Fiber Laser Parameters Research Articles

Distributed Bragg Reflector Laser Based on Composite Fiber Heavily Doped with Erbium Ions

A distributed Bragg reflector (DBR) laser with a specially designed, heavily Er3+-doped composite fiber of a length as short as 1.8 cm is demonstrated. The DBR laser, pumped by a 980 nm laser diode with power of up to 370 mW, generates single-frequency radiation at a wavelength of 1535 nm with a narrow instantaneous linewidth of <100 Hz and a high output power of 2 mW. The obtained Er3+-doped fiber laser parameters pave the way toward a broad range of practical applications from telecommunications and sensing to scientific research.

Analytical study on the steady-state thermal blooming effect of high-power ytterbium-doped fiber lasers propagating through the atmosphere.

Thermal blooming effect is one of the significant factors affecting the propagation performance of high-power ytterbium-doped fiber lasers (YDFLs) in the atmosphere. In this paper, two 20 kW YDFL systems with typical wavelengths (1070 nm and 1080 nm) are fabricated for propagation comparison experiments, which are used to investigate the thermal blooming effect induced by high-power YDFL propagation through the atmosphere. Under approximately the same laser system parameters (except wavelength) and atmospheric environment, the 1070 nm laser has better propagation characteristics than the 1080 nm laser. Due to the combined effect between the different central wavelengths of the two fiber lasers and the spectral broadening caused by output power scaling, the thermal blooming caused by the different absorptivity of water vapor molecules to the two fiber lasers is the main factor for the variation of the propagation properties. Through theoretical analysis and numerical calculation of factors affecting the thermal blooming effect, and considering the industrial manufacturing difficulty of YDFLs, a reasonable selection of fiber laser parameters can effectively improve atmospheric propagation performance and reduce manufacturing costs.

Theoretical and experimental studies on intermodal nonlinear effects of a high-power near-single-mode CW Yb-doped fiber laser.

An intermodal-nonlinearity-induced time-frequency evolution model of high-power near-single-mode continuous-wave fiber lasers (NSM-CWHPFLs) was proposed to simulate the evolution of spectral characteristics and beam quality under the combined action of intermodal and intramodal nonlinear effects. The influence of fiber laser parameters on intermodal nonlinearities was analyzed, and a suppression method involving fiber coiling and seed mode characteristic optimization was proposed. Verification experiments were conducted with 20/400, 25/400, and 30/600 fiber-based NSM-CWHPFLs. The results demonstrate the accuracy of the theoretical model, clarify the physical mechanisms of nonlinear spectral sidebands, and demonstrate the comprehensive optimization of intermodal-nonlinearity-induced spectral distortion and mode degradation.

Effect of Yb: Fiber laser on surface roughness and wettability of titanium

Background/Aim: In recent years, the role of computer aided design (CAD) and computer aided manufacturing (CAM) in dentistry has increasingly become important. However, the influence of different Yb: fiber laser applications on surface roughness of CAD/CAM implant has rarely been studied. The aim of this study is to investigate the effect of different Yb: fiber laser parameters on the surface roughness of CAD/CAM titanium. Material and Methods: Titanium samples, produced by CAD/CAM, were divided into 11 groups according to laser parameters such as scanning types (ST), application angles (AA) and hatch interval (HI). The surface roughness of CAD/CAM titanium was examined for each group. Wettability contact angles (CA) were also determined. Results: The highest surface roughness (43 mm) value was obtained for Group 10 (three-ways ST, 60o AA, 0.07mm HI). The lowest value (2.77 mm) after control group was obtained for Group 6. Surface roughness values, for Group 3, Group 9 and Group 10 were significantly higher than for the other groups (P= 0.000). In contact angle evaluations, the highest contact angle (144o) was observed in Group 10, while the lowest (95o) was observed in control group. Conclusions: Surface roughness was dependent on mixed effect of the laser application parameters. Three-ways ST, 60o AA, 0.07mm HI provided highest surface roughness and wettability contact angles. The surface roughness values of one-way ST, 0.06 mm HI, two-ways HT, 45o AA and 0.08 mm HI and three-ways ST, 60o AA and 0.07 mm HI were significantly higher than for the other groups (P=0.000).

A Study on the Fiber YAG Laser Welding of 304L Stainless Steel

This work aims to optimize the main YAG fiber laser parameters to weld 304L stainless steel plates of 3 mm thick. Different laser powers (2500, 2000, and 1500 W) and speeds (60, 40, and 20 mm/s) were used and merged in heat input, maintaining the defocusing distance at –2 mm to get full penetration. The weld quality and the effect of the laser heat input on the microstructures of the weld and heat-affected zones were investigated. Besides, the fracture strength of the welded joints and hardness distribution through the cross-sections were evaluated. The weld width has a direct relationship with heat input. The laser power of 2800 W produced full penetration joints without any macro defects while reduction in laser power pronounced partial penetration defects. The size of the heat-affected zone in all the processing parameters was very small. The microstructure of the weld zone shows columnar dendrite austenite grains with small arm spacing in most of the welded zone. The size of the dendrites became finer at lower heat input. At a higher heat input, a reasonable amount of lathy equiaxed grains with some delta ferrite occurred. A small amount of delta ferrite was detected in the heat-affected zone, which prevented the crack formation. The hardness of the weld metal was much higher than that of the base metal in all processing parameters and it has a reverse relationship with the heat input. The fracture strength of the welded joints was very close to that of the base metal in the defect-free samples and it increased with decreasing the heat input.

Fiber laser microcutting on duplex steel: parameter optimization by TOPSIS

ABSTRACT Duplex stainless steel (DSS) is hard to machine by conventional methods due to its high strength combined with superior plasticity. The microdomain application of laser cutting is found in sheet metal industries owing to its high accuracy and precision. The current trend in laser technology is the use of fiber laser cutting (FLC) to produce complex shapes and structures. This work highlights the microhole cutting on 0.44 mm thick DSS by a 100 µm fiber laser beam. For optimizing the fiber laser parameters, the entropy with TOPSIS approach is employed. The response surface methodology is applied to find the regression model for FLC parameters, and ANOVA checks the adequacy of the model. The parameters considered for the current research work are the power of laser, frequency of pulse, speed of scanning, and duty cycle. The output responses are surface roughness, heat affected zone, overcut, and metal removal rate. The test results showed that the power of laser is the most prevailing factor that affects the quality of microholes. From the experimentations, it is found that experimental and predicted values are reasonably close to each other. The findings from confirmation experiment validates that the optimal condition produces better surface quality as compared to the initial trails.

Investigating the Effect of Pulsed Fiber Laser Parameters on the Roughness of Aluminium Alloy and Steel Surfaces in Cleaning Processes

Investigating the Effect of Pulsed Fiber Laser Parameters on the Roughness of Aluminium Alloy and Steel Surfaces in Cleaning Processes

A Study on Cross-Shaped Structure of Invar Material Using Cold Wire Laser Fillet Welding (PART I: Feasibility Study for Weldability)

With the need for eco-friendly energy increasing rapidly due to global environmental issues, there is a rapidly increasing demand for liquefied natural gas (LNG). LNG is liquefied at minus 163 degrees Celsius, and its volume decreases to 1/600, giving it a relatively higher storage and transport efficiency than gaseous natural gas (NG). The material for the tanks that store cryogenic LNG must be a material with high impact toughness at cryogenic temperatures. Invar, which contains 36% nickel and has a very low coefficient of thermal expansion, is used for the membranes and corner structures of LNG cargo holds. The cross-shaped Invar structure used in an LNG cargo hold is manufactured through manual tungsten inert gas (TIG) fillet welding, which causes welding distortion and weldability problems. This study is a feasibility study that aims to reduce welding distortion, increase weldability with welding speed, and reduce the steps in an existing process by half by replacing the existing manufacturing method with automatic fiber laser fillet welding. Laser welding using fiber laser parameters are controlled for 1.5 and 3.0 mm thick Invar materials and weldability is secured through cross-section observation. Then, the optimal welding conditions with top and back beads secured are derived through a trial and error method.

Comparison of novel surface treatments of Al 2024 alloy for al/cfrp adhesive bonded joints

The objective of this study is to investigate the effect of silane and fiber laser treatments on the shear strength and failure type characteristic ofAA2024-T3/unidirectional carbon fiber-reinforced epoxy composite [0]8 laminates (Al/CFRP) adhesively bonded joints. Epoxy-based paste 2 part adhesive (Loctite EA 9396 AERO) was used for adhesive joining. Chemical surface treatment was tested with three different silane concentrations (1, 3 and 5 vol%) applied to AA2024-T3 aluminum plates after cleaning. In addition, 50 W pulsed fiber laser was used to AA2024-T3 aluminum plates for laser treatment. For determining the optimum fiber laser parameters (laser power, frequency and scanning speed) L9 orthogonal array Taguchi method (3 variables and 3 levels) was used. The chemical composition of the fiber laser and silane treated AA2024-T3 sample's was analyzed using Fourier transform infrared spectroscopy – attenuated total reflectance (FTIR–ATR). Shear strength values of the Al/CFRP bonded joints were determined by using single lap shear tests. From the test results, the silane concentration of 3 vol% on AA2024-T3 aluminum plates had a significant effect on shear strength of Al/CFRP bonded joints (16.44 MPa) compared to untreated samples (6.46 MPa). In addition, it was determined that the laser treating parameters of scanning speed of 100 mm/s, frequency of 80 kHz and power of 50 W laser power achieved the optimum surface of AA2024-T3 to be strongly bonded with CFRP (23.68 MPa). After mechanical tests, failure modes were also observed by using the digital camera.

Theoretical and experimental studies on direct-liquid-cooling fiber-coiling mode control technology in high-power fiber lasers.

We present a direct-liquid-cooling fiber-coiling mode control technology to flexibly and effectively control the output beam quality of high-power fiber lasers. For theoretical guidelines, we propose a theoretical model of the fiber-coiling mode control method based on the bend loss estimated using the beam propagation method. The model is used to analyze the effects of fiber-coiling methods and fiber laser parameters on fiber-coiling mode control. Based on a theoretical analysis, we constructed two master oscillator power amplifiers with 20/400 and 25/400 fibers, respectively, to carry out experiments. The results demonstrate the accuracy of the theoretical model and the effectiveness of the direct-liquid-cooling fiber-coiling method in controlling the output beam quality.

Experimental and numerical investigation of mid-infrared laser in Pr3+-doped chalcogenide fiber**Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61605095), the Natural Science Foundation of Zhejiang Province, China (Grant No. LY19F050004), the Natural Science Foundation of Ningbo City (Grant No. 2015A610038), the Open Fund of the Guangdong Engineering Technology Research and Development

We report on a chalcogenide glass fiber doped with Pr3+ that can be used for commercialized 1.5- and 2- laser excitations by emitting broadband – fluorescence, which is extruded into a preform and then drawn into a step-index fiber. The spectroscopic properties of the fiber and glass are reported, and the mid-infrared fiber lasers are also numerically investigated. Cascade lasing is employed to increase the inversion population of the upper laser level. The particle swarm approach is applied to optimize the fiber laser parameters. The output power can reach 1.28 W at 4.89- wavelength, with a pump power of 5 W, excitation wavelength at , Pr3+ ion concentration at 4.22 ×1025 ions/m3, fiber length at 0.94 m, and fiber background loss at 3 dB/m.

Effect of fiber laser parameters on laser welded AZ31B Magnesium alloys

Recently, the usage of Magnesium (Mg) alloys has been hugely applied in the industrial application such as in automotive, marine, and electronic due to its advantages of recyclability and lightweight. This alloys required low heat input to be weld since it is easily evaporated due to the Magnesium Oxide (MgO) at the surface and it also possesses lower melting point compared to steel. Laser welding is more convenient to weld Mg alloys due to its high power and lower heat input. AZ31B was selected since it has strong mechanical properties among others Mg alloys due to the major alloying elements; Aluminium (Al) and Zinc (Zn). Low power fiber laser machine with wavelength of 900 nm was used in this experiment. The intention of this work was to investigate the effect of low power fiber laser parameters and effect of shielding gas on weld penetration and microstructure. Another aim in this work was to produce the joint for this thin sheets metal. Penetration depth and microstructure evaluation were emphasized in the analysis section. Bead-on-Plate (BOP) and laser lap welding was conducted on AZ31B with thicknesses of 1.0 mm and 0.6 mm for feasibility study using pulsed wave (PW) mode. Defocusing features was used in order to find better focal position, which has less occurrence of evaporation (underfill). The effect of different angle of irradiation was also investigated. Two types of shielding gases, Argon (Ar) and Nitrogen (N2) were used in order to study the effect of shielding gas. Lastly, the effect of pulsed energy on penetration types and depth of BOP welded samples was investigated. Focus point was found at focal length of 156 mm with 393.75 μm. For BOP experiment, higher pulsed energy used contributes to melt through defect. Meanwhile, Ns shielding gas proved to be better shielding gas in laser welding the AZ31B. Higher angle of irradiation could reduce the underfill defect. Fillet Lap joint of similar metal was successfully done where 2.0 J of pulsed energy reveals better weld joint compared to 2.4 J.

Gain guided and index alternate-guided fibers designed for large-mode-area and single-mode laser with higher output power and slope efficiency

A gain guided and index alternate-guided fiber (GGIA-GF) is proposed and numerically demonstrated. The conditions of single mode oscillation are analyzed based on the fiber laser parameters. The output laser power and slope efficiency of the GGIA-GF laser are derived from the improved rate equations. The results show that the output characteristics of the laser based on GGIA-GF can be greatly improved than that of the gain guided and index anti-guided fiber laser through the optimal design of the fiber laser parameters. GGIA-GF would be better applied in the field of large mode area and single mode fiber lasers.

Set-membership estimation of fiber laser physical parameters from input–output power measurements

The problem of fiber laser parameters estimation from input–output transient power measurements is considered in the paper. The proposed procedure is based on a suitable laser model obtained from the rate and propagation equations. By proper manipulation of the simplified laser equations, the estimation problem is formulated in the bounded error estimation framework, where a priori information on physical parameters can be properly taken into account. First the so-called feasible parameter set is defined. Then, the problem of optimally picking a single model from the set is formulated in terms of central conditional estimation and solved by exploiting recent results by the authors. Properties of the proposed solution are discussed. The proposed algorithm is tested on a set of simulated data obtained from a commercial laser simulator.

Diffraction of digital micromirror device gratings and its effect on properties of tunable fiber lasers

A digital micromirror device (DMD) is a kind of widely used spatial light modulator. We apply DMD as wavelength selector in tunable fiber lasers. Based on the two-dimensional diffraction theory, the diffraction of DMD and its effect on properties of fiber laser parameters are analyzed in detail. The theoretical results show that the diffraction efficiency is strongly dependent upon the angle of incident light and the pixel spacing of DMD. Compared with the other models of DMDs, the 0.55 in. DMD grating is an approximate blazed state in our configuration, which makes most of the diffracted radiation concentrated into one order. It is therefore a better choice to improve the stability and reliability of tunable fiber laser systems.

Distributed feedback ytterbium fiber laser: experiment and analytical model

We compare the slope efficiency of a 1093 nm ytterbium distributed feedback fiber laser obtained in the experiment to the value calculated within the analytical model. The measured reflection and transmission spectra of the laser cavity, which is formed by a 4 cm long π-shifted fiber Bragg grating, allowed us to determine the cavity parameters employed in the analytical model. We took into account pump absorption that is significant for the model of ytterbium fiber lasers. A good agreement between the theory and the experiment is demonstrated. The considered analytical model is suitable for optimizing distributed feedback fiber laser parameters.

Investigation of the Dynamic Response of Erbium Fiber Lasers With Potential Application for Sensors

We derive a theoretical description of the transient response for erbium fiber ring lasers, which includes the effects of amplified spontaneous emission and the large number of longitudinal modes that are present in large cavities. Based on these modified rate equations, the full transient period is simulated and compared with experimental measurements performed at 1560 nm, showing reasonable agreement with theory. Approximate analytical relations are also derived for the key characteristics of the laser response, including steady-state and transient parameters such as build-up time, frequency, and the decay constant of relaxation oscillations. The results are useful in the measurement of fiber laser parameters and in the design of novel fiber laser sensors, such as intracavity laser absorption sensors based on spectral narrowing during the transient period of power build-up in a laser cavity.

Fiber lasers with hybrid birefringence resonators

We propose the combination of low- and high-birefringence fibers (Low-Bi and Hi-Bi, respectively) to form a hybrid birefringence resonator. The transmission characteristics as a function of different parameters for the fibers used within these hybrid resonators are obtained by means of Jones matrix analysis. This yields information on fiber laser features such as polarization mode-beating frequencies (PMB), which are used as readout for polarimetric sensors. We compare theoretical predictions with experimental results on the dependence of PMB frequencies as a function of wavelength and effective birefringence of the laser cavity. Applications of this hybrid fiber laser arrangement for polarimetric sensors and wavelength monitoring through PMB frequencies are also discussed. The results provide a simple way for optimizing fiber laser parameters and increase the sensitivity of PMB signals to wavelength variations.

Dynamic behavior analysis of the 3μm and 2μm cascade Ho3+:ZBLAN fiber lasers

A numerical study of the transient behavior, including upper level ions and laser power relaxation oscillation, of Ho3+:ZBLAN fiber laser is presente d based on the propagation-rate equations. The power propagation equations for pump a nd signal have been treated differently by neglecting the z-dependence of t he fiber laser parameters, for the sake of numerical simplicity. The results sho w that upper level ions of 5I6 and 5I7 manifolds relax alternati vely and go to steady state after the first relaxation oscillation and monotonou s decline. Similarly, the 3μm and 2μm laser powers relax alternatively first, then the 3μm laser power declines monotonously while the 2μm laser power incre ases monotonously, both of them go to steady state after the second relaxation o scillation. Moreover, peak powers of the 3 μm and 2 μm lasers in the course of relaxation oscillation are far larger than that when steady state is reached.

Narrow linewidth, tunable Tm/sup 3+/-doped fluoride fiber laser for optical-based hydrocarbon gas sensing

Operation of an efficient continuous-wave (CW) thulium-doped fiber laser emitting at wavelength, /spl lambda/=2.31 /spl mu/m is reported. The fiber laser parameters are optimized with a view to ultimately producing a compact and efficient laser source for optical absorption based gas sensing. A number of fiber laser configurations are investigated to assess their suitability for narrow linewidth, tunable fiber laser operation emitting around /spl lambda/=2.3 /spl mu/m, which is a wavelength region of significant importance for hydrocarbon gas monitoring. Tuning ranges of 140 nm and linewidths of less than 210 MHz have been demonstrated with lasers with bulk external tuning grating. Preliminary hydrocarbon gas sensing investigation confirm the potential of this source for detection of ppb gas concentrations.