Pulsed Fiber Laser Research Articles

Pulsed fiber laser processing of A4 SS under active and inactive environments: A comparative study

Higher machining productivity and improved surface functionalities are major concerns in laser micromachining. A pulsed fiber laser process (PFLP) is asserted in this study for producing micro-channels on A4 stainless steel (A4 SS) for marine applications. As PFLP is one of the most demanding manufacturing processes, this research aims to enhance PFLP by introducing a novel linear orbit-in-orbit laser beam position approach (LO-OLPA). This innovative method was further investigated in active and inactive gas environments as an existing industrial potential by altering the PFLP variables via tailoring the scan modes of the fiber laser. Furthermore, responses such as material ablation, dimensional, and surface characteristics were compared. The response functions were then used for multi-response whale optimization (MRWO) to acquire the best parametric settings for both environments to enhance productivity and quality. Later, surface analysis (such as surface morphology, elemental diffusions, phase quantifications, and molecular bond identification) was studied in two environments. The results demonstrated that the exothermic chemical reaction boosted the material ablation and dimensional aspects of A4 SS during PFLP but impaired the surface quality when the environment switched from inactive to active. Also, in both conditions, the entry side of the channels is rich in Fe and Cr oxides, but the exit side has just Cr oxide. Elements including Cr, and Fe were revealed to be more abundant in the evacuated molten materiallayer under inactive compared to the active environment. In addition, molecular bond displacement was detected in both environments compared to the base material.

Silver Nanoplate Composites as Nonlinear Saturable Absorbers for a Q-Switched Laser

Metal nanomaterials have promising applications in ultrafast photonics due to their broadband operation, large third-order nonlinear susceptibility, and ultrafast recovery time. We realized a Q-switched pulsed erbium-doped fiber laser based on a silver nanoplate polyvinyl alcohol film as a saturable absorber. This film, with a modulation depth of 15.7%, was integrated into a fiber laser by means of a sandwich structure. We obtained Q-switched pulses in the 1.5-μm band, which plays an important role in telecommunications and atmospheric detection. Stable Q-switched pulses were obtained at the pump power of 135 mW, with a single pulse energy of 33.8 nJ, a pulse width of 2.3 μs, a repetition rate of 62.4 kHz, and a signal-to-noise ratio of about 45 dB. When increasing the pump power up to a maximum value of 246 mW, the maximum single pulse energy of 57.8 nJ was achieved. This study first demonstrates the potential of silver nanoplates as saturable absorbers in generating stable laser pulses with high energy.

Generation of soliton operating at 1.5 µm regime using Indium Selenide based saturable absorber

We successfully accomplished a soliton pulse in an Erbium-doped fiber laser (EDFL) cavity by integrating an Indium Selenide (In2Se3)-based passive saturable absorber (SA). In2Se3 film was prepared by using a common dry cast method and owns saturable intensity, modulation depth, and non-saturable loss of 1066.57 MW/cm2, 1.1 %, and 72.2 %, respectively. By implementing In2Se3 film into the EDF laser cavity, a generation of soliton with 1.880 MHz, at the threshold pump power of 83.63 mW was achieved. A narrow pulse width of 5.51 ps and remarkable temporal stability, as demonstrated by a signal noise ratio (SNR) of 78.52 dB and peak power of 1.00 kW obtained using In2Se3 as SA operating in a 1.5-μm regime proven its potential in photonic applications.

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 Analysis of Nanosecond Pulse Laser Etching of SiCp/Mg Composites.

Due to the introduction of silicon carbide reinforcement, the physical and cutting properties of SiCp/Mg composites are very different from those of metal composites. Nanosecond pulse laser processing is more efficient than traditional processing for SiCp/Mg composites. A low-power pulsed fiber laser was used to etch 3.0 mm thick SiCp/Mg composites. The effect of low laser power (0~50 W) on the morphology and heat-affected zone of the SiCp/Mg composite after etching was studied. The results show that when the laser power increases, the material accumulation at the ablation end of the machining surface becomes more and more serious. With the increase in power, the differences in ablation width and ablation depth on the surface of composite materials do not increase proportionally. When the laser power increases gradually, the width of the heat-affected zone increases in the direction of the perpendicular laser beam and reaches the maximum value at the etched end.

Single-frequency linearly-polarized gain-switched DFB pulsed fiber laser

We report a single-frequency linearly-polarized gain-switched distributed feedback (DFB) pulsed fiber laser. A 976 nm laser diode (LD) which can generate both pulsed and continuous wave (CW) laser is used as the pump source to initiate gain-switched progress. Pulsed fiber laser with single-frequency and linearly-polarization is obtained by applying pressure on a 50 mm long phase shifted fiber Bragg grating (PS-FBG). Through parameter optimization, the laser generates single-frequency linearly-polarized laser pulses with a center wavelength of 1030.78 nm, a narrowest linewidth of 36.1 MHz, a maximum peak power of 3.78 W, and a polarization extinction ratio of better than 19 dB. And the repetition rate of output pulses can be flexibly changed from 1 kHz to 400 kHz with a pulse width of 20–200 ns.

Time-domain flexible pulse fiber laser generation and high-power evolution based on inter-band excitation of lead sulfide nanoflakes

Ultrafast photonics has become an interdisciplinary topic of great significance owing to the spectacular development of compact and efficient ultrafast pulse generation. Saturable absorbers (SAs) are the kernel for ultrafast pulse generation. However, the conventional SAs performance is plateauing owing to the complex preparation process, the diversification of demand for pulse width, and the relatively low laser output at mill watt level. Herein, high-quality comprehensive vertical Lead Sulfide (PbS) nanoflakes were synthesized by the physical vapor deposition (PVD), and a home-build handy dry-transfer system was used to simplify the fabrication process of PbS saturable absorbers device (PbS-SAs). Total-energy calculations by the density functional theory (DFT) were performed to further understand the saturable absorption characteristic of PbS. A time-domain flexible erbium-doped fiber pulse laser has obtained Q-switched, mode-locked, and highest 14th order harmonic mode-locked pulse. Based on a selected mode-locked operation, an all-fiber master oscillator power amplifier (MOPA) pulse laser system was proposed and demonstrated. The integrated system based on PbS-SAs achieved a time-domain flexible fiber pulse laser, high order harmonic mode-locked pulse, and a picosecond pulse (∼287 ps) with high average power of ∼57.5 W and peak power of ∼13.7 kW at the central wavelength of 1562 nm. This research not only provides a simple manufacturing process for high uniformity SAs devices but also greatly improves output power, which would attract interest in exploring the unique properties of nanocomposite SAs for photonic applications.

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.

Switchable property of dissipative soliton and dispersion-management soliton in fiber laser

We numerically and experimentally demonstrated that the central wavelength of the output pulses in an Er-doped mode-locked fiber laser can be switched from ∼1561 to ∼1531 nm, while these two pulses exhibit dispersion-management soliton and dissipative soliton, respectively. The switch capability of our fiber laser with different pulse waveforms can be attributed to combining the double-hump gain spectrum of Er-doped fiber and third-order dispersion (TOD) effect. By considering the TOD effect, the two wavelengths can be operated in different dispersion regime. The transient switch dynamics of these different type of solitons are also observed by time stretched technique. These findings provide a good foundation for comprehensively studying pulse formation dynamics in laser cavities, and benefit for design dual-wavelength fiber lasers.

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.

Dissipative soliton resonance and noise-like pulse in a self-pulsing fiber laser

In this paper, a self-pulsing Er-doped fiber laser operating in the dissipative soliton resonance (DSR) regime is firstly reported. By adjusting the pumping power and intracavity pulse polarization, the generated mode-locking pulse could evolve between soliton pulse, dissipative soliton resonance pulse and noise-like pulse (NLP). In the dissipative soliton resonance mode-locking regime, the generated rectangular-shaped pulses centered at 1570.5 nm with a maximum average output power of 20.6 mW and a pulse duration of 8.9 ns. Meanwhile, in the NLP regime, the maximum average output power is 49.9 mW, corresponding to a pulse energy of 2.5 nJ. The self-pulsing evolving dynamics can be analyzed using weak NPR effect by simultaneously considering the polarization dependent loss from the polarization controller and the reabsorption loss of the un-pumped gain fiber.

Observation of soliton and bound soliton in erbium-doped fiber lasers using single-walled carbon nanotubes mode-lockers under gamma irradiation

This study looked into the generation of soliton and bound-state soliton passively mode-locked Erbium-doped fiber lasers (EDFLs) using gamma (γ) ray irradiated single-walled carbon nanotubes-poly(ethylene oxide) (SWCNT-PEO) film as a saturable absorber (SA). Using the liquid phase exfoliation method, a free-standing SWCNT-PEO film-based SA was developed. The SWCNT-PEO film was non-irradiated before being integrated into the laser cavity, and then subjected to a series of low dose radiations of 50 Gy, 100 Gy, and 200 Gy. The non-irradiated film generated a soliton mode-locked pulsed fiber laser operating at 1560 nm, with a repetition rate of 23.8 MHz and a pulse width of 0.60 ps. Irradiated films of 50 Gy and 100 Gy produced bound-state solitons with pulse separations of 7.68 ps and 2.62 ps, respectively. A soliton mode-locked pulsed fiber laser with an operating wavelength of 1556 nm and a pulse width of 0.59 ps is produced for the 200 Gy irradiated film.

Laser-assisted rapid synthesis of anatase/rutile TiO2 heterojunction with Function-specified micro-zones for the effective photo-oxidation of sulfamethoxazole

A solid-state laser scanning treatment (SLST) was adopted to synthesize anatase/rutile TiO2 heterojunction with effective charge carrier separation and high surface adsorption performances for the photodegradation of sulfamethoxazole (SMX). The 1064 nm pulsed fiber laser could in-situ generate rutile zones on the pristine sheet-like anatase crystal enclosed by (001) facets, which could form the well-defined anatase/rutile interface to promote the formation of dominating active species (h+ and ∙OH) on the anatase zones. X-ray absorption fine structure (XAFS) measurements, low temperature electron paramagnetic resonance (LT-EPR) as well as the density functional theory (DFT) simulation proved that the oxygen vacancies (VO) could both introduce defective energy states to promote the light absorption and enhance the SMX adsorption on anatase zones. Based on the delicately designed micro-zones, the photodegradation efficiency of the optimized catalyst could reach 99.3 %, which demonstrated ∼7 times higher performance than that of pristine TiO2 and exhibited robust stability under environmental conditions. Gaussian and Vienna Ab Initio Package (VASP) programs were used to provide detailed degradation pathways and mechanism for SMX. This SLST could be potentially employed to create function-specified zones on various catalysts for different applicational aims.

Wavelength-switchable noise-like square pulsed fiber laser based on nonlinear effects

We report a fiber laser that can generate switchable wavelength noise-like square pulses (NLSPs) with a tunable pulse width based on nonlinear effects and nonlinear polarization rotation (NPR) mode-locking technology. In the single-wavelength NLSP, the 3 dB bandwidth is 1.68 nm and the central wavelength is 1558.61 nm. The widths of the spike and pulse duration are 1.47 ps and 5.14 μs. In the case of obtaining dual-wavelength noise-like squares, the pulse width is broadened from 84.4 to 875.8 ns by varying the pump power in the range of 60 to 450 mW. The dual-wavelength square pulse has a maximum energy of 27.26 nJ. The phenomena investigated in this work are conducive to a profound understanding of NLSPs formation in fiber laser and are of great significance for broadening the approach for achieving multi-wavelength square pulse.

Passively Q-switched and mode-locked pulses in erbium-doped fiber laser based on Cr2Ge2Te6 saturable absorber

This paper reports the preparation of Cr2Ge2Te6 (CGT)-polyvinyl alcohol (PVA) by the liquid-phase exfoliation method. And the characterization of CGT nanosheets is carried out systematically. In our experiments, CGT-PVA was used as a nonlinear saturable absorber to achieve passively Q-switched erbium-doped fiber laser with wavelengths of 1531 nm and 1556 nm, respectively. The repetition frequency of the Q-switched fiber laser changes from 30.86 kHz to 70.81 kHz, with a tuning range of approximately 40 kHz. In addition, the mode-locked operation can be easily performed by controlling the polarization states in the cavity. A stable 471.2 fs soliton was obtained with a maximum pulse energy of 3.85 mW at a repetition frequency of 18.08 MHz. Our study shows that CGT nanosheets open up new opportunities for the development of future high-performance photonic devices.

Frontier and Hot Topics of Pulsed Fiber Lasers via CiteSpace Scientometric Analysis: Passively Mode-Locked Fiber Lasers with Real Saturable Absorbers Based on Two-Dimensional Materials.

Pulsed fiber lasers, with high peak power and narrow pulse widths, have been proven to be an important tool for a variety of fields of application. In this work, frontier and hot topics in pulsed fiber lasers were analyzed with 11,064 articles. Benefitting from the scientometric analysis capabilities of CiteSpace, the analysis found that passively mode-locked fiber lasers with saturable absorbers (SAs) based on two-dimensional (2D) materials have become a hot research topic in the field of pulsed fiber lasers due to the advantages of self-starting operation, high stability, and good compatibility. The excellent nonlinear optical properties exhibited by 2D materials at nanometer-scale thicknesses have become a particularly popular research topic; the research has paved the way for exploring its wider applications. We summarize the performance of several typical 2D materials in ultrafast fiber lasers, such as graphene, topological insulators (TIs), transition metal dichalcogenides (TMDs), and black phosphorus (BP). Meanwhile, we review and analyze the direction of the development of 2D SAs for ultrafast fiber lasers.

Improvement of peak power of dissipative soliton resonance pulse in a thulium-doped fiber laser

Single pulse energy and pulse width can be theoretically increased indefinitely without pulse-breaking in a dissipative soliton resonance pulse (DSR) generated from a mode-locked fiber laser when the peak power is keeping in a certain value. But in some applications, both high pulse energy and high peak power are needed in one single pulse. To improve the peak power of the DSR pulse, the characteristics of DSR pulses were investigated and found that the position of the gain fiber is a factor to influence the peak power and the pulse width. Here, we demonstrate a thulium-doped mode-locked fiber laser operating in the DSR regime with a nonlinear amplifying loop mirror (NALM). When changing the position of the gain fiber, the peak power of DSR pulse could be improved from 0.38 W to 1.42 W with the same pump power. This approach provides a method for increasing the pulse energy and efficiency in mode locked fiber lasers, which may meet some special application.

Pulse compression of a single-frequency Q-switched fiber laser based on the cascaded four-wave mixing effect

A pulse compressing technology of single-frequency Q-switched laser based on the cascaded four-wave mixing (CFWM) effect is demonstrated theoretically and experimentally, for the first time to the best of our knowledge. A theoretical model of the pulse compression is established through deconstructing the pulse duration evolution in the high-order Stokes and anti-Stokes lights of CFWM. A pulse compression ratio of (2|m|+1)1/2 is quantificationally obtained with m corresponding to the order number of the CFWM light. Utilizing dual-wavelength (DW) single-frequency Q-switched laser injected into a highly nonlinear fiber (HNLF), the pulse compression and the spectral broadening phenomenon are observed simultaneously. As the order number of the CFWM light increases from 0-order to 3-order, the pulse duration has reduced from 115 ns to 47 ns with a compression ratio of 2.45, which is essentially consistent with the theoretical analysis. The pulse compressing technique by CFWM is conducive to promoting the performance development of the single-frequency Q-switched laser, which can improve the system precision in the Lidar, trace gas detection, and high-precision ranging. Furthermore, this technology based on time-frequency transformation dynamics may be generally applicable to other single-frequency pulsed fiber lasers.

Tunable mode-locked thulium doped fiber laser using manganese phosphorus triselenide (MnPSe3) in 2.0 μm

This work demonstrates a passive technique to generate mode-locked pulses in a thulium-doped fiber laser (TDFL) using manganese phosphorus triselenide (MnPSe3) as the saturable absorber (SA). The MnPSe3 solution was prepared through the liquid phase exfoliation technique (LPE) and was then deposited onto an arc-shaped fiber through the drop-casting method. A highly stable mode-locked laser with a center wavelength of 1937.0 nm and a 2.69 nm bandwidth was generated when the MnPSe3 SA was inserted into the fiber laser ring cavity. The fundamental frequency of the mode-locked TDFL was 13.10 MHz and the signal-to-noise ratio (SNR) was 49 dB. The mode-locked pulse had a pulse duration of 1.56 ps. By stretching the arc-shaped fiber using a mechanical stage, the center wavelength of the laser could be tuned from 1937 to 1939 nm. The successful generation of the mode-locking operation indicates that MnPSe3-SA is suitable to operate in the 2.0 μm wavelength region.

A cladding-pumping based power-scaled noise-like and dissipative soliton pulse fiber laser

We report a high-average-power noise-like pulse (NLP) and dissipative soliton (DS) pulse fiber laser. Average power as high as 4.8 W could be obtained at the fundamental mode-locked repetition rate. The NLP can also be transformed into a more powerful DS mode-locking state by optimizing the polarization and losses of intra-cavity pulses in the nonlinear polarization evolution regime. The operation mode between the NLP and DS can be switched, and the laser output performance in both modes has been studied. The main advantage of this work is switchable high-power operation between the NLP and DS. In comparison with conventional single-mode NLP fiber lasers, the multi-function high-power optical source will greatly push its application in supercontinuum generation, coherence tomography, and industrial processing.