Illustration of the applied technique. The figure shows recordings of neutral fragments produced in the storage ring. The upper and lower panels show a measurement of neutrals produced for 65 ms after injection of ions with and without photo excitation of the ions by a 3 ns duration laser pulse, fired 35 ms after the injection into the ring. The black areas are neutrals produced by collisions of the ions with residual gas in the ring. In the figure, green and cyan respectively indicate background window B and B₀, and red and blue signal window S and S₀ used in the calculation of the relative action absorption cross section.