super-Gaussian Beam Research Articles

Designing the Second Target Station with a Coupled Neutronics-Mechanical Optimization Workflow

The Second Target Station (STS) at the Spallation Neutron Source of the U.S. Department of Energy’s Oak Ridge National Laboratory is being designed to become the world’s highest peak brightness source of cold neutrons. As the STS project evolves, neutronics and other engineering analyses will inform many design iterations. To facilitate this process, a fully automated optimization workflow was developed to convert a parameterized computer-aided-design model of the target into an unstructured mesh geometry model and then to run a neutronics calculation and (optionally) a mechanical analysis for each design iteration. This workflow enables efficient, high-fidelity modeling; simulation; and optimization of new designs, as has been demonstrated for the optimization of the STS neutron moderators. In this paper, we present the results of our first major effort to automate the design optimization process for a spallation target. In the first analysis, the goal is to find optimal dimensions of a monolithic tungsten target coupled with an optimal super-Gaussian proton beam profile to deliver maximum brightness of the resulting neutron beams while maintaining good mechanical properties of the target. In the second analysis, geometric and beam parameters are optimized for an alternative design with tungsten plates, which can reach superior mechanical performance without compromising the neutronics performance.

Electrostatic wave assisted super-gaussian laser beam absorption in collisional plasma embedded with static magnetic field

Electrostatic wave assisted super-gaussian laser beam absorption in collisional plasma embedded with static magnetic field

Compact super-Gaussian evanescent beam expanders for integrated photonics

This paper presents the modeling, design and experimental validation of integrated optical super-Gaussian evanescent beam expanders. A general analytical model for converting the mode of a single mode waveguide into a wide super-Gaussian slab mode is derived and the design procedure is described. Several structures have been experimentally verified on wafer scale and the results are in good correspondence with the design. Applications where wide flat-top beams would prove their superiority are, for instance, bio-sensing applications, flow cytometry and on-chip microscopy.

Digital generation of super-Gaussian perfect vortex beams via wavefront shaping with globally adaptive feedback

Abstract High-intensity vortex beams with tunable topological charges and low coherence are highly demanded in applications such as inertial confinement fusion (ICF) and optical communication. However, traditional optical vortices featuring nonuniform intensity distributions are dramatically restricted in application scenarios that require a high-intensity vortex beam owing to their ineffective amplification resulting from the intensity-dependent nonlinear effect. Here, a low-coherence perfect vortex beam (PVB) with a topological charge as high as 140 is realized based on the super-pixel wavefront-shaping technique. More importantly, a globally adaptive feedback algorithm (GAFA) is proposed to efficiently suppress the original intensity fluctuation and achieve a flat-top PVB with dramatically reduced beam speckle contrast. The GAFA-based flat-top PVB generation method can pave the way for high-intensity vortex beam generation, which is crucial for potential applications in ICF, laser processing, optical communication and optical trapping.

Super-Airy beams.

We report on the numerical simulation results of the propagation of Fourier-transformed super-Gaussian beams with cubic phase modulation, which we refer to as super-Airy beams. We show the effect of the truncation profile on the propagation of the "Airy" intensity distribution and propose methods to improve the non-diffracting propagation length. We show that super-Gaussian beams with cubic phase modulation would form, what we believe to be, truncated Airy beams after being optically Fourier-transformed. The results show that Airy beams with smaller curvature would preserve their non-diffracting characteristics for longer propagation distances than Airy beams with larger curvature. Airy beam curvature is a controllable parameter by the phase transformation step. The presented results suggest that Fourier-transforming super-Gaussian beams with cubic phase modulation would form Airy beams with up to > 350% increase in their non-diffracting propagation distance compared to Fourier-transformed Gaussian beams.

Extremal quantum correlation generation using a hybrid channel

The preservation of quantum correlations requires optimal procedures and the proper design of the transmitting channels. In this regard, we address designing a hybrid channel comprising a single-mode cavity accompanied by a super-Gaussian beam and local dephasing parts based on the dynamics of quantum characteristics. We choose two-level atoms and various functions such as traced-distance discord, concurrence, and local-quantum uncertainty to analyze the effectiveness of the hybrid channel to preserve quantum correlations along with entropy suppression discussed using linear entropy. The joint configuration of the considered fields is found to not only preserve but also generate quantum correlations even in the presence of local dephasing. Most importantly, within certain limits, the proposed channel can be readily regulated to generate maximal quantum correlations and complete suppression of the disorder. Besides, compared to the individual parts, mixing the Fock state cavity, super-Gaussian beam, and local dephasing remains a resourceful choice for the prolonged quantum correlations’ preservation. Finally, we present an interrelationship between the considered two-qubit correlations’ functions, showing the deviation between each two correlations and of the considered state from maximal entanglement under the influence of the assumed hybrid channel.

Propagation dynamics of elliptical super-Gaussian bullets in nonlinear metamaterial waveguide

The characteristics of an optical beam propagating in a medium should be preserved for many applications related to fiber optic communication. The phenomenon of self-trapping due to adequate balance among linear and nonlinear effects may preserve the characteristics of an optical beam. In this work, we perform a theoretical investigation on the propagation of a spatiotemporal elliptical super-Gaussian beam in a Kerr nonlinear metamaterial waveguide. We follow the Lagrangian variational method and numerical analysis using the appropriate trial function for the input elliptical super-Gaussian beam and analyze the self-trapping and deformation of the propagating beam in metamaterials. We obtain special conditions to observe the self-trapping and stabilize the dynamics of the elliptical super-Gaussian beam in both negative and positive index regimes of the metamaterial. It is found that in the negative index regime of metamaterial, the phenomenon of self-trapping may exist in the normal dispersion regime with defocusing Kerr nonlinearity. However similar to the conventional medium, the robust balance among the anomalous dispersion and focussing Kerr nonlinearity supports the self-trapping in the positive index regime. There is a critical optical power for the input beam to observe the pulse trapping phenomena. This power is found to be a function of the super-Gaussian parameter as well as the ellipticity of the input beam. The period of self-trapping is also a function of the super-Gaussian parameter and the ellipticity of the input beam.

Final amplifier of an ultra-intense all-OPCPA system with 13-J output signal energy and 41% pump-to-signal conversion efficiency.

Optical parametric chirped-pulse amplification (OPCPA) using high-energy Nd:glass lasers has the potential to produce ultra-intense pulses (>1023 W/cm2). We report on the performance of the final high-efficiency amplifier in an OPCPA system based on large-aperture (63 × 63-mm2) partially deuterated potassium dihydrogen phosphate (DKDP) crystals. The seed beam (180-nm bandwidth, 110 mJ) was provided by the preceding OPCPA stages. A maximum pump-to-signal conversion efficiency of 41% and signal energy up to 13 J were achieved with a 52-mm-long DKDP crystal due to the flattop super-Gaussian pump beam profile and flat-in-time pulse shape.

Dynamics of Gaussian and Super-Gaussian optical beams in weakly nonlinear nonlocal media

We investigate the dynamics of Gaussian and Super-Gaussian optical beams in weakly nonlocal nonlinear media with cubic quintic nonlinearities. Through the variational method, a set of internal parameters of beam propagation are constructed and their properties, illustrated from numerical simulations. We discover that Gaussian and Super-Gaussian optical beams generally perform stable propagation with different dynamics depending on whether beams order, quintic nonlinearity and/or nonlocality are taken into account. The evolution of the light beams is periodic due to the competition between nonlinearities and diffraction. The phase front curvature increases with the beams order when the width decreases. The numerical study of the interaction between a Gaussian and Super-Gaussian optical beams, shows that with or without the quintic nonlinearity and/or nonlocality, various behaviours such as repulsion, attraction and soft shock waves are observed. Moreover, new phenomena are exhibited in the case of the Super-Gaussian, according to their shape.

Effect of Laser Beam Profile on Thermal Transfer, Fluid Flow and Solidification Parameters during Laser-Based Directed Energy Deposition of Inconel 718.

The profile of the laser beam plays a significant role in determining the heat input on the deposition surface, further affecting the molten pool dynamics during laser-based directed energy deposition. The evolution of molten pool under two types of laser beam, super-Gaussian beam (SGB) and Gaussian beam (GB), was simulated using a three-dimensional numerical model. Two basic physical processes, the laser-powder interaction and the molten pool dynamics, were considered in the model. The deposition surface of the molten pool was calculated using the Arbitrary Lagrangian Eulerian moving mesh approach. Several dimensionless numbers were used to explain the underlying physical phenomena under different laser beams. Moreover, the solidification parameters were calculated using the thermal history at the solidification front. It is found that the peak temperature and liquid velocity in the molten pool under the SGB case were lower compared with those for the GB case. Dimensionless numbers analysis indicated that the fluid flow played a more pronounced role in heat transfer compared to conduction, especially in the GB case. The cooling rate was higher for the SGB case, indicating that the grain size could be finer compared with that for the GB case. Finally, the reliability of the numerical simulation was verified by comparing the computed and experimental clad geometry. The work provides a theoretical basis for understanding the thermal behavior and solidification characteristics under different laser input profile during directed energy deposition.

Propagation and focusing dependency of a laser beam with its aberration distribution: understanding of the halo induced disturbance

In various applications, it is necessary to understand laser field dynamics during its propagation, especially at the focal position including the dispersed energy surrounding the main pulse, called the halo effect. For instance, the properties of electron beams produced by laser wakefield acceleration (LWFA) strongly depend on the laser energy distribution and its halo in the vicinity of the focus. Indeed, under certain conditions, this halo, or even its internal structures, can propagate and be self-focused independently of the main pulse in the plasma. This paper aims to provide sufficient tools to properly describe the behavior of a focused laser beam, including the halo. Subsequently, an optical description regarding the source of this halo is provided. A more accurate estimation of the input laser beam that should be used in simulations of high-power laser applications may now be obtained. Finally, one may also find ways to positively manipulate the laser beam. Using Fresnel diffraction theory, the propagation and focusing of an experimental high-power (sub-petawatt) aberrated beam is numerically calculated. The shape of the focused beam pattern within a few Rayleigh lengths is analysed as a function of main aberrations (up to the 14 th term of Zernike polynomials). Furthermore, at the focus position, the spreading of the energy is compared to both the case of a perfect diffraction-limited Gaussian and a super-Gaussian beam.

Self-focusing and defocusing phenomena of super-Gaussian laser beams in plasmas carrying density gradient

Considering nonlinearities due to relativistic mass variation and ponderomotive force driven depression in the electron density, a model is developed for the self-focusing of a super-Gaussian laser beam in inhomogeneous plasmas. Since paraxial ray approximation is not appropriate for the beams of super-Gaussian profile, the formulation is developed based on the moment theory. To have an in-depth understanding of self-focusing and defocusing phenomena and to develop generalized treatment, three different types of plasma density profiles namely linear, tangent and exponential density profiles, are considered and the results are compared. Due to the saturating nature of nonlinear permittivity with laser intensity, the beam is found to undergo periodic focusing because of competition between the diffraction divergence and nonlinear self-focusing effects. The ponderomotive nonlinearity enhances the self-focusing. As the super-Gaussian beam moves into higher density plasma region up to several Rayleigh lengths, stronger self-focusing is achieved and the value of minimum spot size decreases.

Quantification of Quantum Correlations in Two-Beam Gaussian States Using Photon-Number Measurements.

Identification, and subsequent quantification of quantum correlations, is critical for understanding, controlling, and engineering quantum devices and processes. We derive and implement a general method to quantify various forms of quantum correlations using solely the experimental intensity moments up to the fourth order. This is possible as these moments allow for an exact determination of the global and marginal impurities of two-beam Gaussian fields. This leads to the determination of steering, tight lower and upper bounds for the negativity, and the Kullback-Leibler divergence used as a quantifier of state nonseparability. The principal squeezing variances are determined as well using the intensity moments. The approach is demonstrated on the experimental twin beams with increasing intensity and the squeezed super-Gaussian beams composed of photon pairs. Our method is readily applicable to multibeam Gaussian fields to characterize their quantum correlations.

Influence of Curvature Feature on Laser Heating during Tape Placement Process for Carbon Fiber Reinforced Polyether Ether Ketone Composite

The curvature feature makes the irradiance and absorptivity change, resulting in an uneven power density distribution, which affects the quality of composite parts. In this study, a theoretical model-based Super-Gaussian profile beam in the laser irradiation area was established to obtain the heat flux distribution on the curved surface. The effect of curvature on the surface scattering reflection, temperature distribution, and surface morphology were investigated and verified the validity of the theoretical model. Furthermore, the influence of the laser intensity distribution, laser inclination and curvature radius on the power density distribution and distribution uniformity were studied. Research indicated that the power density increases as the distance from the origin increase resulting from the variation of the irradiance and absorptance along the circumference. The flatter the intensity distribution of the laser beam in the height direction, the less uniform the power density distribution. Accordingly, the typical Gaussian profile beam significantly ameliorates the power density distribution. This research provides a novel understanding of using heat sources during laser heating thermoplastic tape placement.

Nonlinear orbital angular momentum conversion with spatial-amplitude independence

Nonlinear optics with structured light can provide a host of important functions for shaping the spatial and temporal structure of light, and the most commonly used is frequency conversion. In this work, we propose and demonstrate a novel nonlinear toolkit capable of tuning the frequency and orbital angular momentum (OAM) of signal beams simultaneously, and importantly that does not change the spatial amplitude structure of the signal. This unique frequency interface is enabled by using a special structured pump called a vortex super-Gaussian beam that has a flattop amplitude distribution and tunable vortex wavefront. This technique provides a dual interface of frequency and OAM, and may inspire many potential applications involving OAM beams.

Two dimensional gradient-index beam shapers fabricated using ultrafast laser inscription.

In this paper gradient-index beam shapers are fabricated using the ultrafast laser inscription method. This method enables the fabrication of two-dimensional refractive index profiles inside silica glass, resulting in highly robust and compact beam shapers. The magnitude of this refractive index change can be tailored by adjusting the laser pulse energy, enabling arbitrary two-dimensional refractive index profiles to be manufactured. The process is then demonstrated by fabricating planar waveguides with quadratic index profiles that predictably resize Gaussian beams. Then a more complex two-dimensional refractive index profile is fabricated to transform an input Gaussian beam into a super-Gaussian (flat-top) beam.

Femtosecond filamentation of optical vortices for the generation of optical air waveguides.

We study the filamentation in air of multi-millijoule optical vortices and compare them with the classical filamentation regime. The femtosecond vortex beam generates multiple plasma filaments organized in a cylindrical geometry. This plasma configuration evolves into a meter-scale tubular neutral gas column that can be used as a waveguide for nanosecond laser pulses at 532 nm. It appears that optical vortices produce a more uniform heating along the propagation axis, when compared with Gaussian or super-Gaussian beams, and that the resulting low-density channel is poorly sensitive to the laser input power thanks to the combination of filamentation intensity clamping and phase vorticity.

Peculiarities of focusing circularly and radially polarized super-Gaussian beams using ring gratings with varying relief height

The focusing features of a super-Gaussian beam, as well as Laguerre-super-Gaussian (1,0) modes with radial and circular polarizations on ring gratings (direct and inverse) with a variable height of individual relief rings were investigated in this paper. The change in the height of the relief from the maximum height in the center to the minimum at the edges of the element (direct ring grating) is considered and the reverse case, when the maximum height of the relief was at the edges and the minimum in the center (reverse ring grating). The comparison was carried out with the action of a diffractive axicon with a comparable grating period. Numerical simulation was carried out by the finite differences in the time domain method. It was shown that the direction of change in the height of the relief rings of elements significantly affects the diffraction pattern in the near zone. In particular, for a super-Gaussian beam, the use of a direct ring grating made it possible to reduce the size of the focal spot by 18.7% for radial polarization ('sigma'=5 μm), the use of a reverse ring grating led to a decrease in the focal spot by 36.9% ('sigma'=12.25 µm) in comparison with the action of a diffractive axicon. It was also shown in the paper that when the reverse ring grating is illuminated by the Laguerre-superGauss (1,0) mode with circular polarization, the formation of a narrow and extended region of reduced intensity on the optical axis (optical trap) is observed.

Two-dimensional atom localization by absorption spectrum using superposition of two super-Gaussian beams

Two-dimensional atom localization by absorption spectrum using superposition of two super-Gaussian beams

Multifocal confocal microscopy using a volume holographic lenslet array illuminator.

Multifocal illumination can improve image acquisition time compared to single point scanning in confocal microscopy. However, due to an increase in the system complexity, obtaining uniform multifocal illumination throughout the field of view with conventional methods is challenging. Here, we propose a volume holographic lenslet array illuminator (VHLAI) for multifocal confocal microscopy. To obtain uniform array illumination, a super Gaussian (SG) beam has been incorporated through VHLAI with an efficiency of 43%, and implemented in a confocal microscope. The design method for a photo-polymer based volume holographic beam shaper is presented and its advantages are thoroughly addressed. The proposed system can significantly improve image acquisition time without sacrificing the quality of the image. The performance of the proposed multifocal confocal microscopy was compared with wide-field images and also evaluated by measuring optically sectioned microscopic images of fluorescence beads, florescence pollen grains, and biological samples. The proposed multifocal confocal system generates images faster without any changes in scanning devices. The present method may find important applications in high-speed multifocal microscopy platforms.