Understanding the changes in generated nanotips will help us pick the right combinations of laser parameters to grow the desired amount and kind of nanotips over the large surface area of dielectric targets. Methods The experiments were performed on plain microscopic slide glass with composition of 60% to 75 wt.% SiO2, 5% to 12 wt.% CaO, AZ 628 clinical trial and 12% to 18 wt.% Na2O. A direct-diode-pumped Yb-doped fiber amplifier/oscillator

system (wavelength, λ = 1,030 nm) capable of Crizotinib in vivo delivering a maximum average output of 16 W was used as a femtosecond laser source to irradiate targets with thickness of 0.90 to 1.0 mm. The laser intensity profile beam was focused into a spot (full width at half-maximum) diameter of 10 μm on the target surface using a telecentric lens of 100-mm effective focal length. The same setup was used to perform these experiments as reported in a previous paper done by our research group [16]. However, for these experiments, a square bracket was placed in front of the target surface which holds six nozzles providing continuous flow of nitrogen gas. The machining was performed in the form of 26 × 26 arrays of

microholes for various femtosecond laser parameters. We investigated the effect of three different pulse widths (214, 428, and 714 fs) on the generation of nanotips for a repetition rate of 13 MHz at a dwell time of 0.5 ms. The effect of various SB273005 laser Orotidine 5′-phosphate decarboxylase pulse repetition rates (4, 8, and 13 MHz)

and different dwell times was also investigated on glass samples. All the aforementioned experiments were done by circular polarization of laser pulses. We also examined how different (linear, p-) polarizations would change the growth of nanotips on the target surface. The linear (p-) polarization of the beam was achieved by placing a half-wave plate in front of the focusing lens. The laser-irradiated glass samples have been analyzed by SEM. Results and discussion It is found that laser conditions have great effect on the nanotip growth. They control the population and the shape of the synthesized nanotips. Table 1 summarizes the observations. Table 1 Summary of effects of laser conditions to tip growth Laser parameters Effects on nanotip growth Pulse width Short pulses yield narrow long tips Repetition rate Higher repetition rate promotes the growth of dense, oriented narrow nanotips Dwell time Longer dwell time increases the population of nanotips. However, beyond an optimum dwell time, over heating will remelt the newly formed nanotips Polarization Linear (p-) polarization increases the population of nanotips Effect of pulse width There are two mechanisms responsible for laser-induced optical breakdown of materials: multiphoton absorption and avalanche ionization.