Beam Shaping Optics Research Articles

35.1: Blue-Diode Laser Annealing of Amorphous Silicon Films for Low-Cost, Large-Scale Manufacturing of Advanced Displays

Blue diode laser annealing (BLA) systems have been successfully developed for low-temperature crystallization from amorphous silicon film on glass substrates. It is demonstrated that it can achieve high quality poly-Si film with large grain sizes, as studied by optical microscopy, Raman spectroscopy and AFM measurements. The p-channel poly-Si TFT on glass using BLA exhibited the field-effect mobility of 168.05 cm2/Vs and subthreshold swing of 220 mV/dec. BLA is scalable to large-scale display manufacturing and significantly lowers the capital expense and operating cost, since diode lasers are highly reliable and rugged, remarkably efficient, and maintenance-free, allowing 24/7 operations without the need of consumables. The BLA system consists of an array of high-power blue diode lasers (λ ~ 450 nm) and beam-shaping optics to produce a line-shaped beam which can be scanned at high speed to anneal the Si film in a single scan, where the high scan speed minimizes thermal stress. The scan-to-scan is seamless to cover a large panel such as G6 or G8 without glass damage. The physical phenomena responsible for melting and recrystallization are explained by heat transfer simulations for process optimization.

Method to improve near-field nonlinearity of a high-power diode laser array on a microchannel cooler

Due to thermal stress, each emitter in a semiconductor laser bar or array is vertically displaced along the p-n junction; the result is that each emitter is not in a line, called near-field nonlinearity. Near-field nonlinearity along a laser bar (also known as “SMILE” effect) degrades the laser beam brightness, which causes an adverse effect on optical coupling and beam shaping. A large SMILE value causes a large divergence angle after collimation and a wider line after collimation and focusing. We simulate the factors affecting the SMILE value of a high-power diode laser array on a microchannel cooler (MCC). According to the simulation results, we have fabricated a series of laser bars bonded on MCCs with lower SMILE value. After simulation and experiment analysis, we found the key factor to affect SMILE is the deformation of the thin MCC because of the distribution of strain and stress in it. We also decreased the SMILE value of 1-cm-wide full bar AuSn bonded on MCCs from 12 to 1 μm by balancing force on MCC to minimize the deformation.

3D printed plano-freeform optics for non-coherent discontinuous beam shaping

The design, fabrication, and characterization of freeform optics for LED-based complex target irradiance distribution are challenging. Here, we investigate a 3D printing technology called Printoptical® technology in order to relax or push forward both the fabrication limits and LED-based applications of thick freeform lenses with small slope features. The freeform designs are carried out with an assumption of small-sized LED source using an existing point-source-based Tailoring method, which is available in the semi-commercial software. The numerical methods of the designs are characterized by ray-tracing software. The irradiance patterns of the 3D printed freeform lenses are promising considering the average shape conformity deviation of around ± 40 µm and center area surface roughness around ± 12 nm, which is to our knowledge by far the best result reported for 3D printed freeform lenses with a thickness greater than 1 mm. Applications of freeform lenses with discontinuous target irradiance distribution patterns are expected in eco-friendly energy efficient lighting such as in zebra-cross lighting.

Slim coherent backlight unit for holographic display using full color holographic optical elements.

The coherent backlight unit (BLU) using a holographic optical element (HOE) for full-color flat-panel holographic display is proposed. The HOE BLU consists of two reflection type HOEs that change the optical beam path and shape by diffraction. The illumination area of backlight is 150 mm x 90 mm and the thickness is 10 mm, which is slim compared to other conventional coherent backlight units for holographic display systems. This backlight unit exhibits a total efficiency of 8.0% at red (660 nm), 7.7% at green (532 nm), and 3.2% at blue (460 nm) using optimized recording conditions for each wavelength. As a result, we could get a bright full color hologram image.

Self-focusing of a partially coherent beam with circular coherence

In a recent publication [Opt. Lett.42, 1512 (2017)OPLEDP0146-959210.1364/OL.42.001512], a novel class of partially coherent sources with circular coherence was introduced. In this paper, we examine the propagation behavior of the spectral density and the spectral degree of spatial coherence of a beam generated by such a source in free space and in oceanic turbulent media. It is found that the beam exhibits self-focusing, which is dependent on the initial coherence and the parameters of oceanic turbulence. The self-focusing phenomenon disappears when the initial coherence is high enough or the oceanic turbulence is strong. The area of high coherence appears in the center and along two diagonal lines. With increasing turbulence, the coherence area reduces gradually along one diagonal line and is retained along the other one. A physical interpretation of the self-focusing phenomenon is presented, and potential applications in optical underwater communication and beam shaping are considered.

Nanotomography endstation at the P05 beamline: Status and perspectives

The Imaging Beamline IBL/P05 at the DESY storage ring PETRA III, operated by the Helmholtz-Zentrum Geesthacht, has two dedicated endstations optimized for micro- and nanotomography experiments [1-3]. Here we present the status of the nanotomography endstation, highlight the latest instrumentation upgrades and present first experimental results. In particular in materials science, where structures with ceramics or metallic materials are of interest, X-ray energies of 15 keV and above are required even for sample sizes of several 10 μm in diameter. The P05 imaging beamline is dedicated to materials science and is designed to allow for imaging applications with X-ray energies of 10 to 50 keV. In addition to the full field X-ray microscopy setup, the layout of the nanotomography endstation allows switching to cone-beam configuration. Kinematics for X-ray optics like compound refractive lenses (CRLs), Fresnel zone plates (FZP) or beam-shaping optics are implemented and the installation of a Kirkpatrick Baez-mirror (KB mirror) system is foreseen at a later stage of the beamline development. Altogether this leads to a high flexibility of the nanotomography setup such that the instrument can be tailored to the specific experimental requirements of a range of sample systems.

Numerical simulation of laser beam welding using an adapted intensity distribution

The automotive industry has a high demand for lightweight solutions for car body components to reduce the carbon dioxide emissions and to increase the range of electric cars. In this context, the joining methods play a significant role in enabling the lightweight construction. Specifically, the use of aluminum alloys for structural components or body panels poses a major challenge for joining technologies. These parts are often made from aluminum alloys AA6xxx, which are very susceptible to hot cracks during fusion welding. As laser beam welding is increasingly used for welding car body components, special techniques are required to avoid hot cracks in weld seams. Besides the use of filler wire, laser welding using an adapted intensity distribution is an innovative approach to get a defect-free weld seam coupled with a high surface quality. Due to the lack of flexible beam shaping optics for investigations on high power material processing using an adapted intensity distribution, a simulation method for this technique is presented. The impact of the adapted intensity on the process characteristics, e.g., the temperature field, the temperature gradients, or the molten pool geometry, can be determined by using this numerical model. The heat input by the adapted intensity distribution is composed of a stationary capillary geometry for the deep penetration welding process and an additional surface heat source. An experimental analysis was carried out to calibrate the simulation model. Using design of experiments, the weld seam geometry depending on the laser parameters can be predicted. Finally, the impact of an adapted intensity distribution on the geometry of the molten pool and the temperature field is shown.

The review of liquid crystal wavefront corrector with fast response property

Liquid crystal wavefront corrector (LCWFC) is an optical device that can modulate wavefront of incident light, and shows advantages of high density pixels, high reliability, and high precision accuracy, and can be used in the field of optical beam shaping, optical information processing and beam transforming. All these application model show broad application prospect of LCWFC. When LCWFC is used in the optics systems, a fast response speed is always required, such as 1 ms. In optical application, specific modulation depth is always required. If the modulation depth is 1 λ , the response time of the commercial LCWFC is slow, such as, 10 ms, which block the application of LCWFC. The response speed of LCWFC always depends on two elements, the properties of LC material and the parameters of LC device. Firstly, fast response liquid crystal material with high birefringence and low viscosity was studied and reviewed in our research group. Secondly, the optimization of LC device parameters and driving method was reviewed. By the research in LC material and device, the response time of LCWFC can be fast to sub-millisecond, which will highly enhance the application region and depth of LCWFC.

2D-3D μXRF elemental mapping of archeological samples

Recently opened for users at LNF XLab-Frascati a μXRF station, named “Rainbow X-ray” – RXR, has been optimized for most of X-ray analytical research fields. The basic principle of the station is in the use of various geometrical combinations of polycapillary optics for X-ray beam shaping (focusing/collimation) at specially designed laboratory unit.In this work we have presented the results of archaeological studies on the artifacts of Paleolithic period and Iron Age (9th century BC to the midway of the 8th BC). The elemental analysis of these artifacts has been first performed by compact laboratory setup. Superficial (2D) and bulk (3D) micro-fluorescence mapping provides useful informations for the geologists in order to identify the possible artifacts provenience and origin. The results presented in this work are a part of wider anthropological/archeological investigations aimed at the understanding of social and economical relations of prehistorical communities.

Ferroelectric Liquid Crystal Dammann Grating by Patterned Photoalignment

In this article, a ferroelectric liquid crystal (FLC) dammann grating (DG) is demonstrated based on the patterned photoalignment technology. By applying low electric field (10 V) on the FLC DG, the grating can switch between a diffractive state with 7 × 7 optical spots array and a non-diffractive state, depending on the polarity of electric field. The FLC DG shows very fast switching speed with switching on time and off time to be only 81 μs and 59 μs respectively. Comparing with other fast LC DGs such as the ones based on blue phase LC or dual-frequency LC, the switching speed of the proposed FLC DG is about one order faster, which provides great potential and perspective for the FLC DG to be applied in a broad range of optical applications such as optical communication and beam shaping.

3D model for rectangular electrowetting lens structures.

The electrowetting-on-dielectric (EWOD) lens is a good candidate for dynamic beam-shaping optics for advanced solid-state lighting systems. A geometric approximation model is described to predict the meniscus shape of a rectangular EWOD lens with arbitrary voltages and small Bond numbers. The model approximates the meniscus geometry as being a part of a compound toroidal surface. The model was compared with free-energy minimization simulations and experiments with the largest standard deviation between the geometric model and the simulation for a wide variety of bias voltages being less than 2%. The experimental validation compared the measured dynamic image shifts of a wire mesh produced with test EWOD cells with the predicted image obtained from the toroidal geometric model using a ray-tracing simulation. The optical performance of the experimental 3D electrowetting lens is described and was found to agree reasonably well with the predicted optical performance of the geometric model for a wide variety of operating conditions.

Effects of laser fluence non-uniformity on ambient-temperature soot measurements using the auto-compensating laser-induced incandescence technique

Multimode pulsed Nd:YAG lasers are commonly used in auto-compensating laser-induced incandescence (AC-LII) measurements of soot in flames and engine exhaust as well as black carbon in the atmosphere. Such lasers possess a certain degree of fluence non-uniformity across the laser beam even with the use of beam shaping optics. Recent research showed that the measured volume fraction of ambient-temperature soot using AC-LII increases significantly, by about a factor of 5–8, with increasing the laser fluence in the low-fluence regime from a very low fluence to a relatively high fluence of near sublimation. The causes of this so-called soot volume fraction anomaly are currently not understood. The effects of laser fluence non-uniformity on the measured soot volume fraction using AC-LII were investigated. Three sets of LII experiments were conducted in the exhaust of a MiniCAST soot generator under conditions of high elemental carbon using Nd:YAG lasers operated at 1064 nm. The laser beams were shaped and relay imaged to achieve a relatively uniform fluence distribution in the measurement volume. To further homogenize the laser fluence, one set of LII experiments was conducted by using a diffractive optical element. The measured soot volume fractions in all three sets of LII experiments increase strongly with increasing the laser fluence before a peak value is reached and then start to decrease at higher fluences. Numerical calculations were conducted using the experimental laser fluence histograms. Laser fluence non-uniformity is found partially responsible for the soot volume fraction anomaly, but is insufficient to explain the degree of soot volume fraction anomaly observed experimentally. Representing the laser fluence variations by a histogram derived from high-resolution images of the laser beam energy profile gives a more accurate definition of inhomogeneity than a simple averaged linear profile across the laser beam.

Advanced Spatial-Division Multiplexed Measurement Systems Propositions-From Telecommunication to Sensing Applications: A Review.

The concepts of spatial-division multiplexing (SDM) technology were first proposed in the telecommunications industry as an indispensable solution to reduce the cost-per-bit of optical fiber transmission. Recently, such spatial channels and modes have been applied in optical sensing applications where the returned echo is analyzed for the collection of essential environmental information. The key advantages of implementing SDM techniques in optical measurement systems include the multi-parameter discriminative capability and accuracy improvement. In this paper, to help readers without a telecommunication background better understand how the SDM-based sensing systems can be incorporated, the crucial components of SDM techniques, such as laser beam shaping, mode generation and conversion, multimode or multicore elements using special fibers and multiplexers are introduced, along with the recent developments in SDM amplifiers, opto-electronic sources and detection units of sensing systems. The examples of SDM-based sensing systems not only include Brillouin optical time-domain reflectometry or Brillouin optical time-domain analysis (BOTDR/BOTDA) using few-mode fibers (FMF) and the multicore fiber (MCF) based integrated fiber Bragg grating (FBG) sensors, but also involve the widely used components with their whole information used in the full multimode constructions, such as the whispering gallery modes for fiber profiling and chemical species measurements, the screw/twisted modes for examining water quality, as well as the optical beam shaping to improve cantilever deflection measurements. Besides, the various applications of SDM sensors, the cost efficiency issue, as well as how these complex mode multiplexing techniques might improve the standard fiber-optic sensor approaches using single-mode fibers (SMF) and photonic crystal fibers (PCF) have also been summarized. Finally, we conclude with a prospective outlook for the opportunities and challenges of SDM technologies in optical sensing industry.

Creation of a refractive lens within an existing intraocular lens using a femtosecond laser

To assess the efficiency and effectiveness of the technology that creates a hydrophilicity-based refractive index change within a standard intraocular lens (IOL) to alter the refractive characteristics of the IOL. Perfect Lens LLC, Irvine, California, USA. Experimental study. The IOL used in this experiment was a standard hydrophobic model (EC-1Y). The refractive index of the material was changed by exposure of the material to a femtosecond laser and the subsequent absorption of water by the material. An experimental system using a femtosecond laser, an acoustic-optic modulator, beam-shaping optics, a scan system, and an objective lens was used to create the refractive index change within the IOL. Experiments were performed to determine the optimum wavelength, energy per pulse, and line spacing to produce the refractive index shaping lens. A power and modulation transfer function (MTF) measurement device for refractive and diffractive IOLs was used to measure the diopter and MTF before and after the creation of the refractive index shaping lens. The technology successfully altered the refractive characteristics of the IOL. The refractive index change altered the diopter (D) of the IOL (to within ±0.1 D of the targeted change) without significant diminution in the MTF (<0.1 or MTF ≥0.51 for the 100 lp/mm measurement). The refractive properties of an IOL can be altered by building a refractive index shaping lens within an IOL using a femtosecond laser with minimal diminution in MTF. All authors are employed by Perfect Lens, LLC and have a financial interest in the products of Perfect Lens, LLC.

Nonlinear Raman-Nath second harmonic generation with structured fundamental wave.

We proposed and experimentally demonstrated that nonlinear Raman-Nath second harmonic can be achieved in real time when a fundamental wave with the phase periodically modulated, termed as structured fundamental wave, incident in a homogeneous nonlinear medium. The diffraction of second harmonic originates from the structured fundamental wave, rather than the grating of a nonlinear photonic crystal. Nonlinear second harmonic generation, in forms of both one- and two-dimensional, was investigated in our experiment. This method circumvents the limitation of nonlinear photonic crystals in some extend and has potential applications in nonlinear frequency conversion, optical signal processing and beam shaping, etc.

Highly integrated optical phased arrays: photonic integrated circuits for optical beam shaping and beam steering

Abstract Technologies for efficient generation and fast scanning of narrow free-space laser beams find major applications in three-dimensional (3D) imaging and mapping, like Lidar for remote sensing and navigation, and secure free-space optical communications. The ultimate goal for such a system is to reduce its size, weight, and power consumption, so that it can be mounted on, e.g. drones and autonomous cars. Moreover, beam scanning should ideally be done at video frame rates, something that is beyond the capabilities of current opto-mechanical systems. Photonic integrated circuit (PIC) technology holds the promise of achieving low-cost, compact, robust and energy-efficient complex optical systems. PICs integrate, for example, lasers, modulators, detectors, and filters on a single piece of semiconductor, typically silicon or indium phosphide, much like electronic integrated circuits. This technology is maturing fast, driven by high-bandwidth communications applications, and mature fabrication facilities. State-of-the-art commercial PICs integrate hundreds of elements, and the integration of thousands of elements has been shown in the laboratory. Over the last few years, there has been a considerable research effort to integrate beam steering systems on a PIC, and various beam steering demonstrators based on optical phased arrays have been realized. Arrays of up to thousands of coherent emitters, including their phase and amplitude control, have been integrated, and various applications have been explored. In this review paper, I will present an overview of the state of the art of this technology and its opportunities, illustrated by recent breakthroughs.

Beam shaping via photopatterned liquid crystals

ABSTRACTDue to the fantastic properties and diverse applications of specific beams, optical beam shaping has attracted intensive attentions recently. Generally, these beams can be converted from Gaussian beams via particular spatial amplitude or phase control. In this work, we present a liquid crystal photopatterning technique based on dynamic microlithography with a polarisation-sensitive photoalignment agent. This technique enables the accurate, arbitrary and reconfigurable azimuthal angle control of liquid crystals, thus providing a powerful approach for the manipulation of light. By this means, the tailoring of arbitrary fine microstructures with binary or continuously space-variant liquid crystal azimuthal orientations are demonstrated. We briefly review our recent work on some specially designed patterns and corresponding specific optical fields. High-quality vortex beams, vector beams and Airy beams are generated with unprecedented flexibility in the design and control of light wavefront. Besides high efficiency, good electrical switchability and broad wavelength tolerance, the proposed devices also exhibit merits of compact size, low cost, dynamic mode conversion and polarisation controllable energy distribution, and are available for short pulse and intense light modulation. This work may pave a bright way towards beam shaping and bring new possibilities for the design of novel advanced liquid crystal photonic devices.

Optofluidic Device Based Microflow Cytometers for Particle/Cell Detection: A Review.

Optofluidic devices combining micro-optical and microfluidic components bring a host of new advantages to conventional microfluidic devices. Aspects, such as optical beam shaping, can be integrated on-chip and provide high-sensitivity and built-in optical alignment. Optofluidic microflow cytometers have been demonstrated in applications, such as point-of-care diagnostics, cellular immunophenotyping, rare cell analysis, genomics and analytical chemistry. Flow control, light guiding and collecting, data collection and data analysis are the four main techniques attributed to the performance of the optofluidic microflow cytometer. Each of the four areas is discussed in detail to show the basic principles and recent developments. 3D microfabrication techniques are discussed in their use to make these novel microfluidic devices, and the integration of the whole system takes advantage of the miniaturization of each sub-system. The combination of these different techniques is a spur to the development of microflow cytometers, and results show the performance of many types of microflow cytometers developed recently.

Adaptive optical beam shaping for compensating projection-induced focus deformation

Abstract Scanner-based applications are already widely used for the processing of surfaces, as they allow for highly dynamic deflection of the laser beam. Particularly, the processing of three-dimensional surfaces with laser radiation initiates the development of highly innovative manufacturing techniques. Unfortunately, the focused laser beam suffers from deformation caused by the involved projection mechanisms. The degree of deformation is field variant and depends on both the surface geometry and the working position of the laser beam. Depending on the process sensitivity, the deformation affects the process quality, which motivates a method of compensation. Current approaches are based on a local adaption of the laser power to maintain constant intensity within the interaction zone. For advanced manufacturing, this approach is insufficient, as the residual deformation of the initial circular laser spot is not taken into account. In this paper, an alternative approach is discussed. Additional beam-shaping devices are integrated between the laser source and the scanner, and allow for an in situ compensation to ensure a field-invariant circular focus spot within the interaction zone. Beyond the optical design, the approach is challenging with respect to the control theory’s point of view, as both the beam deflection and the compensation have to be synchronized.

Propagation characteristics of a non-uniformly Hermite–Gaussian correlated beam

We introduce a new kind of partially coherent beam, non-uniformly Hermite–Gaussian correlated beam, by employing a non-uniformly Hermite function to modulate the spectral degree of coherence. The evolution of such scalar beam on propagation in free space and turbulent atmosphere are investigated. It is demonstrated that the spectral intensity distributions exhibit extraordinary propagation characteristics, such as self-focusing and laterally shifted intensity maxima. The position of the maximum intensity and the intensity profile can be controlled by the order of the Hermite function. The results can be useful in free-space optical communications and beam shaping.