265 research outputs found
Direct observation of ultrafast thermal and non-thermal lattice deformation of polycrystalline Aluminum film
The dynamics of thermal and non-thermal lattice deformation of nanometer
thick polycrystalline aluminum film has been studied by means of femtosecond
(fs) time-resolved electron diffraction. We utilized two different pump
wavelengths: 800 nm, the fundamental of Ti: sapphire laser and 1250 nm
generated by a home-made optical parametric amplifier(OPA). Our data show that,
although coherent phonons were generated under both conditions, the diffraction
intensity decayed with the characteristic time of 0.9+/-0.3 ps and 1.7+/-0.3 ps
under 800 nm and 1250 nm excitation, respectively. Because the 800 nm laser
excitation corresponds to the strong interband transition of aluminum due to
the 1.55 eV parallel band structure, our experimental data indicate the
presence of non-thermal lattice deformation under 800 nm excitation, which
occurs on a time-scale that is shorter than the thermal processes dominated by
electron-phonon coupling under 1250 nm excitation
Synergistic reaction of silver nitrate, silver nanoparticles, and methylene blue against bacteria
In this paper we describe the antibacterial effect of methylene blue, MB, and silver nitrate reacting alone and in combination against five bacterial strains including Serratia marcescens and Escherichia coli bacteria. The data presented suggest that when the two components are combined and react together against bacteria, the effects can be up to three orders of magnitude greater than that of the sum of the two components reacting alone against bacteria. Analysis of the experimental data provides proof that a synergistic mechanism is operative within a dose range when the two components react together, and additive when reacting alone against bacteria
Ultrafast Time-Resolved Structural Changes of Thin-Film Ferromagnetic Metal Heated With Femtosecond Optical Pulses
As a classic ferromagnetic material, nickel has been an important research candidate used to study dynamics and interactions of electron, spin, and lattice degrees of freedom. In this study, we specifically chose a thick, 150 nm ferromagnetic nickel (111) single crystal rather than 10â20 nm thin crystals that are typically used in ultrafast studies, and we revealed both the ultrafast heating within the skin depth and the heat transfer from the surface (skin) layer to the bulk of the crystal. The lattice deformation after femtosecond laser excitation was investigated by means of 8.04 keV subpicosecond x-ray pulses, generated from a table-top laser-plasma based source. The temperature evolution of the electron, spin, and lattice was determined using a three temperature model. In addition to coherent phonon oscillations, the blast force and sonic waves, induced by the hot electron temperature gradient, were also observed by monitoring the lattice contractions during the first couple of picoseconds after laser irradiation. This study further revealed the tens of picoseconds time required for heating the hundred nanometer bulk of the Ni (111) single crystals
Femtosecond Laser Induced Structural Dynamics and Melting of Cu (111) Single Crystal. An Ultrafast Time-Resolved X-Ray Diffraction Study
Femtosecond, 8.04 keV x-ray pulses are used to probe the lattice dynamics of a 150 nm Cu (111) single crystal on a mica substrate irradiated with 400 nm, 100 fs laser pulses. For pump fluences below the damage and melting thresholds, we observed lattice contraction due to the formation of a blast force and coherent acoustic phonons with a period of âŒ69 ps. At larger pump fluence, solid to liquid phase transition, annealing, and recrystallization were measured in real time by monitoring the intensity evolution of the probing fs x-ray rocking curves, which agreed well with theoretical simulation results. The experimental data suggest that the melting process is a purely thermal phase transition. This study provides, in real time, an ultrafast time-resolved detailed description of the significant processes that occur as a result of the interaction of a femtosecond light-pulse with the Cu (111) crystal surface. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4975198
Femtosecond Laser Induced Structural Dynamics and Melting of Cu (111) Single Crystal. An Ultrafast Time-Resolved X-Ray Diffraction Study
Femtosecond, 8.04 keV x-ray pulses are used to probe the lattice dynamics of a 150 nm Cu (111) single crystal on a mica substrate irradiated with 400 nm, 100 fs laser pulses. For pump fluences below the damage and melting thresholds, we observed lattice contraction due to the formation of a blast force and coherent acoustic phonons with a period of âŒ69 ps. At larger pump fluence, solid to liquid phase transition, annealing, and recrystallization were measured in real time by monitoring the intensity evolution of the probing fs x-ray rocking curves, which agreed well with theoretical simulation results. The experimental data suggest that the melting process is a purely thermal phase transition. This study provides, in real time, an ultrafast time-resolved detailed description of the significant processes that occur as a result of the interaction of a femtosecond light-pulse with the Cu (111) crystal surface. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4975198
Electron-lattice kinetics of metals heated by ultrashort laser pulses
We propose a kinetic model of transient nonequilibrium phenomena in metals
exposed to ultrashort laser pulses when heated electrons affect the lattice
through direct electron-phonon interaction. This model describes the
destruction of a metal under intense laser pumping. We derive the system of
equations for the metal, which consists of hot electrons and a cold lattice.
Hot electrons are described with the help of the Boltzmann equation and
equation of thermoconductivity. We use the equations of motion for lattice
displacements with the electron force included. The lattice deformation is
estimated immediately after the laser pulse up to the time of electron
temperature relaxation. An estimate shows that the ablation regime can be
achieved.Comment: 7 pages; Revtex. to appear in JETP 88, #1 (1999
Single-shot compressed ultrafast photography at one hundred billion frames per second
The capture of transient scenes at high imaging speed has been long sought by photographers, with early examples being the well known recording in 1878 of a horse in motion and the 1887 photograph of a supersonic bullet. However, not until the late twentieth century were breakthroughs achieved in demonstrating ultrahigh-speed imaging (more than 10^5 frames per second). In particular, the introduction of electronic imaging sensors based on the charge-coupled device (CCD) or complementary metalâoxideâsemiconductor (CMOS) technology revolutionized high-speed photography, enabling acquisition rates of up to 10^7 frames per second. Despite these sensorsâ widespread impact, further increasing frame rates using CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10^(11) frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an xâyât (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. As a result, CUP can image a variety of luminescentâsuch as fluorescent or bioluminescentâobjects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUPâs capability, we expect it to find widespread applications in both fundamental and applied sciences, including biomedical research
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