Comparative analysis of stable ultrahigh power-density 248 nm channels formed in Kr and Xe cluster targets

Abstract

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.

High-resolution x-ray saturation spectroscopy of krypton L-shell autoionizing transitions

“…Analyzing the signal in reverse, we initially consider the final absorptive phase in the range Z ⩾ 1.1 mm. With the known photoionization cross section σ i ≅ 7 × 10 −19 cm 2 for neutral krypton [11] at ħω ≅ 1652 eV and a krypton density [10] of ∼4.5 × 10 19 cm −3 , we find that the observed value of δ matches well the expected linear absorption length of ∼317 μm. Furthermore, since the saturation parameter is high, with a value of ħω/σ i ≅ 390 J cm −2 , the dominance of linear absorption is expected under these experimental conditions [9,10].…”

“…With the known photoionization cross section σ i ≅ 7 × 10 −19 cm 2 for neutral krypton [11] at ħω ≅ 1652 eV and a krypton density [10] of ∼4.5 × 10 19 cm −3 , we find that the observed value of δ matches well the expected linear absorption length of ∼317 μm. Furthermore, since the saturation parameter is high, with a value of ħω/σ i ≅ 390 J cm −2 , the dominance of linear absorption is expected under these experimental conditions [9,10]. Also, at this longitudinal position, on the basis of measured ionization thresholds [12], the residuum of the diffracted 248 nm pulse has an intensity too low to produce a significant population of even singly ionized Kr + species.…”

“…Previous work [9] has shown that amplification on the Kr 26+ (3s → 2p) transition at 7.504 Å (ħω ≅ 1652 eV) can be produced with the generation of a self-trapped 248 nm plasma channel [10] in a Kr cluster medium. The experimental configuration and corresponding diagnostic suite are fully described in [9] and [10]. As shown by the data obtained in this study and prior work [9], the limit of the spectral resolution achieved is 2-3 eV.…”

“…The achievement of saturation on the autoionizing Kr 15+ and Kr 16+ absorptive transitions is immediately useful, since it enables a lower bound on the energy of the propagating Kr 26+ 7.5 Å beam to be readily estimated [10] from the relation…”

Demonstration of Kr(L) amplification at λ = 7.5 Å from Kr clusters in self-trapped plasma channels

“…We note that the typical longitudinal (Z) structure of the 4π x-ray emission zone in our experiments generally consists of two bright emission regions that are fully separated and occur before and after the formation of the narrow long selftrapped channel [13]. The morphology of this localization is shown in the transversely recorded x-ray pinhole camera images presented in this manuscript.…”