By simulating the filamentation of femtosecond laser pulses with flat top and different steep leading and tailing edges in air, the influence of pulse edges on the filamentation dynamics and supercontinuum (SC) generation is analyzed. It is found that the filamentation length is determined by the leading edge. The different roles of the pulse edges in the SC generation are further revealed. Under a relative lower laser power, the spectral broadening of the laser pulse originates mainly from the self-phase modulation of both pulse edges induced by the Kerr effect, while under a relative higher power condition, the leading edge plays a dominant role in the blue-side extension of the SC due to electron generation.
The purpose of this study was to evaluate the effect of Nd:YAG laser irradiation on the phase velocity of surface acoustic waves (SAWs) of human enamel. A pulsed Nd:YAG laser at 1064 nm wavelength was used to irradiate the human enamel from extracted human premolars. The output power and repetition rate were 250 mJ and 5 Hz, respectively. The SAW phase velocities before and after laser irradiation were determined using a laser photoacoustic method. The laser-treated enamel surface exhibited a higher velocity value for frequencies higher than 3 MHz. The result of this study suggests that there is an important correlation between the elastic properties of human enamel and the pulsed Nd:YAG laser fluence, which increases the SAW phase velocity, and this may help shed some light on the mechanism of laser treatment in dental research.
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