Abstract
The use of gas cluster media as a target for an intense femtosecond laser pulses is considered to be uniquely convenient approach for the development of a compact versatile pulsed source of ionizing radiation. Also, one may consider cluster media as a nanolab to investigate fundamental issues of intense optical fields interaction with sub-wavelength scale structures. However, conventional diagnostic methods fail to register highly charged ion states from a cluster plasma because of strong recombination in the ambient gas. In the paper we introduce high-resolution X-ray spectroscopy method allowing to study energy spectra of highly charged ions created in the area of most intense laser radiation. The emission of CO2 clusters were analyzed in experiments with 60 fs 780 nm laser pulses of 1018 W/cm2 intensity. Theory and according X-ray spectra modeling allows to reveal the energy spectra and yield of highly charged oxygen ions. It was found that while the laser of fundamental frequency creates commonly expected monotonic ion energy spectrum, frequency doubled laser radiation initiates energy spectra featuring of distinctive quasi-monoenergetic peaks. The later would provide definite advantage in further development of laser-plasma based compact ion accelerators.
Highlights
IntroductionThe interaction of laser radiation with nanostructured media (clusters, nano-wires, nano-spheres, carbon nano-tubes, snow targets and etc.) has attracted much attention in the context of studying fundamental properties of matter under extreme conditions[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
Highly charged oxygen ions were not detected in this experiment in measurements with a Thomson parabola because of fast oxygen recombination as a result of propagation inside the spray
Abicht et al.[52], where water droplets were irradiated by powerful laser radiation at intensities up to 5 · 1019 W/cm[2] and no highly charged carbon and oxygen ions were observed with the Thomson parabola technique
Summary
The interaction of laser radiation with nanostructured media (clusters, nano-wires, nano-spheres, carbon nano-tubes, snow targets and etc.) has attracted much attention in the context of studying fundamental properties of matter under extreme conditions[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. Abicht et al.[52], where water droplets were irradiated by powerful laser radiation at intensities up to 5 · 1019 W/cm[2] and no highly charged carbon and oxygen ions were observed with the Thomson parabola technique. This situation is typical for cluster targets[51,52,53,54,55]. Recombination in the surrounding gas leads to a production of neutrals and negative ions, which is well detected in laser–cluster experiments[54,55]
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