Space-time resolved measurements of spontaneous magnetic fields in laser-produced plasma

Abstract

The first space-time resolved spontaneous magnetic field (SMF) measurements realized on Prague Asterix Laser System are presented. The SMF was generated as a result of single laser beam (1.315 μm) interaction with massive planar targets made of materials with various atomic numbers (plastic and Cu). Measured SMF confirmed azimuthal geometry and their maximum amplitude reached the value of 10 MG at the laser energy of 250 J for both target materials. It was demonstrated that spatial distributions of these fields are associated with the character of the ablative plasma expansion which clearly depends on the target material. To measure the SMF, the Faraday effect was employed causing rotation of the vector of polarization of the linearly polarized diagnostic beam. The rotation angle was determined together with the phase shift using a novel design of a two-channel polaro-interferometer. To obtain sufficiently high temporal resolution, the polaro-interferometer was irradiated by Ti:Sa laser pulse with the wavelength of 808 nm and the pulse duration of 40 fs. The results of measurements were compared with theoretical analysis.

Proton Acceleration Driven by a Nanosecond Laser from a Cryogenic Thin Solid-Hydrogen Ribbon

“…5(a) is acquired during a different laser shot but at very similar laser irradiation conditions. The plasma electron density maps can be retrieved after a proper analysis using the "maximum-of-a-fringe" method [19,22], as shown in Figs. 5(i)-5(n) for the four different time frames; thus, the corresponding axial density profile can be calculated [see plots in Figs.…”

“…ATi:sapphire laser system having a wavelength of 808 nm and pulse duration of 40 fs is used to carry out time-resolved measurements that enable the determination of plasma density distribution through a three-frame interferometric system previously optimized and normally used at PALS [19]. The three frames are recorded successively with a time delay of 1 ns.…”

Kinetic magnetization by fast electrons in laser-produced plasmas at sub-relativistic intensities

“…The estimations of different terms, presented in Ref. 23, showed, that the thermocurrent source plays a major role in the conditions of this experimental setup @hBi @t þ c 2 4p r  r  hBi r À r  ðṽ  hBiÞ À c e r  rp þR T n e À cm e e r  dṽ dt % 0;…”

“…20,21 For the SMF measurements, we used the optical diagnostics based on the Faraday effect 22 (rotation of the polarization plane) in combination with the measurement of the electron density distribution implemented earlier on the PALS system. 23 Among many methods used for the magnetic field measurement in the laser-driven plasma, such as proton deflectometry, direct B-dot, and optical techniques, this one allows to obtain probably the most complete information about the magnetic field, in particular, its spatial and temporal distribution, though only in the transparent area of the investigated plasma. However, due to a set of technical difficulties, e.g., time gating, synchronization of the plasma producing and probing beams, plasma self-emission, etc., hitherto this method has limitedly been applied in studies of the magnetized plasmas.…”

“…Recent progress achieved in synchronization of the sub-ns plasma producing beam and the probe femtosecond beam 24 provided a possibility to measure the SMF distribution in the ablative plasma with an extremely high spatial and temporal resolution. 23 Due to collection of these high quality data characterizing the SMF evolution, the understanding of its nature and origin becomes possible.…”