Showing papers on "Flattop published in 2010"

Near-diffraction-limited annular flattop beam shaping with dual phase only liquid crystal spatial light modulators

Abstract: We demonstrate the annular flattop beam shaping technique with dual phase only liquid crystal spatial light modulators (LC-SLM) based on the refractive laser beam shaping systems. One LC-SLM redistributes the intensity distribution, and the other restores the initial underlying wave front. Differing from the conventional annular beam shaping technique, the wave front of the output beam can be maintained. The influences of deviations of beam waist and beam shape on the output beam profile are discussed in detail. Experimental results show that approximate 71% of the power is enclosed in a region with less than 7% rms intensity variation. The 4.1mm diameter near-diffraction-limited beam retains an annular flattop intensity distribution without significant diffraction peaks for a working distance of more than 24cm in the near field.

Near-diffraction-limited flattop laser beam adaptively generated by stochastic parallel gradient descent algorithm

Abstract: We demonstrate the adaptive generation of a near-diffraction-limited flattop laser beam in the near field based on the stochastic parallel gradient descent algorithm and dual-phase-only liquid crystal spatial light modulators (LC-SLMs). One LC-SLM redistributes the intensity, and the other compensates the wavefront of the output beam. The experimental results show that approximately 69% of the power is enclosed in a region with less than 6% rms intensity variation. The 5mm diameter near-diffraction-limited output beam retains a flattop intensity distribution without significant diffraction peaks for a working distance of more than 30 cm.

Adaptive conversion of multimode beam to near-diffraction-limited flattop beam based on dual-phase-only liquid-crystal spatial light modulators

Abstract: We propose and demonstrate the adaptive conversion of a multimode beam into a near-diffraction-limited flattop beam in the near field based on a combination of dual-phase-only liquid-crystal spatial light modulators (LC-SLMs) and the stochastic parallel gradient descent (SPGD) algorithm. One phase-only LC-SLM redistributes the intensity of the multimode beam, and the other compensates the wavefront of the output beam. The SPGD algorithm adaptively optimizes the phase distributions of dual-phase-only LC-SLMs to reduce the variance between the actual beam shape and the target beam shape. The experimental results on a fiber multimode beam show that the system is capable of adaptively creating square and rectangle flattop beams with desired parameters. Beam quality can be greatly improved by this system. The power in the main lobe of the far-field spot is about 4 times larger than that of the input multimode beam.

Applying refractive beam shapers in creating spots of uniform intensity and various shapes

Abstract: Different scientific and industrial laser techniques require not only intensity profile transformation but also creating various shapes of final spots like circles of different diameter, lines and others. As a solution it is suggested to apply combined optical systems consisting of a refractive beam shaper of field mapping type providing a required intensity transformation and additional optical components to vary the shape of final spots. The said beam shapers produce low divergence collimated flattop beam that makes it easy to vary the shape of the beam spot with using either ordinary relay imaging optics, including zoom one, or anamorphotic optics. And the design features of the refractive beam shapers allow controlling the intensity distribution in the final spot (most often flattop one) and providing wide range of spot sizes. This paper will describe some design examples of combined beam shaping systems to create round spots of variable diameter as well as linear spots of uniform intensity. There will be presented results of applying these systems in such applications as laser hardening and others.

Refractive field mapping beam shaping optics: Important features for a right choice

Abstract: There are different kinds of refractive beam shapers of field mapping type used to transform the laser intensity distribution in order to get improvements or special effects in various laser technologies like welding, cladding, hardening, laser techniques in photovoltaics, etc. A right choice of a suitable beam shaper depends on physical specifications of a particular laser application. As a rule, when a final laser spot size is orders of magnitude greater than a laser wavelength, say of millimetre or centimetre scale, it is optimum to apply the beam shapers providing a collimated beam with flattop or another pre-determined output intensity profile. When a final spot size is comparable with the laser wavelength, say tens of microns in micromachining, it is advisable to apply the beam shapers intended to create the required intensity distribution in focal zone of a beam focused. Correspondingly, different kinds of refractive beam shapers, like πShaper or Focal- πShaper, should be applied.This paper will describe important features of intensity profile transformation in optical systems, principles of operation and design features of refractive field mapping beam shapers πShaper and Focal-πShaper. There will be presented examples of intensity transformation and effects on material processing in several industrial applications.There are different kinds of refractive beam shapers of field mapping type used to transform the laser intensity distribution in order to get improvements or special effects in various laser technologies like welding, cladding, hardening, laser techniques in photovoltaics, etc. A right choice of a suitable beam shaper depends on physical specifications of a particular laser application. As a rule, when a final laser spot size is orders of magnitude greater than a laser wavelength, say of millimetre or centimetre scale, it is optimum to apply the beam shapers providing a collimated beam with flattop or another pre-determined output intensity profile. When a final spot size is comparable with the laser wavelength, say tens of microns in micromachining, it is advisable to apply the beam shapers intended to create the required intensity distribution in focal zone of a beam focused. Correspondingly, different kinds of refractive beam shapers, like πShaper or Focal- πShaper, should be applied.This paper will de...

Flattop Beam Generation and Multibeam Processing Using Aspheric and Diffractive Optics

Abstract: State-of-the-art optical techniques have been employed in the recent development of laser materials processing technology. One advanced application of aspheric optics is in homogenization, i.e., flattop beam generation, where an aspheric lens directly controls the wavefront of a laser beam and transforms its Gaussian intensity distribution into one with a circular flat top. Diffractive optics also function as a homogenizer, giving more flexibility in beam shapes, including square, rectangular, linear, or other complex shapes depending on the application. Those aspheric and diffractive homogenizers can be utilized for laser drilling, scribing, annealing, etc. Another important function of diffractive optics is in beam splitting for multibeam processing. A single laser beam is split into multiple beams that are converged onto multiple spot positions on a workpiece by a special lens having an f-sinθ distortion characteristic. Since multibeam processing enables higher throughput with a simpler optical system than the conventional one, diffractive beam splitters are widely used for the laser processes in the mass production of electronic devices. In cases where a flattop multibeam is required, a homogenizer can be installed in the multibeam optical system. In this report, some examples of optical systems for practical applications are presented, with their design concepts and specifications.

High-precision laser beam shaping using binary-amplitude DLP spatial light modulators

Abstract: Laser beams with precisely controlled intensity profiles are essential for many areas of optics and optical physics. We create such beams from real-world lasers: quasi-Gaussian beams obtained directly from a laser and beam-expanding telescope without spatial filtering. Our application is to form optical standing-wave lattices for Bose-Einstein condensates in quantum emulators. This requires controlled amplitude and flat phase, and that the beam be free of temporal modulation from either pixel dithering or refresh cycles. We describe the development of the pattern design algorithms and demonstrate the performance of a high precision beam shaper to make flattop beams and other spatial profiles with similarly low spatial frequency content. The digital micromirror device (DMD) was imaged through a telescope containing a pinhole low-pass filter. An error diffusion algorithm was used to design the initial DMD pixel pattern based on the input beam profile. This pattern was iteratively refined based on output image measurements. We demonstrate forming a variety of beam profiles including flattop beams and beams with 1-D linear intensity variation, both with square and circular cross-sections. Produced beams had less than 0.25% root-mean-square (RMS) error with respect to the target profile and nearly flat phase.

Excess intensity noise suppressed 100-GHz spectrum-sliced WDM-PON with pre-spectrum-sliced seed light source

Abstract: We have demonstrated a 32 × 1.25 Gb/s, 20 km WDM-PON using a pre-spectrum-sliced seed light source and flattop AWGs. The spectral-filtering-induced excess intensity noise efficiently was suppressed in the WDM-PON.

Application of digital narrow band noise to j-parc main

Abstract: Applying narrow band noise to the beam in J-PARC Main Ring (MR) in flattop, while the acceleration voltage is off helps to counteract the effect of magnetic field ripple on the slow extraction. For this purpose, a complex noise sequence provided by a DSP modulates a custom made DDS synthesizer to create single sided spectra with suppressed carrier. The noise is calculated starting from a description in frequency domain. An algorithm creates narrow band spectra with optimized behavior in time domain. Frequency domain data is transformed to time domain, and the amplitude is smoothed. The smoothed data is transformed back to frequency domain, and the spectral shape is restored. This process repeats until the amplitude in time domain has converged, while the desired spectrum shape is preserved. Noise generated in this way can be tailored for different requirements. We explain signal properties, hardware, and preliminary beam test results, when the noise is applied a) to the MR RF system, and b) to the horizontal exciter system.

Beam transport in a proton dielectric wall accelerator

Abstract: To attain the highest accelerating gradient in the compact dielectric wall DWA accelerator, the accelerating voltage pulses should have the shortest possible duration by operating the DWA in the “virtual” traveling mode [1]. Those short accelerating voltage pulses have little or no flattop, which complicates beam transport in the DWA. In this paper, we present PIC simulations of a baseline transport case for a strawman proton therapy machine with timing sensitivity study and an alternative focusing scheme, which indicate that we can meet our design objective.

Wavelength-independent laser beam shaping

Abstract: This paper presents a beam shaping device namely, a Diffractive Optical Element (DOE), which is used to change a beam having a Gaussian intensity profile into a beam with a uniform intensity profile. The DOE used in this work was fabricated from ZnSe and its performance was evaluated using a cw CO 2 laser. In most cases such elements are effective only at a specific design wavelength. However, in this paper we report on the design conditions which allow for wavelength independent elements. It was found that the DOE was able to successfully transform a Gaussian beam into a flattop beam for four different wavelengths in the range 9.2 μm to 10.6 μm. We also present experimental results on misalignment effects and it was found that small radial offsets of the incident beam on the DOE had a significant disruptive effect on the flattop beam profile.

Laser resonator for outputting flattop beam through forward and backward Gaussian oscillation

Abstract: The invention discloses a laser resonator for outputting a flattop beam through forward and backward Gaussian oscillation, which belongs to the technical field of laser devices. It is difficult to generate stable flattop laser beams by the prior art for generating light intensity flattop spatial distribution by light beam homogenization; in addition, an adopted super Gaussian reflector is a soft-edge diaphragm and can modulate the light intensity distribution of the flattop laser beam and destruct the flattop performance of the flattop laser beam. The laser resonator of the invention consists of a total reflector, a laser gain medium and an output coupling reflector, wherein the laser gain medium is positioned between the total reflector and the output coupling reflector and the laser gain medium, the total reflector and the output coupling reflector are coaxial; the output coupling reflector is a mean reflector; an orthopyramid mirror is coaxially arranged on a light path between the total reflector and the laser gain medium; and the reflection surface OO' of the total reflector is positioned at the narrowest part of a zeroth-order Bessel diffraction beam-free area of the orthopyramid mirror. The laser resonator can output a laser beam with flattop spatial distribution light intensity.

Adaptive conversion of a wavefront-distortion beam to near-diffraction-limited flattop beam based on stochastic parallel gradient descent algorithm

Abstract: In this paper, a system of containing dual deformable mirrors (DMs) is proposed to adaptively conversion of input beam with wave front distortion into near-diffraction-limited flattop beam based on the stochastic parallel gradient descent (SPGD) algorithm. In the analysis, the wave front distortion of the input beam is chosen as the Zernike representation of Kolmogoroff spectrum of turbulence. The whole shaping system is controlled by the SPGD algorithm. One DM adaptively redistributes the intensity of the input beam and the other adaptively compensates the wave front of the output beam. The near-diffraction-limited flattop beams with different parameters are realized by this technique. The near-diffraction-limited square flattop beam retains an flattop intensity distribution without significant diffraction peaks for a working distance of more than 60cm in the near field.

Advanced refractive beam shaping optics for advanced laser technologies

Abstract: Performance of various scientific and industrial laser applications can be essentially improved when original intensity distribution of a laser beam is transformed from non-uniform profile to uniform or flattop one. The task of such a transformation is solved by series of refractive beam shaping optics of field mapping type. This solution is important in irradiating the cathode of Free Electron Lasers, confocal microscopy, biomedical fluorescence techniques, many industrial technologies like welding, cladding, hardening, various laser techniques in photovoltaics, homogenizing of pump radiation by building powerful femtosecond lasers and many other applications. The refractive beam shapers can be used with TEM00 and multimode laser beams, achromatic design lets it possible to provide the same conditions of beam shaping for several lasers of a certain spectrum range simultaneously, low inherent losses allow to use them with powerful laser sources, particular models can be implemented either as Galilean Telescope without internal focusing (collimated input / collimated output), or as Collimators (divergent input / collimated output). This paper will describe the principles of operation, design features of the achromatic refractive field mapping beam shapers; there will be presented examples of beam intensity transformation and effects on material processing achieved in several industrial applications.Performance of various scientific and industrial laser applications can be essentially improved when original intensity distribution of a laser beam is transformed from non-uniform profile to uniform or flattop one. The task of such a transformation is solved by series of refractive beam shaping optics of field mapping type. This solution is important in irradiating the cathode of Free Electron Lasers, confocal microscopy, biomedical fluorescence techniques, many industrial technologies like welding, cladding, hardening, various laser techniques in photovoltaics, homogenizing of pump radiation by building powerful femtosecond lasers and many other applications. The refractive beam shapers can be used with TEM00 and multimode laser beams, achromatic design lets it possible to provide the same conditions of beam shaping for several lasers of a certain spectrum range simultaneously, low inherent losses allow to use them with powerful laser sources, particular models can be implemented either as Galilean Tele...

Challenges in simulating mw beams in cyclotrons

Abstract: The 1.3 MW of beam power delivered by the PSI 590 MeV Ring Cyclotron together with stringent requirements regarding the controlled and uncontrolled beam losses poses great challenges with respect to predictive simulations. We describe a large scale simulation effort, which leads to a better quantitative understanding of the existing PSI high power proton cyclotron facility. Initial conditions for the PSI Ring simulations are obtained from a new time structure measurements and 18 profile monitors available in the 72 MeV injection line. The radial beam profile measurement which is just located in front of the extraction septum is compared with simulations. We show that OPAL (Object Oriented Parallel Accelerator Library) can precise predict the radial beam pattern at extraction with a large dynamic range of 4 orders of magnitude. A large turn separation and a narrow beam size at the Ring extraction is obtained by adjusting parameters such as the injection position and angle, the flattop phase and the trim coils. A large turn separation and a narrow beam size are the key elements for reducing the beam losses to acceptable levels. The described simulation capabilities are mandatory in the design and operation of the next generation high power proton drivers.

Tolerancing and analysis of a diffractive beam shaper

Abstract: This paper describes the design and analysis of a deep-UV diffractive beam shaper for converting a collimated Gaussian beam into a collimated flattop beam. Diffractive beam shapers can be manufactured in most common materials to provide good beam control with very low non-uniformity. Beam shapers, however, are generally very sensitive to beam parameters and alignment. Here we examine the sensitivity of the beam shaper to alignment and tilt of the input beam, phase surfaces, and various other fabrication errors. This device was successfully built and comparisons with laboratory measurements show excellent agreement with simulation predictions.

Improving laser technologies in photovoltaics by refractive beam shapers

Abstract: Laser technologies in solar cells production, like P1, P2 and P3 structuring, Vias Drilling, Marking, Edge Isolation, can be improved by applying the beam shaping optics that transforms the intensity distribution of laser beam to flattop, donut-like or other profiles. The flattop profile leads not only to higher quality and stability of such techniques like scribing, drilling, but also increases efficiency of using the laser energy and, hence, increases the manufacturing productivity. Since the final spot size is <100 µm it is advisable to apply the beam shapers intended to create the required intensity distribution by focusing a beam with using a diffraction limited lens. This is a standard task for beam shapers Focal-πShaper which operational principle gives freedom in building various optical systems with using scanning heads, various lenses including F-theta lenses, telecentric lenses. The Focal-πShaper can be easily integrated in existing equipment, so it is possible to upgrade already installed machines.This paper will describe the principles of operation, design features of the refractive field mapping beam shapers Focal-πShaper. There will be presented some practical optical layouts, examples of beam intensity transformation and effects on material processing in scribing of thin-film cells and other processes.Laser technologies in solar cells production, like P1, P2 and P3 structuring, Vias Drilling, Marking, Edge Isolation, can be improved by applying the beam shaping optics that transforms the intensity distribution of laser beam to flattop, donut-like or other profiles. The flattop profile leads not only to higher quality and stability of such techniques like scribing, drilling, but also increases efficiency of using the laser energy and, hence, increases the manufacturing productivity. Since the final spot size is <100 µm it is advisable to apply the beam shapers intended to create the required intensity distribution by focusing a beam with using a diffraction limited lens. This is a standard task for beam shapers Focal-πShaper which operational principle gives freedom in building various optical systems with using scanning heads, various lenses including F-theta lenses, telecentric lenses. The Focal-πShaper can be easily integrated in existing equipment, so it is possible to upgrade already installed mach...

Investigation and evaluation on pulse stackers for temporal shaping of laser pulses

Abstract: A sophisticated research device such as an advanced photo-cathode injector for a high energy acceleratorbased X-ray light source requires drive lasers with a flattop shape both in time and space in order to generate high-quality short electron beam bunches. The practical methods for temporal shaping, in particular in the picosecond or femtosecond regime, are quite limited. One simple way to shape laser pulses is pulse stacking by birefringent crystals. While the method itself has the great advantage of simplicity, the overall performance depends on many factors. In this paper, we will present both calculation analysis and the recent experimental study

Broad flattop transparent photonic band in truncated photonic crystals composed of the symmetric unit cell

Abstract: We theoretically show that a one-dimensional finite all-dielectric periodic structure composed of symmetric unit cells can possess a broad flattop transparent photonic band. In contrast to the conventional viewpoint that the thickness of the truncated photonic crystals affects the transmission within the pass band, the transparent photonic band is insensitive to the change of the periodic number since the equivalent refractive indices of our structures can be nearly equal to that of the background in a wide frequency range. With easy fabrication, this broad flattop transparent photonic band will play an important role in the broadband filtering.

Applying refractive beam shapers to improve other beam shaping techniques

Abstract: Refractive beam shapers of the field mapping type find use in various industrial, scientific and medical applications, where generation of a collimated beam of uniform intensity is required. Due to their unique features, such as: low output divergence, high transmittance and flatness of output beam profile and extended depth of field, refractive field mappers may also be successfully used in combination with beam shaping optics of other operational principles. This combining makes it possible to improve drastically the performance of these beam shaping techniques. For example, the non-uniformity of the beam profile of many lasers leads to complexity and inconvenience in various beam shaping techniques based on applying spatial light modulators (SLM). Applications include Computer Generated Holography (CGH), holographic projection processing applications, holographic lithography, optical trapping and laser illumination in confocal microscopes. With a collimated flattop beam provided by refractive field mappers these techniques become easier to use, more effective and reliable in operation. This paper will describe some design basics of refractive beam shapers of the field mapping type, with emphasis on the features important for applications with SLMs. There will be presented comparative results of applying the refractive beam shapers in systems of holographic lithography and other techniques.

Numerical simulation and analysis of convex two-aspheric-mirror system that converts a Gaussian to a flattop beam

Abstract: The system composed of two aspheric mirrors is able to convert a Gaussian beam to a flattop beam because of its concise structure,compactness,and sound effects in beam reshaping.And in actual production processing,the asphericity and surface roughness of aspheric mirror are the crucial factors.On the basis of reshaping theory on converting a Gaussian to a flattop,by virtue of numerical simulation,we have calculated and analyzed the several characteristical parameters influence on the design of aspheric mirror surface.Then,according to the actual requirements of input expressions in ZEMAX,we get the best structure of aspheric mirror system by mathematical simulation.

Simple and monolithic picosecond pulse shaper based on fiber Bragg gratings

Abstract: In this contribution we present a simple and robust pulse shaping device based on coherent pulse stacking. The device is based on fiber Bragg gratings written in a polarisation maintaining step index fiber and a fiber optical circulator. Up to four pulse replicas are reflected by fiber Bragg gratings and interfere at the output of the device. Temperature control allows tuning of the relative pulse amplitudes and phases of the pulse replicas. We experimentally demonstrated 235 ps and 416 ps long flattop pulses with rising and falling edges shorter than 100 ps. In contrast to other pulse shaping techniques the presented setup is robust, alignment free, provides excellent beam quality and is also suitable for pulse durations up to several nanoseconds.

Design of chirped fiber Bragg grating with ideal box spectra and smoothly time delay

Abstract: A chirped fiber Bragg grating with ideal box spectra and smoothly time delay is designed. The outer cladding of the fiber is etched as sinusoidal function. When the tension applied to the grating in fabricated process is threw off, the fiber grating not only exhibits a flattop spectrum with steep edges and high reflectivity, but also has a smoothly time delay curve. The bandwidth utilization defined as the ratio of −1∶−30 could be achieved a larger value(>0.91).