Ionization-based spectral phase diagnostic for laser plasma accelerators

This paper presents a novel diagnostic of laser spectral phase, based on spectral blueshifting from ionization of a known gas target, which allows in-situ measurements of high-peak-power laser pulses. A simulation was created to deconvolve the effects of high-order dispersion, optical compression, and gas density profile on blueshifted spectra. This simulation demonstrates sensitivity to third and fourth order spectral phase as well as neutral density and coarse spatial profile. Experimental results from the Berkeley Lab Laser Accelerator (BELLA), a laser source rigorously characterized by numerous time-profile measurements, are presented and compared with simulations in order to constrain the target density profile and illustrate the utility of this diagnostic technique.