High-power Ultrashort Laser Research Articles

Fast magnetic-field annihilation in the relativistic collisionless regime driven by two ultrashort high-intensity laser pulses.

The magnetic quadrupole structure formation during the interaction of two ultrashort high power laser pulses with a collisionless plasma is demonstrated with 2.5-dimensional particle-in-cell simulations. The subsequent expansion of the quadrupole is accompanied by magnetic-field annihilation in the ultrarelativistic regime, when the magnetic field cannot be sustained by the plasma current. This results in a dominant contribution of the displacement current exciting a strong large scale electric field. This field leads to the conversion of magnetic energy into kinetic energy of accelerated electrons inside the thin current sheet.

Nonsmooth critical point theorems and its applications to quasilinear schrödinger equations

In this paper, the existence and nonexistence of solutions to a class of quasilinear elliptic equations with nonsmooth functionals are discussed, and the results obtained are applied to quasilinear Schrödinger equations with negative parameter which arose from the study of self-channeling of high-power ultrashort laser in matter.

Noncollinear Polarization Gating of Attosecond Pulse Trains in the Relativistic Regime.

High order harmonics generated at relativistic intensities have long been recognized as a route to the most powerful extreme ultraviolet pulses. Reliably generating isolated attosecond pulses requires gating to only a single dominant optical cycle, but techniques developed for lower power lasers have not been readily transferable. We present a novel method to temporally gate attosecond pulse trains by combining noncollinear and polarization gating. This scheme uses a split beam configuration which allows pulse gating to be implemented at the high beam fluence typical of multi-TW to PW class laser systems. Scalings for the gate width demonstrate that isolated attosecond pulses are possible even for modest pulse durations achievable for existing and planned future ultrashort high-power laser systems. Experimental results demonstrating the spectral effects of temporal gating on harmonic spectra generated by a relativistic laser plasma interaction are shown.

Standing waves for a relativistic quasilinear asymptotically Schrödinger equation

In this paper, we study the standing waves for the relativistic quasilinear asymptotically Schrödinger equationThis model has been proposed in the self-channelling of a high-power ultrashort laser in matter.

High-power pre-chirp managed amplification of femtosecond pulses at high repetition rates

Femtosecond pulses at 250 MHz repetition rate from a mode-locked fiber laser are amplified to high power in a pre-chirp managed amplifier. The experimental strategy offers a potential towards high-power ultrashort laser pulses at high repetition rates. By investigating the laser pulse evolution in the amplification processes, we show that self-similar evolution, finite gain bandwidth and mode instabilities determine pulse characteristics in different regimes. Further average power scaling is limited by the mode instabilities. Nevertheless, this laser system enables us to achieve sub-50 fs pulses with an average power of 93 W.

Chemical two-photon fluorescence.

We describe a method based on a caged fluorescent molecule that can act as a chemical two-photon probe. It is composed of an organic fluorophore and a ruthenium-bipyridine complex that acts as a photoremovable quencher. For the fluorophore to be emissive, two independent photons must act on the molecule: the first photon frees the fluorescent ligand from the Ru complex and the second photon excites the fluorescence. In this two-photon regime, the emission is not proportional to the excitation intensity but rather to its second power, as in traditional two-photon systems based on ultrashort pulsed high-power lasers. This quadratic relationship implies a much higher spatial precision on the z-axis when the probe is used in a microscopy technique. The chemical nature of the two-photon excitation mechanism allows the use of inexpensive low-power lasers.

Shock wave acceleration of protons in inhomogeneous plasma interacting with ultrashort intense laser pulses

The acceleration of protons, triggered by solitary waves in expanded solid targets is investigated using particle-in-cell simulations. The near-critical density plasma is irradiated by ultrashort high power laser pulses, which generate the solitary wave. The transformation of this soliton into a shock wave during propagation in plasma with exponentially decreasing density profile is described analytically, which allows to obtain a scaling law for the proton energy. The high quality proton bunch with small energy spread is produced by reflection from the shock-front. According to the 2D simulations, the mechanism is stable only if the laser pulse duration is shorter than the characteristic development time of the parasitic Weibel instability.

The existence result for a relativistic nonlinear Schrödinger equation

We study the existence of positive solutions for a class of quasilinear elliptic equation. This model has been proposed in the self-channeling of a high-power ultra short laser in matter.

Positive soliton solutions for generalized quasilinear Schrödinger equations with critical growth

This paper is concerned with the positive solutions for generalized quasilinear Schrödinger equations in RN with critical growth which have appeared from plasma physics, as well as high-power ultrashort laser in matter. By using a change of variables and variational argument, we obtain the existence of positive solutions for the given problem.

The Real-Time Temporal and Spatial Diagnostics of Ultrashort High-Power Laser Pulses using an All-Reflective Single-Shot Autocorrelator

An all-reflective, simple noncollinear second harmonic (SH) autocorrelator is described for monitoring the shot-to-shot behavior of ultrashort high-power laser pulses. Two mirrors are used for the dispersion-free splitting of a pulse into two halves. One of the mirrors is able to adjust the delay time and angle between two halves of the laser pulse in a nonlinear crystal. We present the possibility of real-time measurement of the pulse duration, peak intensity (or energy), and the pointing jitters of a laser pulse, by analyzing the spatial profile of the SH autocorrelation signal measured by a CCD camera. The measurement of the shot-to-shot variation of those parameters will be important for the detailed characterization of laser accelerated electrons or protons.

Growth, thermal properties and laser operation of a new disordered crystal: Nd-doped Sr3La2(BO3)4

A novel disordered laser crystal Nd:Sr3La2(BO3)4 is characterized including its crystal growth, structure, thermal properties, inhomogeneously broadened spectra, and laser performance, which result that this crystal should be a promising gain material for the high-power ultrashort pulsed neodymium laser. The complete set of anisotropic thermal properties were systematically studied for the first time. It has been found that all the thermal conductivities along the three crystallographic directions increase with temperature, indicating a glass-like behavior. Polarized absorption and fluorescence spectra of Nd:Sr3La2(BO3)4 crystal were measured at 298.15K and 77.2K, respectively. The results show that both the absorption and the emission spectra of Nd3+ have been inhomogeneously broadened, and thus it is very promising to be used in laser systems to produce femtosecond pulses. CW laser operations at 1.06μm along the b-cut and c-cut directions have been demonstrated for the first time. A maximum power of 533mW with an optical conversion efficiency of 5.5% and slope efficiency of 6.4% was achieved in the c-cut sample.

Crystal growth and characterization of 4 in. YCa4O(BO3)3 crystal

YCa4O(BO3)3 (YCOB) is an important nonlinear optical crystal with good thermal, mechanical and nonlinear optical properties. However, growth of YCOB with large size and high quality was seldom reported. In this work, 4in. YCOB crystals without inclusions and cleavages were grown successfully. These YCOB crystals exhibit excellent nonlinear optical properties, and have been used in high-energy and high-power ultra-short laser systems successfully.

The Existence and Uniqueness Result for a Relativistic Nonlinear Schrödinger Equation

We study the existence and uniqueness of positive solutions for a class of quasilinear elliptic equations. This model has been proposed in the self-channeling of a high-power ultrashort laser in matter.

Adaptive-feedback spectral-phase control for interactions with transform-limited ultrashort high-power laser pulses

Fourier-transform-limited light pulses were obtained at the laser-plasma interaction point of a 100-TW peak-power laser in vacuum. The spectral-phase distortion induced by the dispersion mismatching between the stretcher, compressor, and dispersive materials was fully compensated for by means of an adaptive closed-loop. The coherent temporal contrast on the sub-picosecond time scale was two orders of magnitude higher than that without adaptive control. This novel phase control capability enabled the experimental study of the dependence of laser wakefield acceleration on the spectral phase of intense laser light.

Comparison between geometrically focused pulses versus filaments in femtosecond laser ablation of steel and titanium alloys

Kerr self-focusing of high-power ultrashort laser pulses in atmosphere may result in a structure or structures of high intensity that can propagate over long distances with little divergence. Filamentation has garnered significant interest in the nonlinear optics community due to its unique properties. Salient features of filaments include a central region of intense laser power (greater than the ionization threshold of the propagation medium) and a low temperature plasma column that lasts up to nanoseconds in duration after the passage of the laser pulse. Steel and titanium samples are ablated by filaments and by sharply focused sub-picosecond laser pulses. We then performed metrology on the samples to compare the ablation features in addition to modeling of the plasma ablation process. Ablation with filaments leads to a wider range of material responses as compared to ablation with sharply focused pulse. This results in potential complications for applications of filament ablation that depends on the rate of material removal and spectroscopic analysis.

Generation of ultrashort pulses of electromagnetic radiation in the mid- and far-infrared ranges

Generation of ultrashort pulses of electromagnetic radiation in the range of wavelengths from 3 to 17 μm is experimentally demonstrated using difference-frequency mixing of the signal and idler waves delivered through an optical parametric amplification of a week broadband seed by high-power near-infrared ultrashort laser pulses. Cross-correlation measurements demonstrate that pulses as short as a few cycles of electromagnetic field are produced in the mid- and far-infrared ranges by means of difference-frequency generation.

Filamentation of high-power ultrashort laser radiation: Size factor of a light beam

The single (axial) filamentation regime of high-power collimated femtosecond laser radiation in the atmosphere is theoretically investigated. The effect of initial diameter of a laser beam on characteristics of a filament is analyzed. We consider three filament parameters: the coordinate of the filament start, its length and longitudinal continuity. We found that for the same initial beam power all the above characteristics of the filaments show a dependence on the beam radius. As the main physical cause for this circumstance the diffraction interaction of various beam areas during the filamentation process is considered; the strength of this interaction increases as the beam widens.

Soliton solutions for quasilinear Schrödinger equations

It is established the existence of nontrivial solutions for quasilinear Schrödinger equations with subcritical or critical exponents, which appear from plasma physics as well as high-power ultrashort laser in matter.

Growth, thermal properties and laser operation of Nd:Ca_3La_2(BO_3)_4: A new disordered laser crystal

A novel disordered laser crystal Nd:Ca(3)La(2)(BO(3))(4) is characterized including its crystal growth, structure, thermal properties, inhomogeneously broadened spectra, and laser performance, which result that this crystal should be a promising gain material for the high-power ultrashort pulsed neodymium laser. The complete set of anisotropic thermal properties were systematically studied for the first time. It has been found that thermal contraction happens in the c direction and all the thermal conductivities increase with temperature, indicating a glass-like behavior. Polarized absorption and fluorescence spectra of Nd:Ca(3)La(2)(BO(3))(4) crystal were measured at 298.15 K and 77.3 K, respectively. The results show that both the absorption and the emission spectra of Nd(3+) have been inhomogeneously broadened, and thus it is very promising to be used in laser systems to produce femtosecond pulses. CW laser operations at 1.06 μm along the three crystallographic directions has been demonstrated for the first time. A maximum power of 1.08 W with an optical conversion efficiency of 10.6% and slope efficiency of 12.4% was achieved in the a-cut sample.

Experimental study of filamentation of high-power ultrashort laser pulses with initial angular divergence in air

Experimental study of the nonlinear propagation of near-IR gigawatt femtosecond laser pulses in air in the self-focusing and filamentation regimes have been performed in open air and in laboratory. The influence of the initial geometric divergence (both positive and negative) of the laser beam with an irregular intensity profile on the transverse light energy distribution at the end of the path is studied. It is shown experimentally that the displacement of the filamentation region due to geometric focusing or defocusing, makes it possible to control the number and spatial location of light energy density peaks in the receiving plane. The conditions under which a light filament can be reconstructed after the beam transmission through a linear focal waist are determined. A semi-empirical threshold relation is obtained for the beam focusing force and the beam power, when light beam undergoes filamentation behind the geometric focus of the optical system.