear reaction during high intensity laser irradiation of the solution; the second is the laser fragmentation of produced gold particles into smaller pieces. The gold nanocolloid produced after the fragmentation by excess irradiation showed high stability for at least a week without the addition of any dispersant because of the negative charge on the surface of the nanoparticles probably due to the surface oxidation of gold nanoparticles. A higher laser intensity resulted in a higher efficiency of gold NPs fabrication, which was attributed to a larger effective volume of the reaction.

Shock-induced concentric rings in femtosecond laser ablation of glass

Both the single and multiple pulse ablation of dielectrics with high-intensity femtosecond lasers have been well studied. Additionally, the “pulse-shaping” regime, in which temporal peaks are separated by picoseconds, has also been investigated. In this paper, we show that a “prepulse configuration”—where one pulse is followed several nanoseconds later by a much stronger pulse—is qualitatively different from any of the previously investigated regimes. In particular, it leads to the recently discovered “concentric rings” feature in glass. We show that the damage pattern produced in glass is very different for two pulses separated by nanoseconds than for two pulses separated by either milliseconds or picoseconds. For nanosecond separations, the second pulse interacts with the shock wave created by the first, significantly altering the damage pattern. In addition to producing novel structures, this pump-probe technique provides a new way of studying ablation plume and shockwave dynamics.

Dispersion-less spectrograph for absolute measurement of multi keV x-ray flux from high intensity laser produced plasmas

A back illuminated x-ray CCD detector working in single photon counting mode is described for absolute measurement of x-ray emission spectrum without any additional dispersive device. Image analysis software has been developed to reconstruct the x-ray spectra even from a CCD frame which was exposed above the single photon counting threshold. Characterization of the spectrograph was carried out by measurement of characteristic line and continuum x-ray emission from high intensity femtosecond laser produced plasma in the 2–20 keV energy range. The resolution of spectrograph is ∼ 3% at 4.5 keV and ∼ 1.4% at 17.5 keV which is broadly in agreement with the theoretical value expected with the spectrograph parameters The experimentally determined calibration factor is about 20% higher than the data provided by the CCD manufacturer. The spectrograph is particularly suited for measuring the x-ray emission spectrum in a large energy interval. An example of x-ray emission spectrum from the rear side of the laser heated titanium foil is also presented.

Resonance laser-plasma excitation of coherent terahertz phonons in the bulk of fluorine-bearing crystals under high-intensity femtosecond laser irradiation

The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and were discovered in a calcium fluoride crystal and coherent phonons with frequencies of and were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase after laser irradiation.

Splash plasma channels produced by picosecond laser pulses in argon gas for laser wakefield acceleration

Short-lived, $\ensuremath{\sim}10\text{ }\text{ }\mathrm{ps}$, deep plasma channels, with their lengths of $\ensuremath{\sim}1\text{ }\text{ }\mathrm{mm}$ and diameters of $\ensuremath{\sim}20\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$, are observed and characterized in Ar gas jets irradiated by moderate intensity, $\ensuremath{\sim}{10}^{15--16}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$, laser pulses with a duration from subpicosecond to several picoseconds. The channels, upon 2D particle-in-cell simulations including ionization, fit well in the guiding of high intensity femtosecond laser pulses and, therefore, in laser wakefield acceleration with a controllable electron self-injection.

Femtosecond laser guiding of a high-voltage discharge and the restoration of dielectric strength in air and nitrogen

The use of a low energy, high peak intensity (>100 TW/cm2) femtosecond laser pulse is investigated for guiding and control of a sub-microsecond high voltage discharge. Study of the laser induced plasma channel and measurements of the field required for breakdown in air and nitrogen at atmospheric pressure are presented. Direct imaging of the dynamics of the discharge breakdown shows effective laser guiding. The effectiveness of laser guiding is shown to be critically dependent on the laser focusing geometry, timing, and location relative to the electrodes.

Autocorrelation Measurement of Fast Electron Pulses Emitted through the Interaction of Femtosecond Laser Pulses with a Solid Target

We report the first direct measurement of the emission duration of laser-accelerated fast electrons from the surface of a solid target irradiated by a high-intensity femtosecond laser pulse. The emission duration is determined by autocorrelation measurement using the Coulomb repulsive forces that act on two equivalent electron pulses. The emission duration depends on the laser pulse duration for laser pulses of 200-690 fs. Numerical modeling of three-dimensional charged particle dynamics indicates that the emission duration of fast electrons is almost equal to the duration of the laser pulse.

Application of the Z-scan technique to determine the optical Kerr coefficient and two-photon absorption coefficient of magnetite nanoparticles colloidal suspension

We investigate the occurrence of the optical Kerr effect and two-photon absorption when an oil-based magnetic Fe3O4 nanoparticles colloidal suspension is illuminated with high intensity femtosecond laser pulses. The frequency of the pulses is controlled and the Z-scan technique is employed in our measurements of the nonlinear optical Kerr coefficient (n2) and two-photon absorption coefficient (β). From these values it was possible to calculate the real and imaginary parts of the third-order susceptibility. We observed that increasing the pulse frequency, additional physical processes take place, increasing artificially the absolute values of n2 and β. The experimental conditions are discussed to assure the obtention of reliable values of these nonlinear optical parameters, which may be useful in all-optical switching and optical power limiting applications.

Fabrication of solid-solution gold–platinum nanoparticles with controllable compositions by high-intensity laser irradiation of solution

In the present study, solid-solution gold–platinum (Au–Pt) nanoparticles with controllable compositions were fabricated by high-intensity femtosecond laser irradiation of an aqueous solution of gold and platinum ions without any chemicals and complicated processes. Transmittance electron microscopy revealed that the single nanometer-sized particles were fabricated by femtosecond laser irradiation of mixed aqueous solutions of gold and platinum ions. The crystalline structure of nanoparticles was characterized by electron and X-ray diffractions. Contrary to the bulk Au–Pt binary systems, which commonly contain a pair of diffraction peaks between pure gold and platinum peaks because of its large miscibility gap in phase diagram, or mixture of Au and Pt, the diffraction peaks of Au–Pt nanoparticles fabricated in the experiment showed a characteristic of the fcc-type lattice. Moreover, the diffraction patterns shifted monotonically from the peak position of pure gold to that of pure platinum as the fractions of platinum ions in the solution were increased. These observations strongly imply that the Au–Pt nanoparticles were solid solution with intended compositions. This technique is not only simple and environmentally friendly, but also applicable to other binary and ternary systems.

Three-Photon Absorption in Zno Film Using Ultra Short Pulse Laser

The three-photon absorption (3PA) in nanostructure wide-band gap ZnO semiconductor material is observed under high intensity femtosecond Titanium-Sapphire laser of 800 nm wavelength excitation. The ZnO film was prepared by chemical spray pyrolysis technique with substrate temperature of 400℃. The optical properties concerning the absorp-tion, transmission, reflection, Raman and the photoluminescence spectra are studied for the prepared film. The structure of the ZnO film was tested with the X-Ray diffraction and it was found to be a polycrystalline with recognized peaks oriented in (002), and (102). The measured of three photon absorption coefficient was found to be about 0.0166 cm3/Gwatt2, which is about five times higher than the bulk value. The fully computerized z-scan system was used to measure the nonlinear coefficients from the Gaussian fit of the transmitted laser incident.

超强飞秒激光驱动气体靶致X光源的背光成像

超强飞秒激光驱动气体靶致X光源的背光成像

Nonlinear polarization response of an atomic gas medium in the field of a high-intensity femtosecond laser pulse

Polarization response that appears in silver vapors in the field of a high-intensity femtosecond Ti:sapphire laser has been studied by the direct numerical integration of the time-dependent Schrodinger equation. The regions of applicability have been determined for perturbation theory and the power series expansion of the polarization in the field. The contribution of free electrons to the response at the frequency of the interacting field has been calculated, which is due to the photoionization process and limits the Kerr effect. An important contribution of laser-excited atomic states to nonlinear atomic responses of neutral atoms has been demonstrated.

Three-Photon Absorption in Nanostructure Wide-Band Gap Semiconductor ZnO Using Femtosecond Laser

The three-photon absorption (3PA) in nanostructure wide-band gap ZnO semiconductor material is observed under high intensity femtosecond Titanium-Sapphire laser of 800 nm wavelength excitation. The ZnO nanofilms were prepared by chemical spray pyrolysis technique with substrate temperature of 370 oC. The optical properties concerning the absorption, transmission, and the photoluminescence spectra are studied for the prepared nanofilms. The structure of the ZnO nanofilm was tested with the X-Ray diffraction and it was found to be a polycrystalline with recognized peaks oriented in (002), (101), and (100). The measured nonlinear absorption coefficient was found to be about 0.062 cm3/Gwatt2, which is about ten time higher than the bulk value. The observation of 3PA under the influence of intense laser radiation was attributed to the two-photon absorption followed by free carrier absorption. The fully computerized z-scan system was used to measure the nonlinear coefficients from the Gaussian fit of the transmitted laser incident. The observation of the three-photon absorption under high intensity in nanocrystalline material attributed to the resonance between the 3hvsph and hvflu which is simply achieved in nanostructure.

Activation of color centers in bismuth glass by femtosecond laser radiation

The activation of color centers in the bismuth aluminum-boron-phosphate glass by high-intensity femtosecond laser radiation is experimentally studied. The dynamics of the laser-induced emitting centers in the bulk of sample is characterized. The photoactivation of bismuth glasses is possibly related to the recharging of structural precursors, which serve as effective electron traps and whose possible configuration is discusses. The effect of the femtosecond irradiation involves the initiation of the nonlinear ionization of the glass matrix and the generation of plasma with the concentration of carriers that is sufficiently high to provide almost complete recharging of precursors over several laser pulses.

Effect of laser pulse time profile on its absorption by argon clusters

AbstractThe interaction of medium sized Argon clusters (30 Å) with high-intensity femtosecond laser pulses (806 nm, 8 × 1016 W/cm2) of durations ranging from 10 fs to 120 fs have been studied using a three-dimensional relativistic time dependent molecular dynamic approach. The dynamics of cluster expansion is explained in terms of temporal evolution of electron population in the cluster and snapshots of particle positions at various times. The effects of inter-cluster distance on ionization dynamics are presented. It is observed that the collisional ionization increases with decreasing inter-cluster distance. The effect of pulse duration on laser energy absorption is also studied. For a laser pulse of gaussian time profile, there exists an optimum pulse duration for maximum absorption. No such optimum exists for a nearly flat top (super-gaussian) laser pulse. Results indicate the existence of resonance absorption inside the cluster. It is also observed that the high energy component of ion emission from cluster is anisotropic, showing a preferential direction of emission along laser polarization while the low energy ions emerge almost isotropically.

Analysis of the Complex Interferometry Diagnostics Applicability to Deuterium Clusters Spatial Density Distribution Measurement

Interactions of high-intensity femtosecond lasers with deuterium clusters leading to Coulomb explosions and subsequent production of fusion neutrons have attracted considerable attention in recent years. In order to maximize the neutron yield, finding the dependence of clusters size and their spatial distribution on the experimental conditions has become very important. In this paper, we analyze the possibility of measuring the spatial distributions of deuterium clusters experimentally by using the complex interferometry diagnostics. For this purpose, close-to-reality computer-generated interferograms were produced, which included a small phase-shift disturbance modeling the clusters. Subsequent analysis of these interferograms provided results that identified this diagnostics as potentially suitable for such measurements.

Fabrication of hollow optical waveguides in fused silica by three-dimensional femtosecond laser micromachining

We report on the fabrication of hollow optical waveguides in fused silica using femtosecond laser micromachining. We show that in such hollow waveguides, high-intensity femtosecond laser beams can be guided with low optical loss. Our technique, which was established earlier for fabrication of optofluidic structures in glass, can ensure a high smoothness at the inner surfaces of the hollow waveguides and provide the unique capability of fabrication of hollow waveguides with complex geometries and configurations. A transmission of ∼90% at 633 nm wavelength is obtained for a 62-mm-long hollow waveguide with an inner diameter of ∼250 μm. In addition, nonlinear propagation of femtosecond laser pulses in the hollow waveguide is demonstrated, showing that the spectral bandwidth of the femtosecond pulses can be broadened from ∼27.2 to ∼55.7 nm.

Sensing properties of femtosecond laser-inscribed long period gratings in photonic crystal fiber

The use of near infrared, high intensity femtosecond laser pulses for the inscription of long period fiber gratings in photonic crystal fiber is reported. The formation of grating structures in photonic crystal fiber is complicated by the fiber structure that allows wave-guidance but that impairs and scatters the femtosecond inscription beam. The effects of symmetric and asymmetric femtosecond laser inscriptions are compared and the polarization characteristics of long period gratings and their responses to external perturbations are reported.

Water sprints uphill on glass

As a material, glass has been widely used in traditional fluidic devices and more recently in micro- and nanofluidic devices, and its wetting properties are crucially important in these applications. In this work, by using a high-intensity femtosecond laser structuring technique, we create a unique surface pattern on glass that transfer a regular glass surface to superwicking. As a result, water defies the gravity and sprints vertically uphill along the structured glass surface at an unprecedented velocity of 3.8 cm/sec. Our study shows that the dynamics of this fast self-propelled water flow follows a square root of time dependence.

Femtosecond laser synthesis of bimetallic Pt–Au nanoparticles

Bimetallic Pt–Au nanoparticles were successfully synthesized by irradiating the metal precursor solution with high intensity femtosecond laser. The intense optical field created by femtosecond laser pulse induced the production of highly charged ions and molecules due to the optical decomposition of metal precursor molecules. Further collisions with molecules result in subsequent growth of the nuclei and codeposition of Pt and Au atoms on the nuclei to form the larger ones. The method is a simple, easy-to-control and environmentally benign process. The average size and morphology of bimetallic nanoparticles were examined by transmission electron microscope. The compositional distributions of Pt and Au of individual Pt–Au nanoparticles were examined by X-ray energy dispersive spectroscopy (EDS).