Universal route to optimal few- to single-cycle pulse generation in hollow-core fiber compressors

[EN]The chirped pulse amplification (CPA) technique applied to Titanium Sapphire lasers has made intense near-infrared (NIR) ultrashort pulses in the 20−100 fs range widely available for scientific, biomedical and industrial applications. Special efforts have been devoted to generate even shorter pulses, in the few- and single-cycle regime, due to a number of interesting applications. In particular, such pulses have paved the way for attosecond physics and metrology, via the extreme ultraviolet (XUV) attosecond pulse trains and isolated attosecond pulses that can be obtained by high-harmonic generation (HHG). The use of few-cycle optical pulses with durations close to or shorter than 10 fs in the near-infrared, visible and near-ultraviolet spectral regions has been extended in recent years to a wide range of spectroscopic techniques such as impulsive vibrational spectroscopy, time-resolved stimulated Raman spectroscopy, and ultrafast pump-probe absorption spectroscopy. Few-cycle optical pulses have also become an interesting tool for transient absorption microscopy, near-field imaging techniques and for generating ultrashort terahertz radiation. While it is possible to obtain sub-10 fs pulses from CPA or from optical parametric amplification systems, the former is not easy to accomplish, and the latter is not commonplace. Therefore, post-compression techniques are usually employed for the generation of intense few- and even single-cycle pulses in the near- and mid-infrared spectral regions. In order to post-compress ultrafast pulses down to the few-cycle regime, two steps are usually needed. First, nonlinear processes broaden the pulse spectrum, thus decreasing the Fourier-limited pulse duration. In a second step, the spectral phase resulting from the previous stage is compensated, typically using chirped mirrors, gratings, prisms, or other dispersive systems, resulting in a temporally compressed pulse. This scheme was first proposed in the context of optical fibers in the 1980s, and enabled achieving 6 fs pulses when compensating simultaneously the outcoming group delay dispersion (GDD) and third-order dispersion (TOD)