C. Y. Chien

Ultrafast x‐ray sources*

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.

Highly efficient second-harmonic generation of ultraintense Nd:glass laser pulses

Second-harmonic conversion efficiencies of 80% for type I KDP crystals and 70% for type II have been demonstrated with 500-fs, 1.053-μm laser pulses at intensities as high as 400 GW/cm2. The results are generally in good agreement with simulations and indicate that self-phase modulation and cross-phase modulation may be significant. For type II conversion with a predelay between the input o and e waves, some evidence is obtained of pulse shortening to ~100 fs.

Ultrahigh-contrast Ti:sapphire/Nd:glass terawatt laser system

We have developed a 1.5-TW Ti:sapphire/Nd:glass chirped-pulse amplification system. The laser produces 640-mJ, 400-fs pulses. By using a passive pulse cleaning stage a power contrast ratio of 106 has been obtained.

Production of a high-density and high-temperature plasma with an intense high-contrast subpicosecond laser

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).

Time-resolved kiloelectron-volt spectroscopy of ultrashort plasmas.

We describe a technique for spectrally and temporally resolving the kilo-electron-volt emission fromultrashort plasmas produced from solid targets with a tabletop terawatt 400-fs laser. The firsttime-resolved Al spectra (near 8 Å) 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 K(α) emission component is also measured in our experimental conditions.

Ultrafast x-ray emission from ultrashort plasmas

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.

Long-range, high-resolution laser radar

Abstract A high energy, chirped pulse laser was used to demonstrate long range, high resolution radar. A broadband nanosecond chirped pulse propagated to a target, and upon compression sub-millimeter surface resolution was obtained. This technique avoided the nonlinear effects in air that were seen when a picosecond pulse propagated to the target.

Spectroscopic analysis of short-pulse laser-produced plasmas

Experimental spectra of hot dense plasmas of aluminium produced by the interaction of a subpicosecond laser with solid targets at 10 16 and 5 × 10 17 W/cm 2 are analyzed and discussed. A detailed analysis of the K -shell spectra is given through time-dependent calculations of atomic physics postprocessed to Fokker-Planck calculations of the laser-matter interaction. The non-Maxwellian character of the electron distribution function is shown. An evaluation of the electronic density and of the ion temperature 7 i will be presented through Stark line broadening calculations. An X-ray spectrum from a Tantalum target also will be presented along with a preliminary interpretation.

High-efficiency frequency doubling of ultra-intense Nd:glass laser pulses

Efficient second harmonic conversion (70 - 80%) using Type II and Type I crystals is demonstrated with 400-fs, 1.053-micrometers laser pulses at intensities up to several hundreds of GW/cm2. The experimental results generally agree with the predictions of the code MIXER. For the Type II predelay scheme, evidence is obtained of pulse shortening down to approximately 100 fs.

Laser plasma interactions at electron-relativistic laser intensities

A review is given (intended for the non-expert) of the field of ultrashort laser pulses at ultra high intensities and their interactions with plasmas. The review covers progress and basic concepts for theory, modelling and experiments, with emphasis on the background aspects, the basic experimental considerations and some possible applications.