Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy

Carlström S., Tahouri R., Papoulia A., Dahlström J.M., Ivanov M.Y., Smirnova O., Patchkovskii S.

It has been shown by Fano [1] that photoionization of a cesium atom by a laser pulse tuned to the vicinity of a Cooper minimum generates spin-polarized electrons. Here we show that while photoionization of rare gases does not provide large spin polarization in the vicinity of the Cooper minimum, the Fano resonances yield much higher overall spin polarization (≥40%). The spin polarization increases in angle-resolved photoelectron spectra, and reaches 100% when measured in coincidence with the photoion. A common feature of both Cooper minima and Fano resonances, is the large variation of the photoinization cross section over photon energy, which proves to be vital for efficient generation of spin-polarized electrons. We provide a general framework for achieving spin polarization in photoionization irrespective of the ionization regime. Published by the American Physical Society 2025

Nie H., Zhang P., Loiko P., Lin Z., zeng H., Ge Z., Li Z., Mateos X., Liang H., Petrov V., Chen Z., Chen W.

We report on the generation of sub-30 fs pulses from a diode-pumped Yb,Gd:YAP laser. Using soft-aperture Kerr-lens mode-locking, soliton pulses as short as 23 fs were achieved at 1082.3 nm, with an average output power of 45 mW at a repetition rate of 67.25 MHz. The mode-locked laser also produced a maximum average output power of 101 mW at 1056.5 nm with a slightly longer pulse duration of 34 fs, corresponding to a peak power of 38.9 kW. To the best of our knowledge, this is the first demonstration of Kerr-lens mode-locked operation in a diode-pumped Yb,Gd:YAP laser, with the shortest pulses ever reported from any Yb3+-doped perovskite-type crystal.

zhang Z., Li Z., Loiko P., zeng H., Ge Z., Lin Z., Normani S., BRAUD A., Ma F., Mateos X., Liang H., Petrov V., Jiang D., Su L., Chen W.

We demonstrate direct generation of sub-40 fs pulses from a diode-pumped mode-locked laser using an ytterbium–yttrium codoped multi-component alkaline-earth fluoride crystal and a semiconductor saturable absorber mirror. The Yb,Y:(Ca,Sr)F2 laser delivers soliton pulses as short as 35 fs at 1056.7 nm, with an average output power of 182 mW at a repetition rate of ∼65.7 MHz. By increasing the transmittance of the output coupler, the average output power scales to 322 mW at a somewhat longer pulse duration (49 fs) at 1052.5 nm, corresponding to a peak power of 87.9 kW and an optical efficiency of 32.4%. To the best of our knowledge, these are the shortest pulses from a Yb-doped alkaline-earth fluoride crystal.

Sharma S., Gill D., Krishna J., Dewhurst J.K., Elliott P., Shallcross S.

Miyata K., Kato K., Petrov V.

This paper presents the Sellmeier equations for AgInS2, combined with recently derived equations for AgGaS2, to provide the accurate phase-matching conditions of AgGa1−xInxS2 for nonlinear three-wave mixing across the 0.6164–10.5910 µm range. A new set of these index formulas successfully reproduces the measured 90° phase-matching conditions of AgGa0.46In0.54S2 (x=0.54) for frequency-doubling the emission of Nd:YAG laser-pumped optical parametric oscillators (OPOs) at 2.7780 and 8.6880 µm as well as for frequency-mixing the signal and idler outputs of such an OPO at 1.1940 and 9.7893 µm, respectively.

Chang Y., Liu Y., Huang S., Sun J., Ho S., Tzeng W., Chiu C., Ku Y., Kaur P., Butcher T.A., Piamonteze C., Staub U., Chen Y., Chang C., Kuo C., et. al.

AbstractArtificially aligned or positioned functional materials are essential building blocks for modern devices and nanoelectronics. Since the emergence of 2D materials, the vertical stacking/integration of exotic materials has garnered increasing attention. However, controlling homostructures, e.g. identical materials conjoined with varying crystalline orientations, magnetism, or strain states, along the lateral direction remains challenging. Leveraging on the freestanding thin film growth techniques, the concept of twisted lateral homostructures has been introduced, enabling precise control over the lateral alignment of crystalline directions. Here, using La0.7Sr0.3MnO3, a classic strongly correlated material, the precise manipulation of epitaxial strain alongside the homojunction is demonstrated. This leads to a precisely controllable lateral homostructure composed of polymorphic ferromagnetic and antiferromagnetic La0.7Sr0.3MnO3 regions. It is further identified that the interactions between the ferromagnetic and antiferromagnetic regions of La0.7Sr0.3MnO3 lead to unconventional ultrafast spin dynamics and magnetotransport behavior. The results provide a promising platform for developing novel emergent phenomena and functionalities in the twisted lateral homostructures.

Dewhurst J.K., Gill D., Shallcross S., Sharma S.

A longstanding problem in time-dependent density functional theory has been the absence of a functional able to capture excitonic physics under laser pump conditions. Here we introduce a scheme of coupled Kohn-Sham and Proca equations in a pump-probe setup that we show (i) produces linear-response excitonic effects in the weak pump regime in excellent agreement with experiment, but also (ii) captures excitonic physics in the highly nonlinear regime of ultrafast strong laser pumping. In particular ”bleaching” (i.e., reduction) of the excitonic weight and the appearance of excitonic side bands is demonstrated. The approach is a procedural functional—the Kohn-Sham and Proca equations are simultaneously time propagated—allowing the straightforward inclusion of, for example, lattice and spin degrees of freedom into excitonic physics. The functional is shown to have universal applicability to a wide range of materials, and we also establish a relation between the parameters used in the functional and the exciton Bohr radii of the materials. Published by the American Physical Society 2025

Kozlov M., Ivanov M., McKinstrie C., Sidorenko P.

Fiber-based ultrafast laser sources are rapidly expanding in both scientific and industrial domains, making them highly desirable for a variety of applications. The recently demonstrated gain-managed nonlinear (GMN) regime is particularly appealing because it enables the generation of high-energy, clean sub-50-fs pulses in a straightforward setup. However, the complex interaction between nonlinear pulse evolution and the longitudinally evolving gain shaping presents a scientific challenge in understanding how the parameters of GMN laser systems influence the characteristics of the output pulses. In this work, we introduce a computationally efficient approach using the generalized Method of Moments to analyze the dynamically evolving pulse characteristics. This method considers pulse asymmetry in GMN systems and assesses position- and frequency-dependent gain by solving population inversion rate equations. We apply our approach to demonstrate an effective multidimensional parameter optimization of a GMN amplifier.

Slimi S., Mateos X., Solé R.M., Aguilo M., Diaz F., Chen W., Loiko P., Chen C., Griebner U., Petrov V.

Multi-watt continuous-wave operation is reported for what is believed to be the first time for an in-band-pumped Ho:KLu(WO4)2 laser emitting at 2078 nm in N m polarization. The slope efficiency reached 33.5% with respect to the incident unpolarized pump radiation near 1959 nm, without pronounced roll-off effects. The total tuning range with a 1.5% output coupler covered 117 nm.

Yi S., Klimkin N.D., Brown G.G., Smirnova O., Patchkovskii S., Babushkin I., Ivanov M.

At the fundamental level, full description of light-matter interaction requires quantum treatment of both matter and light. However, for standard light sources generating intense laser pulses carrying quadrillions of photons in a coherent state, the classical description of light during intense laser-matter interaction has been expected to be adequate. Here, we show how nonlinear optical response of matter can be controlled to generate dramatic deviations from this standard picture, including generation of several squeezed and entangled harmonics of the incident laser light. In particular, such nontrivial quantum states of harmonics are generated as soon as one of the harmonics induces a transition between different laser-dressed states of the material system. Such transitions generate an entangled light-matter wave function, which can generate quantum states of harmonics even in the absence of a quantum driving field or material correlations. In turn, entanglement of the material system with a single harmonic generates and controls entanglement between different harmonics. Hence, nonlinear media that are near resonant with at least one of the harmonics appear to be quite attractive for controlled generation of massively entangled quantum states of light. Our analysis opens remarkable opportunities at the interface of attosecond physics and quantum optics, with implications for quantum information science. Published by the American Physical Society 2025

Runge M., Woerner M., Bondar D.I., Elsaesser T.

Das D.S., TEMEL T., Spindler G., Schirrmacher A., Divliansky I., Murray R.T., Piotrowski M., Wang L., Chen W., Mhibik O., Petrov V.

Using a Volume-Bragg-Grating at the signal wavelength in a periodically-poled LiNbO3 non-resonant optical parametric oscillator we achieve a total average power of 11.35 W at 20 kHz corresponding to a conversion efficiency of 63%. The measured signal and idler bandwidths amount to 0.7 and 0.9 nm at ∼1922 and ∼2384 nm, respectively. The spectral features are well reproduced by numerical modeling in the plane-wave approximation taking into account pump depletion and back conversion.

Nie H., Lin Z., Loiko P., zeng H., zhang L., lin Z., Zin Elabedine G., Mateos X., Petrov V., Ge Z., Chen W.

We present the first Kerr-lens mode-locked solid-state laser based on ytterbium-doped monoclinic magnesium monotungstate as an active medium. The diode-pumped Yb:MgWO4 laser delivers soliton pulses as short as 32 fs at 1079 nm with a pulse repetition rate of ∼68 MHz via soft-aperture Kerr-lens mode-locking. To the best of our knowledge, these are the shortest pulses ever achieved from any ytterbium-doped tungstate crystals.

Ilchen M., Allaria E., Rebernik Ribič P., Nuhn H., Lutman A., Schneidmiller E., Tischer M., Yurkov M., Calvi M., Prat E., Reiche S., Schmidt T., Geloni G.A., Karabekyan S., Yan J., et. al.

Free-electron lasers (FELs) are the world's most brilliant light sources with rapidly evolving technological capabilities in terms of ultrabright and ultrashort pulses over a large range of photon energies. Their revolutionary and innovative developments have opened new fields of science regarding nonlinear light-matter interaction, the investigation of ultrafast processes from specific observer sites, and approaches to imaging matter with atomic resolution. A core aspect of FEL science is the study of isolated and prototypical systems in the gas phase with the possibility of addressing well-defined electronic transitions or particular atomic sites in molecules. Notably for polarization-controlled short-wavelength FELs, the gas phase offers new avenues for investigations of nonlinear and ultrafast phenomena in spin-orientated systems, for decoding the function of the chiral building blocks of life as well as steering reactions and particle emission dynamics in otherwise inaccessible ways. This roadmap comprises descriptions of technological capabilities of facilities worldwide, innovative diagnostics and instrumentation, as well as recent scientific highlights, novel methodology, and mathematical modeling. The experimental and theoretical landscape of using polarization controllable FELs for dichroic light-matter interaction in the gas phase will be discussed and comprehensively outlined to stimulate and strengthen global collaborative efforts of all disciplines. Published by the American Physical Society 2025

Babushkin I., Husakou A., Shi L., Demircan A., Kovacev M., Morgner U.

Abstract Photocurrent-induced harmonics appear in gases and solids due to tunnel ionization of electrons in strong fields and subsequent acceleration. In contrast to three-step harmonic emission, no return to the parent ions is necessary. Here we show that the same mechanism produces harmonics in metallic nanostructures in strong fields. Furthermore, we demonstrate how strong local field gradient, appearing as a consequence of the field enhancement, affects photocurrent-induced harmonics. This influence can shed light at the state of electron as it appears in the continuum, in particular, to its initial velocity.