Simple,stable and efficient nonlinear pulse compression through cascaded filamentation in air

Nonlinear compression has become an obligatory technique along with the development of ultrafast lasers in generating ultrashort pulses with narrow pulse widths and high peak power.In particular,techniques of nonlinear compression have experienced a rapid progress as ytterbium(Yb)-doped lasers with pulse widths in the range from hundreds of femtoseconds to a few picoseconds have become mainstream laser tools for both scientific and industrial applications.Here,we report a simple and stable nonlinear pulse compression technique with high efficiency through cascaded filamentation in air followed by dispersion compensation.Pulses at a center wavelength of 1040 nm with millijoule pulse energy and 160 fs pulse width from a high-power Yb:CaAlGdO_(4) regenerative amplifier are compressed to 32 fs,with only 2.4% loss from the filamentation process.The compressed pulse has a stable output power with a root-meansquare variation of 0.2% over 1 hour.

Dual-Wavelength Spectrum-Shaped Mid-Infrared Pulses and Steering High-Harmonic Generation in Solids

Mid-infrared(MIR)ultra-short pulses with multiple spectral-band coverage and good freedom in spectral and temporal shaping are desired by broad applications such as steering strong-field ionization,investigating bound-electron dynamics,and minimally invasive tissue ablation.However,the existing methods of light transient generation lack freedom in spectral tuning and require sophisticated apparatus for complicated phase and noise control.Here,with both numerical analysis and experimental demonstration,we report the first attempt,to the best our knowledge,at generating MIR pulses with dual-wavelength spectral shaping and exceptional freedom of tunability in both the lasing wavelength and relative spectral amplitudes,based on a relatively simple and compact apparatus compared to traditional pulse synthesizers.The proof-of-concept demonstration in steering the high-harmonic generation in a polycrystalline ZnSe plate is facilitated by dual-wavelength MIR pulses shaped in both spectral and temporal domains,spanning from 5.6 to 11.4μm,with multi-microjoule pulse energy and hundred-milliwatt average power.Multisets of harmonics corresponding to different fundamental wavelengths are simultaneously generated in the deep ultraviolet region,and both the relative strength of individual harmonics sets and the spectral shapes of harmonics are harnessed with remarkable freedom and flexibility.This work would open new possibilities in exploring femtosecond control of electron dynamics and light–matter interaction in composite molecular systems.