A large-planar (22 cm diam.) high-density ( ∼2×1012 cm-3) plasma is produced in argon gas at 140 Pa by 2.45 GHz–1 kW discharges, using a microwave launcher of small slot antennas. The two-dimensional distributions of optical emission intensities as well as microwave field intensities are measured near the plasma surface irradiated with microwaves. Both the optical emission and the microwave field clearly show stationary patterns of azimuthal mode m=3 and radial mode n=3 at higher pressures (140 Pa), while a mode change to m=6 and n=2 is observed at lower pressures (44 Pa). These patterns are attributed to the excitation and absorption of standing surface waves near the cutoff layer.

A planar high-density (∼10 12 cm −3 ) plasma, 22 cm in diameter and 9 cm in length, is produced by a 2.45 GHz microwave radiation of 500 W through small slot antennas in argon at 20-350 Pa without a magnetic field. Several types of azimuthal and radial standing wave mode pattern are observed in the optical emission from the plasma depending on the discharge conditions. The microwave field in the plasma measured by a movable antenna decreases exponentially in the axial direction from the quartz wall adjacent to the slot antennas, thus suggesting the propagation of surface waves in the r, θ directions. The measured azimuthal microwave field distributions and the optical emission pattern clearly show a mode transition of the standing surface wave from a TM 33 mode to a TM 62 mode when the pressure is decreased from 140 to 44 Pa at the constant power of 400 W. Here TM mn denotes the transverse magnetic mode of azimuthal mode number m and radial mode number n. A wave dispersion analysis based on a one-interface uniform-density model predicts these modes in a range of electron densities corresponding to those measured by a Langmuir probe in the experiment.

Various electromagnetic surface modes along a finite area dielectric interface can sustain large area overdense plasmas. Mode jumps between these modes have been reported when changing the gas pressure. In this paper we report similar mode jumps caused by changing the wave power at fixed gas pressure. A simple theoretical analysis is proposed to explain this phenomenon on the basis of the resonance behavior of the chamber impedance and a stability criterion is formulated. The theory predicts a hysteresis in the power-density dependence, which was also observed experimentally.

Intense femtosecond irradiation of a solid surface creates transient (-Mbar) intemal pressure because the lattice is heated faster than thermal expansion can occur. Before the pressure is released, the heated surface remains optically sharp and timeresolved ellipsometric measurements can be analyzed with Fresnel's equations. At later times (At 7 1-2 ps). a rarefaction wave front develops at the surface, as the laser induced strong compressional shock wave acts on the solid density plasma. The expansion dynamics can provide diagnostic information on initial pressure-temperature conditions. This expanding rarefaction wave front can also be probed by time-resolved ellipsometry measurements, provided they are analyzed by generalized Helmholtz wave equations. In this presentation, we report comprehensive measurements on free electron metals (Al), semiconductor (Si), and semimetal (graphite) targets using variable probe incidence angle, wavelength, and polarization. 100 fs, 620 nm, laser pump pulses excited the sample surfaces well above the melting threshold (Fh -0.1 J/cm2), and weak timedelayed, s-or p-polarized probe pulses at 620 or 310 run were focused to the pump spot center. In the reflectivity measurements on the highly oriented pyrolytic graphite target excited at a common level F -5 F& for different probe incident angles, a sharp initial reflectivity increase caused by melting of the carbon is observed near At = 0. The subsequent reflectivity dynamics, caused by surface expansion, depends strongly on incident angle. For 8= 30" and 50°, &zo decreases monotonically for both s-and p-polarized light. For 8 = 6 7 O , a slight increase in e 2 0 with -5 ps rise time is observed. The reflectivity responses for a 310 nm probe for the same pump fluence show no initial sharp increase. Monotonic decreases in R310 of varying slope are observed in most cases. However, p-polarized reflectivity at 8 = 67' shows a pronounced, delayed in reflectivity. A theoretical model basedon the evolution of surface density gradient &om a discrete profile to a graded density rarefaction wave front N(x), described by the Riemann solution to the hydrodynamic equations for a solid density plasma experiencing a strong shock wave is used to analyze the data. For free electron metal targets, N(x,At) and v(x,At) characterize the dielectric function e(x,At) of the rarefaction wave front through the Drude formula, allowing numerical solution of the Helmholtz equations at each At. For non-free-electron metal (W) and non-metal (C and Si) targets, even though the long-range order is completely lacking in the molten state, there still can be forbidden gaps in the energy spectrum due to the short-range order in the material and rather strong covalent contribution to the dielectric function can not be ignored. Therefore a densitydependent background dielectric constant &o(N(x)) has been introduced to explain the data (The free electron model fails.). The expansion speed, closely approximates sound speed in all cases, is assumed decaying with time, which...