Experimental Characterization of a Strongly Coupled Solid Density Plasma Generated in a Short‐pulse Laser Target Interaction

Abstract

We have measured high resolution copper Kα spectra from a picosecond high intensity laser produced plasma. By fitting the shape of the experimental spectra with a self-consistent-field model which includes all the relevant line shifts from multiply ionized atoms, we are able to infer time and spatially averaged electron temperatures (Te) and ionization state (Z) in the foil. Our results show increasing values for Te and Z when the overall mass of the target is reduced. In particular, we measure temperatures in excess of 200 eV with Z ∼ 13-14. For these conditions the ion-ion coupling constant is Γii ∼ 8-9, thus suggesting the achievement of a strongly coupled plasma regime.

Spectral analysis of x-ray emission created by intense laser irradiation of copper materials

“…1 Additionally, the ratio of K α to K β radiation has been proposed as a diagnostic of bulk temperature, as the K β fluorescence will decrease as the M-shell is depleted of electrons at higher temperatures. [2][3][4] When line transitions in highly ionized atoms are observed, this verifies a plasma population with sufficient temperature to reach the Li-, He-, or H-like states.…”

Creation of hot dense matter in short-pulse laser-plasma interaction with tamped titanium foils

“…With the larger target, the average bulk temperature slightly decreases to 80 eV, which is expected since the mean energy density should decrease with increasing target size. 4 Analysis shows that the error in the absolute wavelength calibration corresponds to an error in the estimated electron temperature of ±20 eV, as indicated in Fig. 6.…”

“…Following the initial work of Gregori et al,4 in this paper we will show that hot dense plasma conditions can be well characterized using a spectral diagnostics technique that is less susceptible to opacity effects. We directly measure the average ionization state of dense titanium plasma by recording the spectral shifts of the K␣ line emitted from the bulk of the target.…”

“…Temperatures between 200 and 2000 eV in solid targets have been reported in a variety of experiments. [4][5][6][7][8][9][10][11][12] Heating of buried Al layers and the effect of a nanosecond pedestal ahead of the main laser pulse have been recently discussed by Evans et al 13 Measurements of density and temperature of hot dense plasmas have been often inferred from spectroscopic techniques, namely intensity ratios [3][4][5][6][7][8][9][10][11][12] and wavelength shifts 14 of Lyman and Balmer series lines. Use of only line shapes is not sufficient due to the complexity of atomic radiation transport and absorption within the target, thus it becomes important to infer information using radiation-hydrodynamics, particle-incell ͑PIC͒, and collisional radiative atomic codes.…”

Study of electron and proton isochoric heating for fast ignition

“…The HOPG spectrum of the K emission from the wire exhibits broadening to higher energy due to ionization. Following our previous published method of spectroscopic analysis [3] the temporally and spatially averaged temperature is 160 eV. Most K emission occurs where the temperature is highest but the emission occurs at all times during heating from the initially cold state, so that the peak temperate should be about twice the average.…”