ABSTRACT
However, due to the limitation of gain narrowing, the direct output pulse duration of the present CPA systems is near 30fs, which is too long for many applicants and makes the extracavity pulse compressing technology very important. The present compressing technology is mainly based on spectrum broadening introduced by SPM and the corresponding dispersion compensation [5]. At first, normal optical fiber is used as spectrum broadening medium [6], but it is mainly suitable for amplifying the pulses with the energy of nJ level. M. Nisoli et al [7] used hollow fiber filled with noble gas as the broadening medium and obtained pulses of about lOfs with the energy of mJ level. However, the noble gas in the capillary still can be ionized when the intensity of the laser pulse is strong enough, which will affect the spectrum broadening. In addition, vacuum system is necessary and the capillary should be strictly straightened, which makes it difficult to realize.
