High-power Laser Sources Research Articles

Power over fiber system using high-power laser source operating at 1470 nm with maximum power 2.0 W for powering to distance up to 5855 m

We report on the properties of the Power over Fiber (PoF) system using a High-Power Laser Source (HPLS) operating at 1470 nm with an optical power of up to 2.0 W. Graded-index and step-index optical fibers with a core diameter of 50 µm were used for transmission and two types of Photovoltaic Power Converters (PPCs) were used for optical power to electricity conversion. We experimentally demonstrated the powering to a distance of 5855 m, where we achieved the electric power of 44.4 mW and estimated the possibility of powering to distances longer than 9000 m with the input optical power of 15 W, where we expect to achieve the delivery of the electric power around 150 mW.

Power over fiber using a multimode optical power with a core diameter of 50 µm

We report on the properties of the Power over Fiber (PoF) transmission link using a High-Power Laser Source operating at 976 nm and using three types of optical fiber with a core diameter of 50 µm. Two step-index profile multimode optical fibers and one fiber with a gradient index were used for optical power transmission. Optical light was converted to electricity using commercially available Photovoltaic Power Convertors (PPCs) with a maximal optical input power of 1.5 W and experimental PPCs with a maximal optical input power of 4.0 W. We experimentally proved optical power transmission up to a distance of 300 m. In the case of the commercially available working PPC and using the gradient index fiber we achieved a result of 0.534 W of electrical power and using the experimental PPC we achieved 0.645 W. In the case of the step-index optical fiber, the result was 1.3 W.

Postfilament-Induced Two-Photon Fluorescence of Dyed Liquid Aerosol Enhanced by Structured Femtosecond Laser Pulse

Laser-induced fluorescence spectroscopy (LIFS) is actively used for remote sensing of atmospheric aerosols and is currently one of the most sensitive and selective techniques for determining small concentrations of substances inside particles. The use of high-power femtosecond laser sources for LIFS-based remote sensing of aerosols contributes to the development of new-generation fluorescence atmospheric lidars since it makes it possible to overcome the energy threshold for the nonlinear-optical effects of multiphoton absorption in particles and receive the emission signal at long distances in the atmosphere. Our study is aimed at the development and experimental demonstration of the technique of nonlinear laser-induced fluorescence spectroscopy (NLIFS) based on the remote excitation of aerosol fluorescent emission stimulated by a spatially structured high-power femtosecond laser pulse. Importantly, for the first time to our knowledge, we demonstrate the advances in using stochastically structured plasma-free intense light channels (postfilaments) specially formed by the propagation of femtosecond laser radiation through a turbulent air layer to improve NLIFS efficiency. A multiple increase in the received signal of two-photon-excited fluorescence of polydisperse-dyed aqueous aerosols by the structured postfilaments is reported.

Compact and efficient high-power mid-infrared supercontinuum fiber laser source based on a noise-like pulse and germania fiber

Here, we demonstrate a compact and efficient high-power mid-infrared supercontinuum (MIR-SC) laser source based on a tunable noise-like pulse (NLP) fiber laser system and a short section of single-mode germania-core fiber (GCF). The NLP all-polarization-maintaining fiber laser system can deliver the maximum output power of ∼30.6 W and a broadband spectrum (∼1.8-2.7 µm) with a compact single-stage fiber amplifier. By directly pumping only ∼6.5 cm-long GCF with a core diameter of ∼3.5 µm, a MIR-SC (spectral coverage of ∼1.5-3.3 µm) with a maximum power of ∼25.2 W and a power conversion efficiency ∼81.2% is obtained, which represent the highest power and efficiency in any single-mode GCF-based MIR-SCs, to the best of our knowledge. Our study contributes to the high-power MIR-SC laser source with compact all-fiber configuration, and will prompt its practical applications.

Numerical analysis of cascade lasing in Ho:ZBLAN fiber lasers with efficient output at ∼750 nm

Recent advances in blue-emitting laser diodes (LDs) have enabled visible laser operation in rare-earth-doped fluoride fibers. Therefore, investigation of the power scaling of visible fiber lasers enabled by direct blue diode pumping is significant. In this study, we numerically investigated the performance of a continuous-wave (CW) Ho:ZBLAN fiber laser operating at approximately 750 nm for the 5F4,5S2→5I7 transition using a cascade lasing process. Direct diode pumping at 450 nm is used in conjunction with double-clad fiber geometry. Simultaneous lasing for the mid-IR 5I7→5I8 transition effectively depopulated the 5I7 level and significantly enhanced efficiency and power scalability. A slope efficiency of 49% was associated with the calculated CW output power of 14.2 W at a launched pump power of 30 W. This study demonstrates the significance of depopulating the lower laser level in the development of an efficient Ho:ZBLAN 750 nm fiber laser and offers an alternative approach for developing high-power visible laser sources.

Parallel Diffractive Multi‐Beam Pulsed‐Laser Ablation in Liquids Toward Cost‐Effective Gram Per Hour Nanoparticle Productivity

Nanoparticles (NPs) generated by pulsed‐laser ablation in liquids (PLAL) have benefited many key applications due to their versatility, enlarged surface area, and high purity. However, scaling up NPs production represents one of the main requisites to commercialize this technology. The established upscaling strategy demands high power and repetition rate laser source with fast scanning systems, which are not widely available and costly. Herein, a cost‐effective alternative is proposed, the addition of static diffractive optical elements to achieve parallel processing through the multi‐beam PLAL (MB‐PLAL). In MB‐PLAL, the optimum repetition rate is reduced to compensate laser energy splitting, hence achieving a higher interpulse distance, reducing pulse shielding, and increasing NPs productivity. MB‐PLAL with 11 beams reached a factor 4 productivity increase for iron–nickel alloy (Fe50Ni50) NPs compared to the single‐beam setup (0.4–1.6 g h−1), and a factor 3 increase for gold (Au) NPs (0.32–0.94 g h−1). The scalability of the proposed MB‐PLAL technique setup is confirmed by Au and Fe50Ni50 NPs productivity experiments using 1, 6, and 11 beams, showing a linear increase in productivity.

High power tunable Raman fiber laser at 1.2 μm waveband

Development of a high power fiber laser at special waveband, which is difficult to achieve by conventional rare-earth-doped fibers, is a significant challenge. One of the most common methods for achieving lasing at special wavelength is Raman conversion. Phosphorus-doped fiber (PDF), due to the phosphorus-related large frequency shift Raman peak at 40 THz, is a great choice for large frequency shift Raman conversion. Here, by adopting 150 m large mode area triple-clad PDF as Raman gain medium, and a novel wavelength-selective feedback mechanism to suppress the silica-related Raman emission, we build a high power cladding-pumped Raman fiber laser at 1.2 μm waveband. A Raman signal with power up to 735.8 W at 1252.7 nm is obtained. To the best of our knowledge, this is the highest output power ever reported for fiber lasers at 1.2 μm waveband. Moreover, by tuning the wavelength of the pump source, a tunable Raman output of more than 450 W over a wavelength range of 1240.6–1252.7 nm is demonstrated. This work proves PDF’s advantage in high power large frequency shift Raman conversion with a cladding pump scheme, thus providing a good solution for a high power laser source at special waveband.Graphical

Design and performance of a collimated beam projector for telescope transmission measurement using a broad-band light source

Abstract Type Ia supernovae are the most direct cosmological probe to study dark energy in the recent Universe, for which the photometric calibration of astronomical instruments remains one major source of systematic uncertainties. To address this, recent advancements introduce collimated beam projectors (CBPs), aiming to enhance calibration by precisely measuring a telescope’s throughput as a function of wavelength. This work describes the performance of a prototype portable CBP. The experimental set-up consists of a broad-band Xenon light source replacing a more customary but much more demanding high-power laser source, coupled with a monochromator emitting light inside an integrating sphere monitored with a photodiode and a spectrograph. Light is injected at the focus of the CBP telescope projecting a collimated beam onto a solar cell whose quantum efficiency has been obtained by comparison with a NIST-calibrated photodiode. The throughput and signal-to-noise ratio achieved by comparing the photocurrent signal in the CBP photodiode with the one in the solar cell are computed. We prove that the prototype, in its current state of development, is capable of achieving 1.2 per cent and 2.3 per cent precision on the integrated g and r bands of the Zwicky Transient Facility photometric filter system, respectively, in a reasonable amount of integration time. Central wavelength determination accuracy is kept below ∼0.91 and ∼0.58 nm for g and r bands, respectively. The expected photometric uncertainty caused by filter throughput measurement is approximately 5 mmag on the zero-point magnitude. Several straightforward improvement paths are discussed to upgrade the current set-up.

Efficient dual-stage all-solid-state post-compression for 100 W level ultrafast lasers

Abstract We demonstrate efficient and economical all-solid-state post-compression based on dual-stage periodically placed thin fused silica plates driven by a more than 100 W ytterbium-doped yttrium aluminum garnet Innoslab amplifier seeded by a fiber frontend. Not only is a more than eight-fold pulse compression with 94% transmission achieved, but also the pulse quality and spatial mode are improved, which can be attributed to the compensation for the residual high-order dispersion and the spatial mode self-cleaning effect during the nonlinear process. It enables a high-power ultrafast laser source with 64 fs pulse duration, 96 W average power at 175 kHz repetition rates and good spatiotemporal quality. These results highlight that this all-solid-state post-compression can overcome the bandwidth limitation of Yb-based lasers with exceptional efficiency and mitigate the spatiotemporal degradation originating from the Innoslab amplifier and fiber frontend, which provides an efficient and economical complement for the Innoslab laser system and facilitates this robust and compact combination as a promising scheme for high-quality higher-power few-cycle laser generation.

A 7-kW narrow-linewidth fiber amplifier assisted by optimizing the refractive index of the large-mode-area active fiber

Abstract The high-power narrow-linewidth fiber laser has become the most widely used high-power laser source nowadays. Further breakthroughs of the output power depend on comprehensive optimization of stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) and transverse mode instability (TMI). In this work, we aim to further surpass the power record of all-fiberized and narrow-linewidth fiber amplifiers with near-diffraction-limited (NDL) beam quality. SBS is suppressed by white-noise-signal modulation of a single-frequency seed. In particular, the refractive index of the large-mode-area active fiber in the main amplifier is controlled and fabricated, which could simultaneously increase the effective mode field area of the fundamental mode and the loss coefficient of higher-order modes for balancing SRS and TMI. Subsequent experimental measurements demonstrate a 7.03 kW narrow-linewidth fiber laser with a signal-to-noise ratio of 31.4 dB and beam quality factors of Mx2 = 1.26, My2 = 1.25. To the best of our knowledge, this is the highest reported power with NDL beam quality based on a directly laser-diode-pumped and all-fiberized format, especially with narrow-linewidth spectral emission.

Solar side-pumped Nd-doped fiber laser based on a doughnut-shaped hollow reflector

A high-power solar side-pumped Nd-doped fiber laser based on a doughnut-shaped hollow reflector (DHR) is proposed. The primary concentrator consists of twelve off-axis parabolic mirrors. The DHR coupled with an array of three-dimensional compound parabolic concentrators (3D-CPCs) functions as the secondary concentrator, inside which many cycles of Nd-doped fiber is coiled. After being reflected by the off-axis parabolic mirrors, the sunlight is launched into the DHR through the twelve 3D-CPCs, and experiences multiple-times reflection by the DHR, and finally is absorbed by the Nd-doped fiber for laser oscillation. Ray tracing shows that 173-W of solar power can be absorbed by the fiber. By solving the rate equations and power transmission equations, laser output power, slope efficiency and optical-to-optical conversion efficiency of 10.3 W, 6.12% and 5.94%, respectively, are realized. This kind of solar-pumped fiber laser thus offers a new route for achieving high-power solar-pumped laser sources.

Power amplification for 1.6 µm high-order vortex modes.

1.6 µm high-order vortex modes carrying orbital angular momentums (OAMs) play significant roles in long-range Doppler lidars and other remote sensing. Amplification of 1.6 µm high-order vortex modes is an important way to provide high-power laser sources for such lidars and also enable the weak echo signal to be amplified so that it can be analyzed. In this work, we propose a four-pass Er:YAG vortex master-oscillator-power-amplification (MOPA) system to amplify 1.6 µm high-order vortex modes. In the proof-of-concept experiments, 1.6 µm single OAM mode (l = 3) is amplified successfully and the gain ranging from 1.88 to 2.36 is achieved. Multiplexed OAM mode (l=±3) is also amplified with favorable results. This work addresses the issue as the low gain of Er:YAG vortex MOPA, which provides a feasible path for 1.6 µm high-order vortex modes amplification.

Laser cladding of stainless-steel ball valves by a high-power diode laser source with a rectangular beam spot

In this paper, the laser cladding of Ni60 + WC powder on the stainless-steel ball valves is investigated to improve the corrosion resistance and the wear resistance of industrial ball valves. A 2-kW high-power diode laser source based on beam multiplexing is used as the processing source to clad the ball valves. To make this diode laser source more reliable for laser cladding, a homogenizing optical system is designed and optimized to transform a circular beam spot output from the optical fiber to a rectangular spot with a flat-top distribution. Employing this diode laser source, the laser cladding of the stainless-steel ball valve is successfully achieved by use of the pre-set powder feeding. The hardness testing experiments are then performed on the ball valves of different diameters, followed by the evaluation of the thickness and hardness of the cladding coating. It is experimentally demonstrated that the microhardness of the ball valves is improved by 2.7 times and the cladding layer has no cracks, which proves the superior performance of the stainless-steel ball valves by use of the proposed method.

Influence of antireflection Si coatings on the damage threshold of fused silica upon irradiation with mid-IR femtosecond laser pulses.

Recent progress in the development of high-power mid-IR laser sources and the exciting laser driven physical phenomena associated with the irradiation of solids via ultrashort laser pulses in that spectral region are aimed to potentially create novel capabilities for material processing. In particular, the investigation of the underlying physical processes and the evaluation of the optical breakdown threshold (OBT) following irradiation of bulk dielectric materials with mid-IR femtosecond (fs) pulses have been recently presented. In this Letter, we will explore the conditions that generate sufficient carrier excitation levels which lead to damage upon irradiation of a dielectric material (SiO2) coated with antireflection (AR) semiconducting films (Si) of variable thickness with fs pulses. Simulation results demonstrate that the reflectivity and transmissivity of the Si/SiO2 are thickness dependent which can be employed to modulate the damage threshold of the substrate. The study is to provide innovative routes for selecting material sizes that can be used for antireflection coatings and applications in the mid-IR region.

Fiber Coupled High Power Nd:YAG Laser for Nondestructive Laser Cleaning

In this study, a fiber coupled high power side-pumped Nd:YAG laser system for laser cleaning is presented. Based on the two-rod structure and two stages amplifiers, the maximum average output power of 783 W with corresponding pulse energy of 52 mJ at 15 kHz has been achieved. The fiber coupling efficiencies after the master oscillator, one stage amplifier and two stages amplifiers reach to 99%, 98.3% and 94%, respectively. A laser cleaning machine prototype composed of the master oscillator and one stage amplifier with an average output power of greater than 500 W has been developed and achieved better nondestructive cleaning effect for thermal control coating removal compared with commercial fiber laser cleaning machines. This study provides a new method for developing high power laser sources for nondestructive laser cleaning equipment.

Power over fiber using a large core fiber and laser operating at 976 nm with 10 W power

We report on the properties of a powering transmission link based on a High-Power Laser Source operating at 976 nm and large-core 105 μm multimode optical fiber at a distance of 200 m. Six types of Photovoltaic Power Converters were used to convert optical power to electric power and the results are presented and discussed, as well as the properties of transport of the energy through the multimode fiber ending with an optical 1x2Y splitter.

Numerical Simulation of High-Power Optical Amplifiers at 2.3 µm Based on a Special Multicore Fiber

The development of high-power laser sources at 2.3 µm is highly demanded for remote sensing and other applications. However, this wavelength is poorly covered by present-day lasers. To obtain 100 W class high-power radiation at 2.3 μm, we propose to use simultaneously cascade laser amplification at 2 and 2.3 µm with a commercially available diode pump at 793 nm and stimulated Raman scattering between the amplified signal waves in a special zinc–tellurite multicore fiber with ten trivalent-thulium-ion-doped cores arranged in a ring. We demonstrate numerically that the use of an out-of-phase supermode (with spatial phases differing by π in neighboring cores) can provide up to 50% efficiency conversion from the 793 nm pump to the 2.3 µm wave.

Polymer composition with phenanthrenequinone for recording relief holographic gratings

The formation of periodic reliefs of the thickness of photosensitive polymer layers after recording holographic gratings in them and stimulating material deformations by reversible plasticization in a non-solvent liquid is considered. The phenomenon was studied for the composition of a copolymer with side anthracene groups — phenanthrenquinone. Phenantrenquinone transfers the energy of electronic excitation to oxygen molecules entering through the open surface of the polymer layer which then cause the oxidation of anthracene fragments. Holographic gratings with a period of 2–5 μm were recorded by laser radiation at a wavelength of 532 nm in layers about 1 μm thick. The photoreliefs were formed during the subsequent swelling of the layer in the medium of a hydrocarbon developer. The photosensitized oxidation of the anthracene groups of the new polymer under the action of optical radiation in the spectral range 408–532 nm was studied using the electron absorption spectra. It is shown that approaching the excitation wavelength to the long-wavelength absorption maximum of phenanthrenquinone (410 nm) makes it possible to increase the sensitivity of the material layer by a factor of 15 compared to layers with methylene blue as a photosensitizer. It has been experimentally established that the amplitude of weak periodic reliefs of a deformation nature (height less than 0.01 μm), which appear immediately after the recording of holographic gratings, increases many times during the treatment of the layer with liquid hydrocarbon. Their maximum value reaches 25 % of the thickness of the recording layer. Presumably, the deformation of the inhomogeneously irradiated layer is stimulated by the transfer of the polymer material into a highly elastic state during its swelling. Photoreliefs are stable after drying. Their strength can be increased by photocrosslinking the material as a result of photodimerization of residual anthracene groups under uniform irradiation with light at a wavelength of 365 nm. The non-sinusoidality of the photorelief reduces the diffraction efficiency achievable with total reflection to values less than 0.20. The studied polymer composition can be used to form relief-phase diffractive optical elements by radiation in the blue-green region of the spectrum, provided by a number of high-power laser sources.

Target Aiming Point Focusing Strategy for Destroying a Short-Range Target Using Distributed Laser Systems

Consider a scenario where multiple high power laser weapon systems are positioned closed to a base, in order to protect the base from an aerial target, such as a missile. We consider destroying a short-range flying target which is sufficiently close to the base. Using multiple lasers can reduce thermal blooming, which decreases the effective power that can be delivered to a target site in the atmosphere. Thus, this paper proposes utilizing multiple high power laser sources to aim on a single point of the target to maximize the attack efficiency and avoid directional disturbances. Once a target is detected by a search radar system, then the position of the target can be calculated in global coordinate systems and is shared by all laser systems through fiber-based wired links. Then, each laser aims at the target followed by firing at the target. This paper presents how to make multiple high power lasers aim at a single target point for maximizing the attack efficiency. Considering the case where there are more than one high power laser sources, this paper is novel in addressing the control and synchronization of every laser system. MATLAB simulations are used to verify the effectiveness of the proposed multi-laser systems.

A Comprehensive Review of High-Pressure Laser-Induced Materials Processing, Part II: Laser-Driven Dynamic Compression within Diamond Anvil Cells

The field of high-pressure materials research has grown steadily over the last seven decades, with many remarkable discoveries having been made. This work is part II of a three-part series summarising recent progress in laser material processing within diamond anvil cells (L-DACs); this article focuses on the practice of laser-driven dynamic compression within diamond anvil cells (i.e., LDC–DAC experimentation). In this case, materials are initially pre-compressed within diamond anvil cells, then further dynamically compressed through the use of a high-power pulsed laser, often with the intent to isentropically compress, rather than to heat samples. The LDC–DAC approach provides a novel route to much higher dynamic pressures (approaching 1 TPa), as compared to conventional static compression within a single-stage DAC (<300 GPa) and provides a route to mapping Hugoniot curves. Recent proliferation of low-cost, high-power laser sources has led to increased research activity in LDC–DAC materials processing over the last two decades. Through LDC–DAC experiments, a greater understanding of the properties/structure of cold- and warm-dense matter has been obtained, and novel material phases have been realised. In this article, LDC–DAC experimental methods are reviewed, together with the underlying physics of laser dynamic compression in confined spaces. In addition, a chronology of important events in the development of LDC–DAC processing is provided, and emerging trends, gaps in knowledge, and suggestions for further work are considered.