Dark Hollow Research Articles

Generalized dark hollow sine-Gaussian beam and its propagation properties

A model of the generalized dark hollow sine-Gaussian beam (GDHsGB) is proposed to uniformly describe both conventional dark hollow beams (DHBs) and anomalous dark hollow beams (ADHBs) with circular or elliptic geometrical patterns. Using the Collins formula, we derive the analytical expression for GDHsGBs propagating in ABCD paraxial optical systems. We analyze the evolution of the intensity pattern and beam width of circular ADHBs, as well as the ellipticity of elliptic ADHBs, providing mathematical expressions for these physical quantities. The results reveal various evolution forms based on beam parameters, with elliptic ADHBs exhibiting more intricate propagation behavior compared to circular ADHBs. By controlling parameters, the intensity pattern of elliptic ADHBs undergoes a transformation into a petal-like distribution in the near field, later reverting to its original elliptic configuration but rotated 90° from its initial orientation on the source plane in the far field.

Beating of dark hollow laser beams in magnetized plasma under the influence of D.C. electric field to generate THz radiation

Beating of dark hollow laser beams in magnetized plasma under the influence of D.C. electric field to generate THz radiation

Paraxial propagation characteristics of a controllable anomalous hollow vortex beam in free space

Propagation of a recently proposed controllable anomalous hollow vortex (CAHV) beam is investigated. Based on the integral formula of generalized Huygens–Fresnel diffraction, analytical expression for the CAHV beam through a paraxial ABCD optical system is derived. The factors that affect the intensity pattern are determined by the beam’s controllable parameters a, c x, c y, and the topological charge m. Results show that the Gaussian distribution features are controlled by parameter a, and the horizontal and vertical stretching deformations of the beam are adjusted by parameters c x and c y, respectively. For a controllable anomalous hollow (CAH) beam, when propagating in free space, it could initially maintain anomalous hollow property and the size of the spot increases with the increase of the propagation distance. Due to the CAHV beam carries the optical vortex, a dark hollow channel appears in the center of the beam during propagation, and the channel structure changes with the increase of topological charge. Additionally, the Poynting vector of CAHV beam proves the direction of energy flow corresponding to the intensity distribution. Results obtained in this paper could have potential applications in particle trapping and optical control.

Far IR field generation by mixing of cosh-Gaussian and dark hollow Gaussian laser in encapsulated plasma

A scheme of laser-plasma interaction is proposed by mixing of Cosh Gaussian (ChG) and Dark Hollow Gaussian (DHG) laser in rippled density plasma when an external periodic electric field wiggler is applied because of the emission of far infrared field lying in the terahertz frequency regime. The unusual mixing of ChG and DHG laser broadens the field of THz radiation from unifocal to multifocal by controlling beam order and decentralized parameters. Moreover, the wiggler field wavenumber provides two additional resonance conditions, which govern the emission of multiple components of far IR field resonantly that may have extensive medical applications. The field amplitude of such emissions and their efficiency may be increased manifold. Moreover, the efficiency can be increased several times if parallel plates are placed with a few nanometers of separation.

Electron acceleration influenced by sinh-Gaussian laser pulses in a prepared ion channel

The acceleration of electron in a produced ion channel is studied theoretically using a sinh-Gaussian (shG) laser pulse with radial polarization. Compared to Gaussian laser pulses, shG laser pulses propagate differently, presenting as a bright ring encircling a dark hollow core that inhibits early focusing and promotes self-defocusing. They can therefore be used to accelerate electrons to extremely high energies. The electron energy gain is influenced by the laser pulse decentred parameter linked to the shG function, however, the ion stream’s electric field prevents the transverse oscillations from pushing electrons out of the interaction zone. With a decentred parameter of ∼2.15 and a laser pulse intensity value of ∼1020 Wcm −2 incident on density of ∼ 1022 m −3, where the incident pulse phase is ψ 0 = 0, the combined effect of ion channelling and radially polarized (RP) shG laser pulses leads to a significant enhancement of electron energy gain within the ion density channel to the GeV level.

Stabilization of hollow Gaussian beams in nonlinear metamaterial waveguides

Hollow Gaussian beams which possess the dark hollow spatial intensity distribution were found to have interesting applications in trapping nano-sized particles and free-space optical communication. Many applications demand stable dynamics of higher dimensional beams. Here we theoretically study the dynamics of hollow Gaussian beams in cubic and quintic nonlinear negative index metamaterial. We adopt Lagrangian variational analysis and explore the parametric regions characterizing the metamaterial in which the hollow Gaussian beam can execute stable dynamics as well as it can undergo filamentation due to intrinsic collapse. We confirm the analytical results obtained through variational analysis by direct numerical analysis based Crank Nicolson method implemented in Python programming.

Self-focusing of dark hollow Gaussian laser beams in cubic–quintic nonlinear media

Self-focusing of dark hollow Gaussian laser beams in cubic–quintic nonlinear media

Spatially nonuniformly correlated vortex beams and their arrays

We introduce a class of partially coherent sources with spatially nonuniformly correlation properties and an off-axis helicoidal phase. It is shown that the unique correlation and phase properties of such sources lead to radiated fields with extraordinary propagation characteristics, such as dark hollow with zero central intensity, self-focusing and lateral self-shifting light intensity. Based on such novel random sources, two types of nonuniformly correlated vortex beam arrays with radial and rectangular symmetry are explored. Analytical and numerical investigations for the evolutions of such light fields are made by the model decomposition representation of correlation function and fast Fourier transform method. The results demonstrate new opportunities for modeling off-axis self-focusing vortex beams and other beam shaping applications by joint modulation of coherence and phase.

Design of a negative curvature hollow-core fiber for transmitting a single-mode dark hollow beam

We propose a nested negative curvature hollow-core fiber that can stably transmit a single-mode (LP11 mode) dark hollow beam with low loss. A pair of resonant tubes is nested inside the cladding tubes in the horizontal direction to enhance the confinement loss of the fundamental mode LP01. Two pairs of glass sheets at different positions within the four cladding tubes in the non-horizontal direction are introduced to suppress the comparatively low loss higher-order modes LP21 and LP02. The numerical simulation results indicate that the loss ratio between the fundamental mode and LP11 mode can reach 28703 when the transmission wavelength is 1.54 µm, and the LP11 mode has the lowest confinement loss of 0.0049 dB/m. Meanwhile, the loss ratios of higher-order modes such as LP21, LP02, and LP31 with the target LP11 mode are above 100. The effective bandwidth of single-mode dark hollow beam transmission can reach 5 nm. This provides an optical fiber solution for single-mode dark hollow beam transmission, which has potential applications in atomic optics, quantum information, and nonlinear optics.

Flexible tailoring of multifocal spot arrays of partially coherent radially polarized beam with periodical spatial coherence

In this work, a new kind of partially coherent vector beam, namely, partially coherent radially polarized multi-Gaussian Schell-model array (PCRP MGSMA) beam, is introduced and the focusing properties of such beam passing through a thin lens are characterized. One of the most remarkable features of such beam is its capability of producing tunable multifocal spot arrays in the focal plane, and each array lobe can be shaped into dark hollow, Gaussian-like and flat-topped profile by modulating the initial spatial coherence width More interesting, the modulation effect of multiple off-axis vortices can also be acted on each array lobe, thus the creation of triangle-like, square-like and pentagon-like hollow structure arrays can be realized for the high coherence case, but this remarkable characteristic will be vanished in the case of a very low coherence. In addition to the focal spot arrays tailoring, the focal intensity distribution of such beam can be flexibly shaped into diversified flat-topped profiles, such as linear, square and rectangular, by elaborately choosing the matching parameters of the source. These interesting results will be useful for optical multi-particle manipulation, high resolution imaging and material surface processing.

Creation of optical chains with prescribed characteristics

We report a non-iterative method to create an arbitrarily spatially-orientated optical chain with prescribed characteristics through the use of antenna radiation theory and time reversal methodology. A pair of antennas consisting of an electric current line source (ELS) and a magnetic current line source (MLS) are employed to yield the required incident field pattern for focusing system. Numerical results demonstrate that the direction of the generated optical chain is consistent with the orientation of the combined antennas, and the length of the optical chain is approximately equal to the length of the combined antennas, and the amount, position and spacing of the dark hollow spots are determined by the length of the combined antenna and the amplitude periodic coefficient of the ELS. The generated optical chains may find potential applications in multi-points optical capture and particle delivery along prescribed directions.

A study of effects of a turbulent jet engine exhaust on partially coherent Laguerre-Gaussian Schell model vortex beam

In this study, based on the generalized Huygens-Fresnel principle, the evolution properties, such as spectral density, degree of coherence, and beam width of the propagation of partially coherent Laguerre-Gaussian Schell model vortex beam (PCLGSMvB) in jet engine exhaust are studied. Our results show that the spectral density of the corresponding beam can change their form shape during its propagation as the source coherence varies. When the source coherence width is high, the profile of PCLGSMvB changes from initially dark hollow into two spot beams at short propagation distances. If the source coherent width is very small, the shape of PCLGSMvB is converted to a Gaussian shape and keeps its form upon propagation. Also, we found that the spreading of PCLGSMvB is related with their initial parameters, and it will be spread faster with smaller source coherence width, larger mode order n, and longer wavelength. Furthermore, the beam width of the PCLGSMvB increasing as the structural constant increases and it means that the beam can resist to stronger fluctuation of turbulence. Outputs of this study has potential application on deriving the requirements of optical systems on aircrafts like laser range finder, laser designator, optical communication systems and directed infrared countermeasure (DIRCM).

Radially polarized cosine non-uniformly correlated beams and their propagation properties.

We introduce a kind of radially polarized partially coherent (RPPC) beam with a prescribed non-uniform correlation function, called a radially polarized cosine non-uniformly correlated (RPCNUC) beam. Based on the extended Huygens-Fresnel principle, we study the propagation properties in free space and in a turbulent atmosphere. Unlike RPPC beams with uniform coherence, RPCNUC beams possess the invariance of dark hollow cores and radial polarization, and exhibit self-focusing properties. In a turbulent atmosphere, the intensity distribution demonstrates self-healing properties over a certain propagation distance. We also investigate how to adjust the beam parameters to reduce the turbulence-induced degradation in detail.

Design of a high-Q dark hollow beam cavity based on a one-dimensional topological photonic crystal.

Dark hollow beams (DHBs) possess great potential for material processing, holography, and vortex beams, and thus designing a high-Q DHB cavity is significant for these applications. In this Letter, a method of designing and optimizing a high-Q DHB cavity based on a one-dimensional topological photonic crystal (TPhC) is proposed. Furthermore, how the structural parameters control the performance of the cavity is analyzed with the help of finite-element-method (FEM) simulation. According to the simulation results, the Q factor of the designed cavity can reach the order of 105 with only 19 periods of layers. It is critical to mention that, although increasing the layers can improve the average Q of the cavity, it will cause serious fluctuation of both the Q factor and the divergence angle of the output beam. The design method proposed in this Letter may not only help designers of future DHB lasers but also promote the applications of DHBs in various fields.

Propagation properties of partially coherent radially and azimuthally polarized vortex beams in turbulent atmosphere

Analytical formulas for the average intensity of the partially coherent radially and azimuthally polarized vortex (PCRPV and PCAPV) beams propagating through the turbulent atmosphere are derived based on the extended Huygens-Fresnel principle. The effect of the different topological charge number m of PCRPV beam and PCAPV beam in turbulence on average intensity and degree of hollowness (DOH) has been studied in detail. It can be found that PCRPV beam and PCAPV beam in turbulence with the larger topological charge m can greatly keep dark hollow constructure on propagation. And we have studied the orientation angles of the polarization ellipse of the PCRPV and PCAPV beams with different m in atmospheric turbulence. The results show that the capacity to keep radial polarization decline with the increase of topological charge m. In addition, we combined the complex screen method and multi-phase screens method to simulate the propagation of PCRPV beam and PCAPV beam in atmospheric turbulence for verifying our theoretical results. It is shown that the simulated results are consistent with theoretical results. Our study could be important for free-space optical communications.

Perfect Optical Vortex to Produce Controllable Spot Array

The perfect optical vortex has successfully aroused substantial interest from researchers for its central dark hollow caused by spatial phase singularity in recent years. However, the traditional methods of combining the axicon and helical phase to generate the perfect optical vortex lead to an additional focus deviation in the tightly focused systems. Here, we report a multi-foci integration (MFI) method to produce the perfect optical vortex by accumulating a finite number of foci in the focal plane to overcome the additional focus deviation. Furthermore, based on MFI, we superposed two perfect optical vortices to obtain the spot array with controllable phase distribution and the number of spots. This work deepens our knowledge about superposed vortices and facilitates new potential applications. The micromanipulated experimental results agree well with our theoretical simulation. The spot array field provides new opportunities in direct laser writing, optical tweezers, optical communications, and optical storage.

Radially polarized twisted partially coherent vortex beams

We introduce a new type of partially coherent vector beam, named the radially polarized twisted partially coherent vortex (RPTPCV) beam. Such a beam carries the twist phase and the vortex phase simultaneously, and the initial state of polarization (SOP) is radially polarized. On the basis of the pseudo-modal expansion and fast Fourier transform algorithm, the second-order statistics such as the spectral density, the degree of polarization (DOP) and the SOP, propagation through a paraxial ABCD optical system are investigated in detail through numerical examples. The results reveal that the propagation properties of the RPTPCV beam closely depends on the handedness of the twist phase and the vortex phase. When the handedness of the two phases is same, the beam profile is easier to remain a dark hollow shape and the beam spot rotates faster during propagation, compared to the partially coherent vortex beam or the RPTPCV beam with the opposite handedness of the two phases. In addition, the same handedness of two phases resists the coherence induced de-polarization of the beam upon propagation, and the SOP is also closely related to the handedness, topological charge of the vortex phase and the twist factor of the twist phase, providing an efficient way to modulate the beam's DOP and SOP in the output plane. Moreover, we establish an experiment setup to generate the RPTPCV beam. The average spectral density and the polarization properties are examined in the experiment. The experimental results agree reasonable well with the theoretical predictions. Our results will be useful for particle manipulating, free-space optical communications, and polarization lidar systems.

Generation of an Airy-related beam from the sinusoidal dark hollow beam

In this paper, an Airy transformation of sinusoidal dark hollow beam (SDHB) is introduced and used to generate a unique Airy-related beam. The analytical expression for the SDHB passing through an optical Airy transformation system (OATS) is derived based on the Collins diffraction integral formula. Furthermore, dependence of the characteristics of the generated Airy-related beam on several factors, mainly including the control parameter of the OATS and the incident beam’s Gaussian coefficient and order, is investigated. Results show that the intensity distribution, orientation, size, position and number of side lobes of the generated Airy-related beams are modulated and controlled by the self-parameters of the incident SDHB and the parameters of the OATS. The results obtained here will enrich the research on the characteristics of the hollow beam and the generation method of Airy-related beam, and also expand the application of SDHB.

Effect of DC electric field on THz radiation field and efficiency of dark hollow laser beam in plasma

In the present study, a schematic has been proposed for generating terahertz (THz) radiation by beating of two dark hollow (DH) laser beams in plasma when a DC electric field is applied with a perpendicular direction. The small field amplitude and the radiation’s efficiency produced by DH laser beams in plasma as well as DC electric generation and exertion comfortability motivated us to enhance these parameters by applying a perpendicular DC electric field. It was found that applying a DC electric field in addition to increasing the THz field amplitude and efficiency caused the generation of a special THz field, which has an exclusive pattern tunable by the variation of the electric field amplitude. It is shown that due to mutual effects between the spatial profile of the beams and the electric field, the THz radiation field and efficiency have the maximum point that can be used for the production of a desired THz frequency.

Isolation And Characterization Of Biosurfactant Producing Bacteria From Different Environmental Soil Samples

Isolation And Characterization Of Biosurfactant Producing Bacteria From Different Environmental Soil Samples