Abstract
We examine the effect of laser focusing on the effectiveness of a recently discussed scheme [M. F. Ciappina et al., Phys. Rev. A 99, 043405 (2019) and M. F. Ciappina and S. V. Popruzhenko, Laser Phys. Lett. 17, 025301 (2020)] for in situ determination of ultrahigh intensities of electromagnetic radiation delivered by multi-petawatt laser facilities. Using two model intensity distributions in the focus of a laser beam, we show how the resulting yields of highly charged ions generated in the process of multiple sequential tunneling of electrons from atoms depend on the shapes of these distributions. Our findings lead to the conclusion that an accurate extraction of the peak laser intensity can be made either in the near-threshold regime, when the production of the highest charge state happens only in a small part of the laser focus close to the point where the intensity is maximal or through the determination of the points where the ion yields of close charges become equal. We show that for realistic parameters of the gas target, the number of ions generated in the central part of the focus in the threshold regime should be sufficient for a reliable measurement with highly sensitive time-of-flight detectors. Although the positions of the intersection points generally depend on the focal shape, they can be used to localize the peak intensity value in certain intervals. Finally, the slope of the intensity-dependent ion yields is shown to be robust with respect to both the focal spot size and the spatial distribution of the laser intensity in the focus. When these slopes can be measured, they will provide the most accurate determination of the peak intensity value within the considered tunnel ionization scheme. In addition to this analysis, we discuss the method in comparison with other recently proposed approaches for direct measurement of extreme laser intensities.
Highlights
The interaction of high-power electromagnetic radiation with different forms of matter, including free electrons, atoms, molecules, solids, and plasmas, has been an important topic of experimental and theoretical research for more than 50 years, since the early days of laser physics
Using the intensity-dependent populations Ck numerically found in Ref. 23, we calculate the number of highly charged ions of argon, krypton, and xenon in the intensity interval 3 3 1020 W/cm2–5 3 1024 W/cm2
We studied the effect of the focal intensity distribution on the method of peak intensity determination based on the observation of multiple tunneling ionization of heavy atoms
Summary
The interaction of high-power electromagnetic radiation with different forms of matter, including free electrons, atoms, molecules, solids, and plasmas, has been an important topic of experimental and theoretical research for more than 50 years, since the early days of laser physics. Progress in the development and application of high-power laser sources had led to a gradual growth in the maximum available field strengths. This has already made it possible to experimentally explore the nonlinear quantum dynamics of atomic, molecular, and solid state systems subjected to intense laser radiation, the physics of relativistic and ultrarelativistic electron plasmas, and relativistic nonlinear optics For linearly polarized radiation, such an electric field corresponds to an intensity
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