This work demonstrates experimentally the close relation between return currents from relativistic laser-driven target polarization and the quality of the relativistic laser\u2013plasma interaction for laser-driven secondary sources, taking as an example ion acceleration by target normal sheath acceleration. The Pearson linear correlation of maximum return current amplitude and proton spectrum cutoff energy is found to be in the range from \u223c0.70 to 0.94. kA-scale return currents rise in all interaction schemes where targets of any kind are charged by escaping laser-accelerated relativistic electrons. Their precise measurement is demonstrated using an inductive scheme that allows operation at high repetition rates. Thus, return currents can be used as a metrological online tool for the optimization of many laser-driven secondary sources and for diagnosing their stability. In particular, in two parametric studies of laser-driven ion acceleration, we carry out a noninvasive online measurement of return currents in a tape target system irradiated by the 1 PW VEGA-3 laser at Centro de L\u00e1seres Pulsados: first, the size of the irradiated area is varied at best compression of the laser pulse; second, the pulse duration is varied by means of induced group delay dispersion at best focus. This work paves the way to the development of feedback systems that operate at the high repetition rates of PW-class lasers.<\/p>\n","protected":false},"author":1,"featured_media":0,"template":"","meta":{"_acf_changed":false,"inline_featured_image":false},"a_os":[160],"class_list":["post-41143","publications","type-publications","status-publish","hentry","a_os-160","entry"],"acf":[],"yoast_head":"\n