Intense Short Pulse Research Articles

Remote atmospheric breakdown for standoff detection by using an intense short laser pulse

A remote atmospheric breakdown is a very rich source of UV and broadband visible light that could provide an early warning of the presence of chemical-biological warfare agents at extended standoff distances. A negatively chirped laser pulse propagating in air compresses in time and focuses transversely, which results in a rapid laser intensity increase and ionization near the focal region that can be located kilometers away from the laser system. Proof-of-principle laboratory experiments are performed on the generation of remote atmospheric breakdown and the spectroscopic detection of mock biological warfare agents. We have generated third harmonics at 267 nm and UV broadband radiation in air from the compression and focusing of femtosecond laser pulses. Fluorescence emission from albumin aerosols as they were illuminated by the femtosecond laser pulse has been observed.

The Course of Tissue Permeabilization Studied on a Mathematical Model of a Subcutaneous Tumor in Small Animals

One of the ways to potentiate antitumor effectiveness of chemotherapeutic drugs is by local application of short intense electric pulses. This causes an increase of the cell membrane permeability and is called electropermeabilization. In order to study the course of tissue permeabilization of a subcutaneous tumor in small animals, a mathematical model was built with the commercial program EMAS, which uses the finite element method. The model is based on the tissue specific conductivity values found in literature, experimentally determined electric field threshold values of reversible and irreversible tissue permeabilization, and conductivity changes in the tissues. The results obtained with the model were then compared to experimental results from the treatment of subcutaneous tumors in mice and a good agreement was obtained. Our results and the reversible and irreversible thresholds used coincide well with the effectiveness of the electrochemotherapy in real tumors where experiments show antitumor effectiveness for amplitudes higher than 900 V/cm ratio and pronounced antitumor effects at 1300 V/cm ratio.

Suppression of transverse proton beam divergence by controlled electron cloud in laser-plasma interactions

In this paper, suppression of a transverse proton divergence is focused by using a controlled electron cloud. When an intense short pulse laser illuminates a foil plasma target, first electrons are accelerated and they form a strong electrostatic field at the target surface, then ions are accelerated by the strong field. When a target has a hole at the opposite side of the laser illumination, an electron cloud is limited in transverse direction by a neutral plasma at the protuberant part. The proton beam is accelerated and also controlled by transverse shaped electron cloud, and consequently the transverse divergence of the proton beam is suppressed. In 2.5-dimensional particle-in-cell simulations, the transverse shape of the electron cloud is controlled well and the transverse proton beam divergence is suppressed successfully; the transverse emittance is improved by about 28% compared with that in a conventional slab target.

Dissociation of H+2 from a short, intense, infrared laser pulse: proton emission spectra and pulse calibration

The proton energy spectrum from photodissociation of the hydrogen molecular ion by short intense pulses of infrared light is calculated. The time-dependent Schrödinger equation is discretized and integrated. For few-cycle pulses one can resolve vibrational structure, arising from the experimental preparation of the molecular ion. We calculate the corresponding energy spectrum and analyse the dependence on the pulse time delay, pulse length and intensity of the laser for λ ∼ 790 nm. We conclude that the proton spectrum is a sensitive probe of both the vibrational populations and phases, and allows us to distinguish between adiabatic and nonadiabatic dissociation. Furthermore, the sensitivity of the proton spectrum from H+2 is a practical means of calibrating the pulse. Our results are compared with recent measurements of the proton spectrum for 65 fs pulses using a Ti:Sapphire laser (λ ∼ 790 nm) including molecular orientation and focal-volume averaging. Integrating over the laser focal volume, for the intensity I ∼ 3 × 1015 W cm−2, we find our results are in excellent agreement with these experiments.

Generation of a microelectron beam by an intense short pulse laser in the TEM(1, 0) + TEM(0, 1) mode in vacuum

The generation of a high energy microelectron bunch in vacuum by an intense short pulse laser in the TEM(1, 0) + TEM(0, 1) mode is investigated in this paper numerically and analytically. A focused short pulse laser in the TEM(1, 0) + TEM(0, 1) mode has a confinement effect on electrons in the transverse direction due to the transverse ponderomotive force, and at the same time the electrons are accelerated and compressed longitudinally by a longitudinal electric field. In our three-dimensional particle simulations, the maximum kinetic energy of electrons reaches 455 MeV, the maximum density is 3.87 × 1010 cm−3, and the normalized transverse and longitudinal rms emittances of accelerated electrons are of the order of 10−6 m rad at the following parameter values: a0 = eE0/(meω c) = 10 (where a0 is the dimensionless parameter of the laser amplitude, e and me are the electron charge and rest mass, respectively, E0 is the laser amplitude, ω the angular frequency of the laser and c the speed of light in vacuum), a laser wavelength λ = 0.8 µm, laser spot size 20λ, laser pulse length 5λ and initial electron velocity 0.99c. Moreover, the transverse and longitudinal sizes of the compressed electron bunch are about 600λ and 10λ, respectively. In this paper, we also present a scaling law of the maximum electron energy. The estimated results of the maximum electron energy coincide well with the simulation results.

Ponderomotive effect on electron acceleration by plasma wave and betatron resonance in short pulse laser

The ponderomotive force at the front of an intense short pulse laser, propagating through a plasma, strongly influences the acceleration of electrons by a plasma wave or by the laser itself via betatron resonance in self-generated azimuthal magnetic field. It can enhance the electron energy gain several fold through the sustainment of the electron in the accelerating phase of the plasma wave and the laser beam.

Plasma channel charging by an intense short pulse laser and ion Coulomb explosion

The combined effects of relativistic self-focusing and the expulsion of electrons by the ponderomotive force of a radially focused laser create an ion channel, depleted of electrons, of radius r0∼c∕ωp, where ωp is the electron plasma frequency. This charging process takes place on plasma period, ωp−1, time scale. The Coulomb explosion of the channel accelerates ions to several hundreds of keV energy in about an ion plasma period, constituting an important ion acceleration mechanism by short pulse intense laser. In the case of a deuterium-tritium plasma, the accelerated ions can produce fusion energy with an efficiency of ∼0.5%.

Ultrashort-pulse modulation in adiabatically prepared Raman media

We demonstrate the efficient modulation of an approximately 100-femtosecond pulse in a Raman medium coherently prepared by nanosecond pulses. Raman sidebands of the ultrashort pulse spanning 360 THz are generated with an efficiency of >5%. We show that the mechanism permitting the sidebands to be generated is the preparation of a significant vibrational coherence in the medium that is robust to disturbance by an intense short pulse. If the observed sidebands were phase compensated, they would form a short train of approximately ten 3-fs pulses. Focusing would permit the realization of a peak intensity of >10(13) W cm(-2).

Two-Photon Resonant Third Order Harmonic Generation from Atoms and Ions Interacting with Intense Short Laser Pulses

We investigate the third order harmonic generation for model atoms interacting with intense short laser pulses. We focus on the cases where the ponderomotive energy is not big enough to generate high-order harmonics, and where resonant transitions between bound states are also as important as multi-photon ionization and low-order harmonic generation. We find that the third order harmonic intensity from a model hydrogen atom can decrease as the laser frequency draws near a resonance between bound states. We explain this result by looking into the ionization and Rabi oscillation from the numerical calculation of the time-dependent 1-D Schrödinger equation. In order to support our explanation we also investigate the populations of bound states that play an important role in this atomic process.

Quasi-static particle simulation of short pulse laser-plasma interaction

We have successfully developed the two-dimensional quasi-static particle simulation code MLPIC2D, which is an effective numerical tool to be used to describe the long-time plasma behavior under the action of an ultra high intensity short pulse laser. Simple physical modeling, numerical realization and code framework are discussed in detail. Three nonlinear phenomena of laser-plasma interaction:1) production of laser wake-fields, 2)relativistic focusing for short laser pulses, 3)quasi-static magnetic fields, are correctly simulated and analysed.

Nonlinear photon processes in molecules at high intensities-route to XUV—attosecond pulse generation

Numerical solutions of the time-dependent Schroedinger equation, TDSE, for a non-Born Oppenheimer H2+ molecule exposed to the combination of a sub-femtosecond (attosecond) XUV pulse and a short (∼5fs) intense (I≥1013W/cm2) 800nm pulse allow for studying the nonlinear nonperturbative response of electrons and nuclei in molecules exposed to extreme laser conditions. New nonlinear phenomena, such as high order harmonic generation (HOHG), are considerably enhanced. This is a consequence of nonlinear photon processes and offers new routes for ‘attosecond’ pulse generation. Coupling the molecular TDSE to the photon Maxwell equations leads to the synthesis of even shorter attosecond and wavelength pulses, as new ultrashort sources for time-resolved XUV-Raman spectroscopy.

Propagation of intense short laser pulses in a gas of atomic clusters

We present a model and numerical simulations for the propagation of intense short laser pulses in gases of atomic clusters. As the pulse propagates through the clusters, they absorb energy, expand and explode. The clustered gas thus acts as a medium with time dependent effective dielectric constant. A self-consistent model for the cluster expansion and the laser pulse propagation is developed. Self-focusing of the laser pulse, coupling of laser energy to clusters and the evolution of the pulse spectrum are studied for a laser-cluster system with typical laboratory parameters.

Long-distance propagation of intense short laser pulse in air

Long-distance propagation of intense laser pulse in air is reconsidered analytically by generalizing the analogy between the laser spotsize and the orbit of a classical particle. It is shown that multiphoton ionization introduces unique features to the laser-air interaction, thereby enabling the long-distance behavior. Several interesting characteristics of the latter are pointed out.

Study of the magnetic content movement present in the large intestine

A study of the mechanical activity of the large intestine using remanent magnetization (RM) measurement of ingested magnetic tracers is presented. A fluxgate magnetometer is employed to record the movements of magnetic tracers previously ingested by the subject and contained in the right colon. An intense short magnetic pulse magnetizes the magnetic tracers producing a RM and the magnetic content movement in the right colon is assessed by the variations of the RM. The method was capable of revealing both the stimulatory effect of the ingestion of a meal and the reducing effect of an anti-cholinergic drug on the colonic transit in normal subjects.

Nonlinear-absorbing fiber array for large-dynamic-range optical limiting application against intense short laser pulses

A complete quantitative description of a nonlinear fiber array for optical limiting application against laser pulses in the picosecond–nanosecond regime is presented. We discuss the dynamics of the molecular photonic processes accompanying the propagation of a laser pulse through the fiber core made of materials that possess reverse saturable absorption, two-photon absorption (TPA), and excited-state absorption (ESA), and we detail the optical limiting effectiveness and limitations of these nonlinear absorption processes individually and in concert. In particular, we demonstrate the importance of excited-state population recycling in extending the dynamic range of the limiting action. Experimental results obtained from a particular fiber core material that possesses TPA and ESA show good agreement with theoretical expectations and demonstrate the optical limiting capability of such a nonlinear fiber array.

Electron acceleration by an intense short pulse laser in a static magnetic field in vacuum.

Electron acceleration by a laser pulse having Gaussian radial and temporal profiles of intensity has been studied in a static magnetic field in vacuum. The starting point of the magnetic field has been taken around the point where the peak of the pulse interacts with the electron and the direction of the static magnetic field is taken to be the same as that of the magnetic field of the laser pulse. The electron gains considerable energy and retains it in the form of cyclotron oscillations even after the passing of the laser pulse in the presence of an optimum static magnetic field. The optimum value of the magnetic field decreases with laser intensity and initial electron energy. The energy gain also depends upon the laser spot size and peaks for a suitable value. The energy gained by the electron increases with laser intensity and initial electron energy. The electron trajectory and energy gain for different parameters such as laser intensity, initial electron energy, and laser spot size have been presented.

Quantum computer based on activated dielectric nanoparticles selectively interacting with short optical pulses

The operation principle of a quantum computer is proposed based on a system of dielectric nanoparticles activated with two-level atoms — cubits, in which electric dipole transitions are excited by short intense optical pulses. It is proved that the logical operation (logical operator) CNOT (controlled NOT) is performed by means of time-dependent transfer of quantum information over `long' (of the order of 104 nm) distances between spherical nanoparticles owing to the delayed interaction between them in the optical radiation field. It is shown that one-cubit and two-cubit logical operators required for quantum calculations can be realised by selectively exciting dielectric particles with short optical pulses.

Effect of pulse slippage on resonant second harmonic generation of a short pulse laser in a plasma

The process of second harmonic generation of an intense short pulse laser in a plasma is resonantly enhanced by the application of a magnetic wiggler. The wiggler of suitable wave number provides necessary momentum to second harmonic photons to make harmonic generation a resonant process. The laser imparts an oscillatory velocity to electrons and exerts a longitudinal ponderomotive force on them at , where ω1 and are the frequency and the wave number of the laser, respectively. As the electrons acquire oscillatory velocity at the second harmonic, the wiggler magnetic field beats with it to produce a transverse second harmonic current at , driving the second harmonic electromagnetic radiation. However, the group velocity of the second harmonic wave is greater than that of the fundamental wave, hence, the generated pulse slips out of the main laser pulse and its amplitude saturates.

Overview of future directions in high energy-density and high-field science using ultra-intense lasers

The increasing proliferation of 100 TW class ultrashort pulse lasers and the near completion of a number of petawatt class lasers world wide is opening many frontiers in laser science. Some of the most exciting frontiers rest in high energy-density science and high field physics. A multi-TW laser can create heated matter with pressure in excess of a Gbar and can create electric fields of ten to one hundred atomic units. In this paper some of the recent advances in high energy density science and high field physics made using high intensity short pulse lasers will be reviewed with illustrative examples from work performed at the University of Texas and Lawrence Livermore National Laboratory.

Micro Electron Bunch Acceleration and Trapping by Intense Short Laser Pulse in Vacuum

We propose an electron bunch acceleration and trapping mechanism by an intense short laser pulse in vacuum. By using a short laser pulse obtained by the linear combination of a TEM10 mode and a TEM01 mode with the same amplitude and the relative phase shift of π/2, the electrons are accelerated in the longitudinal direction by a longitudinal ponderomotive force, and the electrons divergence in the transverse direction can be suppressed by a transverse ponderomotive force. In order to analyze the electron motion, the relativistic equation of motion including a relativistic radiation damping effect is solved. In our calculations, the electron is accelerated to 179 [MeV] with an acceleration gradient of 5.12 [GeV/m] at the laser intensity of 1.23×1018 [W/cm2]. The rms emittances of the electron bunch accelerated are (1.06, 1.21, 0.348) [mm mrad] in the x, y and z directions, and the spatial size of this electron bunch accelerated in the radial and longitudinal directions are 856 [μm] and 11.7 [μm], respectively.