Beam Shaping System Research Articles

Acousto-optic femtosecond laser beam shaping for bottle-beam generation

Abstract This study explores the properties of a laser beam shaping system comprising an acousto-optic dispersive delay line (AODDL) and an acousto-optic tunable filter (AOTF) for ultrashort laser pulse shaping. The system demonstrates the AODDL’s ability to generate signals with arbitrarily positioned transmission windows and investigates the impact of spectral width on field distributions. The AOTF’s frequency scanning and simultaneous control of two and three spectral components are presented. The experimental setup utilizes femtosecond laser radiation, and the results highlight the system’s versatility for programmable spectral and spatial filtering, offering potential applications in advanced optical manipulation.

Efficient fiber coupling system for simultaneous beam shaping and wavelength combining based on misaligned stepped prism multiplexing

Due to the substantial contrast in the output beam quality between the two directions of the semiconductor laser, efficiently coupling the beam directly into the fiber is difficult. In this study, an efficient shaping method based on step multiplexing of misaligned step prisms is proposed and investigated systematically. First, multiple laser stacks eliminate dark areas to improve the beam quality through the full utilization of the transmission and reflection surfaces of the misaligned stepped prisms, which also improves the efficiency of the stepped prisms. It also simultaneously realizes laser wavelength combining based on reflective surface multiplexing without affecting the quality of the beam on the premise of improving the output power. Finally, the whole beam shaping system is completed without using cut-transform-rearranging prisms. The method couples four groups of laser stacks into a single fiber with a fiber diameter of 400 µm and a numerical aperture of 0.22. It can be seen from the computer-simulated model outputs that the final fiber output power can reach 2255.4 W and that the system as a whole has a light-to-light translation rate of 88.1%.

Design and implementation of dynamic beam shaping in high power laser processing by means of a Deformable Mirror

Optimising the laser intensity distribution in high power laser processes, such as laser welding, laser cladding or laser hardening, can be used to tailor the local thermal fields and thermal cycles which, in turn, determine the final process results. Deformable Mirrors allow to dynamically shape the beam profile and previous studies showed their potential. However, only limited flexibility in achievable beam shapes is shown at higher power levels. In addition the relation between desired laser intensity profiles and required mirror surface profiles is nontrivial. In this work the design and implementation of a dynamic beam shaping system, capable of handling high laser powers (up to 1 kW), is presented and evaluated. To that end, several distinctly different laser intensity profiles are defined, corresponding mirror surfaces are determined and realised with the beam shaping system. Measurements of the laser intensity profiles were compared with laser intensity profiles simulated using a previously presented mathematical framework and showed a good agreement. From the measurements it was concluded that the setup is suitable for high laser powers (up to 1 kW) and is characterised by large depth of focus (<14% change in dimensions at a distance of 100 mm from the focal plane).

Design of a long depth of focus Gaussian beam shaping system via aspheric lenses

This paper presents a beam shaping system that uses a Galilean beam shaper. The light mapping function and the aspherical coefficient, which determines the characteristics of the aspheric lens, are derived based on the law of conservation of energy. Furthermore, optical software (i.e., ZEMAX) was utilized to simulate the design of the shaping system. In addition, a spherical collimation system is introduced to achieve the shaping system with long depth of focus. The results show that the output flat-top beam has the uniformity over 90% within the 300mm depth of focus range and the divergence angle no more than 0.6°, which is in line with the theoretical expectation. Compared to the previous works, our beam shaping system is characterized by long depth of focus, simple structure and good beam shaping effect, which makes the present shaping beam more flexible for the application in the field of laser processing.

Design method of beam shaping system for double free-form surfaces based on Virtual Surface Iteration method

Design method of beam shaping system for double free-form surfaces based on Virtual Surface Iteration method

Improved active sub-terahertz imaging system for parcel inspection

Terahertz radiation has emerged as a prominent solution for imaging and detection beyond visible and infrared. Active terahertz imaging is a widely used technology in this context especially for security applications and screening. Such systems are built around an illuminating source, a detecting module and a beam shaping system to match the detectors geometry. The overall system performance is largely dependent on an optimized choice of these modules. In this work, an active sub-terahertz scanning system working at 100 GHz frequency is proposed to detect concealed objects in parcels and mail. The system is optimized based on an adapted design of the beam shaper and a preprocessing correction of the images to ensure uniformity of response and cleanness. The proposed system demonstrated through experimentation improved resolution with a uniform response along its detection area.

Realization of collimated specific profiles in rotation-symmetrical beam shaping system with divergent light source

A simple numerical method is proposed for the design of two aspherical surfaces, each comprising multiple segmented refractive planes, for generating a collimated beam with a specific irradiance profile in a beam shaping system with a divergent light source. However, in real-world manufacturing, this performance improvement is obtained at the expense of a greater cost and complexity. Accordingly, a second algorithm is proposed which maximizes the number of rays passing through the central regions of the refractive planes in the second aspherical surface and hence minimizes the total number of segments required to achieve the same beam shaping performance. The feasibility of the proposed method is demonstrated through the design of two aspherical lenses for generating collimated output beams with ring- and triangle-like irradiance profiles, respectively. The experimental results show that the beam profiles are in close agreement with the desired irradiance distributions. In general, the results indicate that the proposed method provides a versatile and efficient approach for achieving the desired collimated profile in beam forming systems with a divergent light source.

Independent multicolored bottle-beam generation using acousto-optic spatial shaping of a femtosecond laser beam.

We report on the development of a tunable spectral and spatial frequency shaping system for ultrashort laser pulses using acousto-optic filters. The system enables the creation of arbitrary axially symmetric multi-wavelength field configurations in the Ti:sapphire laser emission range near 800 nm and controlling them at a multi-kilohertz rate. We experimentally demonstrate independent generation of two-colored annular intensity distributions from a single femtosecond laser beam and a bottle beam having the hollow cylindrical volume with the aspect ratio of 9:1. This laser beam shaping system can be useful in creating advanced setups for an optical control of cold atoms.

Three-mirror free-form off-axis antenna design of beam shaping on a circular substrate

This work presents a design of a three-mirror free-form surface beam shaping system with small dimensions, easy assembly, and good collimation. To facilitate integration and assembly, the three mirrors are integrated into a circular substrate with a radius of 90 mm. Based on the law of energy conservation, Fermat’s principle, and the vector theory of reflection, the input–output mapping is derived, and the three free-form mirrors are constructed point by point simultaneously. Ray tracing results demonstrate that the maximum divergence angle is compressed to 0.467 mrad and the standard deviation of the edge beam radius samples (SDRS) is reduced from 5.42mm to 0.985mm on the receiving plane. The light intensity has a relative root mean square deviation (RRMSD) of only 0.049. Furthermore, the results show that the minimum value of SDRS is 0.940mm at a propagation distance of L=1.72 m, while the minimum value of RRMSD is 0.0431 at L=7.03 m. In addition, the effects of astigmatism and light source offsets on the collimated and shaping effect are analyzed. The design of the free-form surfaces antenna system in this work will provide a new design method for practical engineering and application, and will greatly improve the quality and propagation distance of the Gaussian beam.

Multilevel synergically controlling wavefront correction of a high-power slab laser system.

We present a multilevel synergically controlling wavefront correction method that can apply in a slab laser system. To fully utilize the response frequency and the stroke of actuators of the single deformable mirror (DM), we design a set of multilevel wavefront correction devices to reduce the root-mean square of wavefront aberration before the DM. As the wavefront of slab geometry solid-state lasers mainly consists of fourth and longitudinally distributed aberration, such as 5th, 9th, and 14th orders of Legendre polynomials. We design a precompensating level of the aberration with a slow-drift mirror, fast-steer mirror, one-dimensional adjustable slab-aberration compensator, and beam-shaping system to reduce these orders of wavefront aberration with low spatial resolution and large stroke. As the controlling bandwidth of different devices is diverse, the coupling oscillation between the precompensating level and adaptive optics (AO) level occurs, then we develop the multilevel synergically control to address the coupling. With the precompensating level, the experimental result shows the residual wavefront aberration of the slab laser is compensated well by the AO level effectively within the compensating capability. We clean up a 9.8kW slab laser system with the beam quality β of far-field focus spots improved from 17.71 to 2.24 times the diffraction limit.

Tailoring freeform beam-shaping lenses for edge-emitting lasers

The edge-emitting laser diodes (EELs) are widely used in various applications, however, the strongly asymmetric beam profile along the fast and slow axes gives a big challenge to the beam shaping of EEL. Traditional optical devices mainly focus on adjusting the asymmetric divergence angle of the fast and slow axes of the EEL, and it is difficult to achieve flexible and precise control of the luminous distribution of the EEL due to the limited freedom of the conventional beam-shaping element. In this article, we employ freeform lenses to flexibly reshape EEL beams and develop an approach to tackle the obstacles caused by the strongly asymmetric beam profile by generalizing the Monge–Ampère method to tailor freeform beam-shaping lenses. Three typical but challenging beam-shaping tasks show that both the intensity and wavefront of an EEL beam can be reshaped in a desired manner by using a single compact freeform lens without any symmetric restrictions on the architecture of the beam-shaping system.

Wide-spectrum laser beam shaping for full-color volume holographic optical element recording.

For homogeneous diffraction efficiency of the recorded volume holographic optical element (vHOE), a recording beam of uniform intensity is required. A multicolor vHOE is recorded by an RGB laser source with Gaussian intensity distribution; during equal exposure time, recording beams of different intensities would result in different diffraction efficiencies in different recording areas. In this paper, we present a wide-spectrum laser beam shaping system design method, by which the incident RGB laser beam can be controlled into uniform intensity distribution with a spherical wavefront. This beam shaping system can be added to any recording system to obtain uniform intensity distribution without altering the beam shaping effect of the original recording system. The proposed beam shaping system is composed of two aspherical lens groups, and the design method with an initial point design and optimization design method is given. An example is built to demonstrate the feasibility of the proposed beam shaping system.

Design of Integrated Lens Array Beam Shaping System

Design of Integrated Lens Array Beam Shaping System

Design of high-brightness, fiber-coupled, beam shaping system based on a multichip 2D green laser diode array

Small size, high-brightness fiber-coupled laser modules have always been the ultimate goal that all researchers are pursuing. A high-brightness 525 nm wavelength fiber-coupled system is designed and evaluated. Based on a multichip 2D green laser diode array, fast-axis collimators are set inside the light source, and a beam shaping system that can rearrange the beam and improve the beam quality in both axes is designed. The simulation results indicate that 24 single emitters are coupled into a 50μm / 0.15 NA optical fiber successfully and the output power is 22.55 W. The brightness of 16.25 MW / ( cm2 · sr ) is calculated with fiber coupling efficiency is 97%.

Improvement of Thermochemical Processes of Laser-Matter Interaction and Optical Systems for Wavefront Shaping

Laser thermochemical processes of metal surface oxidation are promising for creating new advanced technologies to meet the growing needs of opto- and micro-electronics, photonics, catalysis, sensorics and other high-tech industries. The features of thermochemical processes of laser-matter interaction occurring in matter under exposure to intense light flows and optical systems for controlling the irradiance and wavefront spatial distribution were reviewed. The laser beam offers the possibility of good focusing, which allows us to conduct chemical reactions, including the heterogeneous oxidation of metals, locally, with high spatial resolution. In this case, the absorption mechanisms of the laser beam vary for metals and for oxides, resulting from a thermochemical reaction and represent semiconductors. For semiconductors, the intrinsic, intraband, impurity, or lattice absorption takes place. The morphology of a metal surface also influences its optical absorption capacity. The improvement of beam shaping systems with elements of computer optics, namely diffractive freeform optics, provides an opportunity for an efficient control of chemical processes by achieving the desired redistribution of the laser beam power density. Laser thermochemical processes of the formation of quasi-one-dimensional nanostructured metal oxides are of great interest for advanced research and for a wide range of applications. A special feature of these processes is that, in the case of a frequency-modulated laser beam the synergy between the heat associated effects of the laser pulses and the laser-induced vibrations allows for a significant increase in the diffusion coefficient, which is stimulated by the non-stationary stress-strain state of the material. Ensuring the means of control over the thermochemical reaction in local sections of the laser exposure zone is an issue that can be solved by adapting the shape of the laser beam by the diffractive freeform optics. The gained knowledge contributes as a foundation for new photonic technologies oriented on the formation of nanostructured metal oxides, involving control over the morphology of the synthesized structures.

Primary aberration optimization for double-plane symmetric beam shaping systems using a pair of curved reference surfaces.

The geometric aberration of centered refracting double-plane symmetric optical systems (DPSOS) is investigated. For DPSOS with different defocus values in the tangential plane and the sagittal plane (astigmatic wavefront), a pair of curved reference surfaces which vanishes the quadratic terms of the optical path difference (OPD) between a general ray and a reference ray are deduced. With the curved reference surfaces, the primary (fourth-order) wave aberration function for DPSOS is calculated and analyzed, which can be used for beam shaping designs with astigmatic input wavefront, such as slab lasers and semiconductor lasers. Further, the proposed curved reference surfaces can be applied to analyze the aberrations of general DPSOS.

Anamorphic beam shaping system designed to optimize irradiance distribution in the Cofiblas process for glass nanofibers production

Glass fibers play a key role as reinforcements in composite materials, where increasing mechanical properties at affordable costs are required in applications such aerospace, automotive and wind turbine manufacturing. The production of glass nanofibers augurs a substantial enhancement of their performance. However, although different techniques are currently used to produce glass, polymer or carbon nanofibers, none of them is practical to continuously produce solid, non-porous and separated glass nanofibers with capability to feasibly scaling up for mass production. The continuous fiberizing by laser melting (Cofiblas), makes possible to obtain ultrafine fibers with virtually infinite length.Here, we provide a deep analysis on the influence of the laser beam shaping system on the performance of the Cofiblas technique. Two different optical systems are compared: the first one consists of a beam-splitter coupled to a set of mirrors and spherical lenses. While the second one, is based on an anamorphic system comprising a simple combination of cylindrical and spherical lenses. Both configurations are evaluated and compared in several sets of experiments with the main target of obtaining continuous glass nanofibers with the smallest diameter. The anamorphic system generates an elliptical Gaussian distribution of the laser beam irradiance, which increases the energy absorbed by the preform. As a result, continuous silica nanofibers with diameters 84.5% smaller are obtained with the anamorphic system, compared with the optical system constituted by spherical lenses.

Dynamic optical beam shaping system to generate Gaussian and top-hat laser beams of various sizes with circular and square footprint for Additive Manufacturing applications

The speed of production in laser-based additive manufacturing processes is rather low compared to conventional manufacturing methods and could be improved by using a top-hat laser beam intensity profile, a variable spot size or a combination of both, enabling wider melt pools during processing. This while retaining or possibly even improving part quality. In this work, the design and implementation of a dynamic optical beam shaping system is presented to enable different shapes and sizes of top-hat beams at the build platform of a Laser Powder Bed Fusion machine which is equipped with a fiber laser emitting at 1070nm. The system has been demonstrated by assembling custom-made beam shapers with commercially available beam expanders and by measuring the intensity profiles. Initial results indicate the possibilities for tuning of the spot size at the build platform by a magnification factor ranging from 1x to 4x. Parameter optimization for the Gaussian beam with 4x magnification was performed and a first 316L demonstrator part is further discussed in this work to illustrate a gain in productivity of 44%, while retaining >99% density.

Freeform and precise irradiance tailoring in arbitrarily oriented planes

Freeform and precise irradiance tailoring in arbitrarily oriented planes is an ultimate goal of nonimaging optics and has not been well addressed. In this paper, we develop a general formulation for arbitrary and precise irradiance tailoring in three-dimensional (3D) space using freeform lenses. This method breaks any symmetric constraints imposed on the geometrical arrangement of conventional beam shaping systems, yielding high-performance beam shaping systems with new functions and flexible geometrical arrangements in 3D space. This method paves a way for the broad application of freeform optics. The robustness and effectiveness of the method is demonstrated by two interesting but challenging designs.

Designing a high-efficiency coupling system to couple a hollow Gaussian beam into single-mode fiber.

The low efficiency of coupling a hollow Gaussian beam into single-mode fiber terribly decreases the transmission efficiency of an optical communication system. In this paper, a coupling system containing a shaping lens and a coupling lens is designed based on the vector theory of refraction. The simulation results show that our coupling system can improve coupling efficiency to 81.45%, and the efficiency can still reach 74.73% even though chamfering and other factors are considered. This paper may not only provide engineers with a more efficient coupling system but also provide designers with ideas of hollow-solid (or solid-hollow) beam shaping systems.