1018-nm Fiber Laser Research Articles

Investigations of a 1018 nm gain-switched Yb-doped fiber oscillator.

In this paper, we investigate a 1018nm gain-switched ytterbium-doped fiber oscillator at a low repetition rate in terms of theory and experiment. Theoretically, a numerical model applicable to a 1018nm gain-switched ytterbium-doped fiber laser was established. The influence of the pump peak power and active fiber lengths on the 1018nm gain-switched ytterbium-doped fiber laser was numerically simulated. Experimentally, a compact 1018nm all-fiber-structured pulsed laser oscillator is constructed, in which a pulse width of 110ns and a single-pulse energy of 0.1mJ were obtained. Moreover, the experimental results are in agreement with the numerical simulation ones. To the best of our knowledge, this is the first time that gain-switching technology has been applied to 1018nm fiber lasers to generate nanosecond pulsed lasers. The model and experimental results can provide a reference for the engineering design of the same type of low repetition rate fiber lasers below the kilohertz level.

High-power 1018 nm Yb3+ doped fiber lasers with different YDF core and coiling diameters: theoretical and experimental study.

In this paper, the effect of the active fiber's core/cladding area ratio on the output parameters of 1018nm fiber lasers has been investigated. In this regard, we conducted a comprehensive study of two fiber lasers that utilized 25/400 and 30/250µm ytterbium-doped fibers (YDFs), both theoretically and experimentally. The optimum length of YDFs required for 40dB of amplified spontaneous emission suppression was calculated. Theoretical studies also identified the YDF breaking zone for lengths greater than the optimum. The experimental results showed that selecting the proper dimensions and coiling diameter for the active fiber significantly increased the power and efficiency of the YDF laser. We obtained an output power of 943W with a 75.5% slope efficiency for the co-pumped 30/250µm YDFL which, to the best of our knowledge, is the highest reported value for the 1018nm co-pumped fiber laser. An analysis of the experimental and theoretical results revealed that YDFs with a core/cladding area ratio greater than 1% are more suitable for realizing a high-power 1018nm fiber laser. The findings of this study are crucial for the development of high-power 1018nm fiber lasers with improved performance.

The Design, Realization, and Validation of the Scheme for Quantum Degenerate Research in Microgravity

In microgravity, atoms can be prepared to a lower temperature and manipulated with a longer time. The Cold Atom Physics Research Rack (CAPR) in Chinese Space Station, which aims to prepare quantum degenerate gas for deep cooling and quantum simulation in microgravity, has been designed, realized, and validated. We built an integrated CAPR, consisting of a physical system, an all-fiber 780nm laser system and a low phase noise 1064nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">87</sup> Rb quantum degenerate gas with 1.2ⅹ10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> atoms and a temperature below 30nK was achieved on ground. In this article, we also show the robustness of the rack, based on the experimental results before and after the simulation of the vibration and impact during the launch.

Investigation of the influence of the processing speed and the linear pulse density of the laser surface texturing process

Fine-tuning laser parameters is necessary to achieve the desired quality of the process of laser surface texturing. This requires a set of experiments to assess the influence of the main process parameters on the quality of the surface of a treated alloy. By varying the laser parameters, different laser-material interactions, such as heating, melting, or evaporation can be observed. This study analyzes the influence of two interrelated processing parameters in laser surface texturing – the speed of beam motion on the surface on the one hand, and, on the other, the linear pulse density. They ultimately have a direct impact on the resulting microstructure, hydrophilicity, and electrochemical properties of austenitic steel (AISI 304). By adjusting the pulse repetition rate of a 1064-nm fiber laser from 500 kHz to 1000 kHz at a constant speed of 100 mm/s, the surface wettability changes from hydrophobicity to hydrophilicity. All surfaces treated with laser scanning speeds varying from 20 mm/s to 200 mm/s at a constant rate of 500 kHz are hydrophobic. As a result, the changed ability to repel liquids alters the corrosion properties of the steel in a 0.5 M H2SO4 solution. The results allow one to distinguish ranges of laser-beam parameters that could be useful in selecting certain properties of the stainless-steel surface layer.

Theoretical and experimental studies on high-power laser-induced thermal blooming effect in chamber with different gases

High-power laser induced thermal blooming effects in a closed chamber with three different gases are investigated theoretically and experimentally in this work. In the theoretical treatment, an incompressible gas turbulent model is adopted. In the numerical simulation the gas refractive index as a function of both the temperature and pressure is taken into consideration. In the experimental study the pump-probe technology is adopted. A high-power 1064-nm fiber laser with maximum output power of 12 kW is used to drive the gas thermal blooming, and a 50-mW high-beam-quality 637-nm laser diode (LD) is used as a probe beam. The influences of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality are analyzed for three different gases of air, nitrogen, and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in good agreement with the simulated results.

Tunable laser operation of Tm3+:KY3F10 near 1.9 µm via upconversion pumping at 1064 nm

We experimentally demonstrate, for the first time to our knowledge, that upconversion pumping can be employed with a 1064-nm fiber laser to achieve tunable laser operation with 8 at. % T m 3 + : K Y 3 F 10 crystal near 1.9 µm, in addition to the previously explored upconversion pumping of the 2.3-µm laser transition. Two different sets of cavity optics were used to investigate lasing at 1.9 and 2.3 µm, corresponding to the laser transitions 3 F 4 − 3 H 6 and 3 H 4 − 3 H 5 , respectively. In the case of the 3 F 4 − 3 H 6 laser transition, an x-cavity laser oscillator was constructed with a 2.3% output coupler and as high as 142 mW of output power was obtained at an incident pump power of 1.9 W at 1064 nm. Tunable laser operation could be obtained between 1849 and 1994 nm by using C a F 2 and suprasil prisms. The highest slope efficiency of 29% with respect to average absorbed pump power was obtained with a 5.5% output coupler. For the case of 1.9 µm lasing, it was further demonstrated that the nonlinear absorption of the crystal at 1064 nm depends on the intracavity laser intensity as well as the pump intensity. The 3 H 4 − 3 H 5 laser transition was also investigated with the same crystal in a z-cavity configuration under upconversion pumping, giving as high as 130 mW of output power at the central wavelength of 2344 nm with 1.6 W of incident pump power.

Suppressing the amplified spontaneous emission in the high-power 1018-nm monolithic fiber laser by decreasing the feedback from the inner reflections

We showed that decreasing the feedback that comes from the inner reflections of counter-propagating light could suppress the amplified spontaneous emission (ASE) in the output of 1018-nm fiber lasers. With a simulation model to solve the power spectrum of multiple signals, we calculated the values of the feedback required for aimed power scaling. We realized low feedback by modifying the counter-propagating side of the setup, which included a home-made cladding light stripper on a no-core fiber that was angle-cleaved. With that, we demonstrated a 1018-nm monolithic fiber laser producing 506.4 W with 1 .58 - M 2 beam quality, 84.9% optical–optical efficiency, and 148-pm linewidth. The maximum intensity of the ASE noises was &gt; 50 d B lower than that of the 1018-nm signal, which could allow further power scaling with safety and stability.

Multiplexed electrospray emitters fabricated by rapid laser micromachining

This technical note documents the fabrication and performance of multiplexed electrospray emitters by rapid laser micromachining. A low cost 1064-nm fiber laser marker system is used to precisely, rapidly and selectively remove materials from a sheet of conductive silicone rubber, which is chemically inert. The laser pulse energy, scanning speed and machining path are judicially chosen to create clean and round micro posts that form external nozzle structures. This laser micromachining technique offers sufficient precision for ensuring uniform pressure drop across each fluid flow channel even at relatively low flow rate per nozzle. The uniformity of the operation from nozzle to nozzle is confirmed by measuring the diameter of each cone-jet. The results suggest that the laser micromachining is a rapid and convenient technique for fabricating multiplexed electrospray emitters.

An Efficient 4-kW Level Random Fiber Laser Based on a Tandem-Pumping Scheme

In this letter, we presented a monolithic high-power random fiber laser (RFL) with a tandem-pumping scheme. The RFL seed centered at 1064 nm was pumped by a 1018-nm fiber laser and reached an output power of 8.66 W. After two amplifiers, the seed was amplified to 4020 W, and the 3-dB width of laser spectrum was broadened from 0.78 nm to 0.99 nm. To increase the efficiency of the 4-kW laser, a specially designed high absorption coefficient (0.6 dB/m @ 1018 nm) 30/250- $\mu \text{m}$ Yb-doped fiber and high-brightness 1018-nm pump laser were adopted. The optical-to-optical efficiency could reach as high as 88.5%. No obvious mode instability was found during the experiment. Furthermore, with the same amplifier stage, we have also built another 4-kW level fiber laser seeded by an oscillator consisting of a pair of fiber Bragg gratings. The comparison of the experimental results showed that the high-power laser based on the RFL seed would have a better control on spectral broadening.

Smart laser osteotomy: integrating a pulsed 1064nm fiber laser into the sample arm of a fiber optic 1310nm OCT system for ablation monitoring.

Real-time depth metrology during material removal via laser ablation is useful in many forms of laser machining. Until now, coaxial optical coherence tomography (OCT) metrology was achieved by the coupling of an OCT imaging beam and ablating beams using a dichroic filter. We present an alternative design with all fiber delivery that is more suitable for surgical laser ablation applications. The novel system design integrates a high peak-power pulsed Yb-doped fiber laser (1064nm) coupled directly into the sample arm of a swept-source OCT system (λc = 1310nm). We measured the OCT signal degradation due to dispersion and attenuation through the ablation fiber laser cavity. Ablation progression is measured in real-time using M-mode OCT. The mean depth targeting error was found to range from 10µm to 80µm in phantom ablation experiments and 21µm to 60µm in bone ablation. A number of issues have been solved, including point-spread function (PSF) peak broadening due to signal delay and dispersion, high bending loss due to dissimilar fiber used throughout the design, and problems due to the extremely high ablation power to swept-source power ratio (> 2×104 peak to average power). To our knowledge, this is the first demonstration of thermal-mediated laser ablation drilling integrated with coaxial OCT imaging through a single-mode, single-cladded output fiber, without using dichroic beam splitters or free-space optic filters anywhere in the optical path and with this high ablation laser power to OCT source power ratio. The removal of bulk optics compared to existing designs opens a new path for compact integration of the entire system. Also, since the ablation laser and OCT feedback system exist along the same fiber path, the need for maintenance and repair are greatly reduced since spatial beam alignment and the potential open-air contamination of optical surfaces are virtually eliminated. We believe that this integrated system is a great candidate for adoption in depth-controlled surgical ablation applications.

A 1150-W 1018-nm Fiber Laser Bidirectional Pumped by Wavelength-Stabilized Laser Diodes

This paper presented a high-power 1018-nm ytterbium-doped fiber laser pumped by wavelength-stabilized laser diodes in bidirectional pumping structure. A record output power reaching 1150 W was achieved, along with a slope efficiency of 82.9% and a beam quality factor of M2 = 1.96. The output spectrum exhibited an efficient amplified spontaneous emission and parasitic lasing light suppression. The thermal effects were studied to verify the reliability of our 1018-nm FL as a practical 1-kW light source. Besides, an important investigation was made on the 1080-nm fiber laser tandem pumped by 1018-nm fiber lasers, the experimental result of which was reported to be 3712 W.

Efficient 240W single-mode 1018nm laser from an Ytterbium-doped 50/400µm all-solid photonic bandgap fiber.

Lowering the quantum defect by tandem pumping with fiber lasers at 1018nm was critical for achieving the record 10kW single-mode ytterbium fiber laser. Here we report the demonstration of an efficient directly-diode-pumped single-mode ytterbium fiber laser with 240W at 1018nm. The key for the combination of high efficiency, high power and single-mode at 1018nm is an ytterbium-doped 50μm/400μm all-solid photonic bandgap fiber, which has a practical all-solid design and a pump cladding much larger than those used in previous demonstrations of single-mode 1018nm ytterbium fiber lasers, enabling higher pump powers. Efficient high-power single-mode 1018nm fiber laser is critical for further power scaling of fiber lasers and the all-solid photonic bandgap fiber can potentially be a significant enabling technology.

Scheme for achieving a continuous-wave laser operation at 1178 nm.

We report for the first time, to the best of our knowledge, a new scheme for generating the important 1178nm laser. Based on a high-power 1018nm fiber laser as the pump source and chemical vapor deposition diamond as the Raman gain medium, the Raman laser was capable of generating 34.6W output power centered at 1178.02nm. As far as we know, 34.6W is the highest output power of a 1178nm laser obtained within a crystalline Raman gain medium. The experimental results show the superiority of our scheme in obtaining 1178nm laser generation.

Temperature Dependence of Ytterbium-Doped Tandem-Pumped Fiber Amplifiers

The experimental results of a high power 1080-nm ytterbium-doped fiber amplifier (YDFA) tandem-pumped by a 1018-nm fiber laser for different temperatures have been reported. For a 1.64 m of active fiber, the power conversion efficiency (PCE) of our YDFA has reached 91.1% at room temperature. And for a 0.82 m of active fiber, i.e., half-length of 1.64-m active fiber, the PCE has been improved from 58.7% to 81.3% by increasing the heating temperature from room temperature to 302 °C. In other words, we have traded off ~10% PCE for a 50% reduction of active fiber length. The temperature-dependent signal amplification model simulations agree well with the experiments. Our experimental and theoretical studies confirm that the temperature-dependent absorption and emission cross sections and the long-wavelength pump source are the physical causes of the improved PCE.

Laser transmission welding of Clearweld-coated polyethylene glycol terephthalate by incremental scanning technique

Transmission laser welding using Incremental Scanning Technique(TWIST) mode and conventional contour welding mode were adopted to investigate laser transmission welding of 0.5mm thick PET plate. A 1064nm fiber laser was used to weld PET at the (TWIST) mode, and an 808nm diode laser was applied to conduct the conventional contour welding. The Clearweld coating was used as laser absorbing material. The influences of laser parameters (i.e. defocusing distance, distance between two circles) on the quality of weld seams were analyzed by optical microscopy. Moreover, geometry and shear strength of the weld zone were tested to optimize laser parameters. Additionally, the water vapor permeability (WVP) of weld seams was measured to test hermetical capacity. Results show that the shear strength and hermetic capacity of weld seam by TWIST mode are at the same level in comparison with that of the conventional contour welding.

Tandem-pumped 1120-nm actively Q-switched fiber laser

We report on a tandem-pumped actively Q-switched fiber laser system emitting at 1120 nm. Parasitic oscillation is challenging in Yb-doped Q-switched 1120-nm fiber laser, which is suppressed by pumping with a fiber laser at 1018 nm. At least four times improvement in output peak power is demonstrated in a single laser setup with 1018-nm fiber laser pumping instead of 976-nm laser diode pumping. This is, to the best of our knowledge, the first demonstration of a tandem-pumped Q-switched fiber laser.

UV laser direct texturing for high efficiency multicrystalline silicon solar cell

Surface texturing is a technique used to increase light-trapping by forming certain structures on surface of a photovoltaic cell. We performed direct surface texturing using a 355nm UV laser to create V-shaped grooves on p-type, boron-doped multicrystalline silicon wafer of 200μm thickness. In addition, a 1064nm fiber laser was used to fabricate U-shaped grooves; this was done to determine the effect of light-trapping according to the shape of the structure. The samples were processed by 25% NaOH and acid solutions to remove slag after the direct texturing and isotropic etching. The reflectance and minority carrier lifetimes were measured to analyze the effects of the V-shaped groove and U-shaped groove. The V-shaped groove sample without the etching process showed 8.6% reflectance, while the sample etched for 4min with NaOH and 4.5min with isotropic acid after the laser texturing showed 13.2% reflectance. The minority carrier lifetime of the UV laser, V-shaped groove sample increased from 2.6μs to 20.6μs while that of the fiber laser, U-shaped groove sample increased from 2.3μs to 5.9μs. Etching was essential to remove slag and damages from the laser processes since these defects can induce inefficient electrical performance, as in long carrier lifetime. However, excessive etching flattens the surface and results in reduced effectiveness of light trapping. Consequently, the densely-packed V-shaped textures were more effective for capturing photons than the U-shaped texture.

Experimental Investigation on 1018-nm High-Power Ytterbium-Doped Fiber Amplifier

We present an all-fibered 1018-nm ytterbium-doped double-clad fiber laser in master oscillation power amplification configuration. The output characteristics of 1018-nm laser with seed power, gain fiber length, and fiber type are experimentally investigated. The power of the seed laser needs to be much higher to suppress amplified spontaneous emission and enable the sufficient amplification of the 1018-nm seed laser than the case of 1080-nm amplification. And the requirement of the seed power increases with the gain fiber length. The experimental results also indicate that gain fiber with large pump fill factor and low Yb ion concentration is more appropriate for the high-power 1018-nm fiber laser. With this gain fiber, we demonstrate a 77-W near diffraction limited fiber amplifier emitting at 1018 nm with power conversion efficiency of 75%.

Effect of wavelength on the laser patterning of a cholesteric liquid crystal display electrode

A 1064nm fiber laser and a 355nm ultraviolet solid-state laser with galvanometer scanners and F-theta lenses are used to rapidly etch the silver electrode pattern of a cholesteric liquid crystal display. These results of the two laser processes are that the 1064nm laser effectively reduces the damage to the liquid crystal layer and underlying indium tin oxide layer, and reduces the heat-affected zone of the ablated silver electrode.

Experimental Realization of Silica–Glass Tm-Doped Fiber Amplifier With 11.3-dB Gain

We report the experimental realization of thulium-doped silica-glass fiber amplifier at 1470 nm. The gain was 11.3 dB upon pumping with 1064-nm fiber laser (2000 mW) and noise figure was about 5 dB.