Temperature and $K\alpha$-yield radial distributions in laser-produced solid-density plasmas imaged with ultrahigh-resolution x-ray spectroscopy

We study warm dense matter formed by subpicosecond laser irradiation at several ${10}^{19}\text{W}/{\text{cm}}^2$ of thin Ti foils using x-ray spectroscopy with high spectral $\left(E/\Delta E\sim 15,000\right)$ and one-dimensional spatial $\left(\Delta x=13.5\mu \text{m}\right)$ resolutions. $\text{Ti}K\alpha$ doublets modeled by line-shape calculations are compared with Abel-inverted single-pulse experimental spectra and provide radial distributions of the bulk-electron temperature and the absolute-photon number $K\alpha$ yield in the target interiors. A core with $\sim 40\text{eV}$ extends homogeneously up to ten times the laser-focus size. The spatial distributions of the bulk-electron temperature and $K\alpha$ yield are strongly correlated.

Figure 1

(Color online) Schematic of the experimental setup. The energy dispersion axis $x^{\prime }$ on the x-ray film is perpendicular to the spatial resolution in the $y$ direction.

Figure 2

(Color online) Single-pulse x-ray spectra of the laser-irradiated $10\text{−}\mu \text{m}$-thick Ti foil at laser intensity $I=5\times {10}^{19}\text{W}/{\text{cm}}^2$ and $\lambda =1057\text{nm}$, shown from different target positions $y$. The x-ray film scan (false colors) is given in the inset.

Figure 3

(Color online) Comparison of assorted Abel-inverted experimental spectra (solid lines) from irradiation of a $10\mu \text{m}$ Ti foil and the best-fit modeled spectra (dashed lines).

Figure 4

(Color online) Radial temperature (top) and integrated $K\alpha$-yield (bottom) distributions of the different targets used, irradiated with the $\omega$ and $2\omega$ laser pulses.

Figure 5

(Color online) Comparison of FWHM of the bulk-electron temperature and $K\alpha$-yield radial distributions for different targets and laser pulses.