We have demonstrated the ablation processing of dry-collagen with double pulsed femtosecond lasers through a bent hollow fiber. Using a 320 μm core-diameter hollow fiber, we have delivered an ultrashort pulse with a pulse width of 200 fs (straight condition), 320 fs (bent condition), and a near Gaussian beam profile. Furthermore, a precise biomedical material processing is obtainable with a transmitted femtosecond laser beam through a bent hollow fiber. The material processing speed is increased using femtosecond double pulses and by optimizing the delay time. The optimal delay time between the double pulses is from 1 ps to 3 ps, because the ablation rate decreased due to a plasma shielding effect beyond a 5 ps delay time. Our results will open up new medical endoscopic applications.
We will report on nanostructure fabrication on silicon (Si) substrate by 800 nm femtosecond laser pulses. Spherical alumina particles were placed on the substrate surface. After femtosecond laser irradiation at below-ablation-threshold fluences, we have successfully observed the nanoholes formation with around 100 nm in diameter using scanning electron microscope (SEM) and atomic force microscope (AFM). The dependence of nanohole formation on the laser fluence and laser pulse number was investigated. The mechanism for the nanohole drilling is the near-field optical enhancement effect induced by interaction between local surface plasmon on the particles surface and surface plasmon polariton on the Si substrate surface.