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We use both a Fourier-transform-based analysis and time-retrieval calculations to get time-resolved measurements of the reflectivity and the phase shift of a chirped probe pulse interacting with a fs-laser-produced plasma by spectral interferometry in a single shot. We have devised a novel dual-quadrature Mach–Zehnder configuration in which wavefront division is used to obtain spatial fringes from the perturbed and unperturbed probe simultaneously. We demonstrate the capability of this technique with fully analyzed experimental data on the interaction of a femtosecond laser with C3H6 and C samples, showing 35-fs time resolution.

Monomode guiding over 100 Rayleigh lengths (10 cm) of high intensity ultrashort laser pulses ( ${10}^{16}\mathrm{W}/{\mathrm{cm}}^{2}$, 120 fs) has been demonstrated in hollow dielectric capillary tubes (45--70 \ensuremath{\mu}m internal diameter) without inner wall damage. Analytical predictions for coupling conditions and damping length are confirmed experimentally for tubes under vacuum. With 5 to 40 mbar of He gas in the tube, when laser ionization occurs the energy and duration of the transmitted pulse decrease while its spectrum is broadened.

We report on single-shot frequency-domain interferometric measurements showing space- and time-resolved ponderomotive electron density profile steepening of a short-scale-length ultraintense laser-produced plasma. The density gradient scale length is varied by applying a time-delayed laser prepulse. The measured absolute position of the critical density surface is found to be in agreement with one-dimensional hydrodynamic simulations for the range of scale lengths studied.

In order to extend plasma accelerators, the laser beam has to be guided inside gas or plasma over a distance of the order of the dephasing length, which is typically much larger than the diffraction length z/sub R/ of the laser. A capillary tube can be used as a waveguide for high-intensity laser pulses over distances well in excess of z/sub R/. Experimental demonstration of monomode guiding over 100 z/sub R/ of 10/sup 16/ W/cm/sup 2/ pulses has been obtained in evacuated capillary tubes (45-70-/spl mu/m inner diameter). A drop of transmission has been observed when the intensity of the amplified spontaneous emission (ASE) is high enough to ionize the capillary tube entrance. Propagation in helium gas-filled (10-40 mbar) capillary tubes has been studied at intensities up to 10/sup 16/ W/cm/sup 2/; a plasma column with on-axis density of the order of 10/sup 17/ cm/sup -3/ has been created on a length of the order of 4 cm. The use of a capillary tube for an extended accelerator is discussed for the ease of linear, resonant excitation of plasma waves by laser wakefield.