Nanosecond Pulsed Fiber Laser Research Articles

An investigation into the use of incoherent UV light to augment IR nanosecond pulsed laser texturing of CFRP composites for improved adhesion

The preparation of Carbon Fibre Reinforced Polymers (CFRP) surfaces for adhesive bonding has been widely reported. Such reports include laser texturing using both near-infrared (IR) lasers and ultraviolet (UV) lasers. In this report, we present, for the first time, findings showing that surface treatment of CFRP using incoherent UV light, at 254 nm wavelength, can increase the adhesive bonding strength of CFRP by 75 % compared to non-treated samples. It is also around 10 % stronger than NIR laser-textured samples. However, combination treatments, where the UV irradiation is conducted either before or after laser texturing did not give a significant benefit over the laser-textured samples. A germicidal 46 W 254 nm UV lamp was used for the UV light treatment, while an IR nanosecond pulsed fibre laser operating at 1064 nm was used for the laser texturing treatment. The material tested was an autoclave-cured T700 CFRP composite.The wettability of the treated CFRP surfaces and the adhesive bonding were quantitatively assessed. This study concludes that low-cost incoherent UV treatment effectively reduces the water contact angle of the CFRP surface and activates CFRP surfaces. All treatments led to bonding strengths at least 50% greater than for the untreated surfaces.The predominant failure mode for UV-treated samples was Cohesive Substrate Failure (CSF), indicating that the adhesion strength exceeded the interlaminar shear strength of the CFRP material. All samples treated with the laser (including combined treatment with UV) exhibited Light Fibre Tear Failure.

Nanosecond-pulse fiber laser mode-locked with iron phthalocyanine

Abstract In this paper, we demonstrated a passively mode-locked erbium doped fiber laser (EDFL) using iron phthalocyanine (FePc) material as a saturable absorber (SA). The FePc-SA was prepared via a casting method, integrating FePc powder with polyvinyl alcohol to form FePc-PVA film. When implemented into the mode-locked EDFL cavity, the laser generated 356 ns pulses at a repetition rate of 969 kHz. Operating at a wavelength of 1559 nm, the laser achieved pulse energy of 6.04 nJ, output power of 5.85 mW, and peak power of 0.014 W under a maximum pump power of 128.92 mW. The laser exhibited remarkable stability, evidenced by a signal-to-noise ratio of 71.7 dB at the fundamental frequency. These results demonstrate that FePc material effectively serves as a mode-locker for generating nanosecond pulses.

Microsecond and nanosecond pulse initiator by Mo2Ga2C DSF saturable absorber (SA) with EDFL ring cavity

This paper elaborated the generation of microsecond and nanosecond pulse fiber laser using Mo2Ga2C coating onto DSF. The microsecond pulse commenced at the pump power of 39.826 mW and increased to 81.37 mW with a pulse width of 7.02 µs–5.92 µs. Meanwhile, the repetition rate showed measurements between 42.63 kHz to 64.6 kHz corresponding to the maximum pulse energy of 150.15 nJ. Besides that, the nanosecond pulse was generated with an additional length of 200 m for the SMF. The dual wavelength nanosecond pulse began at the pump power of 95.22 mW with a pulse width of 273.7 ns corresponding to the repetition rate of 961.8 kHz. Maximum pulse energy and maximum peak power were 8.75 nJ and 28.15 mW, respectively. The Mo2Ga2C coated DSF acted as the SA and was integrated into an erbium doped fiber laser cavity. The modulation depth of the Mo2Ga2C DSF SA was approximately 7.2 %.

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

Development of laser structured three-dimensional patterns for improved wettability and performance of electrodes for lithium-ion batteries

The demand for improved performance and higher energy density of LIBs is growing due to their wide range of applications and advancement in the energy storage market for electric vehicles. Three-dimensional (3D) structured electrodes have recently been considered the best and most promising approach to improve battery performance as they exhibit high areal and specific capacity. In the work described here, a nanosecond pulsed fiber laser was used to generate four types of surface patterns named: line, grid, triangular end, and rectangular end patterns with an equal amount of ablated active material volume. A study on wettability was performed using the spread area, wetting time, wetting balance, and capillary rise measurements. Moreover, the Lucas Washburn and extended wettability models were used to quantitatively express the wetting behavior using the term wetting rate. In all approaches, line-patterned electrodes show better wettability along with a higher wetting rate, while poor behavior is seen with an unstructured electrode. Galvanostatic tests were used to examine how these electrode surface patterns influence the electrochemical performance of the battery. The capacity retentions, discharge capacity efficiencies, and cyclic stabilities were improved on cells with line, triangular end, and rectangular end patterned electrodes.

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.