Splitting femtosecond laser pulses by using a Dammann grating

摘要

A Dammann grating can generate an array of uniform intensity and equally spaced spots for an incoming monochromatic light beam. But chromatic dispersion will occur when a beam of femtosecond laser pulse, which contains a broad spectral bandwidth, is split by a Dammann grating. Furthermore, the quantity of chromatic dispersion is different in each diffraction order. As a result, diffraction spots of splitting beams are becoming more elliptical as the diffraction order increases. In this paper, we propose a method of using an m time density's grating to collimate the mth order beam that is split by a Dammann grating. In this way, an array of femtosecond laser beams that are eliminated lateral chromatic dispersion can be obtained by using a Dammann grating and a group of compensation gratings. At the same time, the increased width of the compensated output pulse is briefly discussed with Kirchhoff-Fresnel integral, and in the case of the pulse duration of 100fs, the increased amount of the pulse width at the different diffraction orders and the shape variation of the output diffraction spots are not serious. As a new kind of beam splitter, this splitting and compensation system is high efficiency and material dispersion is avoided if reflection gratings are employed. It should be highly interesting in practical applications of splitting femtosecond laser pulses for pulse-width measurement, pump-probe measurement, and micromachining at multiple points.