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- ItemSub-cycle valleytronics: control of valley polarization using few-cycle linearly polarized pulses(Washington, DC : OSA, 2021) Jiménez-Galán, Álvaro; Silva, Rui E. F.; Smirnova, Olga; Ivanov, MishaSo far, it has been assumed that selective excitation of a desired valley in the Brillouin zone of a hexagonal two-dimensional material has to rely on using circularly polarized fields. We theoretically demonstrate a way to control the valley excitation in hexagonal 2D materials on a few-femtosecond timescale using a few-cycle, linearly polarized pulse with controlled carrier–envelope phase. The valley polarization is mapped onto the strength of the perpendicular harmonic signal of a weak, linearly polarized pulse, which allows to read this information all-optically without destroying the valley state and without relying on the Berry curvature, making our approach potentially applicable to inversion-symmetric materials. We show applicability of this method to hexagonal boron nitride and MoS2.
- ItemHigh-order parametric generation of coherent XUV radiation(Washington, DC : Soc., 2021) Hort, O.; Dubrouil, A.; Khokhlova, M.A.; Descamps, D.; Petit, S.; Burgy, F.; Mével, E.; Constant, E.; Strelkov, V.V.Extreme ultraviolet (XUV) radiation finds numerous applications in spectroscopy. When the XUV light is generated via high-order harmonic generation (HHG), it may be produced in the form of attosecond pulses, allowing access to unprecedented ultrafast phenomena. However, the HHG efficiency remains limited. Here we present an observation of a new regime of coherent XUV emission which has a potential to provide higher XUV intensity, vital for applications. We explain the process by high-order parametric generation, involving the combined emission of THz and XUV photons, where the phase matching is very robust against ionization. This introduces a way to use higher-energy driving pulses, thus generating more XUV photons.
- ItemTwo-color two-dimensional terahertz spectroscopy: A new approach for exploring even-order nonlinearities in the nonperturbative regime(Melville, NY : American Institute of Physics, 2021) Woerner, Michael; Ghalgaoui, Ahmed; Reimann, Klaus; Elsaesser, ThomasNonlinear two-dimensional terahertz (2D-THz) spectroscopy at frequencies of the emitted THz signal different from the driving frequencies allows for exploring the regime of (off-)resonant even-order nonlinearities in condensed matter. To demonstrate the potential of this method, we study two phenomena in the nonlinear THz response of bulk GaAs: (i) The nonlinear THz response to a pair of femtosecond near-infrared pulses unravels novel fourth- and sixth-order contributions involving interband shift currents, Raman-like excitations of transverse-optical phonon and intervalence-band coherences. (ii) Transient interband tunneling of electrons driven by ultrashort mid-infrared pulses can be effectively controlled by a low-frequency THz field with amplitudes below 50 kV/cm. The THz field controls the electron–hole separation modifying decoherence and the irreversibility of carrier generation.
- ItemMilliradian precision ultrafast pulse control for spectral phase metrology(Washington, DC : Soc., 2021) Stamm, Jacob; Benel, Jorge; Escoto, Esmerando; Steinmeyer, Günter; Dantus, MarcosA pulse-shaper-based method for spectral phase measurement and compression with milliradian precision is proposed and tested experimentally. Measurements of chirp and third-order dispersion are performed and compared to theoretical predictions. The single-digit milliradian accuracy is benchmarked by a group velocity dispersion measurement of fused silica.
- ItemDiode-pumped sub-50-fs Kerr-lens mode-locked Yb:GdYCOB laser(Washington, DC : Soc., 2021) Zeng, Huangjun; Lin, Haifeng; Lin, Zhanglang; Zhang, Lizhen; Lin, Zhoubin; Zhang, Ge; Petrov, Valentin; Loiko, Pavel; Mateos, Xavier; Wang, Li; Chen, WeidongWe present a sub-50-fs diode-pumped Kerr-lens mode-locked laser employing a novel “mixed” monoclinic Yb:Ca4(Gd,Y)O(BO3)3 (Yb:GdYCOB) crystal as a gain medium. Nearly Fourier-limited pulses as short as 43 fs at 1036.7 nm are generated with an average power of 84 mW corresponding to a pulse repetition rate of ∼70.8 MHz. A higher average power of 300 mW was achieved at the expense of the pulse duration (113 fs) corresponding to an optical-to-optical efficiency of 35.8% representing a record-high value for any Yb-doped borate crystal. Non-phase-matched self-frequency doubling is observed in the mode-locked regime with pronounced strong spectral fringes which originate from two delayed green replicas of the fundamental femtosecond pulses in the time domain.
- ItemAtomic and molecular suite of R-matrix codes for ultrafast dynamics in strong laser fields and electron/positron scattering(Bristol : IOP Publ., 2020) Wragg, J.; Benda, J.; Mašín, Z.; Armstrong, G.S.J.; Clarke, D.D.A.; Brown, A.C.; Ballance, C.; Harvey, A.G.; Houfek, K.; Sunderland, A.; Plummer, M.; Gorfinkiel, J.D.; Van Der Hart, H.We describe and illustrate a number of recent developments of the atomic and molecular ab initio R-matrix suites for both time-dependent calculations of ultrafast laser-induced dynamics and time-independentcalculations of photoionization and electron scattering. © 2019 Published under licence by IOP Publishing Ltd.
- ItemSESAM mode-locked Tm:Y2O3 ceramic laser(Washington, DC : Soc., 2022) Zhang, Ning; Liu, Shande; Wang, Zhanxin; Liu, Jian; Xu, Xiaodong; Xu, Jun; Wang, Jun; Liu, Peng; Ma, Jie; Shen, Deyuan; Tang, Dingyuan; Lin, Hui; Zhang, Jian; Chen, Weidong; Zhao, Yongguang; Griebner, Uwe; Petrov, ValentinWe demonstrate a widely tunable and passively mode-locked Tm:Y2O3 ceramic laser in-band pumped by a 1627-nm Raman fiber laser. A tuning range of 318 nm, from 1833 to 2151 nm, is obtained in the continuous-wave regime. The SESAM mode-locked laser produces Fourier-transform-limited pulses as short as 75 fs at ∼ 2.06 µm with an average output power of 0.26 W at 86.3 MHz. For longer pulse durations of 178 fs, an average power of 0.59 W is achieved with a laser efficiency of 29%. This is, to the best of our knowledge, the first mode-locked Tm:Y2O3 laser in the femtosecond regime. The spectroscopic properties and laser performance confirm that Tm:Y2O3 transparent ceramics are a promising gain material for ultrafast lasers at 2 µm.
- ItemPropagator operator for pulse propagation in resonant media(Washington, DC : Soc., 2021) Morales, Felipe; Richter, Maria; Olvo, Vlad; Husakou, AntonWe show that, for the case of resonant media, the available models for unidirectional propagation of short pulses can face serious challenges with respect to numerical efficiency, accuracy, or numerical artifacts. We propose an alternative approach based on a propagator operator defined in the time domain. This approach enables precise simulations using short time windows even for resonant media and facilitates coupling of the propagation equation with first-principle methods such as the time-dependent Schödinger equation. Additionally, we develop a numerically efficient recipe to construct and apply such a propagator operator.