Control of vortex orientation of ultrashort optical pulses using a spatial chirp.

Introducing a spatial chirp into a pulse with a longitudinal vortex, such as a standard pulsed Laguerre-Gauss beam, results in a vortex pulse with an arbitrary orientation of the phase line singularity between longitudinal and transverse, depending on the amount of chirp. Analytical expressions are given for such pulses with arbitrary topological charge valid at any propagation distance.

Propagation of higher-order spatiotemporal vortices.

Closed-form, analytical expressions for higher-order, multi-charged spatiotemporal optical vortices (STOVs) propagating in free space or non-dispersive media are provided. We consider two relevant and complementary situations where the multi-charged STOV spreads freely, and where it is focused. Previously reported multi-charged STOV breakup upon spreading is merely an effect of diffraction, not an instability effect. The focused STOV reverses the sign of its topological charge upon passage through the focus. While the spreading STOV carries transverse orbital angular momentum, the ideally focused STOV from the far field does not.

Clarification for the fields of different radially polarized Laguerre-Gaussian light beams.

Radially polarized light beams have found many applications in particle manipulation, laser processing, and microscopy. Just as with linear polarization, radially polarized light beams can have higher-order transverse modes that involve Laguerre polynomials. Fields of a radially polarized Laguerre-Gaussian light beam have been calculated before, even beyond the paraxial approximation. However, there are in fact multiple solutions to the paraxial wave equation that involve Laguerre polynomials with different properties and propagation characteristics. We therefore clarify the discrepancies among three valid radially polarized solutions to the paraxial wave equation that involve Laguerre polynomials.

Effects of orbital angular momentum on few-cycle and sub-cycle pulse shapes: coupling between the temporal and angular momentum degrees of freedom.

We describe the effects of the coupling between the orbital angular momentum (OAM) and the temporal degrees of freedom in pulsed Laguerre-Gauss beams as a significant increase of the duration of few-cycle pulses when the OAM carried by the pulse is large, and as an enhancement to other previously known spatiotemporal couplings as radial red- and blue-shift of the mean frequency. In contrast to other detrimental, but retrievable, effects in the generation and propagation of ultrashort vortices such as spatial, group velocity, and topological charge dispersions, the OAM-temporal coupling effect is unavoidable and, therefore, has an impact on applications such as OAM-based optical communications, or on the generation of vortex-carrying attosecond pulses.

Upper Bound to the Orbital Angular Momentum Carried by an Ultrashort Pulse.

Photons in a ring-shaped vortex light beam can have an arbitrarily high orbital angular momentum (OAM) lℏ, in addition to the spin angular momentum ±â„. For a pulsed vortex beam, there is, however, an upper bound to the integer units l of OAM, or topological charge of the vortex, and a lower bound to the pulse duration to carry OAM. These limits have implications in experiments with ultrashort vortices, e.g., in the generation of twisted attosecond bursts in the extreme ultraviolet, in the temporal resolution in ultrafast spectroscopy, or in the performance of OAM-based optical communications or cryptographic systems, as well as in other areas of physics as acoustics or electron waves.

Self-trapped pulsed beams with finite power in Kerr media excited by time-diffracting, space-time beams.

We study the nonlinear propagation of space-time pulsed beams, also known as time-diffracting beams, a recently introduced class of diffraction-free spatiotemporal wave packets whose temporal-transversal structure is that of diffraction in time. We report on the spontaneous formation of propagation-invariant, spatiotemporally compressed pulsed beams carrying finite power from exciting time-diffracting Gaussian beams in media with cubic Kerr nonlinearity at powers below the critical power for collapse, and also with other collapse-arresting nonlinearities above the critical power. Their attraction property makes the experimental observation of the self-trapped pulsed beams in cubic Kerr media feasible. The structure in the temporal and transversal dimensions of the self-trapped wave packets is shown to be the same as the structure in the axial and transversal dimensions of the self-focusing and (arrested) collapse of monochromatic Gaussian beams.

Gaussian beams diffracting in time.

We show how to transform the mathematical expression of any monochromatic paraxial light beam into the expression of a pulsed beam whose diffraction is switched from the axial direction to its temporal structure. We exemplify this transformation with time-diffracting Gaussian beams. The conditions for the obtained diffraction-free wave to be physically meaningful are discussed.

Lorenz curve of a light beam: evaluating beam quality from a majorization perspective.

We introduce a novel approach for the characterization of the quality of a laser beam that is not based on particular criteria for beam width definition. The Lorenz curve of a light beam is a sophisticated version of the so-called power-in-the-bucket curve, formed by the partial sums of discretized joint intensity distribution in the near and far fields, sorted in decreasing order. According to majorization theory, a higher Lorenz curve implies that all measures of spreading in phase space, and, in particular, all Rényi (and Shannon) entropy-based measures of the beam width products in near and far fields, are unanimously smaller, providing a strong assessment of a better beam quality. Two beams whose Lorenz curves intersect can be considered of relatively better or lower quality only according to specific criteria, which can be inferred from the plot of the respective Lorenz curves.

Quasi-ideal dynamics of vortex solitons embedded in flattop nonlinear Bessel beams.

The applications of vortex solitons are severely limited by the diffraction and self-defocusing spreading of the background beam where they are nested. Nonlinear Bessel beams in self-defocusing media are nondiffracting, flattop beams where the nested vortex solitons can survive for propagation distances that are one order of magnitude larger than in the Gaussian or super-Gaussian beams. The dynamics of the vortex solitons is studied numerically and found to approach that in the ideal, uniform background, preventing vortex spiraling and decay, which eases vortex steering for applications.

Optical rotation of a uniformly, linearly polarized Bessel-like beam in free space.

We report on the observation of a light beam in air whose polarization state is uniform and linear at the transverse region where the intensity is high and rotates uniformly with propagation distance. The beam is obtained by interference of two circularly polarized Bessel beams of opposite helicities and very similar, but not equal, cone angles. The measured rotation rate is in agreement with that expected from theory.

Majorization applied to diffraction.

We apply the statistical tools of majorization to characterize and compare the amount of diffraction caused by different apertures, where variance cannot be applied.

On the dynamics of Airy beams in nonlinear media with nonlinear losses.

We investigate on the nonlinear dynamics of Airy beams in a regime where nonlinear losses due to multi-photon absorption are significant. We identify the nonlinear Airy beam (NAB) that preserves the amplitude of the inward Hänkel component as an attractor of the dynamics. This attractor governs also the dynamics of finite-power (apodized) Airy beams, irrespective of the location of the entrance plane in the medium with respect to the Airy waist plane. A soft (linear) input long before the waist, however, strongly speeds up NAB formation and its persistence as a quasi-stationary beam in comparison to an abrupt input at the Airy waist plane, and promotes the formation of a new type of highly dissipative, fully nonlinear Airy beam not described so far.

Carrier-envelope phase changes in the focal region: propagation effects measured by spectral interferometry.

Spectral interferometric measurements are presented that show how wave propagation affects the carrier-envelope phase (CEP) of an ultrashort pulse in the focal region and results in variations that are different from the Gouy phase shift. Wavelength-dependent properties of the input beam are investigated and are seen to influence how the CEP is altered. The measured CEP changes show characteristics similar to the variations predicted by theory.

Rotation of the polarization direction and reversal of helicity of ultrashort pulsed beams propagating in free space.

We unveil the origin of the recently revealed polarization-state changes of polarization-shaped few-cycle pulses induced by free-space beam propagation. Simple rules are formulated to show how the orientation and ellipticity of the instantaneous polarization ellipse of the source and propagated pulses relate to each other. We demonstrate our findings with examples that clearly display the relationships found and highlight their relevance. We show, for example, that pulses often used in high-harmonic generation or attosecond pulse production rotate as a whole during free-space beam propagation or upon focusing. A pulse that may reverse its ellipticity from right-handed to left-handed during propagation is also introduced. It is shown that these effects are independent of the beam size and/or focal length. We also present how these instantaneous polarization-state changes could be noticed in classical measurements of light polarization using polarizers, phase retarders, and time-integrating detectors.

A hybrid solitary-conical self-guided light beam in self-focusing media.

In addition to subluminal solitons and superluminal conical beams, self-focusing media also support a luminal nonspreading beam with hybrid solitary-conical properties. Its existence reveals that spatial solitons may also have a conical structure, and vice versa.

Diagnóstico y manejo de la neurocisticercosis en el Perú / Neurocysticercosis diagnosis and management in Peru

La neurocisticercosis (NCC) es la parasitosis humana mßs frecuente del sistema nervioso central y es causada por las larvas del céstodo Taenia solium. La NCC es endémica en prßcticamente todos los paises en vías de desarrollo. En general se presenta como formas intraparenquimales asociadas con convulsiones o formas extraparenquimales asociadas con hipertensión endocraneana. La sospecha clínica y epidemiológica es importante pero el diagnóstico se realiza primariamente por imßgenes y se confirma con serología. La tomografía axial computarizada y la resonancia magnética son las pruebas imagenológicas usadas. Como prueba confirmatoria se usa el diagnóstico inmunológico a través de western blot, que actualmente se pude realizar en el Instituto Nacional de Ciencias Neurológicas tanto en suero como en líquido cefalorraquídeo. El tratamiento involucra medidas sintomßticas (control de convulsiones o hipertensión endocraneana según sea el caso) y tratamiento antiparasitario (albendazol o praziquantel). El tratamiento antiparasitario debe hacerse bajo condiciones de hospitalización y en hospitales de tercer nivel.(AU)

Neurocysticercosis (NCC) is the most common parasitic disease of the central nervous system and is caused by larvae of the tapeworn Taenia solium. NCC is endemic in almost all developing countries. It presents as intraparenchymal forms associated with seizures or as extraparenchymal forms associated with intracranial hypertension. The clinical and epidemiological suspicion are important but the diagnosis is made primarily by images and confirmed by serology. Computed tomography (CT) and magnetic resonance imaging tests are used. Inmunodiagnosis by Western Blot, which is currently perform in the Instituto Nacional de Ciencias Neurológicas in serum and cerebrospinal fluid serves as confirmatory test. Treatment involves symptomatic measures (control of seizures or intracranial hypertension) and anticysticercal medications (albendazole and praziquantel). Anticysticercal treatment should be used under hospital conditions because of secondary effects.(AU)

Diagnóstico y manejo de la neurocisticercosis en el Perú / Neurocysticercosis diagnosis and management in Peru

La neurocisticercosis (NCC) es la parasitosis humana más frecuente del sistema nervioso central y es causada por las larvas del céstodo Taenia solium. La NCC es endémica en prácticamente todos los paises en vías de desarrollo. En general se presenta como formas intraparenquimales asociadas con convulsiones o formas extraparenquimales asociadas con hipertensión endocraneana. La sospecha clínica y epidemiológica es importante pero el diagnóstico se realiza primariamente por imágenes y se confirma con serología. La tomografía axial computarizada y la resonancia magnética son las pruebas imagenológicas usadas. Como prueba confirmatoria se usa el diagnóstico inmunológico a través de western blot, que actualmente se pude realizar en el Instituto Nacional de Ciencias Neurológicas tanto en suero como en líquido cefalorraquídeo. El tratamiento involucra medidas sintomáticas (control de convulsiones o hipertensión endocraneana según sea el caso) y tratamiento antiparasitario (albendazol o praziquantel). El tratamiento antiparasitario debe hacerse bajo condiciones de hospitalización y en hospitales de tercer nivel.

Neurocysticercosis (NCC) is the most common parasitic disease of the central nervous system and is caused by larvae of the tapeworn Taenia solium. NCC is endemic in almost all developing countries. It presents as intraparenchymal forms associated with seizures or as extraparenchymal forms associated with intracranial hypertension. The clinical and epidemiological suspicion are important but the diagnosis is made primarily by images and confirmed by serology. Computed tomography (CT) and magnetic resonance imaging tests are used. Inmunodiagnosis by Western Blot, which is currently perform in the Instituto Nacional de Ciencias Neurológicas in serum and cerebrospinal fluid serves as confirmatory test. Treatment involves symptomatic measures (control of seizures or intracranial hypertension) and anticysticercal medications (albendazole and praziquantel). Anticysticercal treatment should be used under hospital conditions because of secondary effects.

A dissipative attractor in the spatiotemporal collapse of ultrashort light pulses.

Spatiotemporal self-focusing in nonlinear lossy media pushes ultrashort pulses towards a universal, non-solitary and non-conical light bullet wave state defined by the medium solely, and characterized by maximum energy losses. Its stationary propagation relies on a balance between nonlinear losses and the refuelling effect of self-focusing. No balancing gain is required for stationarity. These purely lossy dissipative light-bullets can explain many aspects of the filamentary dynamics in nonlinear media with anomalous dispersion.

[Neurocysticercosis diagnosis and management in Peru]. / Diagnóstico y manejo de la neurocisticercosis en el Perú.

Neurocysticercosis (NCC) is the most common parasitic disease of the central nervous system and is caused by larvae of the tapeworm Taenia solium. NCC is endemic in almost all developing countries. It presents as intraparenchymal forms associated with seizures or as extraparenchymal forms associated with intracranial hypertension. The clinical and epidemiological suspicion are important but the diagnosis is made primarily by images and confirmed by serology. Computed tomography (CT) and magnetic resonance imaging tests are used. Immunodiagnosis by Western Blot, which is currently perform in the Instituto Nacional de Ciencias Neurológicas in serum and cerebrospinal fluid serves as confirmatory test. Treatment involves symptomatic measures (control of seizures or intracranial hypertension) and anticysticercal medications (albendazole and praziquantel). Anticysticercal treatment should be used under hospital conditions because of secondary effects.

Freezing the carrier-envelope phase of few-cycle light pulses about a focus.

We study the effects of dispersive media and structures on the carrier-envelope phase (CEP) shift of focused few-cycles pulses. For phase-sensitive interactions with matter requiring focusing in vacuum, the variation of the CEP through the focal region can be significantly slow down by inserting a dispersive slab of adequate thickness between the focusing system and the focus. The focal CEP shift can also be slow down in experiments requiring focusing in a dispersive medium by a suitable choice of the dispersive propagation distance up to the focus.