Abstract
Ultrashort high-energy pulses at wavelengths longer than 1 µm are now desirable for a vast variety of applications in ultrafast and strong-field physics. To date, the main answer to the wavelength tunability for energetic, broadband pulses still relies on optical parametric amplification (OPA), which often requires multiple and complex stages, may feature imperfect beam quality, and has limited conversion efficiency into one of the amplified waves. In this work, we present a completely different strategy to realize an energy-efficient and scalable laser frequency shifter. This relies on the continuous red shift provided by stimulated Raman scattering (SRS) over a long propagation distance in nitrogen-filled hollow-core fibers (HCF). We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with a conversion efficiency higher than 70% and high beam quality. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between higher-order modes of the HCF, can be readily employed to generate pulses ( ∼ 20 f s ) significantly shorter than the pump ones ( ∼ 200 f s ) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules. We envision that this technique, coupled with the emerging high-power Yb laser technology, has the potential to answer the increasing demand for energetic multi-TW few-cycle sources tunable in the near-IR.
Highlights
An increasing number of applications, such as attosecond pulse isolation via high-harmonic generation (HHG) [1], laser-induced field-driven electron emission [2], laser wakefield acceleration [3], laser-induced electron diffraction [4], optical coherence tomography [5], ultra-broadband [6] and high-field [7] terahertz (THz) generation, were shown to benefit from the increase of the driver pulse wavelength
We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with conversion efficiency higher than 70% and high beam quality
In this work we show that, by propagating ~200 fs pulses delivered by Ybbased amplified laser systems in a N2-filled hollow core fibers (HCF), an asymmetric spectral broadening towards longer wavelengths is observed
Summary
An increasing number of applications, such as attosecond pulse isolation via high-harmonic generation (HHG) [1], laser-induced field-driven electron emission [2], laser wakefield acceleration [3], laser-induced electron diffraction [4], optical coherence tomography [5], ultra-broadband [6] and high-field [7] terahertz (THz) generation, were shown to benefit from the increase of the driver pulse wavelength. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between high-order modes of the HCF, can be readily employed to generate pulses (~20 fs) significantly shorter than the pump ones (~200 fs) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules.
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