Conventional Gaussian Beam Research Articles

Optical vortex ladder via Sisyphus pumping of Pseudospin

Robust high-order optical vortices are much in demand for applications in optical manipulation, optical communications, quantum entanglement and quantum computing. However, in numerous experimental settings, a controlled generation of optical vortices with arbitrary orbital angular momentum remains a challenge. Here, we present a concept of “optical vortex ladder” for the stepwise generation of optical vortices through Sisyphus pumping of pseudospin modes in photonic graphene. The ladder is applicable in various lattices with Dirac-like structures. Instead of conical diffraction and incomplete pseudospin conversion under conventional Gaussian beam excitations, the vortices produced in the ladder arise from non-trivial topology and feature diffraction-free Bessel profiles, thanks to the refined excitation of the ring spectrum around the Dirac cones. By employing a periodic “kick” to the photonic graphene, effectively inducing the Sisyphus pumping, the ladder enables tunable generation of optical vortices of any order even when the initial excitation does not involve any orbital angular momentum. The optical vortex ladder stands out as an intriguing non-Hermitian dynamical system, and, among other possibilities, opens a pathway for applications of topological singularities in beam shaping and wavefront engineering.

On the optimum far-field irradiance distribution using Laguerre-Gaussian beams for intersatellite free-space optical communications.

This paper proposes a novel approach to improve the performance of free-space optical communication intersatellite links by combining fundamental Gaussian and higher-order Laguerre-Gaussian beams. We present a comprehensive mathematical model to analyze the system's performance, including received power statistics, average bit error probability, and outage probability. To generate the desired beam profiles, we propose an optical system capable of creating a superposition of orthogonally polarized Laguerre-Gaussian beams that yield the far-field irradiance distributions that optimize the communication performance. Our theoretical analysis demonstrates that the combination of fundamental Gaussian and higher-order modes can significantly enhance system performance compared to conventional fundamental Gaussian beams. In some scenarios, the proposed approach offers savings on the order of 20% to 40% of the required transmitted power.

Steering abrupt autofocusing beams with metasurfaces [Invited

Abrupt autofocusing (AAF) beams, known for their non-diffractive properties, extended focal depth, and self-healing capabilities, are advantageous over conventional Gaussian beams in the biomedical field. Compared to the previous method that can only generate a passive AAF beam, we introduce metasurfaces to achieve a dynamically steered AAF beam at the incident wavelength of 532 nm. By rotating the two metasurfaces in opposite directions of an angle θ, both the generated position of the AAF beam and the autofocusing direction can be altered. Our theoretical analysis and full-wave simulation results confirmed that the deflection angle of the AAF beam can be finely adjusted from to 11° without significantly affecting the focal length or focusing efficiency. This capability allows for precision operation in biomedical applications, including enhanced laser surgery, optical tweezing, and optimized photodynamic therapy.

A Review on Laser Beam Shaping Application in Laser Powder Bed Fusion

Laser powder bed fusion (L‐PBF) is extensively adopted in the aerospace and automobile industries for producing metallic components. The L‐PBF process involves rapid melting and solidification of metallic powders using a laser source to produce dense parts. Most industrial L‐PBF systems use a fiber‐based laser source that emits a Gaussian beam distribution. However, the conventional Gaussian beam used in L‐PBF processes presents inherent limitations that can impact the quality and properties of the final products. This review aims to provide a theoretical background of laser beam shaping techniques and explores the application of alternative beam shapes in L‐PBF. It investigates how different beam profiles affect the melt pool geometry, process stability, productivity, mechanical properties, microstructure, and surface roughness of fabricated parts. Additionally, it discusses different types of beam‐shaping techniques and elements utilized to generate distinct beam shapes. Furthermore, different constraints and limitations that hinder the full exploitation of beam shaping are critically discussed. By analyzing the impact of beam shaping in L‐PBF, this review provides insight into optimizing the AM process, enhancing part quality, and improving processing performance. It will also help readers to overview the research gaps, challenges, and promising future directions in laser beam shaping applications in L‐PBF.This review comprehensively covers and presents the current research trend of laser beam shaping applications in L‐PBF. It delves into the opportunities, challenges, limitations, and futures prospects of beam shaping applications. Furthermore, presents the methods and techniques used to modulate the laser beam profile, including spatial and temporal.This article is protected by copyright. All rights reserved.

Laser beam shaping facilitates tailoring the mechanical properties of IN718 during powder bed fusion

One of the recent technological developments in the Laser Powder Bed Fusion (LPBF) process is the use of non-Gaussian beam profiles of power density distributions. Irrespective of the strategies used to change the beam profile, spatial beam shaping enhances process flexibility since it allows manipulation of the thermal field, the melt pool shape, and the microstructure. This work showcases the impact of novel ring and conventional Gaussian beams on density, melt pool characteristics, and mechanical properties of IN718 superalloy via LPBF. A novel laser source with beam shaping capabilities provided the beam profiles, ranging from Gaussian to ring beams. The results show clear differences between the crystalline patterns obtained with Gaussian and the other ring beams attempted. This study elucidates the impact of melting modes and solidification mechanisms on the texture index, arising from the interplay between laser beam shape modes and laser speed. It also shows how the crystalline configuration associated with each case studied influences the mechanical properties and how it is possible to modify the process parameters and the beam shape mode to extend control over the mechanical properties of the components manufactured using LPBF. This leads to a broader range of mechanical properties and grain size when tailoring the power density distribution towards ring beams. Additionally, the correlation between melt pool shape geometry, texture index, and mechanical properties is discussed, and the limitations and advantages of each mode are defined.

Rydberg-atom acceleration by circular Airy laser pulses.

Circular Airy pulsed beams are introduced to significantly optimize the acceleration of neutral Rydberg atoms. Compared with the conventional pulsed Gaussian beams used in the previous report, the circular Airy structure abruptly self-focuses and subsequently propagates with weak diffraction, resulting in a much higher accelerating efficiency for both radial and longitudinal velocities, as well as a longer accelerating range along the propagation axis. The parameter dependencies of the beams on the acceleration are also analyzed.

A holistic approach for evaluation of Gaussian versus ring beam processing on structure and properties in laser powder bed fusion

In this study, a holistic evaluation strategy employing a complex test artifact, coupled with single line scan tracks, was employed to examine the influence of different laser beam energy profiles on various features of laser-based powder bed fusion of metals (PBF-LB/M). Using IN718, results revealed a significant influence of the laser beam on bead geometry. Specifically, the conventional Gaussian beam produced deeper, concave-shaped melt pools, while the ring beam resulted in wider and shallower beads. In terms of productivity, the artifacts (two each) fabricated using the Gaussian beam required 6 h and 6 min of build time, while those built using ring beam required only 3 h and 49 min (37% build time reduction) but a defocused Gaussian beam (not included in this study) can match the productivity of the ring beam. However, the holistic approach using the complex test artifact highlighted drawbacks associated with the ring beam, including increased lack of fusion porosity, compromised resolution for features below 0.5 mm, and less than 10% elongation to break in both as built and heat-treated conditions. While acknowledging the potential for improvement through further process optimization, the study concludes that the shallower melt pools produced by the ring beam may cause limitations as layer thicknesses increase. Microstructural analysis revealed distinct grain characteristics, with the Gaussian beam producing more equiaxed grains and the ring beam favouring columnar grains positioned along the build direction. The work primarily highlights the need for and benefits from a holistic analysis in PBF-LB/M technology, ensuring data driven outcomes.

Modulated high-order Hermite-Gaussian beams with uniform intensity distribution

Hermite-Gaussian beams have been studied since the early years of laser modes. With the recent development of structured light, different modulation methods have been demonstrated to control the energy, polarization and propagation behavior of Hermite-Gaussian beams. In this work we introduce an inverse design approach to modulate the energy distribution among different lobes of Hermite-Gaussian beams. In this approach, the desired intensity profiles of Hermite-Gaussian beams are the starting point. The required spatial phase masks are calculated through inverse Fourier transform, then projected on a spatial light modulator to convert conventional Gaussian beams into modulated Hermite-Gaussian beams. The experimental modulated high-order (m = 10, n = 10) Hermite-Gaussian beams show much improved energy distribution among different lobes over standard Hermite-Gaussian beams. These modulated Hermite-Gaussian beams also have improved beam quality factor M2 after modulation. These results demonstrated the feasibility to fine-tune the intensity profiles of Hermite-Gaussian beams, which have applications in structured illumination, particle manipulation and optical communications.

Beam wander prediction with recurrent neural networks.

Among the problems that prevent free-space optical communication systems from becoming a truly mainstream technology is beam wander, which is especially important for structured light beams since beam misalignment introduces additional crosstalk at the receiver. The paper suggests a recurrent neural network-based (RNN) solution to predict beam wander in free space optics (FSO). The approach uses past beam center of mass positions to predict future movement, significantly outperforming various prediction types. The proposed approach is demonstrated using under-sampled experimental data over a 260 m link as a worst-case and over-sampled simulated data as a best-case scenario. In addition to conventional Gaussian beams, Hermite- and Laguerre-Gaussian beam wander is also investigated. With a 20 to 40% improvement in error over naive and linear predictions, while predicting multiple samples ahead in typical situations and overall matching or outperforming considered predictions across all studied scenarios, this method could help mitigate turbulence-induced fading and has potential applications in intelligent re-transmits, quality of service, optimized error correction, maximum likelihood-type algorithms, and predictive adaptive optics.

Enhancing fiber-coupling efficiency of beam-to-fiber links in turbulence by spatial non-uniform coherence engineering.

We present a general formula for the fiber-coupling efficiency of various types of non-uniformly correlated beams propagating in a turbulent atmosphere. With it, we calculate the fiber-coupling efficiency of a specific type of non-uniformly correlated beams, Laguerre non-uniformly correlated (LNUC) beams, to investigate how the non-uniform correlation structure plays a role in enhancing the fiber-coupling efficiency. Compared with conventional Gaussian Schell-model beams, the LNUC beams possess better coupling behavior, and the initial coherence length and beam order of such beams can be adjusted to further improve the fiber-coupling efficiency in turbulence. Our results demonstrate how non-uniformly correlated beams can be used for fiber-coupling applications, and demonstrate their intriguing potential for free-space optical communications.

The resilience of zero order Bessel–Gaussian Beams to the impact of dynamic Kolmogorov type of turbulence

Propagation characteristics of Bessel–Gaussian beams and Gaussian beams passing through a dynamic Kolmogorov type of turbulence are analysed at the laboratory level using simulations and experiments. The impact of a rotating pseudo-random phase plate mimicking Kolmogorov type atmospheric turbulence on the Bessel–Gaussian and Gaussian beams is quantitatively characterized by calculating the scintillation index, beam wandering, and qualitatively analysed using intensity line profiles. The analysis is done in the Fresnel, Fourier, and Fraunhofer regions. This is the first time in the literature where the effect of a rotating dynamic turbulence on the Bessel–Gaussian beam is experimentally investigated. Our analysis clearly confirms the resilience of Bessel–Gaussian beams to the impact of dynamic turbulence in Fourier and Fraunhofer regions making them advantageous over conventional Gaussian beams when propagated through a dynamic Kolmogorov kind of turbulence. These results can be effectively applied in free-space optical communication systems.

Ultrafast Cylindrical Vector Beams for Improved Energy Feedthrough and Low Roughness Surface Ablation of Metals

The use of ultrafast cylindrical vector vortex beams in laser-matter interactions permits new ablation features to be harnessed from inhomogeneous distributions of polarization and beam geometry. As a consequence, the ablation process can yield higher ablation efficiency compared with conventional Gaussian beams. These beams prevent surface quality degradation during the ablative processes. When processing stainless steel and titanium, the average surface roughness obtained by deploying the cylindrical vector is up to 94% lower than the Gaussian case, and the processing efficiency is 80% higher.

Laser heating with doughnut-shaped beams

Doughnut-shaped laser beams have applications in laser-based additive manufacturing, laser heating of diamond anvil cells, and optical super-resolution microscopy. In applications like additive manufacturing and heating of diamond anvil cells, a doughnut-shaped beam is frequently used to obtain a more uniform temperature profile relative to that generated by a conventional Gaussian beam. Conversely, in super-resolution microscopy, the doughnut-shaped beam serves to enhance spatial resolution and heating is an undesirable side effect that can cause thermal damage. Here, we develop analytical expressions for the temperature rise induced by a doughnut-shaped laser beam both alone and in combination with a Gaussian beam. For representative, experimentally determined beam radii and a wide range of thermal properties, we find that a doughnut-shaped beam results in a peak temperature rise no more than 90% and often less than 75% of that for a Gaussian beam with the same total power. Meanwhile, the region of the sample surface that reaches 80% of the maximum temperature rise is at least 1.5 times larger for a doughnut-shaped beam than for a Gaussian beam. When doughnut-shaped and Gaussian beams are applied simultaneously, the ratio of the maximum temperature rise for the two beams combined vs a Gaussian beam alone can be up to 2.5 times lower than the ratio of the doughnut-shaped vs the Gaussian beam power. For applications like super-resolution microscopy that require high doughnut-shaped laser beam powers, the doughnut-shaped beam intensity profile is thus advantageous for minimizing the total peak temperature rise when applied together with a Gaussian beam.

Ultra-long anti-diffracting beam volume imaging using a single-photon excitation microscope.

We studied a novel volumetric single-photon excitation microscope with an ultralong anti-diffracting (UAD) beam as illumination. Volumetric fluorescence image direct mapping showed that the axial imaging range of the UAD beam was approximately 14 times and 2 times that of conventional Gaussian and Airy beams, respectively, while maintaining a narrow lateral width. We compared the imaging capabilities of the Gaussian, Airy, and UAD modes through a strongly scattering environment mixed with fluorescent microspheres and agarose gel. Thick samples were scanned layer by layer in the Gaussian, Airy, and UAD modes, and then the three-dimensional structural information was projected onto a two-dimensional image. Benefiting from the longer focal length of the UAD beam, a deeper axial projection was provided, and the volume imaging speed was vastly increased. To demonstrate the performances of the UAD microscope, we performed dynamic volumetric imaging on the cardiovascular system of zebrafish labeled with green fluorescent proteins in the three modes and dynamically monitored substance transport in zebrafish blood vessels. In addition, the symmetrical curve trajectory of the UAD beam and the axial depth of the lateral position can be used for localization of micro-objects.

Quantitative chemical sensing of drugs in scattering media with Bessel beam Raman spectroscopy.

Scattering can seriously affect the highly sensitive detection and quantitative analysis of chemical substances in scattering media and becomes a significant challenge for in vivo application of Raman spectroscopy. In this study, we demonstrated a proof of concept for using the self-reconstructing Bessel beam for Raman spectroscopic sensing of the chemicals in the handmade scattering media and biological tissue slices. The homebuilt Bessel beam Raman spectroscopy (BRS) was capable of accurately detecting the Raman spectra of the chemicals buried in the scattering media, and had a superiority in quantitative analysis. The feasibility of the developed technique was verified by detecting the Raman spectra of pure samples in air. Compared with the spectra acquired by the Gaussian beam Raman spectroscope, the performance of the BRS system in terms of Raman spectrum detection and Raman peak recognition was confirmed. Subsequently, by employing the technique for the detection of acetaminophen buried in the scattering media, the application of the new technology in detecting and quantitating the chemicals in the scattering media were underlined, offering greater detection depth and better linear quantification capability than the conventional Gaussian beam Raman spectroscopy. Finally, we explored the potential of the BRS system for chemical sensing of acetaminophen in biological tissue slices, indicating a significant development towards the evaluation of drug in vivo.

Steady optical beam propagating through turbulent environment.

A steady optical beam (SOB) propagating stably in a disorder medium is constructed by using a specially designed aspherical lens. Our theoretical and experimental results show that the generated SOB exhibits much better propagation features with small divergence and long Rayleigh length, as well as weak deformation through turbulent environment as compared with a conventional Gaussian beam. The beam parameter product of the SOB reaches 49.40% of the Gaussian beam by multiple measurements within a certain distance range. The SOB may find applications in optical communications and optical detection in turbulent transmission conditions.

Super-efficient drilling of metals with ultrafast non diffractive laser beams

A highly efficient drilling process is found in non-transparent metallic materials enabled by the use of non-diffractive ultrafast Bessel beams. Applied for deep drilling through a 200 μm-thick steel plate, the Bessel beam demonstrates twofold higher drilling efficiency compared to a Gaussian beam of similar fluence and spot size. Notwithstanding that surface ablation occurs with the same efficiency for both beams, the drilling booster results from a self-replication and reconstruction of the beam along the axis, driven by internal reflections within the crater at quasi-grazing incidence, bypassing potential obstacles. The mechanism is the consequence of an oblique wavevectors geometry with low angular dispersion and generates a propagation length beyond the projection range allowed by the geometry of the channel. With only the main lobe being selected by the channel entrance, side-wall reflection determines the refolding of the lobe on the axis, enhancing and replicating the beam multiple times inside the channel. The process is critically assisted by the reduction of particle shielding enabled by the intrinsic self-healing of the Bessel beam. Thus the drilling process is sustained in a way which is uniquely different from that of the conventional Gaussian beam, the latter being damped within its Rayleigh range. These mechanisms are supported and quantified by Finite Difference Time Domain calculations of the beam propagation. The results show key advantages for the quest towards efficient laser drilling and fabrication processes.

Robust functional imaging of taste sensation with a Bessel beam.

Functional imaging of intact taste cells in response to various tastant solutions poses a technical challenge since the refractive index of the immersion medium dynamically changes during tastant delivery. Critically, the focal shift introduced by high-index tastant solutions has been the fundamental limit in experimental design. Here we seek to address this issue by introducing an axially elongated Bessel beam in two-photon microscopy. Compared to the conventional Gaussian beam, the Bessel beam provides superior robustness to the index-induced focal shift, allowing us to acquire near artifact-free imaging of taste cells in response to a physiological taste stimulus.

Phase-matching control of high-order harmonics with circular Airy-Gaussian beams.

We investigate the phase-matching of the high harmonics (HHG) driven by the circular Airy-Gaussian beams (CAiGB), which abruptly auto-focus and subsequently propagate without diffraction. The results show that the harmonics corresponding to both short and long quantum paths can be well phase-matched after the focusing point of the CAiGB. Therefore, the effective interaction length of HHG for CAiGB is much longer than that for the conventional Gaussian beams with the same size of the waist. Our numerical simulations reveal that the harmonics continuously gain up to 1 cm of the propagation distance. This work provides a route to enhance the conversion efficiency of HHG by the coherent control of abrupt auto-focusing beams.

An illumination‐compensated Gaussian beam migration for enhancing subsalt imaging

ABSTRACTSeismic images of Earth's subsurface are essential for oil and gas exploration. Gaussian beam migration is popular for seismic imaging owing to its flexibility and efficiency of implementation. However, the practical use of classic Gaussian beam migration is limited for complicated structures such as subsalt because of poor seismic illumination in those areas. We propose an illumination‐compensated Gaussian beam migration under the framework of least‐squares migration, enhancing the subsalt imaging effectively. A novel scheme based on the Born modelling and migration of Gaussian beam is developed to estimate the point spreading function, with which the illumination compensation can be efficiently implemented in the local wavenumber domain. As the aim of least‐squares migration, the proposed illumination‐compensated Gaussian beam migration produces true‐amplitude images in subsalt areas, which facilitates the seismic interpretation of subsalt structures. The total computational cost of the proposed method includes one Born modelling process and two conventional Gaussian beam migrations, and thus it is much more efficient than the classic least‐squares migration which requires multiple iterations. Numerical examples have demonstrated the effectiveness of the adaptive strategies, manifesting applicable potential in oil and gas exploration of subsalt targets.