Abstract

Oscillators directly (i.e. without an external amplification) generating femtosecond pulses with sub- and overmicrojoule energies are of interest for a number of applications, which range from a micromachining to a fundamental physics of the matter-light interactions. Basic technique providing a scalability of the pulse energy is to reduce the oscillator repetition rate [1,2], For a fixed average power this would increase the pulse energy if the pulse instabilities are suppressed. The latter requires reducing the pulse peak power below the self-focusing power in an active medium that can be provided by the pulse stretching. In the negative dispersion regime (NDR) such a stretching demands a large amount of the group-delay dispersion (GDD). Since an oscillator in NDR operates in the solitonic regime, the stretched pulse is uncompressible. In the positive dispersion regime (PDR) the pulse is stretched due to a strong chirp and, thereby, is compressible down to sub-30 fs [3], Since such a heavily-chirped pulse has a broad spectrum (>100 mn for a Ti:Sa oscillator), contribution of the higher-order dispersions (HOD) to the chirped-pulse oscillator (CPO) stability is substantial.

© 2007 IEEE