Abstract

In conventional femtosecond solid state lasers, the intracavity prism pair imposes a severe constraint on the resonator length and thus on the maximum achievable pulse repetition rate. Aside from the problem of introducing negative dispersion in short cavities, the major difficulty in generating ultrashort pulses at high repetition rates relates to the fact that the duration of the solitonlike mode-locked pulse τ ≈ |D|/ϕW is inversely proportional to both the self-phase modulation coefficient ϕ and the intracavity pulse energy W (D is the net cavity group delay dispersion, GDD), both of which decrease as the cavity length is reduced. Hence, it is imperative that the magnitude of negative intracavity GDD is kept at very small values if femtosecond pulses are to be generated at high repetition rates. However, high-order dispersion severely limits the reduction of negative GDD in oscillators using refractive dispersive components. Chirped dielectric mirrors can be designed to be virtually free from high-order dispersion. Therefore their use as resonator mirrors overcomes not only the limitation imposed by prismatic dispersion compensators on the cavity length, but also allows reducing |D| to significantly lower values than attainable in prism-controlled systems.

© 1996 IEEE