Observation of universal Hall response in strongly interacting Fermions.

The Hall effect, which originates from the motion of charged particles in magnetic fields, has deep consequences for the description of materials, extending far beyond condensed matter. Understanding such an effect in interacting systems represents a fundamental challenge, even for small magnetic fields. In this work, we used an atomic quantum simulator in which we tracked the motion of ultracold fermions in two-leg ribbons threaded by artificial magnetic fields. Through controllable quench dynamics, we measured the Hall response for a range of synthetic tunneling and atomic interaction strengths. We unveil a universal interaction-independent behavior above an interaction threshold, in agreement with theoretical analyses. The ability to reach hard-to-compute regimes demonstrates the power of quantum simulation to describe strongly correlated topological states of matter.

Measurement of two-photon-absorption spectra through nonlinear fluorescence produced by a line-shaped excitation beam.

We propose an innovative experimental approach to estimate the two-photon absorption (TPA) spectrum of a fluorescent material. Our method develops the standard indirect fluorescence-based method for the TPA measurement by employing a line-shaped excitation beam, generating a line-shaped fluorescence emission. Such a configuration, which requires a relatively high amount of optical power, permits to have a greatly increased fluorescence signal, thus avoiding the photon counterdetection devices usually used in these measurements, and allowing to employ detectors such as charge-coupled device (CCD) cameras. The method is finally tested on a fluorescent isothiocyanate sample, whose TPA spectrum, which is measured with the proposed technique, is compared with the TPA spectra reported in the literature, confirming the validity of our experimental approach.

Miniaturized photogenerated electro-optic axicon lens Gaussian-to-Bessel beam conversion.

We experimentally demonstrate an electro-optic Gaussian-to-Bessel beam-converter miniaturized down to a 30×30 µm pixel in a potassium-lithium-tantalate-niobate (KLTN) paraelectric crystal. The converter is based on the electro-optic activation of a photoinduced and reconfigurable volume axicon lens achieved using a prewritten photorefractive funnel space-charge distribution. The transmitted light beam has a tunable depth of field that can be more than twice that of a conventional beam with the added feature of being self-healing.

Continuous Solitons in a Lattice Nonlinearity.

We study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern.

Volume integrated phase modulator based on funnel waveguides for reconfigurable miniaturized optical circuits.

We demonstrate the integration of a miniaturized 30(x) µm×30(y) µm×2.7(z) mm electro-optic phase modulator operating in the near-IR (λ=980 nm) based on the electro-activation of a funnel waveguide inside a paraelectric sample of photorefractive potassium lithium tantalate niobate. The modulator forms a basic tassel in the realization of miniaturized reconfigurable optical circuits embedded in a single solid-state three-dimensional chip.

Photorefractive light needles in glassy nanodisordered KNTN.

We study the formation of 2D self-trapped beams in nanodisordered potassium-sodium-tantalate-niobate (KNTN) cooled below the dynamic glass transition. Supercooling is shown to accelerate the photorefractive response and enhance steady-state anisotropy. Effects in the excited state are attributed to the anomalous slim-loop polarization curve typical of relaxors dominated by non-interacting polar-nano-regions.

Observation of electro-activated localized structures in broad area VCSELs.

We demonstrate experimentally the electro-activation of a localized optical structure in a coherently driven broad-area vertical-cavity surface-emitting laser (VCSEL) operated below threshold. Control is achieved by electro-optically steering a writing beam through a pre-programmable switch based on a photorefractive funnel waveguide.

Anti-diffracting beams through the diffusive optical nonlinearity.

Anti-diffraction is a theoretically predicted nonlinear optical phenomenon that occurs when a light beam spontaneously focalizes independently of its intensity. We observe anti-diffracting beams supported by the peak-intensity-independent diffusive nonlinearity that are able to shrink below their diffraction-limited size in photorefractive lithium-enriched potassium-tantalate-niobate (KTN:Li).

Aging solitons in photorefractive dipolar glasses.

We study experimentally the aging of optical spatial solitons in a dipolar glass hosted by a nanodisordered sample of photorefractive potassium-sodium-tantalate-niobate (KNTN). As the system ages, the waves erratically explore varying strengths of the nonlinear response, causing them to break up and scatter. We show that this process can still lead to solitons, but in a generalized form for which the changing response is compensated by changing the normalized wave size and intensity so as to maintain fixed the optical waveform.

Rejuvenation in scale-free optics and enhanced diffraction cancellation life-time.

We demonstrate rejuvenation in scale-free optical propagation. The phenomenon is caused by the non-ergodic relaxation of the dipolar glass that mediates the photorefractive nonlinearity in compositionally-disordered lithium-enriched potassium-tantalate-niobate (KTN:Li). We implement rejuvenation to halt aging in the dipolar glass and extend the duration of beam diffraction cancellation.

Diffraction cancellation over multiple wavelengths in photorefractive dipolar glasses.

We report the simultaneous diffraction cancellation for beams of different wavelengths in out-of-equilibrium dipolar glass. The effect is supported by the photorefractive diffusive nonlinearity and scale-free optics, and can find application in imaging and microscopy.