Diffractive Beam Shaping Research Articles

Improving the Processing Efficiency of Femtosecond Laser Sulfur Hyperdoping of Silicon by Diffractive Beam Shaping

Improving the Processing Efficiency of Femtosecond Laser Sulfur Hyperdoping of Silicon by Diffractive Beam Shaping

Diffractive Beam Shaper for Multiwavelength Lasers for Flow Cytometry.

Illumination spot in a flow cytometer is a crucial factor determining the measurement accuracy and stability. The traditional mechanism is to precisely calibrate multiple optical components to convert circular Gaussian beams into elliptical Gaussian beams, making it difficult to shape multiwavelength lasers simultaneously. A diffractive beam shaper for multicolor lasers with high simplicity, only containing one diffractive optical element and one focusing lens is created in this work. It can produce rectangular spots, of which the number, the sizes, and the positions are accurately determined by the incident wavelengths. Demonstrated in the customized microflow cytometer, the coefficient of variations (CV) of the optical signals by the beam shaper are 3.6-6.5%, comparable to those derived from the commercial instrument with 3.3-6.3% CVs. Benefiting from the narrow rectangular spots and the flexibility of diffractively shaped lasers, the measurement of bead sizes with 4-15 μm diameters and the real-time detection of flow velocity from 0.79 to 9.50 m/s with the CV of <5% are achieved. © 2020 International Society for Advancement of Cytometry.

Tailored micro-optical freeform holograms for integrated complex beam shaping

Modern optical measurement technologies such as structured light microscopy or fringe-projection profilometry rely fundamentally on structured illumination of the specimen or probe. Miniaturizing the applied illumination concept enables the availability of these methodologies even in spatial domains that have remained inaccessible so far. Here we introduce a design methodology to realize complex illumination patterns with high diffraction efficiencies in a strongly miniaturized and functional integrated approach. This is achieved by combining the advantages of refractive freeform wavefront tailoring and diffractive beam shaping. This novel concept overcomes classical stray light issues known from conventional diffractive beam shaping and remains valid for micro-optical systems, i.e., beyond the geometric optical regime. Moreover, the design process is in particular optimized to reduce the aspect ratio of the obtained surface features. This strongly improves the manufacturability and as-built performance of the designed optical element, and the feasibility of the approach is demonstrated by the design and realization of monolithic beam shaping units on the tips of optical fibers via two-photon direct laser writing. This provides the means to realize complex illumination patterns in an integrated and mechanically flexible approach.

Beam Shaping for Advanced Laser Materials Processing

AbstractFor recent industrial materials processing with advanced high power lasers, beam shaping optics are utilized as a key technology. Aspheric or diffractive beam shapers transform a Gaussian intensity profile of a single mode (TEM00) laser beam into a flattop one. While an aspheric beam shaper can make a circular flattop, a diffractive one can realize much flexibility in output beam shapes, like square, rectangular, linear, or other complex beam shapes. The beam shaping is often combined with a scanning optical system, consisting of galvanometric mirrors and an f‐theta lens. Those beam shapers are used for either pulsed or CW single mode laser applications, i. e. ablation, cutting, drilling, scribing, annealing, etc. of thin films or bulk materials. This article describes principles, design concepts and specification examples of those optical systems used in practical applications.

Comparison between interferometric and diffractive laser beam shaping

We consider the transformation of a Gaussian laser beam into a flat-top intensity profile or into an optical bottle beam (OBB) by resorting to a diffractive or an interferometric method. The diffractive technique is based on the use of a diffractive optical element consisting in a π-plate, while the interferometric technique uses a Michelson interferometer (MI). The coaxial superposition of two coherent Gaussian beams yields to a flat-top or a OBB in the focal plane of a lens depending on the geometric characteristics of the MI. The performances of the two techniques are compared.

Laserscribing of Thin Films Using Top-Hat Laser Beam Profiles

We present a comparative study of laser scribing different thin solid films using nanosecond laser pulses with different wavelengths and laser beam profiles. In particular, we show the influence of the used laser beam profile for the processing of a 150nm thin Indium Tin Oxide transparent conductive film and a multilayer system, consisting of different metal and transparent conductive oxide (TCO) layers deposited on a soda lime glass substrate. For laser scribing the wavelengths 1064nm, 532nm and 355nm were used with a Gaussian and a Top-Hat beam profile. The homogenous TopHat beam profile is generated with both, a refractive and diffractive beam shaper. The results show several advantages of using a Top-Hat laser beam shape for thin film laser scribing, such as less energy consumption, high rim quality with simultaneous small pulse overlap and protection of the underlying substrate, respectively. Our results prove that the application of beam shapers can improve the process quality and increase the scribing speed for the investigated materials.

Trade-off between diffraction efficiency and uniformity for design of binary diffractive laser beam shaper

The trade-off between diffraction efficiency and uniformity is studied when a binary phase-only diffractive optical element (DOE) is designed for transforming a Gaussian beam to an expanded squared uniform intensity distribution. The simulated annealing (SA) algorithm and Fresnel diffraction theory are applied in our design. Two types of cost functions are utilized in the SA algorithm, and the cases of different incident Gaussian diameters and bright-area sizes of the target patterns are studied. The mechanisms of reducing nonuniformity by the two cost functions are essentially different, and the mechanism combining nonuniformity and the intensity difference between the reconstructed and target patterns has better results. Satisfactory performance can be obtained under the trade-off between them.

Low speckle laser illuminated projection system with a vibrating diffractive beam shaper

Currently the major issues in applying the laser as an illumination source for projectors are beam shaping and laser speckle. We present a compact total solution for both issues by using a diffractive beam shaper associated with a cylindrical lens for the illumination optics and a vibrating motor attached to the beam shaper to eliminate speckle on the projection screen. The diffractive beam shaper features a double-sided microlens array with a lateral shift to each other. The illumination pattern is free of zero diffraction order mainly due to the continuous and spherical surface relief of the lenslet, which can be accurately fabricated with diamond turning and injection molding without quantizing surface relief, so that the illumination pattern on the microdisplay can match the design very well with high diffraction efficiency. In addition, the vibration of the diffractive beam shaper in the longitudinal mode has been found effective for eliminating the dot pattern in the illumination and reducing laser speckle on the projection screen. The proposed laser illuminator has been implemented on a three-panel LCoS projector engine to replace the traditional UHP lamp. The uniformity and speckle contrast are measured to be 78% and 5.5% respectively, which demonstrates the feasibility and potential of the proposed scheme.

Effects of the spatial frequency composition of the target pattern and the number of quantization levels in diffractive beam shaper design

A mathematical model is derived, and numerical simulation is analyzed for laser beam shaping by using multilevel phase-only diffractive optical elements (DOEs). We used the simulated annealing algorithm to design the beam shapers. The result has an essential effect on the diffractive pattern quality caused by the spatial frequency composition of target patterns for the same incident gaussian beam size and target pattern area. The root mean square error between the diffractive and target patterns is smaller for the target patterns with lower spatial frequencies. Moreover, the effect of spatial frequency composition can be relaxed for the cases of larger incident gaussian beam size. In addition, finer quality control of a diffraction pattern can be obtained by increasing the number of quantization levels at the DOEs.

32.3: Laser‐Illuminated Three‐Panel LCoS Projector with a Vibrating Diffractive Microlens‐Array Beam Shaper

AbstractA RGB lasers illuminated three‐panel LCoS projector has been developed to demonstrate the viability of a double‐side microlens array as a diffractive beam shaper. By oscillating the beam shaper, both the uniformity and speckle pattern were significantly improved. The contrast ratio of the image speckle was measured to be below 8%.

Refractive and diffractive laser beam shaping optics

AbstractEspecially for micro machining lasers have opened new possibilities which were not accessible by traditional mechanical processes (e.g. intravolume glass marking). For many applications the raw Gaussian laser beam profiles are not optimal adapted for material processing. Therefore optimized beam profiles like those with homogeneous intensity (so called Top Hat) or with ring shape are often desired to enhance process efficiency and quality.

Multiwavelength Blue Light Source Based on MgO : PPLN SHG Using Vertically Stacked Grating-Coupled Surface-Emitting Lasers

In this letter, we present the first experimental results of frequency doubling the output of vertically stacked grating coupled surface-emitting laser/dual-grating reflector devices with different emitting wavelengths. We used a multigrating 5% magnesium-oxide-doped periodically poled lithium niobate (MgO : PPLN) crystal as the nonlinear conversion medium. In pulse operation, 0.6 W of multiwavelength total second-harmonic peak power was obtained. The individual emitter output is focused into each channel of the crystal by diffractive beam shaping optical element array to minimize the footprint area of the whole setup.

Diffractive beam shapers provide excellent control

Diffractive beam shapers provide excellent control

Approach to improve beam quality of inter-satellite optical communication system based on diffractive optical elements

For inter-satellite optical communication transmitter with reflective telescope of two-mirrors on axis, a large mount of the transmitted energy will be blocked by central obscuration of the secondary mirror. In this paper, a novel scheme based on diffractive optical element (DOE) is introduced to avoid it. This scheme includes one diffractive beam shaper and another diffractive phase corrector, which can diffract the obscured part of transmitted beam into the domain unobscured by the secondary mirror. The proposed approach is firstly researched with a fixed obscuration ratio of 1/4. Numerical simulation shows that the emission efficiency of new figuration is 99.99%; the beam divergence from the novel inter-satellite optical communication transmitter is unchanged; and the peak intensity of receiver plane is increased about 31% compared with the typical configuration. Then the intensy patterns of receiver plane are analyzed with various obscuration ratio, the corresponding numerical modelling reveals that the intensity patterns with various obscuration ratio are nearly identical, but the amplify of relative peak intensity is getting down with the growth of obscuration ratio. This work can improve the beam quality of inter-satellite optical communication system without affecting any other functionality.

Diffractive Line Beam Shaper

A diffractive laser beam shaper has been proposed as a lossless approach to transfer a Gaussian laser beam into a thin line beam with a uniform distribution along the line direction for scanning material processing or illumination application. With the consideration for the feasibility of fabrication, the optical performance of the diffractive beam shaper with its surface relief quantized at different levels has been analyzed with scalar diffraction theory, which shows that an 8 level solution is sufficient for keeping the uniformity in the line direction while the focusing function in the orthogonal dimension needs to be performed by an extra cylindrical lens.

Fabrication of beam shapers in the bulk of fused silica by femtosecond laser pulses.

We reported a new approach to the fabrication of three-dimensional refractive-index-modified microstructures inside transparent materials by combining two-dimensional writing by scanning the focus of the femtosecond laser pulse and by forming the long filament in the third dimension. In this way, embedded diffractive beam shapers of grid, square, and ring gratings were obtained in the bulk of fused silica by use of a femtosecond laser with a wavelength of 810 nm and a repetition rate of 1 KHz. These structures and their refractive efficiencies were optimized by selection of the appropriate fabrication parameters, including the pulse energy, grating period, scanning speed, and scanning repetition. The good performance of these devices indicates that, owing to its simple and flexible method for fabricating complex phase elements inside transparent materials, this technique has potential applications to integrated optics.

Diffractive beam shaper for blood cells optical characterization

In this paper we propose a new design for blood cells optical characterization systems. This design relies on a diffractive beam shaper especially adapted to blood cells differentiation. This beam shaper has been synthesized integrating both optical blood cells characterization constraints and diffractive optics synthesis constraints. A prototype has been realized and the proposed system has shown enhanced measurements stability as well as relaxed positioning constraints compared to existing blood cell optical characterization systems.

Efficient pseudo-nondiffracting beam shaping using a quasicontinuous-phase diffractive element

We report a new diffractive beam shaper that transforms an incident Gaussian beam into a pseudo-nondiffracting beam with a relatively flat on-axis intensity distribution in the propagation range. The compact single-element beam shaper with a quasicontinuous phase structure demonstrated beam-forming efficiency of 87.5%. The effects of misalignment and beam size error on beam-forming quality are also addressed.

Diffractive shaping of excimer laser beams

We address the problem of shaping the intensity distribution of a highly directional partially coherent field, such as an excimer laser beam, by means of diffractive optics. Our theoretical analysis is based on modelling the multi-transverse-mode laser beam as a Gaussian Schell-model beam. It is shown numerically that a periodic element, which is unsuitable for the shaping of a coherent laser beam, works well with an excimer laser beam because of its partial spatial coherence. The conversion of an approximately Gaussian excimer laser beam into a flat-top beam in the Fourier plane of a lens is demonstrated with a diffractive beam shaper fabricated as a multilevel profile in SiOl by electron-beam lithography and proportional reactive-ion etching.

New diffractive beam shaper generated with the aid of e‐beam lithography

New diffractive beam shaper generated with the aid of e‐beam lithography