Precision Laser Processing Research Articles

The Temporal Measurement of Infrared Femtosecond Fiber Laser Pulse with Complex Spectra: SPIDER and FROG

Femtosecond fiber laser pulse (FFLP) is very suitable for precision laser processing (PLP) with the advantages of high power, compact integrated structure, and easy installation. However, with the power increasing, nonlinear optical effects (NOE) of fiber, such as self-phase modulation (SPM), will be greatly enhanced, and the spectra of the output pulse will be very complex, which considerably increases the temporal complexity of FFLP and takes an immeasurable influence on PLP, so it is of great significance to accurately measure the temporal property of FFLP for higher accuracy of PLP. This paper presents a self-referencing spectral phase interferometry for direct electric-field reconstruction based on a single grating stretcher (SGS-SPIDER) with the two-step phase shift (TSPS) method for measuring FFLP with complex and infrared spectra. Meanwhile, we present a modified pulse-retrieval algorithm called an adaptive pulse-retrieval algorithm (APRA) of frequency-resolved optical gating (FROG) to reconstruct the measured pulse accurately. The duration of the reconstructed pulse measured by FROG is 162 fs, whose autocorrelation curve is similar to the measured autocorrelation curve including the picosecond background. The error of the reconstructed FROG trace is 0.42%, which is reliable enough according to the literature experience. Finally, the unique advantages of FROG for measuring complex ultrashort pulses such as FFLP are compared with SPIDER; that is, FROG has a wider spectral phase measuring range than SPIDER. These studies provide a new diagnostic technique for the complete temporal characterization of FFLP with complex spectra and extend the measurement range and application of SPIDER at the infrared wavelength band, which is significant for improving the accuracy of PLP using FFLP.

In-process monitoring in laser grooving with line-shaped femtosecond pulses using optical coherence tomography

A line-shaped beam is useful for increasing the processing speed in laser grooving and scribing. In laser grooving, depth control of the processed structure is important for performing precise processing. In this paper, in-process monitoring of the depth of a structure formed by femtosecond laser processing with a line-shaped beam using swept-source optical coherence tomography (SS-OCT) was demonstrated. In the evaluation of the SS-OCT system, the depth resolution, measurement accuracy, and axial measurable range were 15.8 μm, ±2.5 μm and 5.3 mm, respectively. In laser grooving, the structural shape and the distribution of deposited debris were successfully monitored. The measured depth agreed well with the depth obtained using a laser confocal microscope. The proposed method will be effective for precise laser processing with feedback control of the laser parameters based on in-process monitoring of the processed structure.

Temperature dependence of the loss coefficients during the formation of surface laser-stimulated nanostructures

Numerical simulation of the formation of nanocraters on a solid surface during powerful laser processing was performed. System of two interconnected differential equations for the dynamics of the crater form and surface pressure underlies the problem under consideration. This system describes a process of high precision laser processing without the formation of a melt. It contains parameters, which are the optical and thermal loss coefficients for the initial flow when it reaches the interface. The coefficients of optical and heat losses at the interface between the solid and plasma-gas phases make it possible to divide the consideration of the problem into two independent problems in each of the phases. It was found that the sum of these coefficients is, with good accuracy, equal to one. This made it possible to focus only on optical loss. Generally optical losses represent as the sum of the reflection coefficient and the dimensionless scattering factor. The dependences of the reflection coefficient and scattering factor on temperature, radius of surface roughness and pressure in the plasma-gas phase are found.

The History and Future of Precise Laser Processing by Stealth Dicing

The History and Future of Precise Laser Processing by Stealth Dicing

Experimental investigation of the strength of polymer-steel direct adhesion (PSDA) joints with micro-structures ablated by laser

The key issue for polymer-steel direct-adhesion (PSDA) technology is to find an effective and efficient way to enhance the adhesion strength. A high-power precision laser processing method was utilized to form a periodic microstructure on the metal surface before PSDA joining. The corresponding theoretical model was proposed to optimize the processing parameters and establish the relationship between microstructures and adhesion fracture energy. Additionally, single-lap tensile shear tests of PSDA samples with various mircostructures were carried out. The experimental results show that the proposed method could increase the ultimate tensile load by nearly 1.5 times higher than the traditional chemical surface pretreatment. Due to the processing of periodic microstructure could be controlled accurately by machines, the dimensional precision was improved. The investigation also discovered that the packing arrangement of interfacial microstructures affects the adhesion strength and fracture energy, but independent of the roughness. The present method is demonstrated to be an effective, efficient, and economic interface treatment for polymer-steel hybrid structures.

Cost‐Effective Absorber Patterning of Perovskite Solar Cells by Nanosecond Laser Processing

Perovskite solar cells have shown a tremendous performance increase in the last years with conversion efficiencies >20%. For the successful application of this technology, an interconnection process is required to create large area solar modules, preferably with the help of precision laser processing. By now, only a few groups have started investigations of this topic. Here, we report on methods and ways to characterize and optimize the perovskite absorber removal process (P2), by means of nanosecond pulsed laser ablation with wavelengths of 355, 532, and 1,064 nm. With short‐pulsed lasers, the underlying ablation mechanisms of the perovskite material differ significantly from other thin‐film photovoltaic technologies, and the characterization with regards to the formation of contact resistances is indispensible. We show that process optimization based on a morphological evaluation is not sufficient to generate interconnections, without severe influence on the solar module performance.

High Precision Laser Processing of Steel Surfaces with Sub-ns-lasers

Ultrashort pulsed lasers like ps- and fs-lasers with single pulses and pulse bursts allow a high ablation rate combined with a superior quality for several materials like copper and brass as well as glass and dielectrics.In case of steel surfaces this known quality could not be transferred, because after a defined ablation depth the surface roughness increases. An increased roughness is mainly caused by a growing area of cone like protrusion structures (CLP) with increasing of the ablation depth. To avoid this phenomenon a melt concomitant ablation, due to some 100ps pulse duration was applied with a moderate pulse energy of 30 μJ. The results show no CLP structures and a decreased surface roughness in combination with an acceptable recrystallization of melt residues around the ablation area. The non-melt-free ablation process with residual molten volume caused by the longer pulse duration (compared to USP-lasers) has to be compensated through a higher laser power. This investigation shows an approach with a parallelization of several separate modulated laser spots for increasing the processing speed.

초고속/초정밀/대면적의 레이저 가공시스템 설계

Current electronic products are dominated by the laser processing and the application will be extended this time. Especially, demands for high precision laser processing with a large area has been increasing for a number of applications such as in solar cell battery, display parts, electronic component and automobile industry. In this paper we designed an on-the-fly system for ultrafast/high precision/large area laser processing. In addition, we have developed the path algorithm for large area. Expansion of the area in which laser processing is an important factor to handle the ultrafast/wide area processing, it will require a processing path. Processing path is path of 2- axis stage and stage of change in velocity can be smooth as possible. We proposed a path of the user concept using NURBS(Non-Uniform Rational B-Spline)method. Through our experiment with the chopper, was to prove the continuity of edge parts. Through basic shape experiments, we proved that large area can be processed using laser. We developed a simulation tool using Visual C++.

Continuous Laser Fabrication Method using Adaptive Cell Decomposition

A one-axis on-the-fly method was developed in order to extend the processing area of the existing laser processing systems. Demands for high precision laser processing with wide areas have been increasing in a number of applications such as solar cell batteries, display parts, electronic components, the automobile industry, and so on. However, ultra-high speed laser scanner systems are limited by the size of the scanning area, for example 50 x 50 mm. Even though a laser scanner system that can scan a wide area has been developed recently, the distortion of the scanning quality becomes more serious as the scan area increases. In this paper, an algorithm using adaptive cell decomposition is proposed. The developed method is differentiated from the existing step and scan method in that it can guarantee continuous stage movements, which may improve the processing speed and laser fabrication quality.

Plasmonic Enhancement During Femtosecond Laser Drilling of Sub-wavelength Holes in Metals

Precise ablation of metals using tightly focused femtosecond laser pulses with intensities close to the damage threshold can yield sub-wavelength, nanometer-sized holes or craters. These structures in metals can exhibit plasmonic effects, thereby affecting the interactions involved. We numerically simulate light propagation inside such holes and model the ablation process. We show that surface plasmon resonances can be excited at near-infrared and visible wavelengths. At resonance wavelengths, significant enhancement of aspect ratio is possible. Our results show that plasmonic effects are essential for the understanding of precision laser processing of metals, and they can be exploited to significantly enhance the performance of laser micro- and nano-machining.

An atomic-level study of material ablation and spallation in ultrafast laser processing of gold films

Ablation and spallation of gold thin films by an ultrashort laser pulse are simulated by using an integrated two-temperature model and molecular dynamics method with inclusion of the hot electron blast force. The simulation results show that the ultrafast laser-induced nonthermal ablation and spallation both are essentially due to dynamic tensile stress that exceeds the local material strength. It is also demonstrated that a simultaneous use of femtosecond and picosecond laser pulses could induce spallation without causing undesired front-side damage to the film. This may be suited to peel an ultrathin film (1 μm in thickness or less) from its substrate or to improve the material removal rate of precise laser processing.

Multifunctional laser process system for the high-precision processing of three-dimensional large-scale 3×3×06-m items with complex surface shapes

The LSP-2000 (Laser System Processor-2000) laser process system for forming a specified surface profile of arbitrary topology on curvilinear surfaces, as well as precision laser processing of large three-dimensional items, has been developed, created, and investigated. This system implements not only processing regimes (cutting, welding, ablation), but also the measurement of the actual geometry of three-dimensional objects with an arbitrary surface shape. A brief description is presented of the main technical decisions and the experimental results of the certification of the LSP-2000 system. The measurement error in the start-stop regime does not exceed 2μm, and the processing error when the actuator moves along an arbitrary continuous contour is no more than 20μm, The working speed for surface microprofiling exceeded 9m/min. The time of continuous operation in the automatic regime has reached more than 15hr in the temperature range from +18to+30°C.

2705 広領域・3次元レーザ微細加工装置の開発と加工性能評価(S66-2 卒業研究コンテスト(2),S66 卒業研究コンテスト)

2705 広領域・3次元レーザ微細加工装置の開発と加工性能評価(S66-2 卒業研究コンテスト(2),S66 卒業研究コンテスト)

Precise laser ablation processing of black widow spider silk

Contact-free precise laser processing of black widow spider (Latrodectus hesperus) dragline silk by laser ablation at λ=157 nm is achieved. At this wavelength, the small optical penetration depth, below 100 nm, allows efficient and gentle material removal above the ablation threshold of Φth=29 mJ/cm2. The ablation rate in nm/pulse is measured against laser fluence Φ and simultaneously calibrated with ultrapure polymethylmethacrylate (PMMA). Ripple formation in fiber ablation can be overcome by a suitable combination of ablation removal and laser polishing steps using exposure sequences at different irradiation angles α, such as vertical at 0° followed by oblique irradiation at 70°. In this way ripples are destroyed until the fiber is automatically smoothed over the entire laser-exposed length. This allows precise laser ablation processing of spider silk fibers and other highly absorbing materials without affecting the bulk mechanical, and other material, properties.

Precision laser processing of curved surfaces of revolution

A study was made of the transfer, by a laser beam, of an image of a pattern from a planar optical mask onto a real curved surface of revolution. Patterns with specified geometric dimensions and shape were formed on inner surfaces of a hemisphere, a cone, and a two-sheet hyperboloid transforming into a cone. 'Latent images' were also produced on inner surfaces of a torus and a paraboloid.