Negative Refraction in Time-Varying Strongly Coupled Plasmonic-Antenna-Epsilon-Near-Zero Systems.

Time-varying metasurfaces are emerging as a powerful instrument for the dynamical control of the electromagnetic properties of a propagating wave. Here we demonstrate an efficient time-varying metasurface based on plasmonic nano-antennas strongly coupled to an epsilon-near-zero (ENZ) deeply subwavelength film. The plasmonic resonance of the metal resonators strongly interacts with the optical ENZ modes, providing a Rabi level spitting of ∼30%. Optical pumping at frequency ω induces a nonlinear polarization oscillating at 2ω responsible for an efficient generation of a phase conjugate and a negative refracted beam with a conversion efficiency that is more than 4 orders of magnitude greater compared to the bare ENZ film. The introduction of a strongly coupled plasmonic system therefore provides a simple and effective route towards the implementation of ENZ physics at the nanoscale.

Superradiant Amplification of Acoustic Beams via Medium Rotation.

Superradiant gain is the process in which waves are amplified via their interaction with a rotating body, examples including the evaporation of a spinning black hole and electromagnetic emission from a rotating metal sphere. In this Letter we elucidate how superradiance may be realized experimentally in the field of acoustics, and predict the possibility of nonreciprocally amplifying or absorbing acoustic beams carrying orbital angular momentum by propagating them through an absorbing medium that is rotating. We discuss a possible geometry for realizing acoustic superradiant amplification using existing technology.

Rotation-dependent nonlinear absorption of orbital angular momentum beams in ruby.

We investigate the effect of a rotating medium on orbital angular momentum (OAM)-carrying beams by combining a weak probe beam shifted in frequency relative to a strong pump beam. We show how the rotational Doppler effect modifies the light-matter interaction through the external rotation of the medium. This interaction leads to an absorption that increases with the mechanical rotation velocity of the medium and with a rate that depends on the OAM of the light beam.

Spontaneous Photon Production in Time-Dependent Epsilon-Near-Zero Materials.

Quantum field theory predicts that a spatially homogeneous but temporally varying medium will excite photon pairs out of the vacuum state. However, this important theoretical prediction lacks experimental verification due to the difficulty in attaining the required nonadiabatic and large amplitude changes in the medium. Recent work has shown that in epsilon-near-zero (ENZ) materials it is possible to optically induce changes of the refractive index of the order of unity, in femtosecond time scales. By studying the quantum field theory of a spatially homogeneous, time-varying ENZ medium, we theoretically predict photon-pair production that is up to several orders of magnitude larger than in non-ENZ time-varying materials. We also find that while in standard materials the emission spectrum depends on the time scale of the perturbation, in ENZ materials the emission is always peaked at the ENZ wavelength. These studies pave the way to technologically feasible observation of photon-pair emission from a time-varying background with implications for quantum field theories beyond condensed matter systems and with potential applications as a new source of entangled light.

Enhanced Nonlinear Refractive Index in ε-Near-Zero Materials.

New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here, we demonstrate a universal approach based on the low linear permittivity values attained in the ε-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a sixfold increase of the Kerr nonlinear refractive index (n_{2}) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics.

Spectral broadening and temporal compression of ∼ 100 fs pulses in air-filled hollow core capillary fibers.

We experimentally study the spectral broadening of intense, ∼ 100 femtosecond laser pulses at 785 nm coupled into different kinds of hollow core capillary fibers, all filled with air at ambient pressure. Differently from observations in other gases, the spectra are broadened with a strong red-shift due to highly efficient intrapulse Raman scattering. Numerical simulations show that such spectra can be explained only by increasing the Raman fraction of the third order nonlinearity close to 100%. Experimentally, these broadened and red-shifted pulses do not generally allow for straightforward compression using, for example, standard chirped mirrors. However, using special hollow fibers that are internally coated with silver and polymer we obtain pulse durations in the sub-20 fs regime with energies up to 300 µJ.

Self-reconstructing spatiotemporal light bullets.

We show that spatiotemporal light bullets generated by self-focusing and filamentation of 100 fs, 1.8 µm pulses in a dielectric medium with anomalous group velocity dispersion (sapphire) are extremely robust to external perturbations. We present the experimental results supported by the numerical simulations that demonstrate complete spatiotemporal self-reconstruction of the light bullet after hitting an obstacle, which blocks its intense core carrying the self-compressed pulse, in nonlinear as well as in linear (free-space) propagation regimes.

Nature of spatiotemporal light bullets in bulk Kerr media.

We present a detailed experimental investigation which uncovers the nature of light bullets generated from self-focusing in a bulk dielectric medium with Kerr nonlinearity in the anomalous group velocity dispersion regime. By high dynamic range measurements of three-dimensional intensity profiles, we demonstrate that the light bullets consist of a sharply localized high-intensity core, which carries the self-compressed pulse and contains approximately 25% of the total energy, and a ring-shaped spatiotemporal periphery. Subdiffractive propagation along with dispersive broadening of the light bullets in free space after they exit the nonlinear medium indicate a strong space-time coupling within the bullet. This finding is confirmed by measurements of a spatiotemporal energy density flux that exhibits the same features as a stationary, polychromatic Bessel beam, thus highlighting the nature of the light bullets.

Amplification of electromagnetic fields by a rotating body.

In 1971, Zel'dovich predicted the amplification of electromagnetic (EM) waves scattered by a rotating metallic cylinder, gaining mechanical rotational energy from the body. This phenomenon was believed to be unobservable with electromagnetic fields due to technological difficulties in meeting the condition of amplification that is, the cylinder must rotate faster than the frequency of the incoming radiation. Here, we measure the amplification of an electromagnetic field, generated by a toroid LC-circuit, scattered by an aluminium cylinder spinning in the toroid gap. We show that when the Zel'dovich condition is met, the resistance induced by the cylinder becomes negative implying amplification of the incoming EM fields. These results reveal the connection between the concept of induction generators and the physics of this fundamental physics effect and open new prospects towards testing the Zel'dovich mechanism in the quantum regime, as well as related quantum friction effects.

Blackbody emission from light interacting with an effective moving dispersive medium.

Intense laser pulses excite a nonlinear polarization response that may create an effective flowing medium and, under appropriate conditions, a blocking horizon for light. Here, we analyze in detail the interaction of light with such laser-induced flowing media, fully accounting for the medium dispersion properties. An analytical model based on a first Born approximation is found to be in excellent agreement with numerical simulations based on Maxwell's equations and shows that when a blocking horizon is formed, the stimulated medium scatters light with a blackbody emission spectrum. Based on these results, diamond is proposed as a promising candidate medium for future studies of Hawking emission from artificial, dispersive horizons.

Negative-frequency resonant radiation.

Optical solitons or solitonlike states shed light to blueshifted frequencies through a resonant emission process. We predict a mechanism by which a second propagating mode is generated. This mode, called negative resonant radiation, originates from the coupling of the soliton mode to the negative-frequency branch of the dispersion relation. Measurements in both bulk media and photonic-crystal fibers confirm our predictions.

Generation of broadly tunable sub-30-fs infrared pulses by four-wave optical parametric amplification.

We report on the generation of sub-30-fs near-IR light pulses by means of broadband four-wave parametric amplification in fused silica. This is achieved by frequency downconversion of visible broadband pulses provided by a commercial blue-pumped beta-barium borate crystal-based noncollinear optical parametric amplifier. The proposed method produces the IR idler pulses with energy up to ∼20 µJ and tunable in wavelength from 1 to 1.5 µm. The shortest pulse duration is 17.6 fs, measured at 1.2 µm.

Wide-awake anesthesia in Dupuytren's contracture treated with collagenase.

The injection of collagenase followed by cord manipulation is one of the most popular treatments for Dupuytren's contracture. This is traditionally performed under local anesthesia or regional nerve block potentially with sedation. Neither the treatment with collagenase, nor the wide-awake anesthesia are novel techniques for hand surgeons. Nevertheless, we report the first experience of cord manipulation using the wide-awake approach. In this prospective study, we compared the pain perception of patients who underwent wide-awake anesthesia versus traditional local anesthesia. We recorded the pain sensation on a visual analog scale (VAS) (0 to 10) during anesthetic injection, during cord manipulation and before discharge. Wide-awake anesthesia significantly reduced pain levels during anesthetic injection (p=0.003) and cord manipulation (p=0.0009). Pain levels did not differ significantly right before discharge in the two groups (p=0.54). Wide-awake anesthesia can be successfully applied to cord manipulation after collagenase injection in Dupuytren's contracture. This way, it is possible to improve the patient's subjective perspective of the procedure.

Super-resolution time-resolved imaging using computational sensor fusion.

Imaging across both the full transverse spatial and temporal dimensions of a scene with high precision in all three coordinates is key to applications ranging from LIDAR to fluorescence lifetime imaging. However, compromises that sacrifice, for example, spatial resolution at the expense of temporal resolution are often required, in particular when the full 3-dimensional data cube is required in short acquisition times. We introduce a sensor fusion approach that combines data having low-spatial resolution but high temporal precision gathered with a single-photon-avalanche-diode (SPAD) array with data that has high spatial but no temporal resolution, such as that acquired with a standard CMOS camera. Our method, based on blurring the image on the SPAD array and computational sensor fusion, reconstructs time-resolved images at significantly higher spatial resolution than the SPAD input, upsampling numerical data by a factor [Formula: see text], and demonstrating up to [Formula: see text] upsampling of experimental data. We demonstrate the technique for both LIDAR applications and FLIM of fluorescent cancer cells. This technique paves the way to high spatial resolution SPAD imaging or, equivalently, FLIM imaging with conventional microscopes at frame rates accelerated by more than an order of magnitude.

Multi-dorsal metacarpal artery perforator adipofascial turnover flap for index to little finger reconstruction: Anatomical study and clinical application.

Reconstruction of the dorsum of the hand and fingers is one of the main challenges in hand surgery. Regional flaps from the forearm, free flaps, or pocket procedures are options when multiple digits are injured with tendon damage and bone exposure. These procedures can be technically demanding and are often plagued by a texture mismatch. We conducted an anatomical study of 20 fresh frozen hands. The second, third and fourth intermetacarpal spaces were analyzed with the aim of defining the vascular foundation of dorsal hand adipofascial-turnover flaps based on dorsal metacarpal artery (DMA) perforators, analyzing their potential for reconstruction procedures on the dorsum of the hand. In three cases, the 4th intermetacarpal space lacked the DMA. A mean of 3.5 arterial communications were found between the DMA and palmar arterial system. Each hand had 11 ± 2 dorsal skin perforators, which were equally distributed among different intermetacarpal spaces. At least one perforator was present in each one-third of the space. The most distal perforators were the largest in all spaces but missing in two hands. A clinical case of multiple index finger to little finger reconstruction with this new multi-dorsal metacarpal artery perforator (mDMAP) adipofascial turnover flap is presented. Our anatomical study confirmed previous descriptions of the anatomy of the dorsum of the hand. It supports the safety of the mDMAP adipofascial turnover flap based on all distal arterial perforator for the simultaneous reconstruction of index to little finger injuries. Similarly, adipofascial turnover flaps can be raised from more proximal perforators arising from DMAs if more than one intermetacarpal space is included.

Space-time focusing of Bessel-like pulses.

We report on a space-time compression technique allowing for complete and independent control of the longitudinal dynamics and of the transverse pulse localization by means of spatial beam shaping. We experimentally observe both strong temporal compression and high transverse localization, of the order of a few wavelengths, along free-space propagation.

Quantum radiation from superluminal refractive-index perturbations.

We analyze in detail photon production induced by a superluminal refractive-index perturbation in realistic experimental operating conditions. The interaction between the refractive-index perturbation and the quantum vacuum fluctuations of the electromagnetic field leads to the production of photon pairs.

Hawking radiation from ultrashort laser pulse filaments.

Event horizons of astrophysical black holes and gravitational analogues have been predicted to excite the quantum vacuum and give rise to the emission of quanta, known as Hawking radiation. We experimentally create such a gravitational analogue using ultrashort laser pulse filaments and our measurements demonstrate a spontaneous emission of photons that confirms theoretical predictions.

Spatiotemporal amplitude and phase retrieval of Bessel-X pulses using a Hartmann-Shack sensor.

We propose a new experimental technique, which allows for a complete characterization of ultrashort optical pulses both in space and in time. Combining the well-known Frequency-Resolved-Optical-Gating technique for the retrieval of the temporal profile of the pulse with a measurement of the near-field made with an Hartmann-Shack sensor, we are able to retrieve the spatiotemporal amplitude and phase profile of a Bessel-X pulse. By following the pulse evolution along the propagation direction we highlight the superluminal propagation of the pulse peak.

Long spatio-temporally stationary filaments in air using short pulse UV laser Bessel beams.

The formation of long stationary filaments resulting in uniform high density plasma strings in air using short pulse UV laser Bessel beams is shown. The length and the electron density of the plasma strings can be easily tuned by adjusting the conical Bessel wavefront angle. It is shown that in this regime the length of the plasma string can be extended over meter-long scales without any compromise in the string uniformity or any temporal evolution of the filamented laser pulse.