Nanosecond Pulsed Fiber Laser Research Articles

Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser

Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser

A novel method for air assisted nanosecond pulsed fiber laser beam transmission micro-channelling on thick PMMA material

The demand for scaling up polymeric materials for mass production or scaling down for microscale applications is at its peak in the modern era. Laser beam technology enables the formation of micro-channels on polymers, specifically polymethyl methacrylate (PMMA). This study examines the viability and cost-effectiveness of employing the diode pump fiber laser transmission technique to create micro-channels on thick, transparent PMMA under air-assisted circumstances for biomedical engineering and micro-fluidics applications. The analysis has included process variables such as pulse frequency, power, and cutting speed, as well as machining parameters including depth of cut, kerf width, and heat-affected zone (HAZ) width. The results of multi-objective optimization indicate that the following parameters—a pulse frequency of 51.30 kHz, a working power of 13 % of 50 W, and a cutting speed of 0.60 mm/s—contribute to the desired microfluidics response values: 12.54 µm depth of cut, 24.05 µm kerf width, and 5.98 µm HAZ width.

Versatile design for temporal shape control of high-power nanosecond pulsed fiber laser amplifier.

This research proposed a novel pulse-shaping design for directly shaping distorted pulses after the amplification. Based on the principle of the design we made a pulse shaper. With this pulse shaper, we successfully manipulate the pulse's leading edge and width to achieve an 'M'-shaped waveform in an amplification system. Comparative experiments were conducted within this system to compare the output with and without the integration of the pulse shaper. The results show a significant suppression of the nonlinear effect upon adding the pulse shaper. This flexible and effective pulse shaper can be easily integrated into a high-power all-fiber system, supplying the capability to realize the desired output waveform and enhance the spectral quality.

Nanosecond-pulse fiber laser mode-locked with polyaniline saturable absorber

We prove that mode-locking of an Erbium-doped fiber laser (EDFL) with a Polyaniline (PANI) saturable absorber (SA) can produce nanosecond pulses at repetition rate of 962 kHz in the elongated ring cavity. The SA is fabricated by embedding a PANI into PVA. The conducting polymer-based SA exhibits a good optical nonlinear property with a modulation depth of 2.3%. The laser operated in nanosecond regime due to the saturable absorption of the PANI PVA SA instead of nonlinear polarization evolution. A clean single pulse is observed, and the pulse train exhibits low jitter. It operated at 1530.8 nm with a pulse duration of 228 ns and a maximum pulse energy of 3.1 nJ. Due to its extremely large chirp property, the proposed laser is suited for application in the chirped-pulse amplification systems.

Understanding the role of oxide layers on color generation and surface characteristics in nanosecond laser color marking of stainless steel

This study conducts an experimental analysis of Laser Color Marking (LCM) on Stainless Steel, aiming to elucidate the role of oxides in color formation. Employing a nanosecond pulsed fiber laser, we systematically varied process parameters to successfully generate a diverse array of distinctive colors. Remarkably, a myriad of colors became evident at the micro-scale, offering a striking contrast to the macroscopic view dominated by a singular prominent color. These colors exhibited a notable increase in oxygen composition, reaching levels as high as 24.5%, coupled with the formation of a thin oxide film spanning thicknesses from 220 to 850 nm. The prevalence of chromium oxides resulted in greenish or bluish shades, whereas iron oxides’ dominance produced brownish and reddish hues. Particularly intriguing was the revelation of a multi-layer oxide film in samples like brown. Furthermore, the nature of oxides was also found to have an influence on surface characteristics. Chromium oxide-dominated colors exhibited ablation depth, while iron oxide-dominated colors resulted in surface overgrowth due to their porous nature. Correspondingly, Vickers hardness of samples dominated by chromium oxides showcased a significant enhancement in microhardness compared to those with iron oxide dominance. Lastly, we observed minimal degradation in surface roughness characteristics after LCM, with variations ranging from 262 nm to 463 nm, compared to 150 nm for untreated samples. These comprehensive findings provide valuable insights for optimizing the LCM process for stainless-steel color markings.

Monolithic 2-µm single-frequency linearly-polarized gain-switched distributed feedback fiber laser by femtosecond laser direct-writing.

We report a single-frequency, linearly polarized gain-switched, distributed feedback (DFB), 2-µm thulium doped silica fiber laser (TDFL), with an effective cavity length of 2.5 mm. The cavity is based on a heavily thulium doped non-polarization-maintaining silica fiber and composed of a π-phase-shifted fiber Bragg grating (FBG) with a total FBG length of 35 mm. The DFB FBG was written by femtosecond-laser point-by-point (PbP) method. In-band pumping scheme is chosen with a 1550 nm nanosecond pulsed erbium-doped silica fiber laser pump. Single-longitudinal, linearly polarized, gain-switched TDFL at 2002 nm, with a recorded shortest pulse duration of 4.7 ns, a repetition rate of 20 kHz, a maximum peak power of 170 W, and single pulse energy of 0.8 µJ, has been obtained, benefitting from the ultrashort DFB cavity made by the femtosecond laser direct-writing method.

Applicability of a laser pre-treatment for a robust subsequent bending of thin sheet metal

In conventional bending, locally varying residual stress states are one of the main causes for dispersion of bending angle. In this paper, a novel approach is investigated to reduce the dispersion of bending angle by modifying the residual stress state of thin sheets prior to the forming process. For this purpose, steel sheets were pre-treated with a nanosecond-pulsed fiber laser in confined ablation. The deflections were compared to sheets processed with thermal laser bending. It is revealed that the thermal mechanism dominates with respect to the deflection of the sheet because the deflection is in the same direction as that of laser-bent sheets. However, the induced deflection is smaller compared to the laser-bent ones. Moreover, it can be demonstrated that the robustness of subsequent bending operations is increased by the laser pre-treatment. The increase in robustness allows to achieve narrower tolerance windows for thin sheet metal without using cost-intensive tools and high punch forces.

Surface Alloying of Tool Steels with Ytterbium Pulse Fiber Laser

The present research shows the possibility of using an ytterbium nanosecond pulsed fiber laser for wear resistance improvement of carbon and alloy steels. The wear test was performed in accordance with the block-on-ring scheme with dry sliding friction on a friction machine. Surface dispersing/alloying was carried out from a boron carbide paste. This leads to a significant wear resistance improvement of steels. It was revealed that the mass loss during wear test reduced by several times after laser treatment compared to the non-treated samples. The wear mechanism differs depending on the type of steel and largely refers to their microstructure and composition. The tribo-oxide layer forms during the wear test.

Efficient Raman pulse fiber laser pumped by a dissipative soliton resonance pulse near 2 µm.

A high-efficiency Raman conversion from 1.987 µm to 2.177 µm is demonstrated experimentally in 45 m GeO2-doped silica fiber, adopting a dissipative soliton resonance (DSR) rectangular pulse as the pump. Over the entire spectral distribution, the spectral purity of the first-order Raman pulse is up to 96.8%, suggesting a nearly complete pump depletion before the onset of cascaded Raman shifts. The corresponding pump-to-Raman conversion efficiency of 67.4% is the highest up to date in this spectral region. Meanwhile, a large Raman pulse energy of 1.03 µJ was obtained at the repetition rate near MHz level, corresponding to 0.893 W average power. In the total output, the Raman-dominated spike has a Full Width Half Maximum (FWHM) of 1.18 ns far narrower than DSR's pulse duration of 10.25 ns. The results indicate that DSR is a promising candidate for developing efficient Raman nanosecond pulse fiber laser in mid-infrared (MIR) region.

10 kW peak power, single-frequency 1553 nm nanosecond pulsed fiber laser for time-of-flight LIDAR

A 10 kW peak power, 10 ns duration and 6 kHz repetition rate fiber laser system at 1553 nm based on an Er/Yb co-doped large-mode-area fiber, is demonstrated experimentally. The seed laser is provided by a DFB laser switched with a semiconductor optical amplifier. Its optical spectrum, linewidth, and beam quality are measured and discussed. This pulsed laser with short pulse duration and high peak power could be a candidate for the laser source of time-of-flight light detection and ranging (LIDAR).

Underwater laser texturing for enhanced adhesive joint bonding strength of Al-Mg alloy

In this research work, nanosecond pulsed fiber laser texturing was performed on Aluminum-Mg alloy (AA5754). Effect of laser texturing as a surface pre-treatment method in adhesive bonding process was investigated in details. Laser texturing was performed in under open air condition, under static water condition and under flowing water conditions. Grid shaped textures were fabricated on Al-Mg alloy work-pieces. The geometrical parameters of grid texturing were varied at two levels. Pitch of the lines were kept at 300 and 400 μm in both horizontal as well as vertical directions. Scanning speed of laser texturing process was also varied at two levels that is 2.5 and 5 mm/s. Total four experiments were conducted in each atmospheric conditions. Surface roughness and water contact angle of each surface was evaluated. Surfaces were also characterized using scanning electron microscope. Lap shear strength of each samples were evaluated using a universal tensile testing machine (UTM). Failed surfaces were analyzed to investigate the mode of failure. It was observed that the textures created in flowing water conditions resulted in cohesive mode of failure while samples fabricated in open air and in under static water conditions failed in adhesive and mixed mode respectively. Samples prepared in flowing water conditions resulted in higher lap shear strengths compared to static water, open air, and plain surfaces.

3-µm Nanosecond Pulsed Fiber Laser Enabled by the Porous Coordination Network Yellow Material

We report a passively Q-switched erbium-doped fiber laser operating at ~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3~\mu \text{m}$ </tex-math></inline-formula> based on the porous coordination network yellow material (PCN-128Y), which was synthesized by the hydrothermal method. The modulation depth, non-saturable loss and saturable intensity of the PCN-128Y at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vphantom {_{\int }}~2.87~\mu \text{m}$ </tex-math></inline-formula> were measured to be 17.74%, 40.31%, and 0.0051 GW/cm2, respectively. By incorporating the PCN-128Y into an Er <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\mathrm {3+-}}$ </tex-math></inline-formula> doped ZBLAN fiber laser, stable Q-switched laser with a wavelength of 2785.2 nm was obtained. The maximum average output power of 350.1 mW at the repetition rate of 162.35 kHz was realized when the launched pump power was 2.07 W. The corresponding pulse energy and pulse width were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.16~\mu \text{J}$ </tex-math></inline-formula> and 604 ns, respectively, and the slope efficiency was 13.08%. This is the first time to demonstrate that the PCN-128Y can serve as a saturable absorber for the generation of 3- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> mid-infrared laser pulses, to the best of our knowledge. These results reveal the nonlinear absorption property of the PCN-128Y and will open the door for use of PCN-128Y in the 3- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> mid-infrared band.

Mechanism of surface corrosion resistance of 304 stainless steel processed by nanosecond laser pulses

AbstractA nanosecond pulsed fiber laser was used to modify the surface of 304 stainless steel. The compactness, microstructure, chemical composition, and corrosion resistance of the stainless steel passive film were observed by the blue dot detection method, scanning electron microscopy, x‐ray photoelectron spectroscopy, and electrochemical methods. The influence of different laser fluences on the stability and corrosion resistance of the stainless steel passive film was studied. The results show that with increasing laser fluence, the discoloration reaction time of the stainless steel surface increases first and then decreases, while the surface roughness decreases first and then increases. When the laser fluence is lower than 11.19 J/cm2, a compact and uniform passive film is formed. When the laser fluence is larger than this value, the stainless steel substrate is prone to secondary corrosion. Chromium oxides are enriched in the passive film, and the anodic dissolution rate decreases, which promotes a positive shift in the corrosion potential of the stainless steel, decreases the corrosion current density and increases the polarization resistance and the corrosion resistance. The surface corrosion resistance is thus significantly improved.

Remote laser spot welding of AISI 430 sheets by fiber lasers—A phenomenal effect in refining weld microstructure with nanosecond pulses

In the present work, we have compared the results of microstructural and mechanical property characterization of AISI 430 ferritic stainless steel spot welds made remotely using a repetitive nanosecond pulsed fiber laser and a CW fiber laser. Optical/electron microscopy, microhardness test, and tensile shear tests were performed for evaluation of the welds. Welds made by the pulsed nanosecond laser were found to be superior due to the presence of the very narrow heat-affected zone along with finer grains in the fusion zone. The welds were also found to withstand more load before fracture and were more ductile. Use of short duration laser pulses with lower heat input were found to be responsible for the refinement of grains in the fusion zone and improvement of mechanical properties of nanosecond laser weld specimens.

Laser Fabrication of Highly Ordered Nanocomposite Subwavelength Gratings.

Optical nanogratings are widely used for different optical, photovoltaic, and sensing devices. However, fabrication methods of highly ordered gratings with the period around optical wavelength range are usually rather expensive and time consuming. In this article, we present high speed single-step approach for fabrication of highly ordered nanocomposite gratings with a period of less than 355 nm. For the purpose, we used commercially available nanosecond-pulsed fiber laser system operating at the wavelength of 355 nm. One-dimensional and two-dimensional nanostructures can be formed by direct laser treatment with different scan speed and intensity. These structures exhibit not only dispersing, but also anisotropic properties. The obtained results open perspectives for easier mass production of polarization splitters and filters, planar optics, and also for security labeling.

Influence of Pulse Energy and a Material’s Magnetic Field on the Morphology of the Dimples Produced with Nanosecond Pulsed Laser on a Magnet

Magnets made of NdFeB alloys are applied in numerous industries because they have excellent magnetic properties and good thermal stability. However, their low corrosion resistance and fragility reduce the number of the applications in harsh environments. Laser surface texturing is a powerful technique to improve the properties of materials via surface functionalisation. The characteristics of the textures define the properties of the functionalised surfaces and the laser parameters in turn influence the texture features. Pulse energy is a laser parameter with high influence on the geometry and the morphology of the textures. The magnetic field of these magnets are also expected to have an influence on the texture features. In this present work, the influence of the pulse energy (from 5µJ to 696µJ) on the dimple characteristics created with an infrared (1064 nm) nanosecond pulsed (200ns) fibre laser single pulses on NdFeB alloy (magnetic material) have been studied. The shape features of the laser textures on the samples were analysed through optical microscopy and profilometry. This work shows that the single pulses produced textures of U-type dimple kind on the metallic material. The shapes of the dimples were also altered by magnetic field of the material, which indicates that the magnetic properties of the alloys remain in liquid state. The factors of the laser beam-material interaction, pulse energy and energy depth penetration, are furthermore presented in this paper. These factors can be employed to design the width, diameter and depth of the dimples.

Effect of Swing-Spiral-Trajectory on pulsed fiber laser welding stainless steel/Copper dissimilar metals

The dissimilar metal combinations of SUS303 stainless steel and C19210 pure copper with a thickness of 0.2 mm by utilizing a nanosecond pulsed fiber laser was performed in lap welding with swing-spiral-trajectory. The weld effect was evaluated by means of microstructural and mechanical examinations. The influence of pulse frequency, speed and swing frequency as well as pulse waveform on mechanical properties and microstructure was clarified. The metallurgical behavior and weld penetration inside the fusion zone were observed with microscopic inspection of the welded joints and the welded surface. Part of molten pool materials inserted into copper plate formed an intertwined nails for enhancing the interfacial bonding strength was observed in the cross-section of the weldment. Additionally, the presence of a thin intertwined transition layer with solid solutions accomplished by the copper and liquid stainless steel mutual diffusion at the fusion line, indicated that the swing spiral welding pattern can strengthen the interface fusion. Some defects, such as porosities and microcracks, were also found in the welded joints. They were mainly due to the significantly different linear expansion coefficients of copper and steel. Energy dispersive spectroscopy (EDS) analysis confirmed that the interdiffusion and dissolution of copper and stainless steel occurred inside the molten pool, and the surface composition of the weld pool was dominated by iron. The microhardness (MH) study showed that the heat-affected zone (HAZ) was harder than the fusion zone on the stainless steel side, and the fusion interface microhardness much variation indicated microstructural change alongside the weld interface. The tensile test results revealed that the fracture location was in the molten pool on the stainless steel side, the fracture was protruded and the fracture mode was intergranular brittle fracture.

Fabrication of metallic patterns on ordinary polymer substrates by laser direct activation and electroless plating

In recent years, the fabrication of metallic patterns on polymer substrates has been given increasing attention because of its wide and important applications in many fields. This paper reported a selective metallization technology on ordinary polymer substrates basing on laser direct activation of copper hydroxyl phosphate [Cu2(OH)PO4] and electroless deposition of copper. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the interaction mechanism between nanosecond-pulsed fiber laser (1064 nm wavelength) and Cu2(OH)PO4. It was found that after laser modification and activation by appropriate parameters, the special surface microstructure (e.g., porous sponge-like) appeared and explained the good adhesion strength (the highest grade of 5B) between the copper layer and substrate. At the same time, Cu+ was generated from the Cu2(OH)PO4, adsorbed on the microstructure, and acted as catalytic active centers to realize the selective copper deposition in the laser-activated zone. In addition, the copper layer possessed good selectivity (< 3% error of line space and width) and electrical conductivity (10−6 Ω·cm volume electrical resistivity). By comparison with laser direct structuring (LDS) technology and with palladium chloride as laser sensitive material, this was a more universal and less-cost technical pathway to fabricate planar and/or three dimensional (3D) metallic patterns on more kinds of ordinary polymer substrates.

Nanosecond pulse fiber laser patterning of bilayer molybdenum thin film on 2-sq inch soda-lime glass substrate for CIGS thin film solar cell applications

Nanosecond pulse fiber laser patterning of bilayer molybdenum thin film on 2-sq inch soda-lime glass substrate for CIGS thin film solar cell applications

Laser fabrication and evaluation of holographic intrinsic physical unclonable functions

Optical Physical Unclonable Functions (PUFs) are well established as the most powerful anticounterfeiting tool. Despite the merits of optical PUFs, widespread use is hindered by existing implementations that are complicated and expensive. On top, the overwhelming majority of optical PUFs refer to extrinsic implementations. Here we overcome these limitations to demonstrate for the first time strong intrinsic optical PUFs with exceptional security characteristics. In doing so, we use Computer-Generated Holograms (CGHs) as optical, intrinsic, and image-based PUFs. The required randomness is offered by the non-deterministic fabrication process achieved with industrial friendly, nanosecond pulsed fiber lasers. Adding to simplicity and low cost, the digital fingerprint is derived by a setup which is designed to be adjustable in a production line. In addition, we propose a novel signature encoding and authentication mechanism that exploits manifold learning techniques to efficiently differentiate data reconstruction-related variation from counterfeit attacks. The proposed method is applied experimentally on silver plates. The robustness of the fabricated intrinsic optical PUFs is evaluated over time. The results have shown exceptional values for robustness and a probability of cloning up to 10^{-14}, which exceeds the standard acceptance rate in security applications.