Disentangling the volume effect through intensity-difference spectra: application to laser-induced dissociation of H2+.

An intensity-difference spectrum method is developed to disentangle the intensity volume effect inherent in focused laser beam interaction with gas-phase matter. This method is applicable to a Gaussian beam of constant axial intensity, which keeps the exact contribution from a predetermined intensity range and eliminates the contributions from lower intensities. We apply this method to the angularly resolved kinetic energy release spectrum of laser-induced dissociation of H2+. The difference spectrum at higher intensities is found to be dominated by the bond-softening process, and the distribution shifts to lower energy and becomes narrower with increasing intensity.