Showing papers by "Gerard Mourou published in 1993"
TL;DR: In this article, a 2 psec temporal resolution of plasmas produced by the interaction between solid targets and a high contrast sub-picosecond table top terawatt (T3) laser at 1016 W/cm2 is used to study the basic processes which control the x-ray pulse duration.
Abstract: Time‐resolved spectroscopy (with a 2 psec temporal resolution) of plasmas produced by the interaction between solid targets and a high contrast subpicosecond table top terawatt (T3) laser at 1016 W/cm2, is used to study the basic processes which control the x‐ray pulse duration. Short x‐ray pulses have been obtained by spectral selection or by plasma gradient scalelength control. Time‐dependent calculations of the atomic physics [Phys. Fluids B 4, 2007, 1992] coupled to a Fokker–Planck code [Phys. Rev. Lett. 53, 1461, 1984] indicate that it is essential to take into account the non‐Maxwellian character of the electron distribution for a quantitative analysis of the experimental results.
120 citations
TL;DR: In this paper, the spectral gain narrowing was identified as one of the main issues, and a solution was proposed to solve it. But it was only applied to a Ti:sapphire/Nd:silicate glass power chain.
Abstract: Femtosecond pulses in the 50–60-TW power range have been generated at 1064 nm by using the chirped-pulse-amplification technique applied to a Ti:sapphire/Nd:silicate glass (90-mm output aperture) power chain. We have identified the spectral gain narrowing to be one of the main issues, and we show how to solve it.
108 citations
TL;DR: Pulses are stretched by an all-reflective-optics stretcher with 1200-line/mm holographic gratings and amplified to an energy of 0.7 mJ in a regenerative amplifier to produce transform-limited pulses.
Abstract: 40-fs pulses are stretched to 372 ps by an all-reflective-optics stretcher with 1200-line/mm holographic gratings and are then amplified to an energy of 0.7 mJ in a regenerative amplifier. After compression, 0.35-mJ, 55-fs transform-limited pulses are produced.
84 citations
TL;DR: It is shown that x-ray-line polarization spectroscopy can be a powerful diagnostic to study laser-produced plasmas and indicate non-Maxwellian behavior and strong anisotropy due to nonlocal electron heat flow.
Abstract: In this work, we show that x-ray-line polarization spectroscopy can be a powerful diagnostic to study laser-produced plasmas. Kinetic calculations are compared to experiments designed to probe the lowdensity plasma region (with a 1-ps laser pulse) and the overdense plasma (with a 400-fs laser pulse). We observe the transition from a "pancakelike" electron distribution function at low density to a "beamlike" electron distribution function in the overdense plasma. The results are in agreement with the calculations which indicate non-Maxwellian behavior and strong anisotropy due to nonlocal electron heat flow.
82 citations
TL;DR: In this paper, a simple model for the propagation of high-frequency signals on coplanar striplines with lossy semiconductor substrates is proposed and demonstrated, which incorporates the effect of a conductive substrate through the loss tangent in a distributed-circuit analysis extended to high frequencies.
Abstract: A simple model for the propagation of high-frequency signals on coplanar striplines with lossy semiconductor substrates is proposed and demonstrated. This model incorporates the effect of a conductive substrate through the loss tangent in a distributed-circuit analysis extended to high frequencies. Very strong attenuation and dispersion due to the substrate are observed even when the GaAs conductance is only 1 mho/cm, corresponding to a doping density of around 10/sup 15/ cm/sup -3/. The accuracy of this model is tested with a direct comparison to experimental data of picosecond pulse propagation on a doped GaAs coplanar stripline (CPS) measured in the time domain using the electro-optic (EO) sampling technique. Good agreement is found in terms of the attenuation and phase velocity of the distorted pulses at four propagation distances up to 300 mu m. The pulse propagation on a multiple modulation-doped layer is also studied experimentally as a prototype of high-frequency signal propagation on the gate of a modulation-doped field-effect transistor (MODFET). The attenuation shows linear frequency dependence up to 1.0 THz, contrary to the cubic or quadratic dependence of coplanar transmission lines on low-loss substrates. >
51 citations
TL;DR: After the laser intensity is increased from 1016 to 5 × 1017 W/cm2, the kiloelectron-volt x-ray emission is brighter by approximately an order of magnitude and is still produced from very dense plasma.
Abstract: We report on the observation of high-electron-density (ne ≈ 15nc where nc is the critical density, 4 × 1021 cm−3 for λ = 0.53 μm) and high-temperature (Te ≈ 400 eV) plasma obtained when an intense high-contrast 400-fs laser pulse interacts with a solid Al target. After the laser intensity is increased from 1016 to 5 × 1017 W/cm2, the kiloelectron-volt x-ray emission is brighter by approximately an order of magnitude and is still produced from very dense plasma (6 × 1022 cm−3).
42 citations
TL;DR: In this article, the authors amplified 160-fs pulses at a repetition rate of 10 kHz and generated more than 2 W of average power after compression, which is a significant amount of power for a 10 kHz frequency band.
Abstract: We amplified 160-fs pulses at a repetition rate of 10 kHz. More than 2 W of average power is generated after compression.
40 citations
TL;DR: The first time-resolved Al spectra (near 8 Å) obtained with a 2-ps time resolution are presented, and it is demonstrated that the resonance emission width decreases as the plasma density increases.
Abstract: We describe a technique for spectrally and temporally resolving the kilo-electron-volt emission from ultrashort plasmas produced from solid targets with a tabletop terawatt 400-fs laser. The first time-resolved Al spectra (near 8 A) obtained with a 2-ps time resolution are presented. The results clearly demonstrate that the resonance emission width decreases as the plasma density increases. The ultrafast Kα emission component is also measured in our experimental conditions.
21 citations
TL;DR: In this article, the lattice mismatched growth of LT-InxGa1−xAs on GaAs appears to be the most suited for high-speed detector applications in the near-infrared wavelength range used in optical communications.
Abstract: GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures (≈200°C) exhibits the desired properties of a high-speed photoconductor: high resistivity, high mobility, high dielectric-breakdown strength, and subpicosecond carrier lifetime. The unique material properties are related to the excess arsenic content in the MBE grown epilayers. Due to the combination of the above properties, dramatically improved performance has been observed in photoconductive detectors and correlators using submicron spaced electrodes. In addition to GaAs, low-temperature growth of InxGa1−xAs alloys also leads to the incorporation of excess arsenic in the layers, and therefore this material system exhibits many beneficial photoconductor properties as well. In particular, the lattice-mismatched growth of LT-InxGa1−xAs on GaAs appears to be the most suited for high-speed detector applications in the near-infrared wavelength range used in optical communications. The material issues and the photodetector characteristics required to optimize their performance are discussed.
17 citations
TL;DR: In this paper, the authors present results of their effort to develop an efficient, user-friendly, table-top ultrafast X-ray source, and the factors affecting the duration and the intensity of the Xray emission in the keV range are studied.
Abstract: We present recent results of our effort to develop an efficient, user-friendly, table-top ultrafast X-ray source. The factors affecting the duration and the intensity of the X-ray emission in the keV range are studied. Time-dependent calculation of the atomic physics coupled to a Fokker- Planck code is used for a quantitative analysis of the experimental results.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
11 citations
22 Oct 1993
TL;DR: In this article, the authors summarized the work performed during a 3-year URI program on Transport in Microstructures in the Microwave and Millimeter-Wave Regime and described significant achievements in both basic investigations of transport physics and in applications to high speed electronics and optoelectronics.
Abstract: : This report summarizes the work performed during a 3-year URI program on Transport in Microstructures in the Microwave and Millimeter-Wave Regime It describes significant achievements in both basic investigations of transport physics and in applications to high-speed electronics and optoelectronics Fundamental advances were made in measurements of transport in semiconductors under high-field conditions A variety of ultrafast optical and optoelectronic techniques were used to perform the most comprehensive experimental study to date of the dynamics of high-field transport in semiconductors, including the first observations of the ballistic acceleration of electrons, of field-dependent velocity overshoot, and of the dynamics of impact ionization Carrier dynamics in low-temperature-grown (LT) semiconductors and high-critical-temperature superconductors were investigated, and optimum materials growth conditions determined The work on LT GaAs led to significant advances in high speed electronic measurement, including electro-optic network analysis up to 300 GHz bandwidth, and novel photoconductive probes with ps response, high spatial resolution, and microvolt sensitivity LT GaAs MSM photodetectors were developed with bandwidths up to 375 GHz and both high sensitivity and large-signal capability, representing significant improvements over the prior state of the art Novel femtosecond lasers were developed, which made possible the development of new high speed measurement techniques Ultrafast optics, High-speed electronics, Electron transport in solids, Resonant tunneling time-resolved RHEED, Fast modulators, Fast detectors, LT-GaAs, Ballistic transport
Proceedings Article•
02 May 1993
TL;DR: The authors amplified 160-fs pulses at a repetition rate of 10 kHz and found that more than 2 W of average power is generated after compression.
Abstract: We amplified 160-fs pulses at a repetition rate of 10 kHz. More than 2 W of average power is generated after compression.
25 Jan 1993
TL;DR: In this paper, a photoconductive probe sampling technique was developed for the measurement of S-parameters of mm-wave circuit components with a 120-GHz measurement bandwidth, which can be applied to the measurements of vector network analyzers, spectrum analyzers and sampling oscilloscopes.
Abstract: Conventional purely electronic measurement instruments such as vector network analyzers, spectrum analyzers and sampling oscilloscopes are not effective at above 100 GHz. One major limitation is imposed by the connectors and waveguides needed for signal coupling between the test instrument and the device under test. To overcome those limitations of present measurement techniques, we have developed a photoconductive probe sampling technique which can be applied to the measurement of S-parameters of mm- wave circuit components with a 120-GHz measurement bandwidth [1]. The photoconductive probe sampling technique combines the ultrafast optical technology of 120-fs Ti-Sapphire short pulse laser [2] and microfabrication technology of Silicon-On-Sapphire (SOS) photoconductive sampling probe, which consists of a high-impedance interdigitated photoconductive switch. The probe technology has demonstrated a 2.1 ps temporal resolution and low-invasiveness making this very attractive for external circuit testing of mm-wave circuits with a 120-GHz measurement bandwidth.