Abstract
Most of transparent solids in the mid-IR exhibit anomalous dispersion which enables a soliton-like pulse propagation regime characterized by a balance between the positive GDD, associated with the nonlinear phase of the self-phase modulated pulse, and the negative GDD of the material[1,2]. In general, the critical power of self-focusing Pcr in transparent dielectrics in the mid-IR is in the range of tens of MW, which for (sub-)100-fs pulses corresponds to microjoule pulse energies. The situation becomes qualitatively different in the case of millijoule pulses for which the peak power P exceeds Pcr by a few orders of magnitude. Propagation of a beam carrying pulses with high P/Pcr ratios over an extended distance in a nonlinear media results in a rapid beam disintegration into multiple filaments. However, as confirmed experimentally and theoretically in this work, for multi-mJ few-cycle pulses in the mid-IR it is fortunately possible to complete efficient nonlinear self-compression in a millimeter-scale bulk crystal and thus avoid the beam breakup. Sub-100-fs pulses centered at 3.9 µm at a repetition rate of 20 Hz were generated in a hybrid OPA/OPCPA system [3] based on Type-II KTP/KTA crystals and later self-compressed in the pair of thin YAG wedges. Self-compressed pulses were characterized by SHG FROG measurements. The spectra of mid-IR pulses were recorded by acousto-Optic based scanning spectrometer (MOZZA, FASTLITE).
© 2015 IEEE
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