Quadrupole distribution in laser induced plasmas in air with 532 nm

Summary form only given. We present an experimental investigation of the electric field generated by a laser induced plasma (LIP) in air for times t<; 100 ns. The laser used was a Nd:YAG, with pulses of 7 ns at FWHM, and irradiance I ≈ 10
¹²
W/cm
²
. The measurements were made by using a central core of a 50 Ω coaxial cable. Our results show different spatio-temporal structures of the electric field potential depending if the LIP was produced using either 1064 or 532 nm, the magnitude of such electric field potential obtained by applying an external electric field
¹
. By focusing the pulse of the fundamental with a lens (3.5, 5, 10 cm of focal distance) the LIP generates a dipole configuration
²
, where we observed the formation of a single plasma. In contrast, if the plasma was induced with pulses of 532 nm we found a double plasma with a quadrupolar distribution of the charge in the LIP, consisting of two oppositely directed dipoles, either one in each of the plasmas. It has been reported that the aberration produced with the focusing lens could generates a double plasma in air
^3,4
. Such configuration was aligned with the laser beam axis. Also, a quadrupolar structure was found in Ref.[5]. Laser shadowgraphy and fast photography diagnostics techniques were used to study the spatial and temporal evolution of the plasma core for both wavelengths.