We report on the observation and application of near-field speckles with a laboratory x-ray source. The detection of speckles is possible thanks to the enhanced brilliance properties of the used liquid-metal-jet source, and opens the way to a range of new applications in laboratory-based coherent x-ray imaging. Here, we use the speckle pattern for multimodal imaging of demonstrator objects. Moreover, we introduce algorithms for phase and dark-field imaging using speckle tracking, and we show that they yield superior results with respect to existing methods.

We consider $N\times N$ Gaussian random matrices, whose average density of eigenvalues has the Wigner semicircle form over $[-\sqrt{2},\sqrt{2}]$. For such matrices, using a Coulomb gas technique, we compute the large $N$ behavior of the probability ${\mathcal{P}}_{N,L}(N_L)$ that $N_L$ eigenvalues lie within the box $[-L,L]$. This probability scales as ${\mathcal{P}}_{N,L}(N_L={\kappa }_{L}N)\approx \exp \mathbf{(}-\beta N^2{\psi }_L({\kappa }_L)\mathbf{)}$, where $\beta$ is the Dyson index of the ensemble and ${\psi }_L({\kappa }_L)$ is a $\beta$-independent rate function that we compute exactly. We identify three regimes as $L$ is varied: (i) $N^{-1}\ll L<\sqrt{2}$ (bulk), (ii) $L\sim \sqrt{2}$ on a scale of $\mathcal{O}(N^{-2/3})$ (edge), and (iii) $L>\sqrt{2}$ (tail). We find a dramatic nonmonotonic behavior of the number variance $V_N(L)$ as a function of $L$: after a logarithmic growth $\propto \ln (NL)$ in the bulk (when $L\sim \mathcal{O}(1/N)$), $V_N(L)$ decreases abruptly as $L$ approaches the edge of the semicircle before it decays as a stretched exponential for $L>\sqrt{2}$. This “dropoff” of $V_N(L)$ at the edge is described by a scaling function ${\tilde{V}}_{\beta }$ that smoothly interpolates between the bulk (i) and the tail (iii). For $\beta =2$ we compute ${\tilde{V}}_2$ explicitly in terms of the Airy kernel. These analytical results, verified by numerical simulations, directly provide for $\beta =2$ the full statistics of particle-number fluctuations at zero temperature of 1D spinless fermions in a harmonic trap.

We introduce a new family of generalized $\mathcal{P}\tilde{T}$-symmetric cavities that involve gyrotropic elements and support reconfigurable unidirectional lasing modes. We derive conditions for which these modes exist and investigate a simple electronic circuit that experimentally demonstrates their feasibility in the radio-frequency domain.

We investigate the mechanics of thin sheets decorated by noninteracting creases. The system considered here consists of parallel folds connected by elastic panels. We show that the mechanical response of the creased structure is twofold, depending both on the bending deformation of the panels and the hingelike intrinsic response of the crease. We show that a characteristic length scale, defined by the ratio of bending to hinge energies, governs whether the structure’s response consists in angle opening or panel bending when a small load is applied. The existence of this length scale is a building block for future works on origami mechanics.

Heavy inertial particles transported by a turbulent flow are shown to concentrate in the regions where an advected passive scalar, such as temperature, displays very strong frontlike discontinuities. This novel effect is responsible for extremely high levels of fluctuations for the passive field sampled by the particles that impacts the heat fluxes exchanged between the particles and the surrounding fluid. Instantaneous and averaged heat fluxes are shown to follow strongly intermittent statistics and anomalous scaling laws.

We show how careful control of the incident polarization of a light beam close to the Brewster angle gives a giant transverse spatial shift on reflection. This resolves the long-standing puzzle of why such beam shifts transverse to the incident plane (Imbert-Fedorov shifts) tend to be an order of magnitude smaller than the related Goos-Hänchen shifts in the longitudinal direction, which are largest close to critical incidence. We demonstrate that with the proper initial polarization the transverse displacements can be equally large, which we confirm experimentally near Brewster incidence. In contrast to the established understanding, these polarizations are elliptical and angle dependent. We explain the magnitude of the Imbert-Fedorov shift by an analogous change of the symmetry properties for the reflection operators as compared to the Goos-Hänchen shift.

We expose two scenarios for the breakdown of quantum multifractality under the effect of perturbations. In the first scenario, multifractality survives below a certain scale of the quantum fluctuations. In the other one, the fluctuations of the wave functions are changed at every scale and each multifractal dimension smoothly goes to the ergodic value. We use as generic examples a one-dimensional dynamical system and the three-dimensional Anderson model at the metal-insulator transition. Based on our results, we conjecture that the sensitivity of quantum multifractality to perturbation is universal in the sense that it follows one of these two scenarios depending on the perturbation. We also discuss the experimental implications.

We demonstrate the experimental realization of a multiresonant metamaterial for Lamb waves, i.e., elastic waves propagating in plates. The metamaterial effect comes from the resonances of long aluminum rods that are attached to an aluminum plate. Using time-dependent measurements, we experimentally prove that this metamaterial exhibits wide band gaps as well as sub- and suprawavelength modes for both a periodic and a random arrangement of the resonators. The dispersion curve inside the metamaterial is predicted through hybridizations between flexural and compressional resonances in the rods and slow and fast Lamb modes in the plate. We finally underline how the various degrees of freedom of such system paves the way to the design of metamaterials for the control of Lamb waves in unprecedented ways.

This work presents direct numerical simulations of capillary wave turbulence solving the full three-dimensional Navier-Stokes equations of a two-phase flow. When the interface is locally forced at large scales, a statistical stationary state appears after few forcing periods. Smaller wave scales are generated by nonlinear interactions, and the wave height spectrum is found to obey a power law in both wave number and frequency, in good agreement with weak turbulence theory. By estimation of the mean energy flux from the dissipated power, the Kolmogorov-Zakharov constant is evaluated and found to be compatible with the exact theoretical value. The time scale separation between linear, nonlinear interaction, and dissipative times is also observed. These numerical results confirm the validity of the weak turbulence approach to quantify out-of equilibrium wave statistics.

Soliton mode locking is an essential technique for building compact mode-locked lasers with multigigahertz repetition rates. In this scheme, pulses behave like dissipative solitons due to the presence of gain, loss, frequency filtering, and nonlinear absorption in the cavity. The continuum waves that radiate from the perturbed soliton act back on the soliton, resulting in periodic changes in the electric field of the pulse. We find that, in the presence of gain filtering or two-photon absorption, this field modulation is converted to power modulation, which is observable from the radio-frequency spectrum of the laser’s output power. We investigate its physical origin in the context of soliton perturbation theory. For comparison, we also perform numerical simulations and experiments.

Dynamic wavelength conversion (DWC) is obtained by controlling copropagating slow-light signal and control pulse trajectories. Our method is based on the understanding that conventional resonator-based DWC can be generalized, and is linked to cross-phase modulation. Dispersion-engineered Si photonic crystal waveguides produce such slow-light pulses. Free carriers generated by two-photon absorption of the control pulse dynamically shift the signal wavelength. Matching the group velocities of the two pulses enhances the shift, elongating the interaction length. We demonstrate an extremely large wavelength shift in DWC (4.9 nm blueshift) for the signal wavelength. Although DWC is similar to the Doppler effect, we highlight their essential differences.

The interaction between a large number of laser filaments brought together using weak external focusing leads to the emergence of few filamentary structures reminiscent of standard filaments, but carrying a higher intensity. The resulting plasma is measured to be 1 order of magnitude denser than for short-scale filaments. This new propagation regime is dubbed superfilamentation. Numerical simulations of a nonlinear envelope equation provide good agreement with experiments.

We investigate the relationship between passive mode locking and the formation of time-localized structures in the output intensity of a laser. We show how the mode-locked pulses transform into lasing localized structures, allowing for individual addressing and arbitrary low repetition rates. Our analysis reveals that this occurs when (i) the cavity round-trip is much larger than the slowest medium time scale, namely the gain recovery time, and (ii) the mode-locked solution coexists with the zero intensity (off) solution. These conditions enable the coexistence of a large quantity of stable solutions, each of them being characterized by a different number of pulses per round-trip and with different arrangements. Then, each mode-locked pulse becomes localized, i.e., individually addressable.

We demonstrate a coexistence of coherent and incoherent modes in the optical comb generated by a passively mode-locked quantum dot laser. This is experimentally achieved by means of optical linewidth, radio frequency spectrum, and optical spectrum measurements and confirmed numerically by a delay-differential equation model showing excellent agreement with the experiment. We interpret the state as a chimera state.

We report on compact and efficient laser-based THz generation in the terahertz frequency gap (1–10 THz). The radiation is generated by optical rectification of a midinfrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited tabletop THz sources to $\mathrm{GV}/\mathrm{m}$ electric and several tesla magnetic field at millijoule pulse energy. In agreement with simulations, the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded ${\chi }^{(2)}$ process in the organic crystals accompanied by a significant redshift of the pump spectrum. The scheme provides a compact, tabletop THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue toward novel nonlinear THz applications.

We predict the possibility of observing integer and fractional self-imaging (Talbot) phenomena on the discrete angular spectrum of periodic diffraction gratings illuminated by a suitable spherical wave front. Our predictions are experimentally validated, reporting what we believe to be the first observation of self-imaging effects in the far-field diffraction regime.