Two-photon ablation with 1278 nm laser radiation

We report on precise two- photon ablation with 110 fs laser pulses at 1278 nm, emitted from a Cr: forsterite laser. Selective two- photon ablation of Muntjac deer chromosomes is demonstrated. The two- photon absorption at 639 nm was enhanced by using Methylene blue dye as a photosensitizer. This stain has a strong absorption in the region around 650 nm but 100% transmission around 1300 nm, allowing increased specificity: material that has absorbed the dye is ablated but undyed material is left unaffected. The low group velocity dispersion in glass at 1278 nm led to negligible pulse broadening in the focusing objective where the 100 fs pulses stretched to 110 fs. This contrasts to the 100 fs pulses at 780 nm that were measured to stretch to 300 fs under the same conditions.