Revealing the subfemtosecond dynamics of orbital angular momentum in nanoplasmonic vortices.

The ability of light to carry and deliver orbital angular momentum (OAM) in the form of optical vortices has attracted much interest. The physical properties of light with a helical wavefront can be confined onto two-dimensional surfaces with subwavelength dimensions in the form of plasmonic vortices, opening avenues for thus far unknown light-matter interactions. Because of their extreme rotational velocity, the ultrafast dynamics of such vortices remained unexplored. Here we show the detailed spatiotemporal evolution of nanovortices using time-resolved two-photon photoemission electron microscopy. We observe both long- and short-range plasmonic vortices confined to deep subwavelength dimensions on the scale of 100 nanometers with nanometer spatial resolution and subfemtosecond time-step resolution. Finally, by measuring the angular velocity of the vortex, we directly extract the OAM magnitude of light.

Sub-100 nm focusing of short wavelength plasmons in homogeneous 2D space.

We present a direct measurement of short-wavelength plasmons focused into a sub-100 nm spot in homogeneous (translation invariant) 2D space. The short-wavelength (SW) surface plasmon polaritons (SPP) are achieved in metal-insulator-insulator (MII) platform consisting of silver, silicon nitride, and air. This platform is homogeneous in two spatial directions and supports SPP at wavelength more than two times shorter than that in free space yet interacts with the outer world through the evanescent tail in air. We use an apertureless (scattering) near-field scanning optical microscope (NSOM) to map directly the amplitude and phase of these SW-SPP and show they can be focused to under 70 nm without structurally assisted confinement such as nanoantennas or nanofocusing. This, along with the use of visible light at 532 nm which is suitable for optical microscopy, can open new directions in direct biological and medical imaging at the sub-100 nm resolution regime.

Manipulating polarization of light with ultrathin epsilon-near-zero metamaterials.

One of the basic functionalities of photonic devices is the ability to manipulate the polarization state of light. Polarization components are usually implemented using the retardation effect in natural birefringent crystals and, thus, have a bulky design. Here, we have demonstrated the polarization manipulation of light by employing a thin subwavelength slab of metamaterial with an extremely anisotropic effective permittivity tensor. Polarization properties of light incident on the metamaterial in the regime of hyperbolic, epsilon-near-zero, and conventional elliptic dispersions were compared. We have shown that both reflection from and transmission through λ/20 thick slab of the metamaterial may provide nearly complete linear-to-circular polarization conversion or 90° linear polarization rotation, not achievable with natural materials. Using ellipsometric measurements, we experimentally studied the polarization conversion properties of the metamaterial slab made of the plasmonic nanorod arrays in different dispersion regimes. We have also suggested all-optical ultrafast control of reflected or transmitted light polarization by employing metal nonlinearities.

Nano-plasmonic antennas in the near infrared regime.

Plasmonic nano-antennas constitute a central research topic in current science and engineering with an enormous variety of potential applications. Here we review the recent progress in the niche of plasmonic nano-antennas operating in the near infrared part of the spectrum which is important for a variety of applications. Tuning of the resonance into the near infrared regime is emphasized in the perspectives of fabrication, measurement, modeling, and analytical treatments, concentrating on the vast recent achievements in these areas.

Light flowers from coherent vertical-cavity surface-emitting laser arrays.

Emission of symmetric flower-shaped light patterns from coherently locked hexagonal vertical-cavity semiconductor laser arrays is reported. The flower patterns preserve their shape while propagating in free space. The emission of these unique light distributions is explained as being due to the combined effects of thermal lensing and the loss patterns employed for array definition. A theoretical model for strongly coupled arrays matches the results.

Environmental asbestos exposure and mesothelioma.

Epidemiologic studies of mesothelioma have focused primarily on occupational exposures to asbestos. Nonoccupational exposure to asbestos can be grouped into three main categories: paraoccupational (familial), neighborhood, and true environmental exposures. Elevated mesothelioma rates not attributable to occupational exposures have been observed in asbestos mining and manufacturing areas. Asbestos is one of the most dangerous environmental carcinogens because of the small dose known to cause mesothelioma and the rapid lethality of the disease once it develops. Further research is needed to characterize the contribution and risk profile for environmental asbestos and mesothelioma, and for the development of public health policy.

Optical vortices crystals: spontaneous generation in nonlinear semiconductor microcavities

Broad-area, vertical-cavity surface-emitting lasers were shown to switch their emission mode from the regular single or multilobed light fields to exhibit complex arrays of "dark beams." Examination of these dark spot arrays revealed that they consist of multiple, closely packed optical vortices: optical fields that have phase singularities and show increased complexity as the injection current level is raised. Contrary to their complex appearance, most of these light distributions are not the result of a multimode (multiple-frequency) operation but exhibit single-frequency characteristics. The dark beam patterns can be described as emanating from a spontaneous process of transverse mode locking of nearly degenerate modes, assisted by the laser nonlinearity. Surprisingly, these patterns show high resemblance to patterns generated in other nonlinear scenarios that are completely different both in scale and in mechanism.

Interactions and switching of spatial soliton pairs in the vicinity of a nonlinear interface.

The interaction of spatial soliton pairs with a nonlinear interface was studied theoretically. With mediation of the interface, the two solitons exhibited efficient switching and double switching. A closed-form particlelike model, validated by propagation calculations, yielded the soliton trajectories and switching characteristics.

Coupling of concentric semiconductor microring lasers.

Coupling between whispering-gallery modes of concentric microcavity lasers was analyzed, and a closed-form three-dimensional vectorial solution for the coupled fields was obtained. Experiments performed with concentric gain-guided vertical cavity ring lasers resulted in regimes of resonant coupling in good agreement with the theory.

Cyclic vertical cavity semiconductor laser arrays with odd numbers of elements: lasing modes and symmetry breaking.

Array modes of cyclic vertical cavity laser arrays with odd numbers of elements were explored experimentally and theoretically. The odd antiphase array mode is prohibited by the circular symmetry, and the lowestloss modes are degenerated. Slight inhomogenities drive the array mode structure to experience spontaneous symmetry breaking, leading by means of mode degeneracy removal to stable operation characterized by an antiphase lasing mode with an even number of lobes. Circular laser arrays of 3-19 elements were measured; all were lasing in a stable even-array mode, exhibiting 2-18 intensity lobes for both the near and the far fields.

Synchronized two-color operation of a passively mode-locked erbium-doped fiber laser by dual injection locking.

The recently introduced harmonic injection locking is a method for generating pulse trains at high repetition rates from passively mode-locked lasers. We report the simultaneous injection locking of two spectral bands in an erbium-doped fiber laser by injection of two spectrally distinct and temporally synchronized pulse trains. The injection-locked laser simultaneously produced pulses at wavelengths of 1.53 and 1.55 microm, each at a 7.5-GHz repetition rate and with a pulse width of 10 ps. We compared the experimental results with those of a passively mode-locked laser.

Noise reduction by harmonic injection locking of passively mode-locked erbium-doped fiber lasers.

Harmonic injection locking can generate pulse trains at high repetition rates from passively mode-locked lasers. We have examined experimentally the mutual interaction of noise with the locking process. For injected signals with large timing and amplitude noise, the mode-locked fiber laser generated a pulse train with reduced noise. Injected signals with low timing and amplitude noise were employed for the reduction of the internal noise of the passively mode-locked laser. The achieved output pulse-to-pulse timing jitter in the range of 20-2500 Hz was ~0.6 ps, comparable with that of actively stabilized fiber lasers.

Injection locking of an actively mode-locked semiconductor laser.

We report what is to our knowledge the first observation of synchronous coherent injection locking of an actively mode-locked extended cavity semiconductor laser to an external light pulse train. In the temporal domain, we observed experimentally and verified theoretically a significant narrowing of the output pulse of the mode-locked laser. In the spectral domain, we demonstrated experimentally the narrowing of the output optical spectrum that was due to rejection of spectral components outside the spectral band of the locking pulses. Locking ranges, in the time and the frequency domains, were measured to be ~200 ps and ~5 nm, respectively.

Integration of planar Fresnel microlenses with vertical-cavity surface-emitting laser arrays.

We report a technique of integrating planar Fresnel microlenses with InGaAs/GaAs-based vertical-cavity surfacee-mitting laser arrays by selectively ion-beam milling the substrate. Depending on the application, one can focus, collimate, and bend the individual laser beams using such microlenses. An example is presented where a 32 x 32 array of microlenses, each with an aperture of 80microm and a focal length of 108 microm is integrated with a laser array. As expected, arrays of focused beams, each with a 2-microm spot size, are generated at a distance of approximately 110 microm.

[A post-traumatic locked-in syndrome with delayed onset]. / Locked-in syndrome post-traumatique d'installation retardée.

We report a case of locked-in syndrome occurring two days after a cranio-cervical trauma in a 28 years old male patient. It was a consequence of basilar thrombosis after left vertebral artery dissection secondary to a vertebral fracture at the C6 level. Decerebrate rigidity and apparent unconsciousness led to misdiagnosing it for post traumatic coma. It took several days to correct this mistake. To avoid this pitfall, we insist on the clinical features of this syndrome and discuss which investigations are needed and which therapy is available.

The locked-in syndrome: a review and presentation of two chronic cases.

The locked-in syndrome (LIS) is a state of an upper motor neurone quadriplegia involving the cranial nerve pairs with usually a lateral gaze palsy, paralytic mutism, full consciousness and awareness by the patient of his environment. A historical presentation of the LIS is given as well as a short description of the clinicoanatomic lesion causing LIS. The usual cause is vascular and corresponds to a pontine infarction due to an obstruction of the basilar artery but other lesions in the brainstem can also be the cause. Non-vascular aetiologies, especially traumatic, are reviewed. The use of electroencephalography (EEG), brain auditory evoked potentials (BAEP) and somesthesic evoked potentials (SEP) are discussed as well as the use in the acute stage of computed tomography (CT), angiography, and magnetic resonance imagery (MRI). The last method may show well delineated ischaemic lesions some time after the event. The communication disability is probably the most difficult to overcome. Two cases of LIS are presented.