Abstract
High-harmonic generation (HHG) is a unique tabletop light source with femtosecond-to-attosecond pulse duration and tailorable polarization and beam shape. Here, we use counter-rotating femtosecond laser pulses of 0.8 µm and 2.0 μm to extend the photon energy range of circularly polarized high-harmonics and also generate single-helicity HHG spectra. By driving HHG in helium, we produce circularly polarized soft x-ray harmonics beyond 170 eV-the highest photon energy of circularly polarized HHG achieved to date. In an Ar medium, dense spectra at photon energies well beyond the Cooper minimum are generated, with regions composed of a single helicity-consistent with the generation of a train of circularly polarized attosecond pulses. Finally, we show theoretically that circularly polarized HHG photon energies can extend beyond the carbon K edge, extending the range of molecular and materials systems that can be accessed using dynamic HHG chiral spectro-microscopies.
Highlights
High harmonic generation (HHG) is the most extreme nonlinear optical process observed to date, [1,2,3] upconverting femtosecond laser light into short-wavelength high harmonics that can span >5000 orders [4]
We demonstrate that high harmonics driven by bicircular MIR laser fields can exhibit a photon energy cutoff that extends well into the soft X-ray (SXR) region
Such a combination has allowed us, for the first time, to generate a high-harmonic spectrum consisting of a single helicity without the need of additional optics or beamline components
Summary
High harmonic generation (HHG) is the most extreme nonlinear optical process observed to date, [1,2,3] upconverting femtosecond laser light into short-wavelength high harmonics that can span >5000 orders [4]. The properties of the emitted HHG radiation are exquisitely sensitive to the driving laser field [29] and the electronic structure of the HHG medium These principles have been successfully exploited to tailor the spectral, temporal, spatial, and polarization properties of high harmonics, enabling the generation of circularly polarized EUV/SXR radiation [30,31,32,33,34], high-harmonics with unique spatial angular momentum structure [35,36,37], single attosecond pulses [13,15,28,38], and bright phase-matched high-harmonics spanning from EUV to keV photon energies [4,5,7,11,12]
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