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TOP-HAT Shaping

　　Introduction 　　In the laser processing industry, how to focus the original laser beam to a well-defined size and shape with uniform intensity (flat top) catches more and more people's attention. Beijing Homolaser Technology Co., Ltd. provides top-hat elements with a high uniformity, a clear-cut border, customized spot size and shape according to specific demand. Applications 　　lLaser cutting 　　lLaser wielding 　　lLaser scribing 　　lFilm processing, solar panel cutting, LED filament processing 　　Working principle: 　　The most rudimentary set-up in a beam shaping system consists of a laser, a refractive / diffractive beam shaper element and a focusing lens. See the figure below. Top-hat elements have a high demand for laser quality. For good quality beam shaper performance, the laser output should be Single Mode (TEM00) with an M2 value under 1.3. A large M2 will degrade the uniformity and sharp edge of the top-hat spot. In this case, it may still be possible to reduce the M2 value by inserting a spatial filter in between the laser and the DOE lens component. 　　Top-hat element is a phase element that transforms the Gaussian input beam into a uniform spot with sharp edges at a specific working distance WD. Note that the Top-Hat spot is NOT at the minimum spot location (minimum waist), but near it (about a few microns from the focal plane). 　　Each top-hat element is designed for specific use with a unique set of optical system parameters provided by our customers: 　　lLaser wavelength 　　lInput spot size 　　lWorking distance 　　lOutput spot size 　　Beam shaper elements are sensitive to various parameter tolerances. Altering any one of the vales in this parameter set will degrade the performance of the Top-Hat beam shaper element, and possibly render it useless. 　　We highly recommend a beam expander and collimator in using top-hat element. a larger beam reduces the sensitivity of the beam shaper output to tolerances, and enable achieving a smaller output spot. 　　As was mentioned above, the beam shaper element requires that the input beam will be collimated. 　　For this reason, as well as for purposes of stability, it is recommended to work with the beam shaper element in the waist of the laser. Nonetheless, if the beam has a small divergence angle (<1º), which means, due to some constraints, the diffractive optical element (DOE) will be located at a distance from the beam waist, there should not be any noticeable effect on the Top-Hat output quality, it will though change the working distance. In short, it is more convenient to design a DOE and get the ideal performance based on an accurate high-quality wavefront 　　When designing the desired output Top-Hat size, it is important to be familiar with the physical limits of the minimum spot size. The formula for the diffraction-limited spot size: Where: 　　L：working distance 　　D：input beam size（on the focusing element） 　　Some basic rules： 　　lIt is impossible to get a Top Hat size smaller than the diffraction limited spot size. 　　lthe minimum beam shaper spot size will be between 1.5 to 5 times the diffraction-limited spot size. 　　lThe best performance will be obtained for a well-positioned perfectly aligned part, located precisely in the plane of the nominal working distance. 　　Characteristics Operating principle 　　Minimum top-hat optical element (hereinafter referred to as the element) is a product of Beijing HOMOlaser S&T CO., Ltd with a fully independent patent, which is used to focus a Gaussian beam with M2<1.5 to a well-defined size and shape with uniform intensity (flat top).The element. The element has such advantages as simple installation, high transmittance, conservation of initial optical systems. 　　Here is the procedures of installation and adjustment. 　　A.Galvanometric system 　　1．Conditions: a galvanometric system, a lens mount，an x-y adjuster 　　2．Procedures of installation and adjustment 　　Firstly，collimate and expand laser beam to get the required spot size by the element. 　　Secondly，Conventional optical adjustment makes galvanometer system achieve its conventional capabilities. 　　Thirdly，put the element between the beam expanding collimator and the galvanometer. Beam divergence conserves in a few meters. 　　Fourthly，roughly adjust the element to locate the center of it in the optical axis of the system before turning on the laser. 　　Fifthly，put on anti-laser goggles，turn on the laser，make the beam illuminate a piece of A4 paper，adjust the laser power until a spot is visible. 　　Sixthly，put the A4 paper behind the element wearing the anti-laser goggles，observe carefully to get the projection of the central pattern on the element. For example，the projection of square top-hat element is a square spot, the projection of circular top-hat element is a circular spot. Based on the location of the projection, adjust the location of the element to make sure the center of it is in the optical axis of the system. For round sh

Diffuser/Homogenizer

　　Diffractive optical diffuser 　　Introduction 　　Beijing HOMOlaser S&T CO., Ltd produces optical Diffuser/Homogenizer (DF/HM) diffractive optical element (DOE) which transforms a single or multi-mode input beam into a well-defined output beam, characterized with a desired shape, and homogenized flat-top intensity (or other intensity profile, see below). 　　Homolaser’s optical diffuser DOE performs a homogenized spot with accurately defined sharp shaped edges, while enabling high efficiency. 　　Characteristics 　　lWorks with single or multi mode input beams 　　lFused silica mainly, glass or plastic materials available 　　lAny output shape or symmetry 　　lUniform/Tailored intensity profile 　　lExact diffusion angles 　　Applications 　　lLaser homogenizing/shaping 　　lLaser material processing: perforation, ablation, derailing, marking, scribing and welding 　　llaser test/ detection 　　lMedical/aesthetic laser treatment 　　Specifications General definition 　　Homolaser is enabled to design an element that will produce any arbitrary shape, intensity profile with precise angle and size of the output, which is obtained in the far field or focal plane if an focusing lens is used. The diffuser performance strongly depends on the incident beam parameters. In general, one can distinguish between two qualities： 　　1.single mode laser beam with M2<5，highly coherent beam. Best results in terms of intensity profile, uniformity, efficiency and transfer region for single mode lasers can be achieved by using Top Hat (TH) designs like in 　　page: PRODUCT->TOP-HAT Shaping. 　　2. Multi-Mode laser beam with M2>5，When the incident beam is more complex to define – by having an arbitrary intensity distribution and not a near-to-perfect Gaussian (higher M2) one, the uniformity performance may be improved at the cost of a sharp edge. 　　The figure below shows the circular homogenized generated by our diffuser DOE illuminated by a single mode laser beam. The spot border is considerably clear, while the zero order is fairly noticeable due to the high coherence. 　　Operation principle and design considerations 　　1.design considerations 　　uwavelength 　　uOutput shape and intensity profile 　　uDivergence angle (of output shape) or image size and EFL 　　uBeam quality M2 　　2.The most rudimentary set-up in a beam shaping system consists of a laser, a refractive / diffractive beam shaper element and a focusing lens. See the figure below θ：diffusion angle 　　EFL：effective focal length 　　D：output beam size 　　The optical parameters of the diffuser can be easily calculated from geometric point of view。 　　1.The minimum diffusion angle is equivalent to approximately 5-10 times the diffraction-limit. In addition, a larger angle ratio (to a certain level) will increase the performance quality. The formula for the diffraction-limited spot diameter at 1/e2 (D.L.spotsize) follows： 　　L：working distance 　　D：output beam size（on the focusing element） 　　1.According to diffraction theory, The ratio between input divergence angle to diffusion angle, determines our processing difficulty . 　　2.Additional improvement in the uniformity performance may be achieved by using a high M2 input beam. 　　3.In addition，the diffractive pattern can be etched on the Plano side of the focusing lens (plano-convex lens). The advantages of this solution include less optical surfaces, compact dimension and low weight. 　　Beam shaping: single-mode versus multi-mode: 　　Currently，Homolaser produces a new homogenizer for laser beam with a low M2，effectively reduced the zero order at the cost of energy efficiency. 　　Refractive optical homogenizer 　　Introduction 　　Beijing HOMOlaser S&T CO., Ltd produces refractive optical element(ROE) which transform a laser beam to a well-defined output beam, characterized with a desired shape, and homogenized flat-top intensity and a desired diffusion angle. See the performance of our elements below： Applications 　　lLaser display 　　lMedical laser 　　lLaser pumping 　　lLaser lift-off 　　lLaser communication, etc. 　　Operation principle 　　The operation principle of using refractive optical element is fairly simple. All you need to do is to block the laser with the element. See below. Characteristics 　　Our refractive homogenizer’s energy efficiency is as high as 99% and more. The diffusion angle（specified byFWHM，that is the spot size in one meter’s distance which can be obtained by calculating the arc tangent of the half diffusion angle）is as big as 41 degrees. The diffusion angle is custom-tailored. 　　Design consideration 　　Design considerations according to customers’ demand：laser wavelength，diffusion angle. 　　Notification

Multi-Focus DOE

　　Introduction 　　Diffractive multifocal element/lens of Beijing Homolaser Technology Co., Ltd allow a single incident beam to focus simultaneously at several focal lengths along the propagation axis. The number of foci is determined during the design according to the customer's application requirements. The figure below shows cross-section of processed sapphire using our 5-foci element and focusing lens，the intervals  basically keep consistent，energy irregularity is kept under 6%. 　　Besides，considering the convenience of application，we have produced a multifocal lens showed below，which allows for plug and play. Its internal structure consists of two part: multifocal element, focusing lens system wrapped up in stainless steel mechanical components. This lens finds its wide application in cutting transparent material，such as glass and sapphire. This manual is meant to aid the user's understanding of the functionality and considerations when using a diffractive multifocal element. Working principle 　　The straightforward operational principle is using a collimated input beam (single mode or multi-mode), see below. The foci spot at the "zero" order refers to the refractive focal length of the lens being used. The other diffractive foci spots, orders +/-1,2,3…, appearing symmetrically around the refractive "zero" order, are in fixed numbers and  locations predetermined during the design of the DOE based on the customer's system requirements. An approximation of the distance between the foci spots can be described by the equation below: 　　fm：Focal Length for "m" diffractive order 　　ffocus：Focal Length of the refractive lens 　　fDOE：Focal Length of the diffractive lens 　　m：order of multi-focal spot，see below. Multifocal lens 　　Aiming at transparent material cutting market，we released a multifocal cutting lens in a superb quality with accurate foci intervals and good energy uniformity. See our 11 foci lens parameters below. 　　The figure below is cross-section of dissected sapphire, with the surface roughness under 2um. Besides，we are capable to provide custom-tailored product covering multiple parameters including mechanical material, interface parameter, foci location, foci number, foci intervals. Notification

Beam Splitter

　　Introduction 　　A Beam Splitter of Beijing HOMOlaser S&T CO., Ltd is a diffractive optical element (DOE) used to split a single laser beam into several beams, each with the characteristics of the original beam (except for power and angle of propagation). A beam splitter can generate either a 1-dimensional beam array (1xN) or a 2-dimensional beam matrix (MxN). The figure below shows a 32*32 splitted beam, taken from actual items. Based on that, a common variation of the laser beam splitter / multi-spot DOE is a multi-line array, where instead of a 1xN array of spots, the user will get a 1xN array of lines, whose length and separation angle are determined during the design according to the customer's application requirements. Applications 　　lLaser cutting 　　lLaser drilling 　　l3-D sensors 　　lLaser scribing 　　lFiber optics 　　Operation principle 　　In principle, A Beam Splitter demands a collimated input beam, the output beams exit from Beam Splitter DOE with a separation angle that is determined based on the customer's system requirements during the design of the DOE. The separation angle designed for far-field is highly accurate (<0.03mR error). 　　Homolaser is also able to design a custom beam splitter and so activate and deactivate any order of the beam splitter. 　　Normally, the customer wishes to get well-focused spots at a certain distance. This is easily achieved by the addition of a simple focusing lens after the DOE, whose BFL (back focal length) determines the working distance (WD) to the multi-spot focal plane. 　　Characteristics 　　In double-spot configuration, power efficiency can reach nearly 80% due to physical constraints, while the multi-spot (>2) configurations can reach nearly 85% in binary etching process, and nearly 95% in multi-level etching. The remaining power is distributed among the other (parasitic) orders. 　　In order to obtain an ideal performance, it is recommended for our customers to provide the input beam size, which is at least 3-5 times the period of the pattern on the DOE, 5 times better. 　　Design consideration 　　Design considerations according to customers’ demand：laser wavelength，beam size, focal length of the focusing lens (if needed), and the diffraction angles. 　　Notification

Pattern Generator

　　Introduction 　　Beijing HOMOlaser S&T CO., Ltd is able to design and produce customer-specific pattern generators element which project required pattern after illuminated by lasers. We can realize a variety of complex patterns using multi-level DOE if necessary, such as flag, portrait, sight picture, multiple lines, grid and so on. Applications 　　• Laser calibration 　　• Laser measurement 　　• Laser package 　　• Outdoor advertising 　　• Structured light generator 　　• Virtual keyboard 　　Operation principle 　　In principle, a pattern generator requires a collimated input beam and thus a clear pattern can be obtained. 　　The full divergence angle of required pattern should be provided by our customers. 　　Pattern generator element with top-hat element in the field of laser package is to achieve the optimal solution with high accuracy, low temperature, low stress, wafer-level bonding package. 　　Characteristics 　　Power efficiency of a pattern generator can reach nearly 80%, divergence angle 80 degrees, and inhomogeneity of zero order 2%. 　　Design Consideration 　　Design considerations according to customers’ requirements：laser wavelength，input beam size, focal length (if a focusing lens is needed), full divergence angle of the required pattern . 　　Notification

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