Laser Ablation Tool Research Articles

The art of laser ablation in aeroengine: The crown jewel of modern industry

In this perspective, laser interaction with materials and its applications in precision engineering are mainly introduced for the manufacturing, as well as maintenance, repair, and overhaul (MRO) of aeroengines. In precision engineering, the laser ablation tool has also been more applicable considering its great advantages in microprocessing and nanofabrication. It is interesting to explore the specific process and characteristics of laser ablation, which play an important role in advanced manufacturing. Due to the complicated production procedures of an aeroengine, it is important to explore the physics behind laser interaction with aerospace and aeronautical metallic materials in order to properly utilize the unique characteristics of lasers, such as high monochromaticity, high brightness, high directivity, and high coherence. Meanwhile, it is beneficial to study the dynamic process of interactions and its mechanisms in laser applications, such as laser cleaning, texturing, and shock peening. There exist both photo-chemical and photo-thermal processes when lasers and materials interact. Several typical cases are introduced, which have great potential and high impact applications in the manufacturing and MRO industry of aeroengines. Based on laser ablation in specific industries, the building-up of MRO support system for aeroengines could be provided by a dynamic mechanism between the pioneering research results and industrial demand, leading to the fast development of advanced high-end manufacturing equipment.

Quantitative Raman calibration of sulfate-bearing polymineralic mixtures: a S quantification in sedimentary rocks on Mars

AbstractThe NASA 2020 Mars mission is a Curiosity-type rover whose objective is to improve the knowledge of the geological and climatic evolution of Mars and to collect rock samples for return to Earth. The new rover has a payload of seven instruments including the SuperCam instrument which consists of four tools including a Raman spectrometer. This Raman device will be non-destructive and will analyse the surface remotely in order to determine the mineralogy of rocks and, by extent, to detect and quantify major elements such as sulfur. Sulfur has been detected as sulfate (Ca,Mg,Fe-sulfates) in sedimentary rocks. This element is difficult to quantify using the laser ablation tool of the ChemCam instrument on-board the Curiosity rover.We propose a Raman calibration to constrain the sulfur abundance in polymineralic mixtures. We acquired Raman signatures on binary and ternary mechanical mixtures containing Ca and Mg sulfates, mixed with natural silicate minerals supposed to be relevant to basaltic-sedimentary rocks at the surface of Mars: olivine, clinopyroxene, orthopyroxene and plagioclase. Using the Voigt function to process the Raman spectra from samples extracted from our mixtures allows us to calculate the initial proportions of our preparations of Ca and Mg sulfates. From these simulations, calibration equations have been provided allowing us to determine sulfate proportions (CaSO4and MgSO4) in a mixture with basaltic minerals. With the presented calibration, S can be quantified at a lower limit of 0.7 wt.% in Martian soil.

Quantitative Defect Analysis of Ablator Capsule Surfaces Using a Leica Confocal Microscope and a High-Density Atomic Force Microscope

High-density carbon (HDC) is being evaluated as an alternative to the current National Ignition Facility (NIF) point-design ablator material (glow discharge plasma, or GDP, plastic) due to its high density and optimal opacity, which leads to a higher implosion velocity. Chemical-vapor-deposition-coated HDC capsules have a near perfect surface figure but a microscopically rough surface. After polishing, the surface becomes smooth at nanometer scales but has numerous micron-sized surface pits, whose volumes, morphology, and distribution must be quantified to guide NIF target selection. Traditional metrology tools for GDP surface defects, such as the atomic force microscope (AFM) based Spheremapper and a phase-shifting differential interferometer, lack the resolution to characterize these localized features. In this paper, we describe how this metrology challenge is met by developing automated surface metrology solutions based on a high-density (HD) AFM and a Leica confocal microscope. These tools are complementary in nature. HD-AFM has a 0.1-μm spatial resolution and determines the overall shape distortion and pit statistics by tracing great circles on a capsule with high throughput. The Leica confocal microscope maps the two-dimensional (2-D) surface at low magnification to find all large defects that could be missed by HD-AFM. Then, a high magnification scan inspects at a <0.3-μm lateral resolution to characterize the defect volume. These 2-D maps provide an opportunity for modeling the shell performance at the peak implosion velocity, thereby aiding capsule selection. These new and improved metrology tools provide quantitative data for the continual refinement of the NIF specifications for HDC capsules. Finally, we report on the development of a laser ablation tool that, when combined with the Leica confocal microscope, can identify, quantify, and laser-ablate GDP domes that do not meet NIF specifications.

Mission feasibility analysis on deflecting Earth-crossing objects using a power limited laser ablating spacecraft

This paper analyzes several mission capabilities to deflect Earth-crossing objects (ECOs) using a conceptual future spacecraft with a power limited laser ablating tool. A constrained optimization problem is formulated based on nonlinear programming with a three-dimensional patched conic method. System dynamics are also established, considering the target ECO’s orbit as being continuously perturbed by limited laser power. The required optimal operating duration and operating angle history of the laser ablating tool are computed for various types of ECOs to avoid an Earth impact. The available final warning time is also determined with a given limited laser power. As a result, detailed laser operating behaviors are presented and discussed, which include characteristics of operating duration and angle variation histories in relation to the operation’s start time and target object’s properties. The calculated durations of the optimal laser operation are also compared to those estimated with first-order approximations previous studies. It is discovered that the duration of the laser operation estimated with first-order approximations could result in up to about 50% error if the operation is started at the final warning time. The laser operation should be started as early as possible because an early start requires a short operating duration with a small operating angle variation. The mission feasibility demonstrated in the present study will give various insights into preparing future deflection missions using power limited spacecraft with a laser ablation tool.

Spacecraft formation flying for Earth-crossing object deflections using a power limited laser ablating

A formation flying strategy with an Earth-crossing object (ECO) is proposed to avoid the Earth collision. Assuming that a future conceptual spacecraft equipped with a powerful laser ablation tool already rendezvoused with a fictitious Earth collision object, the optimal required laser operating duration and direction histories are accurately derived to miss the Earth. Based on these results, the concept of formation flying between the object and the spacecraft is applied and analyzed as to establish the spacecraft’s orbital motion design strategy. A fictitious “Apophis”-like object is established to impact with the Earth and two major deflection scenarios are designed and analyzed. These scenarios include the cases for the both short and long laser operating duration to avoid the Earth impact. Also, requirement of onboard laser tool’s for both cases are discussed. As a result, the optimal initial conditions for the spacecraft to maintain its relative trajectory to the object are discovered. Additionally, the discovered optimal initial conditions also satisfied the optimal required laser operating conditions with no additional spacecraft’s own fuel expenditure to achieve the spacecraft formation flying with the ECO. The initial conditions founded in the current research can be used as a spacecraft’s initial rendezvous points with the ECO when designing the future deflection missions with laser ablation tools. The results with proposed strategy are expected to make more advances in the fields of the conceptual studies, especially for the future deflection missions using powerful laser ablation tools.

Redistribution of pads on a singulated IC die using laser direct-write ablation

The use of laser direct-write technology is demonstrated for rapid turnaround redistribution of pads on known good integrated circuit dice. The technology, which is suitable for rapid prototyping of advanced electronic packages, employs an automated laser ablation system with wavelength at 355nm to pattern thin copper films to form the interconnect and vias in the polyimide interlevel insulator. The ablation tool is designed to directly accept the CAD data and write the metallization and via level patterns with excellent (/spl plusmn/3/spl mu/m) layer-to-layer registration. This process is maskless and, except for cleaning steps, does not require patterning by wet chemical etching. The implementation of a change in the design can be done rapidly and involves modifying the CAD data, downloading it to the laser ablation tool, and fabricating a part according to the new design. This paper illustrates the use of laser direct-write ablation for fabrication of via chain test structures and redistribution of pads on functional integrated circuits on singulated dice. Comparable electrical test results were obtained between structures fabricated using laser ablation technology and those fabricated on full 150-mm diameter wafers using conventional photolithography and etch processes.

Fabrication of concave micro lens array using laser patterning and isotropic etching

Micro lens arrays are widely used in optical communication and laser-fiber coupling applications. In this paper, a technique to fabricate concave micro lens arrays on glass substrate using a third harmonic Nd:YAG laser direct patterning and followed by chemical wet isotropic etching is presented. The patterning process was done on gold film, which was coated on a glass substrate by using a NC controlled laser ablation tool paths. The glass substrate is then etched by using hydrofluoric acid (HF) solutions whereby the exposed area will be dissolved away by chemical reaction with HF. The type of etching process is an isotropic etching which the etching rate is equal at all direction thus produce hemispherical concave profile on glass. The optimum laser patterning parameters is obtained and the effect of different types of HF solutions on etching efficiency is studied. The surface morphology, 2D and 3D profiles are also measured. Various micro lens diameters are fabricated with different values of lens sag.

Masks for laser ablation technology: New requirements and challenges

Laser ablation is used as a dry patterning process in which an intense beam of light from an excimer laser is used to pattern a material directly. This process has found extensive application in the microelectronics industry for patterning of polymer materials. A typical laser ablation tool is very similar to a conventional optical lithography projection tool; the primary difference is the wavelength and the intensity of the light used in the ablation process. Conventional chromium-coated quartz masks are incompatible with 1× laser ablation tools because the chromium layer is rapidly damaged. This paper discusses a mask technology which has been developed specifically for excimer laser ablation. The mask consists of a quartz substrate with a stack of dielectric films which have been selected for the laser ablation wavelength. Mask fabrication is accomplished with standard microelectronic processes and equipment. Such masks have been used in IBM manufacturing since 1987 and have met all process specifications such as resolution, defect density, and damage resistance.