SP-B/OB mixed mode

The SP-B/OB mixed mode is obtained within the wavelength domain of the SP mode, i.e. in the UV, for local intensities below OB threshold, and above the threshold of MPI and AI. We know that SPI is very wavelength sensitive, and if no absorption band is matched we only have a pure B/OB mode. The dose distributions, as well as the plasma density in the SP-B/OB mixed mode are similar to the pure B/OB mode. The difference is in the nature and the relative yield of the primary photolytic species generated, due to the contribution of the SPI process, which is very selective. As for the energy spectrum of the free electrons and their dependence on different parameters of the laser beam, the section on the B/OB mode gives a clear description.

Converging lenses are normally used to control the local intensity at the target, as well as the size, the shape, and the position within the sample of the affected area. The pulse duration affects the AI process, and therefore it controls the intensity range of the SP-B/OB mixed mode in-between the SP pure mode (lower limit of the range) and SP-OB mixed mode (higher limit of the range). At longer pulse durations, where AI becomes dominant, OB threshold becomes statistically unstable, and SP-B/OB becomes unsustainable.