Papers by Keyword: Femtosecond Pulse Laser

Abstract: Femtosecond laser with ultrashort pulse (≤35fs) is used to investigate the damage threshold and light-to-electric conversion efficiency of gallium arsenide solar cells. Different from nanosecond or picosecond lasers, the damage threshold of the solar cell illuminated by femtosecond laser is slightly higher than that under the illumination of continuous-waves laser with the same wavelength. Because the thermal non-equilibrium effect becomes obvious, heat conduction phenomenon no longer obeys the law of Fourier, when the heating pulse time of femtosecond laser is equal to or shorter than the electron-phonon coupling time. The photovoltaic properties of gallium arsenide solar cells under femtosecond pulse laser illumination are measured. The device shows better short circuit current and the light-to-electric conversion efficiency under femtosecond pulse laser than that under continuous-waves laser of the same wavelength.

Abstract: Experiments are carried out on a femtosecond laser micromachining system with the wavelength 775nm. The ablated patterns on Si (100) and Si (111) surfaces affected by femtosecond pulse laser parameters are presented. The periodic structure termed ripples on silicon surface is investigated. Two kinds of ripples on the ablated surface are observed by SEM. The whole ablation region indicates the ablated field of all amount of laser energy. The ablation region forms two circular areas. The cross section image of the ablated region is showed which is cut by FIB in the orthogonal direction of the line of the center ripples. The depth of ripples is measured. Adjusted the laser fluence as about 0.3~0.33J/cm2 and the pulse number as changeable from 1 to 50, the forming process of the ripples is observed and studied by AFM. Another experiment is done that the wave-plates are inserted into the space between the objective and sample, the result of the direction of ripples changed with the wave-plates of 1/2 or 1/4 is reviewed.