Measurement Of Ultrafast Ionization Dynamics Of Gases By Multipulse Interferometric Frequency-Resolved Optical Gating

Ultrafast ionization dynamics of femtosecond laser-irradiated noble and simple diatomic gases were studied using a novel two-color time-domain technique which eliminated significant complications seen in past experiments. Ultrafast depletion of the probing laser pulse was observed strictly coincident with the ionization front and attributed to a previously unobserved nonlinear frequency mixing via the transverse plasma current [F. Brunel, J. Opt. Soc. Am. B 7, 52 (1990)]. Good quantitative agreement of the measured single-atom ionization rates with Ammosov-Delone-Krainov rates was found, except for O2 which showed a 200× smaller rate. © 2001 The American Physical Society

Burst-Mode Femto-Machining Of Copper And Lexan

Femtosecond ablation of both absorbing and transparent materials has several distinct advantages: the threshold energy fluence for the onset of damage and ablation is orders of magnitude less than for traditional nanosecond laser machining, and by virtue of the rapid material removal of approximately an optical penetration depth per pulse, femtosecond machined cuts can be cleaner and more precise than those made with traditional nanosecond or longer pulse lasers. However, in many materials of interest, especially metals, this limits ablation rates to 10-100 nm/pulse. We will present the results of using multiple pulse bursts to significantly increase the per-burst ablation rate compared to a single pulse with the same integrated energy, while keeping the peak intensity of each individual pulse below the air ionization limit. Femtosecond ablation using 850-nm single and eight-pulse 30-ns duration bursts with 4-mJ integrated energy was seen to yield a five-fold increase in the copper ablation rate in ambient air

Burst-Mode Femtosecond Ablation In Copper And Lexan

We present the results of a comparative study of 850-nm femtosecond ablation using single and eight-pulse 30-ns duration bursts with 4-mJ integrated energy. Five-fold increase in the copper ablation rate in ambient air was seen. ©2002 Optical Society of America

Coherent Ultrafast Mi-Frog Spectroscopy Of Optical Field Ionization In Molecular H2, N2, And O2

Quantitative phase-sensitive measurements of ultrafast optical-field ionization rates in molecular H2, N2, and O2 are obtained using a temporally gated frequency-domain interferometric pulse measurement technique: multipulse interferometric frequency-resolved optical gating (MI-FROG). By measuring the pump-induced frequency change on a weak copropagating probe pulse, the optical field ionization dynamics can be completely time-resolved with subpulsewidth time resolution. A one-dimensional nonrelativistic electromagnetic fluid code model is used to compute the ionization dynamics and optical field propagation through the plasma. Using the Ammosov-Delone-Krainov (ADK) tunnel ionization rate model originally developed for atoms, the relatively simple model proposed here has been shown to compare favorably with the MI-FROG measured ionization rates in noble gases in the intermediate intensity regime (1014 W/cm2) [1]. We attempt to unify our studies in noble gases and molecules by performing experiments on N2 and O2, which have nearly identical ionization potentials as Ar and Xe, respectively. For the molecules studied here, we show that an ADK-like description of molecular ionization rates calculated from the model agree with the experimentally measured rates using the MI-FROG technique for H2 and N2. In the case of O2, however, the experimentally measured ionization rate is approximately two orders of magnitude lower than that expected from the standard ADK formula. This is in agreement with the previously observed suppressed O2 ionization rate in ion mass spectroscopy studies [2]. We attribute the suppressed ionization rate in O2 to a multielectron screening effect and show that a modified version of the ADK formula, taking into account the electron screening as proposed in [2], well approximates the MI-FROG O2 ionization rate data

Femtosecond X-Ray Diffraction Of Short-Pulse Irradiated Semiconductors

Ultrafast optical-pump, x-ray diffraction probe experiments are providing new ways to study transient processes in physics, chemistry, and biology. In addition, the direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reaction take place is included as well. As such, current table-top-terawatt femtosecond laser systems provide an attractive source of few-hundred femtosecond duration bursts of angstrom-scale x-ray radiation with fluxes comparable to standard rotating-anode sources

Femtosecond X-Ray Diffraction Of Short-Pulse Irradiated Semiconductors

Femtosecond X-ray diffraction of short-pulse irradiated semiconductors was discussed. Ultrafast non-thermal solid-to-liquid transition in thin single-crystal Ge-111 films grown on Si-111 substrates were also studied. Proposed 4th generation light sources based upon single-pass x-ray free-electron lasers permitted single-shot structural determination of complex biomolecules

Wavelength Scaling of Laser Wakefield Acceleration for the EuPRAXIA Design Point

Scaling the particle beam luminosity from laser wakefield accelerators to meet the needs of the physics community requires a significant, thousand-fold increase in the average power of the driving lasers. Multipulse extraction is a promising technique capable of scaling high peak power lasers by that thousand-fold increase in average power. However, several of the best candidate materials for use in multipulse extraction amplifiers lase at wavelengths far from the 0.8–1.0 μm region which currently dominates laser wakefield research. In particular, we have identified Tm:YLF, which lases near 1.9 µm, as the most promising candidate for high average power multipulse extraction amplifiers. Current schemes to scale the laser, plasma, and electron beam parameters to alternative wavelengths are unnecessarily restrictive in that they stress laser performance gains to keep plasma conditions constant. In this paper, we present a new and more general scheme for wavelength scaling a laser wakefield acceleration (LWFA) design point that provides greater flexibility in trading laser, plasma, and electron beam parameters within a particular design point. Finally, a multipulse extraction 1.9 µm Tm:YLF laser design meeting the EuPRAXIA project’s laser goals is discussed

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