Electron density profile of Xe self-trapped channel
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Figure 5. Electron density profile of Xe self-trapped channel. (a) Section A–A from panel (b) of the electron density that reveals an extended plateau of ionization. The two brown lines show the expected profile from linear absorption of Xe(M) ~ 1 keV x-rays in surrounding neutral Xe. The existence of the extended peripheral zone signals saturated absorption. The peak of the Thomson signal is ~ 35-fold above that for the onset of the plateau. (b) Taken from figure 2(a) and illustrates the location of the A–A section through the peripherally ionized region. (c) Taken from figure 2(b) with the position of section A–A indicated.
Comparative single-pulse studies of self-trapped plasma channel formation in Xe and Kr cluster targets produced with 1–2 TW femtosecond 248 nm pulses reveal energy efficient channel formation (>90%) and highly robust stability for the channeled propagation in both materials. Images of the channel morphology produced by Thomson scattering from the electron density and direct visualization of the Xe(M) and Kr(L) x-ray emission from radiating ions illustrate the (1) channel formation, (2) the narrow region of confined trapped propagation, (3) the abrupt termination of the channel that occurs at the point the power falls below the critical power Pcr, and, in the case of Xe channels, (4) the presence of saturated absorption of Xe(M) radiation that generates an extended peripheral zone of ionization. The measured rates for energy deposition per unit length are ~ 1.46 J cm−1 and ~ 0.82 J cm−1 for Xe and Kr targets, respectively, and the single pulse Xe(M) energy yield is estimated to be > 50 mJ, a value indicating an efficiency >20% for ~ 1 keV x-ray production from the incident 248 nm pulse.