Mechanism study of silica ablating on photonic crystal fiber by 157 nm laser

To test 157nm silica ablating effect,the profile of micro holes on the end cross section of silica photonic crystal fiber is employed under the exposure of 157nm laser to quantitatively analyze the ablating depth and degree.The photon energy of 157nm laser is 7.9eV,can be absorbed by silica.Under 157nm laser,the defect formations in silica are accumulated to produce a large quantity of free electrons.Meanwhile,the dopants in fiber silica considerably reduce the breakdown threshold.Because the rate of single-photon absorption outclasses the rate of multi-photon absorption,it can be inferred that the mechanism of interaction between 157nm laser and silica is a process of single-photon absorption of electron-avalanche.It breaks all bonds in silica,a half of them is ionic bonds and the other half is covalent bonds.The actual ablating velocity 210nm/pulse has demonstrated that the 157nm laser can be absorbed strongly by silica material and that thermal process accompanies with the ablation,however,because the period of damage is only 20ns,the heat on the silica can be limited in a extremely small area,therefore,an ablating result with good quality can be ensured.