Transition metal dichalcogenides (TMDCs) are semiconducting 2D-materials with a direct bandgap in a range of 1.0 to 2.5 eV [1] . They exhibit strong second-order nonlinearity per unit thickness, making them interesting for nonlinear light-conversion devices [2] . Due to their small thickness, an interaction enhancement is paramount for efficient operation [3] . We have previously demonstrated that such enhancement can be acchieved by embedding TMDCs into monolithic resonators [4] if a gentle coating process compliant with the sensitive nature of the monolayer TMDC flakes is utilized.
The amplification of waves in the scattering with rotating black holes is a fundamental process in gravitational physics. It was introduced by Roger Penrose in 1969 as a way to extract energy from these astrophysical objects [1] . Soon after Penrose proposal, in 1971 Zel’dovich predicted a similar superradiant amplification for electromagnetic waves scattered by a metallic rotating cylinder [2] . In Zel’dovich proposal, waves get amplified if their angular frequency ω satisfies the condition ω < m Ω, where m is the waves topological charge and Ω is the cylinder angular velocity. Despite this amplification process is ubiquitous in wave scattering physics, and not limited to electromagnetic waves and astrophysics only, direct measurements are limited to an experiment with waves in a water vortex in a draining bathtub experiment [3] . The related, but not identical, Zel’dovich amplification has been observed for acoustic waves [4] .
This tutorial will describe how ultrashort x-ray pulses are generated using free-electron lasers, including their spectral, temporal, coherence properties, and, their application to study photo-initiated electronic and nuclear dynamics in gas and liquid phase.
The generation of XUV supercontinua is of high interest for different applications in that region of the spectrum, such as spectral interferometry and spectroscopy. In high-order harmonic generation (HHG) supercontinua are usually obtained only when a single attosecond pulse is produced, but this implies gating techniques or sub-3-fs IR driving pulses. In this work we demonstrate a new approach for tailoring supercontinuum spectra by exploiting the microscopic and macroscopic properties of HHG.
The process of high-order harmonic generation requires laser intensities around 1014 W/cm2, most easily reached with laser pulses of high energy, thus implicitly limiting the repetition rate of attosecond sources. A route towards multi-MHz attosecond sources relies on HHG inside a passive enhancement cavity [1]. Although successfully demonstrated for attosecond pulse trains, the generation of single attosecond pulses (SAPs) inside a cavity remains an unsolved challenge, mainly limited by dispersion management and out-coupling problems. We recently proposed a new gating concept for SAP generation [2], noncollinear optical gating (NOG) which has the potential to facilitate SAP gating and efficient out-coupling at once. Similar to the recently introduced attosecond lighthouse [3] NOG employs attosecond angular streaking [4] and combines this concept with noncollinear HHG, proposed earlier [5] as out-coupling method for intra cavity HHG. (Less)
It is a fundamental challenge in quantum optics to deterministically generate indistinguishable single photons through non-deterministic nonlinear optical processes, due to the intrinsic coupling of single- and multi-photon-generation probabilities in these processes. Actively multiplexing photons generated in many temporal modes can decouple these probabilities, but key issues are to minimize resource requirements to allow scalability, and to ensure indistinguishability of the generated photons. Here we demonstrate the multiplexing of photons from four temporal modes solely using fibre-integrated optics and off-the-shelf electronic components. We show a 100% enhancement to the single-photon output probability without introducing additional multi-photon noise. Photon indistinguishability is confirmed by a fourfold Hong–Ou–Mandel quantum interference with a 91±16% visibility after subtracting multi-photon noise due to high pump power. Our demonstration paves the way for scalable multiplexing of many non-deterministic photon sources to a single near-deterministic source, which will be of benefit to future quantum photonic technologies.
Penrose superradiance is the amplification of waves scattered by a rapidly rotating object. This process was proposed in 1969 by Penrose for a rotating black hole [1] and in 1971 by Zel’dovich for electromagnetic waves scattered by a metallic rotating cylinder [2]. Wave whose angular frequency 𝜔 satisfies the condition 𝜔 < 𝑚Ω are amplified, where 𝑚 is the waves’ angular momentum and Ω is the cylinder’s angular velocity. Superradiant scattering is not unique to for electromagnetic waves. Recently a direct measurement of superradiance in water waves has been reported in a draining bathtub experiment [3].
New techniques capable of accessing ultrafast demagnetisation processes on the sub-10 femtosecond timescale are presently in great demand. Achieving a high temporal resolution in pump-probe time-resolved experiments is very important for studying ultrafast processes in matter, providing an ideal platform for understanding interaction mechanisms, such as the spin-orbit coupling, the exchange interaction, the structural anisotropy of the materials and the spin-phonon interaction, among others. These mechanisms are responsible for the modification of the magnetic order in nanostructures which are subject to an external perturbation on the temporal scale that extends from a few femtoseconds to the nanosecond regime
We present post-compression of a TW class laser in a planar hollow waveguide. The viability of the compressed pulses for applications in strong-field physics is demonstrated by generating high-order harmonics in a gas jet.
Summary form only given. Passively modelocked optically pumped semiconductor disk lasers (SDLs) [1] based on InGaAs quantum wells (QWs) such as vertical external-cavity surface-emitting lasers (VECSELs) or modelocked integrated surface-emitting lasers (MIXSELs) are an appealing ultrafast laser technology for applications that require compelling combinations of short femtosecond pulses and gigahertz pulse repetition rates. Recent development of pulse shortening strategies resulted in record-short 107-fs pulses from a VECSEL [2] and 253-fs pulses from a MIXSEL [3]. However, this progress in shorter pulse durations has come with the trade-off of significantly lower optical-to-optical pump efficiency even below 1% and only moderate average output power of around 100 mW so far.Here, we develop a rate equation model to investigate the carrier dynamics in the SDL gain and absorber QWs with the aim to better understand the underlying physical reasons for this trade-off. In contrast to ab initio approaches [4], our goal is to simplify the model and still obtain full agreement with our experimental results.
We present the experimental observation of type-II optical Weyl points and corresponding Fermi arcs in a three-dimensional photonic structure. We employ a system composed of an array of staggered helical waveguides fabricated using the direct laser writing technique. Weyl points are established by observing conical diffraction and Fermi arcs are demonstrated by showing surface confinement (and deconfinement) at wavelengths above (below) the Weyl point.
Wavelength meters are central for many applications such as in telecommunication systems or laser monitoring. The primary function of a wavelength meter is to provide an output signal that changes sensitively with the wavelength of the input light. Of central importance is the reproducibility of the output signal over long time intervals during which external perturbations might negatively affect the reproducibility of the displayed wavelengths.
Lead-halide hybrid perovskite crystals have emerged as potentially materials for solar cells due to their power conversion efficiency over 20% [1]. In this work we conduct a comparative study between two hybrids (CH3NH3PbBr3 and CH3NH3PbCl3) and an all-inorganic lead-halide perovskite (CsPbBr3). Both have the general ABX3 perovskite formula, with similar band gap (2.2 eV) and similar structural phase sequence, orthorhombic at low temperature, changing to tetragonal and then to cubic as temperature is increased [2]. Theoretical studies suggested that dynamic disorder, imposed by the rotation of anisotropic organic molecules in the inorganic octahedral network, plays an important role in the high photovoltaic activity presented by this perovskites [3,4]. In many materials, the quasi-elastic scattering spectral continuum is a characteristic of relaxational dynamics which can be observed by many techniques as well as Raman scattering [5]. In order to investigate this dynamic, low frequency Raman spectra were analyzed using the imaginary part of the Debye relaxation model for the central peak and the imaginary part of the damped Lorentz oscillator model for fit the Raman peaks (Figure 1).
We generate large effective χ(2) nonlinearities in a purely χ(3)-nonlinear Si3N4 microring-resonator using the coherent photon conversion scheme and measure a normalized effective second harmonic generation efficiency above 77%/mW.
