Experimental configuration used for the Thomson and x-ray imaging of the plasma channel dynamics of 248 nm femtosecond pulses interacting with Kr and Xe cluster targets
Figure 1. Experimental configuration used for the Thomson and x-ray imaging of the plasma channel dynamics of 248 nm femtosecond pulses interacting with Kr and Xe cluster targets. The pinhole camera used for imaging the Xe(M)/Xe(L) or Kr(L) emissions, the Thomson imaging system, and the cooled pulsed-valve are designated. Also shown is the transverse von Hámos mica spectrometer. The spatial resolution of the Thomson system was measured to be 22 µm with the use of the standard calibrated USAF resolution target.
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.