We have developed a single-shot spectral interferometer using the supercontinuum pulse generated by self-focusing in atmospheric pressure air. The diagnostic can be used to measure ultrafast refractive index transients either in a direct frequency-to-time mapping mode or in a full Fourier transform mode. In the direct mapping mode, temporal resolution is shown to be strongly restricted by the pulse chirp. In the transform mode, the ultimate temporal resolution is limited by the supercontinuum pulse bandwidth and the maximum pump-induced phase shift.

Abstract. Addressing the origin of the energetic particle injections into the inner magnetosphere, we investigate the 23 February 2004 substorm using a favorable constellation of four Cluster (near perigee), LANL and Geotail spacecraft. Both an energy-dispersed and a dispersionless injection were observed by Cluster crossing the plasma sheet horn, which mapped to 9-12 R E in the equatorial plane close to the midnight meridian. Two associated narrow equatorward auroral tongues/streamers propagating from the oval poleward boundary could be discerned in the global images obtained by IMAGE/WIC. As compared to the energy-dispersed event, the dispersionless injection front has important distinctions consequently repeated at 4 spacecraft: a simultaneous increase in electron fluxes at energies ∼1..300 keV, ∼25 nT increase in B Z and a local increase by a factor 1.5-1.7 in plasma pressure. The injected plasma was primarily of solar wind origin. We evaluated the change in the injected flux tube configuration during the dipolarization by fitting flux increases observed by the PEACE and RAPID instruments, assuming adiabatic heating and the Liouville theorem. Mapping the locations of the injection front detected by the four spacecraft to the equatorial plane, we estimated the injection front thickness to be ∼1 R E and the earthward propagation speed to be ∼200-400 km/s (at 9-12 R E ). Based on observed injection properties, we suggest that it is the underpopulated flux tubes (bubbles with Correspondence to: S. V. Apatenkov (apatenkov@geo.phys.spbu.ru) enhanced magnetic field and sharp inner front propagating earthward), which accelerate and transport particles into the strong-field dipolar region.

[1] Cluster crossed the magnetotail neutral sheet on four occasions between 16:38 and 16:43 UT on 08/17/2003. The four-spacecraft capabilities of Cluster are used to determine spatial gradients from the magnetic field vectors and, for the first time, full electron pressure tensors. We find that the contribution to the electric field from the Hall term (max of $6 mV/m) pointed towards the neutral sheet, whereas that from the electron pressure divergence (max of $1 mV/m) pointed away from the neutral sheet. The electric field contributions in this direction were closely anti-correlated. During this period Clusters 1 and 4 were sometimes above and below the neutral sheet respectively. This allowed the simultaneous observation of magnetic fields that are interpreted as two quadrants of the Hall magnetic field system. An associated field-aligned current system was detected using the curlometer and moments of the particle distributions. Citation:

The superluminal group velocity of an ultrashort optical Bessel beam pulse is measured over its entire depth of field, corresponding to approximately 2x10(4) optical wavelengths. The method used is to measure the traveling ionization front induced by the pulse.

A highly stable version of spectral interferometry is demonstrated, allowing single shot measurement of ultrafast high field processes using modest energy lasers, with pump and probe pulses totaling less than 1 mJ. The technique makes possible reconstruction of ultrafast refractive index transients with one-dimensional spatial resolution, limited only by the bandwidth of the supercontinuum pulse (~100 nm) and instrument resolution. The ultrafast nonlinear Kerr effect in glass, and in Ar, N(2), and N(2)O gases is measured, along with plasma generation in Ar. The inertial contribution to the nonlinear index from N(2) and N(2)O molecular rotation is also observed.