  Weibel-type instability can self-generate and amplify magnetic fields in both
space and laboratory plasmas with temperature anisotropy. The electron Weibel
instability has generally proven more challenging to measure than its ion
counterpart owing to the much smaller inertia of electrons, resulting in a
faster growth rate and smaller characteristic wavelength. Here, we have probed
the evolution of the two-dimensional distribution of the magnetic field
components and the current density due to electron Weibel instability, in $\rm
CO_2$-ionized hydrogen gas (plasma) with picosecond resolution using a
relativistic electron beam. We find that the wavenumber spectra of the magnetic
fields are initially broad but eventually shrink to a narrow spectrum
representing the dominant quasi-single mode. The measured $k$-resolved growth
rates of the instability validate kinetic theory. Concurrently,
self-organization of microscopic plasma currents is observed to amplify the
current modulation magnitude that converts up to $\sim 1\%$ of the plasma
thermal energy into magnetic energy.

Plasma Physics