Dark Beam Research Articles

Power and efficiency enhancement of THz radiation in a plasma by dark hollow laser beams: Effects of magnetic field

The power and efficiency of terahertz radiation (THz) in a rippled density plasma by dark hollow laser beams are very small due to the collisional effect. We show that when a magnetic field is applied perpendicularly to the plasma, the THz radiation power and efficiency significantly enhance. Also, the magnetic field changes the THz radiation profile to a profile similar to a dark hollow laser beam. The mutual effect between the laser beams and THz radiation in plasma, which is important in high energy transfer between laser beams and THz radiation, is taken into account. We find that the maximum efficiency obtained in our scheme is more than four orders of magnitude greater than the efficiency in the absence of magnetic field.

Generating electromagnetic dark and antidark partially coherent sources

We present two methods to generate an electromagnetic dark and antidark partially coherent source. The first generalizes a recently published scalar approach by representing the stochastic electric field vector components as sums of randomly weighted, randomly tilted plane waves. The second method expands the field’s vector components in series of randomly weighted dark and antidark coherent modes. The statistical moments of the random weights—plane waves in the former method, coherent modes in the latter—are found by comparing the resulting means and covariances to those of the desired electromagnetic dark and antidark source. We validate both methods by simulating the generation of an electromagnetic dark or antidark source and comparing the simulated results to the corresponding theoretical predictions. We find that both methods converge to the theoretical, ensemble-averaged (long-time-averaged) statistics within roughly 500 random field instances. The methods presented in this paper will find use in applications that utilize dark and antidark beams, e.g. atomic optics and optical trapping.

Enhanced second harmonic generation of dark hollow Gaussian laser beam in collisionless magneto-plasma

This paper presents an analysis and subsequent discussion of self-focusing and second harmonic generation (SHG) of a dark hollow Gaussian (dhG) laser beam in a magneto plasma, considering ponderomotive non-linearity. As a result of collisionless non-linearity, non-uniform distribution of plasma electrons takes place due to non-uniform irradiance of intensity along the wavefront of the laser beam which leads to the self-focusing of laser beam and production of density gradient in the transverse direction. As a result of density gradient, an electron plasma wave is excited at pump frequency that interacts with the pump beam to produce its second harmonics of frequency twice that of latter. To envision the spot size and dynamics of propagation of dhG laser beam, moment theory in Webtzel-Kramers-Brillouin (WKB) approximation has been used. The nature of self-focusing and second harmonic yield (SHY) is highlighted through critical curves as a plot of dimensionless beam width parameter and power of second harmonic radiation versus the dimensionless distance of propagation. The effect of magnetic field on self-focusing and SHY of various orders of dhG laser beam has also been explored.

Bidirectional dark-soliton fiber lasers for high-sensitivity gyroscopic application.

Bidirectional mode-locked lasers are very useful in laser sensing and optical communications. Here we report a bidirectional domain wall soliton (DWS) fiber laser with an anomalous dispersion cavity. Two mode-locked dark pulse trains propagating in the opposite directions have been generated. Moreover, the specific application as a gyroscopic effect has been demonstrated by mounting this DWS laser on a rotating platform. The beat frequency of the two dark pulse DWS beams is measured as a linear function of the rotation velocity. The rotation sensitivity reaches 3.31kHz/(deg/s), which are comparable with the one in a bright pulse laser gyroscope. Without the limit of using tunable delay lines, the DWS laser gyroscope has the advantages of simple structure, high sensitivity, and low cost, while possessing the entire superiority of a mode-locked laser gyroscope. It is more promising for the applications in modern inertia navigation systems.

Propagation characteristics of dark and antidark Gaussian beams in turbulent atmosphere

In this work, we investigated theoretically the propagation characteristics of dark and antidark Gaussian beams (DADGBs) in turbulent atmosphere. Based on the Huygens–Fresnel diffraction integral and by mean of the expansion form of a hard aperture function into a finite sum of Gaussian functions we derived analytically the on-axis intensity distribution of an apertured DADGB propagating in turbulent atmosphere. The dependence of the axial intensity distribution on the turbulent strength and on the parameters of the beam is illustrated with numerical examples. The results show that the axial intensity decreases rapidly when the turbulent strength parameter is large, and the propagation distance is shorter for large wavelengths and for small beam waist width.

Generating dark and antidark beams using the genuine cross-spectral density function criterion.

In this work, we demonstrate how to generate dark and antidark beams-diffraction-free partially coherent sources-using the genuine cross-spectral density function criterion. These beams have been realized in prior work using the source's coherent-mode representation and by transforming a J0-Bessel correlated partially coherent source using a wavefront-folding interferometer. We generalize the traditional dark and antidark beams to produce higher-order sources, which have not been realized. We simulate the generation of these beams and compare the results to the corresponding theoretical predictions. The simulated results are found to be in excellent agreement with theory, thus validating our analysis. We discuss the pros and cons of our synthesis approach vis-à-vis the prior coherent modes work. Lastly, we conclude this paper with a brief summary, and a discussion of how to physically realize these beams and potential applications.

Experimental realization of dark and antidark diffraction-free beams.

We report the first, to the best of our knowledge, experimental realization of high-quality dark and antidark diffraction-free beams, first theoretically proposed by Ponomarenko etal. [Opt. Lett.32, 2508 (2007)OPLEDP0146-959210.1364/OL.32.002508]. Our method employs a single spatial light modulator (SLM) and is based on superposing mutually uncorrelated but spatially coherent in the time domain Bessel modes with modal weights proportional to the SLM display times of the corresponding modes. We also experimentally verify diffraction-free properties of the generated beams upon their free space propagation.

Effect of Complex Phase Plate on Tight Focusing of Azimuthally Polarized Dark and Anti-Dark Gaussian Beam

Effect of Complex Phase Plate on Tight Focusing of Azimuthally Polarized Dark and Anti-Dark Gaussian Beam

Terahertz radiation for medical application

Terahertz (THz) radiations focused at multiple positions are quite useful for their medical application. For this, we propose to employ beating of dark hollow Gaussian laser beams (DHGBs) of different beam orders in plasma. In view of realistic situations, we also include the collisions between the electrons and the neutrals. Because of a special intensity gradient distribution in DHGBs, the emitted THz radiation is found to have a unique field profile with multiple focii. The dependence of plasma density, order of the beams and collision frequency on the THz field amplitude is discussed. The important feature to consider hollow Gaussian laser beams is having the same power at different beam orders. It is found that the amplitude of the emitted radiation is highly sensitive to the beam order of the incident lasers. An optimization of the plasma parameters and the lasers characteristics can lead to the enhancement in the THz intensity and the efficiency of the mechanism.

Control of peaks of terahertz radiation and tuning of its frequency and intensity

We propose to employ dark hollow laser beams (DHBs) for obtaining multifocal terahertz (THz) radiations which are quite useful in medical applications. The number of peaks in the THz field can be suppressed if we apply external magnetic field and use intense lasers so that the relativistic effects are prominent. It means we can achieve strong bifocal THz radiation with this scheme. However, multifocal THz radiation can be reconstituted by increasing the beating frequency of the lasers. The separation of the peaks can be controlled by wisely choosing the orders of the lasers, and also by varying the strength of the magnetic field. The magnetic field is found to enhance the THz field, and also it tunes the frequency of the THz field. The DHBs of higher and equal orders are found to be most significant for efficient THz radiation generation with respect to the role of the magnetic field and density ripples.

Gyrator transform of phase-flipped Gaussian beams and conversion of an edge-dislocation into a vortex

Based on the Gyrator transform (GT) formula, the closed-form field expression of a phase-flipped Gaussian beam (PFGB) passing through a GT system is presented. It is proved that PFGBs with edge dislocation can be converted into dark hollow vortex error-Gaussian beams with topological charge 1 through GT optical systems. With the help of numerical method, the influences of Fresnel number FN and GT transform angle α on intensity and phase distributions of the vortex beam are investigated. Moreover, the optimum relation between Fresnel number FN and the corresponding transform angle α for realizing a perfect dark hollow pattern is obtained.

The European Bauman

The European Bauman

Conical diffraction of Dark and Antidark beams modulated by a Gaussian profile in biaxial crystals

In this paper, we study the evolution of internal conical diffraction with a new type of laser beams family by concerning Dark and Antidark beams modulated by a Gaussian profile propagating along an optic axis of a biaxial crystal. Analytical expressions giving the outgoing conical diffraction components of the considered beams behind the crystal are derived in detail. With the help of numerical simulation, the present study shows the conical diffraction beam evolution in a biaxial crystal. Our results indicate to illustrate the effects of some parameters on propagation properties of produced beams, including the incident beam parameter α, the ratio between the conical refraction radius R0 and the waist radius of the input beam ω, and the propagation distance. The intensity pattern of circularly polarized Gaussian beam transformed by the effect of conical diffraction in a biaxial crystal is also discussed in this investigation as a particular case.

Poynting theorem in terms of beam shape coefficients and applications to axisymmetric, dark and non-dark, vortex and non-vortex, beams

Electromagnetic arbitrary shaped beams may be described by using expansions over a set of basis functions, with expansion coefficients containing sub-coefficients called beam shape coefficients which encode the structure of the beam. In this paper, the Poynting theorem is expressed in terms of these beam shape coefficients. Special cases (axisymmetric, dark and non-dark beams) are thereafter considered, as well as specific applications to paradigmatic examples, from trivial cases (plane waves and spherical waves) to the more sophisticated case of vortex beams.

Appearance of fractional vortex dipoles by using spiral linear zone plate

We present a novel technique based on linear zone plate (LZP) by which linear singularities regarded as fractional vortex dipoles are efficiently generated. Our approach requires applying spiral phase to a LZP, so fractional vortex dipoles are then acquired. By also implementing transverse phase shift to the spiral LZP, we are able to equally divide the number of the produced dark beams carrying mixed phase dislocations into two transverse separate parts. As a result, by varying a so called the controlling parameter the lateral positions of the focused fractional vortex dipoles are changed. Since we are able to generate dark beams in different and specific linear positions, therefore we suggest these features will be of great interest in one-dimensional optical trapping. All results are completely verified by experimental works.

Dark matter beams at LBNF

High-intensity neutrino beam facilities may produce a beam of light dark matter when protons strike the target. Searches for such a dark matter beam using its scattering in a nearby detector must overcome the large neutrino background. We characterize the spatial and energy distributions of the dark matter and neutrino beams, focusing on their differences to enhance the sensitivity to dark matter. We find that a dark matter beam produced by a $Z'$ boson in the GeV mass range is both broader and more energetic than the neutrino beam. The reach for dark matter is maximized for a detector sensitive to hard neutral-current scatterings, placed at a sizable angle off the neutrino beam axis. In the case of the Long-Baseline Neutrino Facility (LBNF), a detector placed at roughly 6 degrees off axis and at a distance of about 200 m from the target would be sensitive to $Z'$ couplings as low as 0.05. This search can proceed symbiotically with neutrino measurements. We also show that the MiniBooNE and MicroBooNE detectors, which are on Fermilab's Booster beamline, happen to be at an optimal angle from the NuMI beam and could perform searches with existing data. This illustrates potential synergies between LBNF and the short-baseline neutrino program if the detectors are positioned appropriately.

Alignment sensing and control for squeezed vacuum states of light.

Beam alignment is an important practical aspect of the application of squeezed states of light. Misalignments in the detection of squeezed light result in a reduction of the observable squeezing level. In the case of squeezed vacuum fields that contain only very few photons, special measures must be taken in order to sense and control the alignment of the essentially dark beam. The GEO 600 gravitational wave detector employs a squeezed vacuum source to improve its detection sensitivity beyond the limits set by classical quantum shot noise. Here, we present our design and implementation of an alignment sensing and control scheme that ensures continuous optimal alignment of the squeezed vacuum field at GEO 600 on long time scales in the presence of free-swinging optics. This first demonstration of a squeezed light automatic alignment system will be of particular interest for future long-term applications of squeezed vacuum states of light.

Generation of terahertz radiation in collisional plasma by beating of two dark hollow laser beams

AbstractThis paper presents a scheme of terahertz radiation generation based on beating of two dark hollow laser beams with different frequencies, the same electric field amplitudes, in actual plasma with spatially periodic density that electron–neutral collisions have taken into account. The main feature of considered hollow laser beams is, having the same power at different beam orders. Because of special distribution in beam intensity gradient in dark hollow laser beam, the produced terahertz radiation has special field profile. The effects of laser and plasma parameters on terahertz radiation generation are investigated analytically. It can be deduced that by increasing beating frequency, efficiency of terahertz generation decreases which can be compensated by manipulating density ripple magnitudes and dark-size adjusting parameter. The intensity of the emitted radiations is found to be highly sensitive to the beam order. Based on the results of this paper, optimization of laser and plasma parameters can increase the efficiency of terahertz radiation generation strongly.

Optical Amplification of Tweezers and Bright Soliton Using an Interferometer Ring Resonator System

System of optical soliton amplification which consists of an add/drop multiplexer system is presented. Optical dark and bright soliton pulses can be amplified significantly. Dark soliton and Gaussian laser beam are input into the configured system and travel within the waveguide. Continuous soliton pulse will be sliced into smaller pulses by the nonlinear effect known as chaos, thus large bandwidth of optical signals can be obtained. Amplification occurs when the soliton propagates along the add/drop multiplexer system. Amplified optical tweezers signals with power of 487 W and FWHM of 6.8 nm are simulated. The amplified bright soliton could be obtained with maximum power of 360 W and FWHM of 1.5 nm. Therefore amplification of soliton pulses can be used to perform the long distance optical communication.

GeV-scale dark matter: production at the Main Injector

Assuming that dark matter particles interact with quarks via a GeV-scale mediator, we study dark matter production in fixed target collisions. The ensuing signal in a neutrino near detector consists of neutral-current events with an energy distribution peaked at higher values than the neutrino background. We find that for a $Z'$ boson of mass around a few GeV that decays to dark matter particles, the dark matter beam produced by the Main Injector at Fermilab allows the exploration of a range of values for the gauge coupling that currently satisfy all experimental constraints. The NO$\nu$A detector is well positioned for probing the presence of a dark matter beam, while future LBNF near-detectors would provide more sensitive probes.