Femtosecond pulsed laser induced damage characteristics on Si-based multi-layer film

In order to understand the ultrafast laser-induced damage mechanisms of typical imaging sensor's film structures, the damage characteristics of Si-based multi-layer films irradiated by a femtosecond pulsed laser were investigated, and the laser pulse fluence ranges and threshold conditions corresponding to various damage phenomena were evaluated. Si-based multi-layer films that were similar in structure of CCD were prepared by electron beam deposition. The damage characteristics of these films irradiated by a femtosecond pulsed laser with wavelength of 800 nm and pulse width of 100 fs under different pulse fluences and numbers were investigated using a metallurgical microscope. Experimental results showed that the laser-affected zone size increased linearly with pulse fluence in the range of 1.01 to 24.7 J/cm2. Surface damage caused by oxidation/amorphization, non-thermal ablation, and laser-induced plasma ablation could be observed in the laser irradiated zone, which tightly depended on the pulse fluence. Multi-layer damage could be observed and the damage probability increased from 1% to 51% in the pulse fluence range from 2.42 to 24.7 J/cm2. Irradiated by sequent pulses at a fluence of 1.01 J/cm2, the laser affected zone remained almost unchanged and the ablated depth increased with the pulse number. From the single pulse damage experiment data, the femtosecond pulse laser-induced surface damage threshold was evaluated to be 0.543 J/cm2 and laser-induced multi-layer stress damage threshold was linearly fitted to be 2.16 J/cm2. Sequent pulse irradiation with low fluence(≤ 1.01 J/cm2) also could lead to deep damage on the multi-layer film.