Abstract

Compression of laser pulses by a fiber-grating compressor has been demonstrated to be a powerful technique for generating shortest optical pulses clown to the fs range [1]. Also relatively long pulses from cw mode-locked Nd:YAG lasers could efficiently be reduced with single-stage compression ratios up to 80 [2]. However, when higher peak powers, as available from these lasers, are coupled into the fiber, the pulse intensities can easily exceed the Raman threshold and then not only the desired effect of self-phase modulation (8PM) but also stimulated Raman-scattering (SRS) appears in the fiber and will distort the pulse profile as well as the chirp of the laser pulses. Under these conditions only unstable compressor operation and a reduced effectiveness of pulse compression in terms of the pulse width, the pulse quality and the maximum power level transferable through the fiber was expected. Therefore the operation of a fiber-grating compressor in this regime was generally avoided. But at sufficiently high intensities, well above the Raman threshold, we could observe a considerable further shortening of optical pulses with low substructures. Therefore we have investigated systematically the compression of intense Md:YAG laser pulses in the presence of strong SRS.

© 1988 Optical Society of America