Characterization of the spectral phase of an intense laser at focus via ionization blueshift

An in situ diagnostic for verifying the spectral phase of an intense laser pulse at focus is presented. This diagnostic relies on measuring the effect of optical compression on ionization-induced blueshifting of the laser spectrum. Experimental results from the Berkeley Lab Laser Accelerator, a laser source rigorously characterized by conventional techniques, are presented and compared with simulations to illustrate the utility of this technique. These simulations show distinguishable effects from second-, third-, and fourth-order spectral phase.