Picosecond laser filament-guided electrical discharges in air at 1 kHz repetition rate.

Laser-induced filaments have been shown to reduce the voltage necessary to initiate electrical discharges in atmospheric air and guide their propagation over long distances. Here we demonstrate the stable generation of laser filament-guided electrical discharge columns in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of 7 ps duration at repetition rates up to 1 kHz and we discuss the processes leading to breakdown. A current proportional to the laser pulse energy is observed to arise as soon as the laser pulse arrives, initiating a high impedance phase of the discharge.

Homogeneous, Micron-Scale High-Energy-Density Matter Generated by Relativistic Laser-Solid Interactions.

Short-pulse, laser-solid interactions provide a unique platform for studying complex high-energy-density matter. We present the first demonstration of solid-density, micron-scale keV plasmas uniformly heated by a high-contrast, 400 nm wavelength laser at intensities up to 2×10^{21}  W/cm^{2}. High-resolution spectral analysis of x-ray emission reveals uniform heating up to 3.

Amplification of elliptically polarized sub-femtosecond pulses in neon-like X-ray laser modulated by an IR field.

Amplification of attosecond pulses produced via high harmonic generation is a formidable problem since none of the amplifiers can support the corresponding PHz bandwidth. Producing the well defined polarization state common for a set of harmonics required for formation of the circularly/elliptically polarized attosecond pulses (which are on demand for dynamical imaging and coherent control of the spin flip processes) is another big challenge. In this work we show how both problems can be tackled simultaneously on the basis of the same platform, namely, the plasma-based X-ray amplifier whose resonant transition frequency is modulated by an infrared field.

Micro-scale fusion in dense relativistic nanowire array plasmas.

Nuclear fusion is regularly created in spherical plasma compressions driven by multi-kilojoule pulses from the world's largest lasers. Here we demonstrate a dense fusion environment created by irradiating arrays of deuterated nanostructures with joule-level pulses from a compact ultrafast laser. The irradiation of ordered deuterated polyethylene nanowires arrays with femtosecond pulses of relativistic intensity creates ultra-high energy density plasmas in which deuterons (D) are accelerated up to MeV energies, efficiently driving D-D fusion reactions and ultrafast neutron bursts.

Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: Scaling to terabar pressures.

Ultrahigh-energy density (UHED) matter, characterized by energy densities >1 × 10 J cm and pressures greater than a gigabar, is encountered in the center of stars and inertial confinement fusion capsules driven by the world's largest lasers. Similar conditions can be obtained with compact, ultrahigh contrast, femtosecond lasers focused to relativistic intensities onto targets composed of aligned nanowire arrays. We report the measurement of the key physical process in determining the energy density deposited in high-aspect-ratio nanowire array plasmas: the energy penetration.

Nanoscale Ultradense Z-Pinch Formation from Laser-Irradiated Nanowire Arrays.

We show that ultradense Z pinches with nanoscale dimensions can be generated by irradiating aligned nanowires with femtosecond laser pulses of relativistic intensity. Using fully three-dimensional relativistic particle-in-cell simulations, we demonstrate that the laser pulse drives a forward electron current in the area around the wires. This forward current induces return current densities of ∼0.

Extreme degree of ionization in homogenous micro-capillary plasma columns heated by ultrafast current pulses.

Homogeneous plasma columns with ionization levels typical of megaampere discharges are created by rapidly heating gas-filled 520-μm-diameter channels with nanosecond rise time current pulses of 40 kA. Current densities of up to 0.3  GA cm^{-2} greatly increase Joule heating with respect to conventional capillary discharge Z pinches, reaching unprecedented degrees of ionization for a high-Z plasma column heated by a current pulse of remarkably low amplitude.

Collimation of dense plasma jets created by low-energy laser pulses and studied with soft x-ray laser interferometry.

The physical mechanisms driving the collimation of dense plasma jets created by low-energy ( approximately 0.6 J) laser pulse irradiation of triangular grooves were studied for different target materials using soft-x-ray interferometry and hydrodynamic code simulations. The degree of collimation of jets created by irradiating C, Al, Cu, and Mo targets at intensities of I=1x10(12) W cm(-2) with 120 ps laser pulses was observed to increase significantly with the atomic number.

Dynamics of a dense laboratory plasma jet investigated using soft x-ray laser interferometry.

The formation and evolution of a collisional aluminum plasma jet created by optical laser irradiation of triangular grooves with pulses of 120ps duration at an intensity of 1x10(12)W cm(-2) were studied with experiments and simulations. Series of high-contrast soft x-ray laser interferograms obtained with a 46.9nm laser mapped the plasma density evolution of an initially narrow plasma jet that expands along the symmetry plane and evolves into a broader plasma plume with significant side lobes.

Spectroscopically pure metal vapor source for highly charged ion spectroscopy and capillary discharge soft x-ray lasers.

We describe a compact, pulsed metal vapor source used for the production of dense plasma columns of interest for both soft x-ray laser research and spectroscopy of highly ionized plasmas. The source generates spectroscopically pure cadmium vapor jets in a room-temperature environment by rapidly heating an electrode with a capacitive discharge. In the configuration described herein, the metal vapor jet produced by the source is axially injected into a fast (up to 15 kA/ ns), high current (up to 200 kA peak) capillary discharge to generate highly ionized cadmium plasma columns.

Demonstration of transient gain x-ray lasers near 20nm for nickellike yttrium, zirconium, niobium, and molybdenum.

We demonstrate strong lasing on the Ni-like 4d(1)S(0)?4p(1)P(1) transition at 18.9, 20.3, 22.

Demonstration of a neonlike argon soft-x-ray laser with a picosecond-laser-irradiated gas puff target.

We demonstrate a neonlike argon-ion x-ray laser, using a short-pulse laser-irradiated gas puff target. The gas puff target was formed by pulsed injection of gas from a high-pressure solenoid valve through a nozzle in the form of a narrow slit and irradiated with a combination of long, 600-ps and short, 6-ps high-power laser pulses with a total of 10 J of energy in a traveling-wave excitation scheme. Lasing was observed on the 3p (1)S(0)?3s (1)P(1) transition at 46.

Dynamics of converging laser-created plasmas in semicylindrical cavities studied using soft x-ray laser interferometry.

The evolution of dense aluminum and carbon plasmas produced by laser irradiation of 500-microm -diam semicylindrical targets was studied using soft x-ray laser interferometry. Plasmas created heating the cavity walls with 120-ps -duration optical laser pulses of approximately 1x10;{12}Wcm;{-2} peak intensity were observed to expand and converge on axis to form a localized high-density plasma region. Electron density maps were measured using a 46.

Plasma conditions for improved energy coupling into the gain region of the Ni-like Pd transient collisional x-ray laser.

We have directly probed the conditions in which the Ni-like Pd transient collisional x-ray laser is generated and propagates by measuring the near-field image and by utilizing picosecond resolution soft x-ray laser interferometry of the preformed Pd plasma gain medium. The electron density and gain region of the plasma have been determined experimentally and are found to be in good agreement with simulations. We observe a strong dependence of the laser pump-gain medium coupling on the laser pump parameters.

Capillary discharge-driven metal vapor plasma waveguides.

We report the generation of dense plasma waveguides containing a large concentration of silver ions by means of a fast (approximately 55 ns first half-cycle) microcapillary discharge. Concave plasma density profiles with axial electron density > 1 x 10(19) cm(-3) were measured from discharge ablation of 330 or 440 microm diameter Ag2S capillaries with 3-5 kA peak amplitude current pulses. The dynamic of this plasma waveguide was studied with interferometry, absorption measurements, and hydrodynamic model simulations.

High-repetition-rate grazing-incidence pumped x-ray laser operating at 18.9 nm.

We have demonstrated a 10 Hz Ni-like Mo x-ray laser operating at 18.9 nm with 150 mJ total pump energy by employing a novel pumping scheme. The grazing-incidence scheme is described, where a picosecond pulse is incident at a grazing angle to a Mo plasma column produced by a slab target irradiated by a 200 ps laser pulse.

Observation of a multiply ionized plasma with index of refraction greater than one.

We present clear experimental evidence showing that the contribution of bound electrons can dominate the index of refraction of laser-created plasmas at soft x-ray wavelengths. We report anomalous fringe shifts in soft x-ray laser interferograms of Al laser-created plasmas. The comparison of measured and simulated interferograms shows that this results from the dominant contribution of low charge ions to the index of refraction.

Saturated high-repetition-rate 18.9-nm tabletop laser in nickellike molybdenum.

We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain-length product GL of 15.

Picosecond-resolution soft-x-ray laser plasma interferometry.

We describe a soft-x-ray laser interferometry technique that allows two-dimensional diagnosis of plasma electron density with picosecond time resolution. It consists of the combination of a robust high-throughput amplitude-division interferometer and a 14.7-nm transient-inversion soft-x-ray laser that produces approximately 5-ps pulses.

Two-dimensional effects in laser-created plasmas measured with soft-x-ray laser interferometry.

Soft-x-ray laser interferograms of laser-created plasmas generated at moderate irradiation intensities (1 x 10(11)-7 x 10(12) W cm(-2)) with lambda=1.06 microm light pulses of approximately 13-ns-FWHM (full width at half maximum) duration and narrow focus (approximately 30 microm) reveal the unexpected formation of an inverted density profile with a density minimum on axis and distinct plasma sidelobes. Model simulations show that this strong two-dimensional hydrodynamic behavior is essentially a universal phenomena that is the result of plasma radiation induced mass ablation and cooling in the areas surrounding the focal spot.

Picosecond x-ray laser interferometry of dense plasmas.

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas.

High-power-density capillary discharge plasma columns for shorter wavelength discharge-pumped soft-x-ray lasers.

We report the generation of plasma columns in gas-filled capillary channels using discharge excitation powers that exceed those of previous studies by one to two orders of magnitude. Current pulses up to 200 kA and 10-90 % rise time of about 10 ns (current increase rate equivalent to 1.5 x 10(13) A/s) were utilized to excite plasmas in 3.

Dynamics of a microcapillary discharge plasma using a soft x-ray laser backlighter.

We have used the new technique of soft x-ray laser shadowgraphy in combination with traditional plasma emission spectroscopy and theoretical modeling to study the dynamics of a plasma column created by a discharge through a 380 &mgr;m diameter evacuated microcapillary. The transient microcapillary plasma was imaged with high-spatial and temporal resolution using a tabletop discharge pumped 46.9-nm laser backlighter.

Gain saturation regime for laser-driven tabletop, transient Ni-like ion X-Ray lasers.

We have demonstrated small signal gain saturation on several transient-gain Ni-like ion x-ray lasers by using a high-power, chirped-pulse amplification, tabletop laser. These results have been achieved at wavelengths from 139-203 A using a total of 5-7 J energy in a traveling-wave excitation scheme. Strong amplification is also observed for Ni-like Sn at 119 A.