The effects of resonantly enhanced fields in picosecond laser produced plasmas

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:5636742

Uchida, S

Picosecond laser-plasma interactions have been studied experimentally using a 1-ps, 1-[mu]m laser interacting with solid targets. The experiments have been conducted with a detailed knowledge of the laser pulse shape. High intensity contrast laser pulses ensure that no performed plasma exists before the arrival of the main picosecond pulse in an intensity range where nonlinear processes start to dominate the laser absorption namely from 10[sup 14] to 10[sup 16] W/cm[sup 2]. When no preformed plasma exists, the resonantly oscillating field at the critical surface can be significantly enhanced and can accelerate plasma particles to superthermal energies. This field enhancement was studied in terms of the amplitude of p-polarized (laser electric field vector component parallel to the plane of incidence) component through an extensive characterization, ion charge state as a function of velocity and velocity distribution. Two primary findings from this characterization are: (1) the ion blowoff characteristics depend entirely on the p-polarized component of laser and not on the laser energy, and (2) the nonthermal electrons driving the plasma expansion are highly monoenergetic. These findings are supported by several other plasma diagnostics which include laser energy absorption, continuum and K[sub [alpha]] x-ray measurements. It is suggested from the experimental observation that the electrons are accelerated by the ponderomotive force in the resonantly oscillating field. The intensity enhancement at the critical surface was calculated based on the ponderomotive picture using experimentally measured electron kinetic energy. The experimental values are compared with theoretical values that include plasma-wave dispersion effects on the resonantly oscillating field strength. The ponderomotive acceleration mechanism is compared to wavebreaking as an explanation for the non-thermal electron acceleration.

• Research Organization: Rochester Univ., NY (United States)
• OSTI ID: 5636742
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700350* -- Plasma Production
Heating
Current Drive
& Interactions-- (1992-)
ABSORPTION
ELECTROMAGNETIC RADIATION
ENERGY ABSORPTION
EXPANSION
INTERACTIONS
K ABSORPTION
LASER RADIATION
LASER TARGETS
LASER-PRODUCED PLASMA
PLASMA
PLASMA DIAGNOSTICS
PLASMA EXPANSION
PONDEROMOTIVE FORCE
PULSES
RADIATIONS
RESONANCE
SORPTION
TARGETS