Generation of sub-5 fs pulses in vacuum ultraviolet using four-wave frequency mixing in hollow waveguides

Onset of Bloch oscillations in the almost-strong-field regime

In the field of high-order harmonic generation from solids, the electron motion typically exceeds the edge of the first Brillouin zone. In conventional nonlinear optics, on the other hand, the excursion of band electrons is negligible. Here, we investigate the transition from conventional nonlinear optics to the regime where the crystal electrons begin to explore the first Brillouin zone. It is found that the nonlinear optical response changes abruptly already before intraband currents due to ionization become dominant. This is observed by an interference structure in the third-order harmonic generation of few-cycle pulses in a non-collinear geometry. Although approaching Keldysh parameter γ = 1, this is not a strong-field effect in the original sense, because the iterative series still converges and reproduces the interference structure. The change of the nonlinear interband response is attributed to Bloch motion of the reversible (or transient or virtual) population, similar to the Bloch motion of the irreversible (or real) population which affects the intraband currents that have been observed in high-order harmonic generation.

Simple route toward efficient frequency conversion for generation of fully coherent supercontinua in the mid-IR and UV range

Fiber supercontinua represent light sources of pivotal importance for a wide range of applications, ranging from optical communications to frequency metrology. Although spectra encompassing more than three octaves can be produced, the applicability of such spectra is strongly hampered due to coherence degradation during spectral broadening. Assuming pulse parameters at the cutting edge of currently available laser technology, we demonstrate the possibility of strongly coherent supercontinuum generation. In a fiber with two zero-dispersion wavelengths a higher-order soliton experiences a temporal breakdown, without any compression or splitting behavior, which leads to nearly complete conversion of input solitonic radiation into resonant nonsolitonic radiation in the dispersive wave regime. As the process is completely deterministic and shows little sensitivity to input noise, the resulting pulses appear to be compressible down to the sub-cycle level and may thus hold a new opportunity for direct generation of attosecond pulses in the visible to near ultraviolet wavelength range.

High energy sub-10 fs pulse generation in vacuum ultraviolet using chirped four wave mixing in hollow waveguides

We numerically study chirped four-wave mixing for VUV pulse generation in hollow waveguides filled with a noble gas. Taking into account ionization effects we predict the generation of signal pulses at 160 nm with shortest durations up to 6.5 fs, highest pulse energy up to the mJ level and maximum energy efficiency of about 30% by broadband chirped idler pulses at 800 nm and narrow-band pump pulses at 270 nm. Using cascaded processes sub-10-fs pulses in the spectral range from 90 to 140 nm can also be generated.