Ultrashort pulsed fiber laser welding and sealing of transparent materials

In-Volume Glass Modification Using a Femtosecond Laser: Comparison Between Repetitive Single-Pulse, MHz Burst, and GHz Burst Regimes

In this study, we report, for the first time, to the best of our knowledge, on in-volume glass modifications produced by GHz bursts of femtosecond pulses. We compare three distinct methods of energy deposition in glass, i.e., the single-pulse, MHz burst, and GHz burst regimes, and evaluate the resulting modifications. Specifically, we investigate in-volume modifications produced by each regime under varying parameters such as the pulse/burst energy, the scanning velocity, and the number of pulses in the burst, with the aim of establishing welding process windows for both sodalime and fused silica.

An optoelectronic implantable neurostimulation platform allowing full MRI safety and optical sensing and communication

A novel programmable implantable neurostimulation platform based on photonic power transfer has been developed for various clinical applications with the main focus of being safe to use with MRI scanners. The wires usually conveying electrical current from the neurostimulator to the electrodes are replaced by optical fibers. Photovoltaic cells at the tip of the fibers convert laser light to biphasic electrical impulses together with feedback signals with 54% efficiency. Furthermore, a biocompatible, implantable and ultra-flexible optical lead was developed including custom optical fibers. The neurostimulator platform incorporates advanced signal processing and optical physiological sensing capabilities thanks to a hermetically sealed transparent nonmetallic casing. Skin transparency also allowed the development of a high-speed optical transcutaneous communication channel. This implantable neurostimulation platform was first adapted to a vagus nerve stimulator for the treatment of epilepsy. This neurostimulator has been designed to fulfill the requirements of a class III long-term implantable medical device. It has been proven compliant with standard ISO/TS10974 for 1.5 T and 3 T MRI scanners. The device poses no related threat and patients can safely undergo MRI without specific or additional precautions. Especially, the RF induced heating near the implant remains below 2 °C whatever the MRI settings used. The main features of this unique advanced neurostimulator and its architecture are presented. Its functional performance is evaluated, and results are described with a focus on optoelectronics aspects and MRI safety.

Picosecond laser microwelding of AlSi-YAG for laser system assembly

We report the successful picosecond laser welding of AlSi and YAG. This material combination is of significant interest to the field of laser design and construction. Parameter maps are presented that demonstrate the impact of pulse energy and focal position on the resultant weld. Weld performance relevant to industrial applications is measured, i.e., shear strength, process yield, and absolute thermal resistance are presented.

MXenes: synthesis, incorporation, and applications in ultrafast lasers

The rapid expansion of nanotechnology and material science prompts two-dimensional (2D) materials to be extensively used in biomedicine, optoelectronic devices, and ultrafast photonics. Owing to the broadband operation, ultrafast recovery time, and saturable absorption properties, 2D materials become the promising candidates for being saturable absorbers in ultrafast pulsed lasers. In recent years, the novel 2D MXene materials have occupied the forefront due to their superior optical and electronic, as well as mechanical and chemical properties. Herein, we introduce the fabrication methods of MXenes, incorporation methods of combining 2D materials with laser cavities, and applications of ultrafast pulsed lasers based on MXenes. Firstly, top-down and bottom-up approaches are two types of fabrication methods, where top-down way mainly contains acid etching and the chief way of bottom-up method is chemical vapor deposition. In addition to these two typical ones, other methods are also discussed. Then we summarize the advantages and drawbacks of these approaches. Besides, commonly used incorporation methods, such as sandwich structure, optical deposition, as well as coupling with D-shaped, tapered, and photonic crystal fibers are reviewed. We also discuss their merits, defects, and conditions of selecting different methods. Moreover, we introduce the state of the art of ultrafast pulsed lasers based on MXenes at different wavelengths and highlight some excellent output performance. Ultimately, the outlook for improving fabrication methods and applications of MXene-based ultrafast lasers is presented.

Prediction of internal modification size in glass induced by ultrafast laser scanning

The modification at the interface between glass plates induced by ultrafast laser is important for the glass welding strength, therefore the relationship between the modification size and processing parameters should be identified. The experimental method has its limitation in understanding the nature of the modification. In this study, a numerical model for the temperature distribution determining the modification size induced by ultrafast laser scanning is developed, in which a three-dimensional steady model for the beam propagation with a transient ionization model is established to estimate the free electron density by the single laser pulse, and then a heat accumulation model for multiple laser pulses is employed to describe energy transportation within the irradiated bulk. The experiment for the internal modifications in single-piece fused silica samples irradiated by a picosecond laser with different pulse energies and scanning velocities is performed to validate the present model.

High-quality welding of glass by a femtosecond laser assisted with silver nanofilm

Glass products with high joint strength are highly demanded in the field of microelectromechanical system (MEMS). While the quality requirement of MEMS is getting higher and higher, much attention has been paid to further improving the welding strength of the glass. Herein, a femtosecond laser welding method assisted by silver nanofilm for quartz glass is proposed. To optimize the welding results, the influence of the laser power on the location of the heat-affected zone is studied. The effect of coated silver nanofilm at the interface of two glass substrates on femtosecond laser absorptivity is conducted. Also, the welding spot size under different irradiation periods is investigated. In addition, the welding strength with and without the silver nanofilm is measured and compared. It is demonstrated that the welding strength was increased nearly 20% on average by our proposed method compared with direct femtosecond laser welding. In addition, even at the lower laser power than the welding threshold, the welding process could be realized by the proposed method.

3D Manufacturing of Glass Microstructures Using Femtosecond Laser

The rapid expansion of femtosecond (fs) laser technology brought previously unavailable capabilities to laser material processing. One of the areas which benefited the most due to these advances was the 3D processing of transparent dielectrics, namely glasses and crystals. This review is dedicated to overviewing the significant advances in the field. First, the underlying physical mechanism of material interaction with ultrashort pulses is discussed, highlighting how it can be exploited for volumetric, high-precision 3D processing. Next, three distinct transparent material modification types are introduced, fundamental differences between them are explained, possible applications are highlighted. It is shown that, due to the flexibility of fs pulse fabrication, an array of structures can be produced, starting with nanophotonic elements like integrated waveguides and photonic crystals, ending with a cm-scale microfluidic system with micro-precision integrated elements. Possible limitations to each processing regime as well as how these could be overcome are discussed. Further directions for the field development are highlighted, taking into account how it could synergize with other fs-laser-based manufacturing techniques.

Investigation of the reaction mechanism and optical transparency in nanosecond laser welding of glasses assisted with titanium film

The welding of glasses is widely used in many fields, such as optics, microfluidics, and microelectromechanical systems. In this paper, two pieces of 1 mm soda lime glass substrates were welded using a 1064 nm nanosecond laser assisted with a 14 nm titanium-coated thin film coating. Results show that after the laser irradiation, the welded area becomes highly transparent much like uncoated glass. The maximum change rate of transmittance of the welded zone is 8.88% in the wavelength range of 400-1800 nm, compared to a piece of 2 mm glass substrate. The chemical reaction process between the titanium film and the glass substrate of the highly transparent welded sample was analyzed by x-ray photoelectron spectroscopy. Welded quality and shear strength were characterized by scanning acoustic microscopy and shear tests.

Picosecond laser seal welding of glasses with a large gap

Ultra-fast lasers can realize selective welding of glasses through nonlinear effect and have the advantages of having high welding accuracy, having small heat-affected zone, having high joint strength and not requiring intermediate absorption layer, which provides a new idea for chip packaging. However, this method is limited to the condition of optical contact, which is difficult to use in engineering applications. To solve this problem, an innovative seal welding method by picosecond laser is presented in this paper. In this method, a picosecond laser performs firstly rapid oscillating scan local welding of the two natural overlap glasses with a large contact gap to form a closed area consisting of spot welds. The glass contact gap in the closed area can be reduced to about 1.5 μm through the solidification shrinkage effect of spot welds. Then a good seal weld without plasma ablation, micro-hole, and micro-crack defects can be achieved by picosecond laser in this closed area to realize seal welding of glasses with a large contact gap. The sealing test results show that the seal welding samples can keep good sealing performance for more than one week.

Towards industrial ultrafast laser microwelding: SiO2 and BK7 to aluminum alloy

We report systematic analysis and comparison of ps-laser microwelding of industry relevant Al6082 parts to SiO₂ and BK7. Parameter mapping of pulse energy and focal depth on the weld strength is presented. The welding process was found to be strongly dependent on the focal plane but has a large tolerance to variation in pulse energy. Accelerated lifetime tests by thermal cycling from -50° to +90°C are presented. Welds in Al6082-BK7 parts survive over the full temperature range where the ratio of thermal expansion coefficients is 3.4:1. Welds in Al6082-SiO₂ parts (ratio 47.1:1) survive only a limited temperature range.

A compact field-portable double-pulse laser system to enhance laser induced breakdown spectroscopy

This paper reports the development of a compact double-pulse laser system to enhance laser induced breakdown spectroscopy (LIBS) for field applications. Pumped by high-power vertical-surface emitting lasers, the laser system that produces 16 ns pulse at 12 mJ/pulse with total weight less than 10 kg is developed. The inter-pulse delay can be adjusted from 0μs with 0.5μs increment. Several LIBS experiments were carried out on NIST standard aluminum alloy samples. Comparing with the single-pulse LIBS, up to 9 times enhancement in atomic emission line was achieved with continuum background emission reduced by 70%. This has led to up to 10 times improvement in the limit of detection. Signal stability was also improved by 128% indicating that a more robust and accurate LIBS measurement can be achieved using a compact double-pulse laser system. This paper presents a viable and field deployable laser tool to dramatically improve the sensitivity and applicability of LIBS for a wide array of applications.

Picosecond laser welding of similar and dissimilar materials

We report picosecond laser welding of similar and dissimilar materials based on plasma formation induced by a tightly focused beam from a 1030 nm, 10 ps, 400 kHz laser system. Specifically, we demonstrate the welding of fused silica, borosilicate, and sapphire to a range of materials including borosilicate, fused silica, silicon, copper, aluminum, and stainless steel. Dissimilar material welding of glass to aluminum and stainless steel has not been previously reported. Analysis of the borosilicate-to-borosilicate weld strength compares well to those obtained using similar welding systems based on femtosecond lasers. There is, however, a strong requirement to prepare surfaces to a high (10-60 nm Ra) flatness to ensure a successful weld.