Wavefront Rotation Research Articles

Self-referenced characterization of space-time couplings in near-single-cycle laser pulses.

We report on the characterization of space-time couplings in high-energy sub-2-cycle 770 nm laser pulses using a self-referencing single-frame method. Using spatially encoded arrangement filter-based spectral phase interferometry for direct electric field reconstruction, we characterize few-cycle pulses with a wavefront rotation of 2.8×1011 rev/s (1.38 mrad per half-cycle) and pulses with pulse front tilts ranging from -0.33 fs/μm to -3.03 fs/μm in the focus.

Diffraction pattern by nanometric thin films under illumination of an orbital angular momentum beam with integer topological charge

The orbital angular momentum of light has a big contribution in many engineering applications like optical communications, because this physical property allows eigenstates characteristic of the wavefront rotation when the beam is propagated. The nature of these eigenstates allows that information can be encoded and gives immunity to electromagnetic interference, allowing an increase of bandwidth, cadence and capacity of the communication channel. This work shown the methodology using nanometric thin films like Titanium based (TiO2) grown over strontium titanate (SrTiO3) support, to distinguish and discriminate a well- defined integer value of the topological charge of an OAM beam.

Controlling attosecond angular streaking with second harmonic radiation.

High harmonic generation, which produces a coherent burst of radiation every half cycle of the driving field, has been combined with ultrafast wavefront rotation to create a series of spatially separated attosecond pulses, called the attosecond lighthouse. By adding a coherent second harmonic beam with polarization parallel to the fundamental, we decrease the generating frequency from twice per optical cycle to once. The increased temporal separation increases the pulse contrast. By scanning the carrier envelope phase, we see that the signal is 2π periodic.

Quasi-ray description of intermode interference of the radiation of optical vortices in short fiber lightguides

This paper presents a quasi-ray physical model that takes into account the curvature of the reflecting surface of the core when a ray propagates in a fiber lightguide. It is shown to be possible to use such an approach to estimate the intensity distribution of radiation coming out of a short lightguide. The effect in which spiral distributions appear is explained. It is experimentally confirmed that oblique rays in fibers predominantly create optical vortices with a single direction of wave-front rotation.

The general theory of first-order spatio-temporal distortions of Gaussian pulses and beams

We present a rigorous, but mathematically relatively simple and elegant, theory of first-order spatio-temporal distortions, that is, couplings between spatial (or spatial-frequency) and temporal (or frequency) coordinates, of Gaussian pulses and beams. These distortions include pulse-front tilt, spatial dispersion, angular dispersion, and a less well-known distortion that has been called "time vs. angle." We write pulses in four possible domains, xt, xomega, komega, and kt; and we identify the first-order couplings (distortions) in each domain. In addition to the above four "amplitude" couplings, we identify four new spatio-temporal "phase" couplings: "wave-front rotation," "wave-front-tilt dispersion," "angular temporal chirp," and "angular frequency chirp." While there are eight such couplings in all, only two independent couplings exist and are fundamental in each domain, and we derive simple expressions for each distortion in terms of the others. In addition, because the dimensions and magnitudes of these distortions are unintuitive, we provide normalized, dimensionless definitions for them, which range from -1 to 1. Finally, we discuss the definitions of such quantities as pulse length, bandwidth, angular divergence, and spot size in the presence of spatio-temporal distortions. We show that two separate definitions are required in each case, specifically, "local" and "global" quantities, which can differ significantly in the presence of spatio-temporal distortions.

Specific features of partially coherent holography of dynamic objects

A method for recording partially coherent holographic interferograms is proposed, which makes it possible to control the sensitivity to the object point displacement by instrumental means. In this case, a decrease in sensitivity is accompanied by a decrease in the depth of the reconstructed image, which simplifies automated inputting of the resulting interferogram into a computer for further processing. The calculations showed that the partially coherent holograms using transverse scale transformation in one of the arms of a recording interferometer with a scale factor different from −1 possess the interferometric sensitivity, whereas the partially coherent holograms with the wave-front rotation in one of the arms of a recording interferometer lack the interferometric sensitivity to the displacement of object points during recording. The latter feature allows us to record objects whose displacement considerably exceeds the wavelength of recording radiation.

Spread of excitation in a myocardial volume: simulation studies in a model of anisotropic ventricular muscle activated by point stimulation.

The purpose of this study was to present simulations of excitation wavefronts spreading through a parallelepipedal slab of ventricular tissue measuring 6.5 x 6.5 x 1.0 cm. The slab incorporates the anisotropic properties of the myocardium including the transmural counterclockwise fiber rotation from epicardium to endocardium. Simulations were based on an eikonal model that determines excitation times throughout the ventricular wall, which is represented as an anisotropic bidomain. Excitation was initiated by delivering ectopic stimuli at various intramural depths. We also investigated the effect of a simplified Purkinje network on excitation patterns. Excitation wavefronts in the plane of pacing, parallel to epicardial-endocardial surfaces, were oblong with the major axis approximately oriented along the local fiber direction, with bulges and deformations due to attraction from rotating fibers in adjacent planes. The oblong intersections of the wavefront with planes at increasing distance from pacing plane rotated clockwise or counterclockwise, depending on pacing depth, but wavefront rotation was always less than fiber rotation in the same plane. For all pacing depths, excitation returned toward the plane of pacing. Return occurred in multiple, varying sectors of the slab depending on pacing depth, and was observed as close as 6 mm to the pacing site. Curvature of wavefronts and collision with boundaries of slab markedly affected local velocities. Shape and separation of epicardial isochrones and spatial distribution of epicardial velocities varied as a function of site and depth of pacing. When the Purkinje network was added to the model, epicardial velocities revealed the subendocardial location of the Purkinje-myocardial junctions. Considerable insight into intramural events could be obtained from epicardial isochrones. If validated experimentally, results may be applicable to epicardial isochrones recorded at surgery.

Optical radiation filtration with nondegenerate four-photon interaction

The effects of frequency shift between incident and reflected waves, conversion efficiency, and positive feedback coefficient on quality of wave-front rotation are studied for nondegenerate four-photon interaction.