We present results on tunable few-cycle laser pulses generated in the near infrared region obtained by filamentation in a krypton cell combined with group velocity dispersion compensation in fused silica. We obtain a spectral broadening of a factor ∼2–3 over the entire spectral domain studied. The central wavelength is tuned from 1.6 μm to 2 μm via an optical parametric amplification source. In optimum experimental conditions, where the input central wavelength is set to 1.7 μm, 1.8 μm, and 1.9 μm, the incident power to the gas cell exceeded the critical power of Krypton by a factor of ∼4 and the achieved spectral broadening covered ∼300 nm. Using group velocity compensation in bulk fused silica, we obtain near infrared output pulses as short as 2–3 optical cycles with 200 μJ energy per pulse. This near infrared filamentation tunable few-cycle pulse source is an important achievement for strong field physics applications such as attoscience, where wavelength scaling has an important effect.

Abstract. We report on the development of tunable few-cycle pulses with central wavelengths from 1.6 µm to 2 µm. Theses pulses were used as a proof of principle for high harmonic generation in atomic and molecular targets. In order to generate such pulses we produced a filament in a 4 bar krypton cell. Spectral broadening by a factor of 2 -3 of a 40 fs near infrared input pulse was achieved. The spectrally broadened output pulses were then compressed by fused silica plates down to the few-cycle regime close to the Fourier limit. The auto-correlation of these pulses revealed durations of ∼ 3 cycles for all investigated central wavelengths. Pulses with a central wavelength of 1.7 µm and up to 430 µJ energy per pulse were employed to generate high order harmonics in Xe, Ar and N 2 . Moving to near infrared few-cycle pulses opens the possibility to operate deeply in the non-perturbative regime with a Keldysh parameter γ << 1. Hence, this source is suitable for the study of the non-adiabatic tunneling regime in most generating systems used for high order harmonic generation and attoscience.

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