Abstract

The simultaneous determination of the pulse width and coherence time of ultrashort laser pulses is highly desirable for the interpretation of many experiments involving nonlinear processes. We show that self-diffraction from a transient grating formed by interfering two picosecond pulses from the laser on a thin sample gives access to both quantities. This method is simple, does not require phase matching, and works best with highly absorbing materials. In our experiments, the pulses are produced by a mode-locked Nd:YAG or picosecond dye laser. The samples are thin semiconductor or dye films. We compare the self-diffraction results to those obtained by noncollinear autocorrelation. The effect of changing the absolute and relative intensity, the polarization, and pulse duration of the beams is investigated. Our data are examined in the light of a general theory recently developed by Trebino.¹ We include thermal and electronic contributions to the signal. Our results are compared with the related results of Smirl et al.² Finally, we discuss the scalability of this method to shorter pulse width and shorter wavelength and indicate an optimization procedure.

© 1985 Optical Society of America