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Showing papers on "Pulse duration published in 2022"


Journal ArticleDOI
01 Jul 2022
TL;DR: In this paper , a passively Q-switched er-doped fiber laser with two wavelength at 1530 nm and 1556 nm wavelength was designed based on the titanium disulfide (TiS2) saturable absorber, the ultra-fast modulator was fabricated with TiS2 by liquid-phase exfoliation and spin-coating methods and transferred onto a fiber ferrule.
Abstract: A passively Q-switched Er-doped fiber laser with two wavelength at 1530 nm and 1556 nm wavelength was designed based on the titanium disulfide (TiS2) saturable absorber, the ultra-fast modulator was fabricated with TiS2 by the liquid-phase exfoliation and spin-coating methods and transferred onto a fiber ferrule. In the experiment, two single-mode 980 nm pump sources were applied in order to detect the high damage threshold of TiS2. The shortest pulse duration and maximum output power of the stable self-starting Q-switched fiber laser are 1.45 µs and 3.93 mW, respectively. The adjustable range of the repetition rate is from 25.8 kHz to 126.8 kHz with about 100 kHz tuning range, and the pulse with energy up to 39.3 nJ. Our experimental results conclusively suggest that TiS2 nanocrystals were advanced nanomaterial with high damage threshold would have extensive application prospects in the field of pulse fiber lasers.

56 citations


Journal ArticleDOI
TL;DR: In this paper , the front end of a 100 PW-class laser facility was developed for the front-end of an optical parametric chirped-pulse amplification (OPCPA) based on lithium triborate (LBO) crystals.
Abstract: Here, we report the recent progress on the front end developed for the 100 PW-class laser facility. Using 3 stages of optical parametric chirped-pulse amplification (OPCPA) based on lithium triborate (LBO) crystals, we realized a 5.26 J/0.1 Hz amplified output with a bandwidth over 200 nm near the center wavelength of 925 nm. After the compressor, we obtained a pulse duration of 13.4 fs. As the compression efficiency reached 67%, this OPCPA front end could potentially support a peak power of 263 TW at a repetition rate of 0.1 Hz. To the best of our knowledge, among all the 100 TW-level OPCPA systems, it shows the widest spectral width, the shortest pulse duration, and it is also the first OPCPA system working at a repetition-rate mode.

23 citations


Journal ArticleDOI
TL;DR: In this paper, a solid nanocomposite film is prepared by the drop-casting method where nanodiamond particles are embedded into polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE).
Abstract: In this paper, we investigate nanodiamond (ND) particles as saturable absorber (SA) to produce Q-switched pulses in Erbium doped fiber laser (EDFL). The solid nanocomposite film is prepared by the drop-casting method where ND is embedded into polyvinylidene fluoride-trifluoroethylene (PVDF-TRFE) as a host polymer. Both physical and optical properties of the prepared film are experimentally demonstrated. To analyze the structure of fabricated ND-PVDF-TRFE film, various measurement methods are adopted. The ND-SA is positioned in the ring cavity of the EDFL to explore their abilities for generating stable Q-switched pulses. The results show that the fabricated ND-SA can generate stable laser pulses. Furthermore, the ND composite film proves that 10% of ND could be presented as an excellent promising material for various photonic applications. The Q-switched EDFL with 10% ND-SA began to self-start of stable Q-switch pulse at a saturated pump power of 59 mW with a 77.84 kHz repetition rate and pulse width of 4.34 μs. Besides, at a pump power of 187 mW, the Q-switched EDFL generates very stable pulses with a wavelength of 1558 nm, a repetition rate of 127.2 kHz, pulse duration of 1.565 μs, and an output power of 0.447 mW.

20 citations


Journal ArticleDOI
TL;DR: Process optimization indicates that while operating with laser processing parameters resulting in the highest MRR, the best ratio between the MRR and surface roughness appears at ~50% overlap of the laser pulses, regardless of the material being processed.
Abstract: In this paper, we investigate the influence of the following parameters: pulse duration, pulse repetition rate, line-to-line and pulse-to-pulse overlaps, and scanning strategy on the ablation of AISI 316L steel and CuZn37 brass with a nanosecond, 1064-nm, Yb fiber laser. The results show that the material removal rate (MRR) increases monotonically with pulse duration up to the characteristic repetition rate (f0) where pulse energy and average power are maximal. The maximum MRR is reached at a repetition rate that is equal or slightly higher as f0. The exact value depends on the correlation between the fluence of the laser pulses and the pulse repetition rate, as well as on the material properties of the sample. The results show that shielding of the laser beam by plasma and ejected material plays an important role in reducing the MRR. The surface roughness is mainly influenced by the line-to-line and the pulse-to-pulse overlaps, where larger overlap leads to lower roughness. Process optimization indicates that while operating with laser processing parameters resulting in the highest MRR, the best ratio between the MRR and surface roughness appears at ~50% overlap of the laser pulses, regardless of the material being processed.

15 citations


Journal ArticleDOI
TL;DR: In this article , the optical performance of passively mode-locked pulses in erbium-doped fiber laser incorporating gold-nanoparticles (Au-NPs) as a saturable absorber (SA) was demonstrated.
Abstract: We demonstrate the optical performance of passively mode-locked pulses in erbium-doped fiber laser incorporating gold-nanoparticles (Au-NPs) as a saturable absorber (SA). Au-NPs of diameters between 5 to 15 nm were synthesized using the pulsed laser ablation method and blended with polydimethylsiloxane polymer. The resulting nanocomposite was deposited on the tapered region of a microfiber with a spin-coating method. The proposed Au-NPs SA recorded a modulation depth of 0.4% and low saturation intensity of 0.1 MW/cm2 leading to stable mode-locking operation in the erbium-doped fiber laser cavity at a low threshold pump power of about 45.6 mW. A mode-locked pulse train with a duration of 933 fs, pulse repetition rate of 6.25 MHz, and peak-to-pedestal extinction ratio of 54.1 dB was achieved at a pump power of 168.1 mW. The obtained results demonstrate that the spherical Au-NPs synthesized by pulsed laser ablation is a feasible material for SA fabrication, validating its saturable absorption properties in a 1.55 μm wavelength region.

15 citations


Journal ArticleDOI
TL;DR: In this paper , a fiber-chirped-pulse amplifier system with a two-stage multipass-cell compression was presented to achieve sub-2-cycle (5.8) and sub-1.07"mJ pulses at 100 kHz centered at 1030"nm with excellent spatial beam quality.
Abstract: Two-stage multipass-cell compression of a fiber-chirped-pulse amplifier system to the few-cycle regime is presented. The output delivers a sub-2-cycle (5.8 fs), 107 W average power, 1.07 mJ pulses at 100 kHz centered at 1030 nm with excellent spatial beam quality (M2 = 1.1, Strehl ratio S = 0.98), pointing stability (2.3 µrad), and superior long-term average power stability of 0.1% STD over more than 8 hours. This is combined with a carrier-envelope phase stability of 360 mrad in the frequency range from 10 Hz to 50 kHz, i.e., measured on a single-shot basis. This unique system will serve as an HR1 laser for the Extreme Light Infrastructure Attosecond Light Pulse Source research facility to enable high repetition rate isolated attosecond pulse generation.

13 citations


Journal ArticleDOI
TL;DR: In this article , the effect of laser peak in pulse shaping as a preheating and cooling approach for the melt pool of TiC − Fe based cermet using the pulse shaping technique was investigated.

13 citations


Journal ArticleDOI
TL;DR: In this paper , an Er-doped Mamyshev oscillator with short pulse-duration and low mode-locking threshold based on an external seed was demonstrated, which is the first time to the best of our knowledge that the sub-90 fs pulse output was observed directly from the output coupler without extra compression.

11 citations


Journal ArticleDOI
TL;DR: In this article , a review of wire cut EDM optimization parameters is presented, where the authors suggest the most influencing process parameters and best optimization method for various steel materials, and different kinds of result with best material removal rate (MRR) and surface roughness (SR).
Abstract: Stainless steel is a material which has high corrosive resistance and oxidation resistance at high temperature with the combination of chromium, nickel, and niobium as a primary constituent. This material which is difficult to machine with complex shape is taken by using wire cut electric discharge machining. Wire electrical discharge machining is a nontraditional process widely taken for cutting and machining for complex shapes. This review paper involves wire cut EDM optimization parameters. Pulse interval, pulse duration, wire feed, voltage, and mean current are the operational parameters. The Taguchi orthogonal array method, analysis of variance (ANOVA), and grey relation analysis (GRA) methods are taken for different kinds of machining various kinds of materials, and different kinds of result with best material removal rate (MRR) and surface roughness (SR) are analyzed. This work suggests the most influencing process parameters and best optimization method for various steel materials.

11 citations


Journal ArticleDOI
TL;DR: In this article , the authors reported the first Q-switching operation at ∼ 2.3 µm based on a Tm3+:YAlO3 (Tm:YAP) crystalline gain medium and a zeolitic imidazolate framework-67 (ZIF-67) saturable absorber.
Abstract: In the present work, we report the first Q-switching operation at ∼ 2.3 µm based on a Tm3+:YAlO3 (Tm:YAP) crystalline gain medium and a zeolitic imidazolate framework-67 (ZIF-67) saturable absorber. The ZIF-67 nanomaterials were designed and fabricated to possess a small size in the range from 200 to 500 nm in order to the reduce the possible scattering when working as the nonlinear optical modulator. Based on the conventional Z-scan technique with a home-made excitation source at 2275 nm, the modulation depth of ZIF-67 saturable absorber was determined as large as 6.9%, indicating the great potential in the short Q-switching pulse generation. With an output coupler (OC) of T = 0.5%, a maximum output power of 455 mW was achieved with a slope efficiency of 27%. For the Q-switching operation at 2.3 µm with ZIF-67 saturable absorber, the highest output power of 220 mW and a minimum pulse duration of 220 ns were obtained with a pulse repetition rate of 95 kHz at 2271.7 nm.

10 citations


Journal ArticleDOI
TL;DR: In this article , an all-fiber Er-doped Mamyshev oscillator with short pulse duration and high peak power was demonstrated, achieving a peak power of 86 kW.
Abstract: We demonstrated an all-fiber Er-doped Mamyshev oscillator with short pulse duration and high peak power. Through the dispersion management technique and accumulation of sufficient nonlinear phase shift, stable pulses with repetition rate of 6.55 MHz, 20-dB spectral bandwidth of 78.2 nm, pulse duration of 72 fs and peak power of 86 kW were achieved from output coupler (OC) device directly without extra compression. Simulations have been performed to show the direct generation of ultrafast laser pulse from the Mamyshev oscillator based on the extended nonlinear Schrödinger equation. To the best of our knowledge, this is by far the shortest pulse duration, the highest experimental peak power Er-doped Mamyshev oscillator.

Journal ArticleDOI
TL;DR: In this article, the authors reported the first Q-switching operation at 2.3µm based on a Tm3+:YAlO3 (Tm:YAP) crystalline gain medium and a zeolitic imidazolate framework-67 (ZIF-67) saturable absorber.
Abstract: In the present work, we report the first Q-switching operation at ∼ 2.3 µm based on a Tm3+:YAlO3 (Tm:YAP) crystalline gain medium and a zeolitic imidazolate framework-67 (ZIF-67) saturable absorber. The ZIF-67 nanomaterials were designed and fabricated to possess a small size in the range from 200 to 500 nm in order to the reduce the possible scattering when working as the nonlinear optical modulator. Based on the conventional Z-scan technique with a home-made excitation source at 2275 nm, the modulation depth of ZIF-67 saturable absorber was determined as large as 6.9%, indicating the great potential in the short Q-switching pulse generation. With an output coupler (OC) of T = 0.5%, a maximum output power of 455 mW was achieved with a slope efficiency of 27%. For the Q-switching operation at 2.3 µm with ZIF-67 saturable absorber, the highest output power of 220 mW and a minimum pulse duration of 220 ns were obtained with a pulse repetition rate of 95 kHz at 2271.7 nm.

Journal ArticleDOI
TL;DR: In this article , the NRP discharge unexpectedly swings among different regimes (corona → glow → spark → corona → …) in one pulse train, which is characterized by the periodical spark quench and reestablishment.
Abstract: Intuitively, the nanosecond repetitively pulsed (NRP) corona and spark regimes are sustained successively after onsets due to the high background electron density and/or the surplus heat. In this paper, the NRP discharge unexpectedly swings among different regimes (corona → glow → spark → corona → …) in one pulse train, which is characterized by the periodical spark quench and reestablishment. We have investigated discharge regime instabilities by applying long-term repetitive high-voltage nanosecond pulses of ∼15 ns duration to needle–needle and needle–plane gaps in atmospheric-pressure N2 and N2–O2 mixtures. Pulse-sequence resolved electrical and optical diagnostics have been implemented to capture transition processes. The initial corona gradually grows into glow and then spark ‘pulse-by-pulse’, however, the spark regime was interrupted after a certain number of voltage pulses until the next reestablishment. Narrow pulse width impedes the discharge instability growth within one pulse, and a certain number of voltage pulses are required for the discharge regime transition. The addition of O2 dramatically boosts the duration length of spark regime. A lower output impedance of the power supply induces a higher deposited energy into a spark, however, not necessarily leads to a longer spark regime duration, although both the energy storage and the average electric field strength are approximate. Polarity effects, conventionally diminished in pulse-periodic discharges, are still evident during the discharge regime transition. The periodical discharge regime transition is qualitatively explained based on the plasma–source coupling and the evolution trajectory along the power transfer curve. Feedback mechanisms and residual-conductivity related screening effect in NRP spark discharges are analyzed based on a simplified 0D simulation. The periodical feature is probably caused by the insufficient average deposited energy per unit distance per one pulse cycle. In-depth understandings of ‘non-binary’ regimes (neither corona nor spark) and memory effect mechanisms of NRP discharges could be reached.

Journal ArticleDOI
TL;DR: In this article , the results show that a material removal rate of 0.293mm3/min was obtained with factors of 10 µs pulse on duration, 7 m/min of wire feed, and 12 g of wire tension (the higher the better).
Abstract: The Ti-6Al-2Sn-4Zr-2Mo alloy was machined using the wire electrical discharge machining (WEDM) method in this research. The consequences of input values like pulse on duration, wire tension, and wire feed on metal removal rate (MRR) and surface roughness (SR) have indeed been observed. After conducting 27 experiments using Taguchi’s L27 type of research technique, empirical designing and analysis of variance (ANOVA) were performed. For process optimization, the Taguchi technique, which is based on the grey relational analysis approach, is used. The results show that a material removal rate of 0.293 mm3/min was obtained with factors of 10 µs pulse on duration, 7 m/min of wire feed, and 12 g of wire tension (the higher the better), and surface roughness of 2.129 µm was obtained with factors of 6 µs pulse on duration, 3 m/min of wire feed, and 8 g of wire tension (the lower the better). The percentage of errors between results obtained and grey relational analysis (GRA) predicted results varies around 6%. Wire electrical discharge machining with Ti-6242 alloy to optimum conditions resulted in better MRR and surface integrity with good surface finish and integrity as evidenced by a substantial reduction in the crack formation, lumps, and accumulated surfaces.

Journal ArticleDOI
TL;DR: In this article , the authors compare the pulse characteristics and stone ablation efficiency of the Moses technology with Quanta's Vapor Tunnel™ with an in vitro study, and show that the latter is superior in 2 mm single crater testing.
Abstract: Introduction: Manipulation of Holmium:Yttrium–Aluminum–Garnet laser parameters such as pulse energy (PE), frequency, and duration can impact laser lithotripsy ablation efficiency. In 2017, Lumenis introduced Moses™ Technology, which uses pulse modulation to enhance the delivery of energy from fiber to stone as well as to minimize stone retropulsion. Since the introduction of Moses Technology, other companies have brought additional pulse modulation concepts to market. The purpose of this in vitro study is to compare the pulse characteristics and stone ablation efficiency of Lumenis Moses Technology with Quanta's Vapor Tunnel™. Materials and Methods: Submerged BegoStone phantoms were systematically ablated using either the Lumenis Moses Pulse 120H or the Quanta Litho 100 clinical laser system. Two PEs (0.4 and 1 J), three fiber-stone standoff distances (SDs) (0.5, 1, 2 mm), and all available pulse duration and modulation modes for each laser were tested in combination. Fiber speed was adjusted to scan across the stone surface at either 1 or 10 pulses/mm to form single pulse craters or an ablation trough, respectively. Volumes of single craters and 1 mm trough segments were imaged and quantified using optical coherence tomography. Results: Ablation volumes decreased with decreasing PE and increasing SD. Statistically significant variability was seen between pulse types (PT) at every tested parameter set. Among pulse modulation modes, Moses Distance (MD) was superior at 0.5 mm in all testing and at 2 mm in trough testing. Vapor Tunnel (VT) was superior in 2 mm single crater testing. All modulated pulses performed similarly at 1 mm. Conclusions: In this benchtop model of laser lithotripsy, stone ablation was significantly impacted by PT. MD demonstrated superior or noninferior stone ablation at most tested parameters. VT maintained its efficacy the best as SD increased. Future work should focus on the mechanistic differences of these modes relative to other traditional laser pulse modes.

Journal ArticleDOI
TL;DR: In this paper , a new type of ferromagnetic insulator and its nonlinear optical absorption characteristics and related ultrafast modulation applications were investigated, and the experimental results reveal that Cr2Si2Te6 with excellent saturable absorption characteristics can be used as a SA to obtain ultrafast pulse lasers.
Abstract: In our work, a new-type, to the best of our knowledge, ferromagnetic insulator and its nonlinear optical absorption characteristics and related ultrafast modulation applications were investigated. Cr2Si2Te6 saturable absorbers (SAs) with a modulation depth and a saturable intensity of 9.7% and 3.5MW/cm2 were fabricated. By adjusting the pump power to 120 mW and optimizing the polarization state, traditional soliton operations were obtained successfully; the corresponding duration of pulse and the fundamental repetition rate were ∼1.33ps and 6.70 MHz, and the signal-to-noise ratio was 50 dB. The experimental results reveal that Cr2Si2Te6 with excellent saturable absorption characteristics can be used as a SA to obtain ultrafast pulse lasers.

Journal ArticleDOI
TL;DR: In this article , the influence of the pulsed Nd:YAG laser welding process on the microstructure and mechanical characteristics of Inconel 718 alloy weldments of 1 mm thin sheets was investigated.
Abstract: ABSTRACT The influence of the pulsed Nd:YAG laser welding process on the microstructure and mechanical characteristics of Inconel 718 alloy weldments of 1 mm thin sheets was investigated. By varying the selected input variables such as laser power, weld speed, and pulse duration, an analysis has been done on the weld characteristics, namely penetration and top and bottom width by Taguchi’s approach. The results were presented by focusing on weld bead geometry, grain structure in the Fusion Zone (FZ), Heat Affected Zone (HAZ), and the tensile properties. The FZ and HAZ microstructure consists of equiaxed, columnar grain structures, respectively, and clear ductile failure was observed with weldment. The combination of laser power at 2.5 kW, weld speed at 2.38 mm/min, and pulse duration at 6.6 ms achieves minimum top and bottom width. Similarly, a combination with 3.3 kW laser power, 2.02 mm/min weld speed, and 8.4 ms pulse duration offers maximum possible penetration that results in quality weldments. The influence of process variables was analyzed by ANOVA. A hybrid Grey–ANFIS model is evolved for determining the multiple performance index. From the validation outcomes attained (MAPE – 0.0413, correlation coefficient – 0.9991), it is proved that the evolved model is proficient for precise prediction.

Journal ArticleDOI
TL;DR: In this article, a new kind of saturable absorber (SA) based on sol-gel technology was designed in order to improve the long-term stable mode-locking operation comparing with the SA based on organic film.
Abstract: A new kind of saturable absorber (SA) based on sol-gel technology was designed in this study. The integration of this SA is different from the traditional transmission coupling, which drops the TI/ SiO 2 sol-gel glass on the fiber end facet and forms a complete glass to cover the fiber core after drying naturally. According to the nonlinear optical character test, the modulation depth, saturable intensity and nonsaturable loss of this SA are 39.31%, 32.21 MW/ cm 2 and 13.41%, respectively. Besides, the SA based on sol-gel glass has a remarkable improvement in long-term stable mode-locking operation comparing with the SA based on organic film by aging-resistant testing and damage threshold of SA based on sol-gel glass increases by almost an order of magnitude. The fundamental mode-locking (FML) is observed at 1569 nm with pulse duration of 718 fs at the pump power of 90mW when this SA is integrated into the erbium-doped fiber (EDF) laser. As further increasing the pump power, the harmonic mode-locking (HML) appears. The highest harmonic order is to 119 with pulse duration of 4.48 ps at the pump power of 395mW. These results indicate that this TI/ SiO 2 SA prepared by the sol-gel method offers a new opportunity for the integration way of SA.

Journal ArticleDOI
TL;DR: In this paper , a double-grating Offner stretcher with a conjugated Treacy compressor was used for optical parametric chirped pulse amplification (OPCPA) with low material dispersion.
Abstract: The aberration-free characteristic endows the double-grating Offner stretcher with the advantages of good beam quality and perfect-dispersion-match with conjugated Treacy compressor, and therefore makes it an ideal pulse stretcher for optical parametric chirped pulse amplification (OPCPA) systems featuring with low material dispersion. We numerically and experimentally demonstrate the feasibility of dispersion control in OPCPA systems by the use of double-grating Offner stretcher. The numerical results indicate that near Fourier-transform-limited (FTL) pulses can be realized in the double-grating Offner stretcher based petawatt (PW) level broadband OPCPA systems. Moreover, in a proof-of-principle experiment, amplified pulses with ∼210 nm spectral bandwidth and ∼3 ns chirped pulse duration are also compressed to near FTL pulse duration of 15.4 fs just by cooperating a double-grating Offner stretcher with a Treacy compressor. To our knowledge, it is the first time to realize near FTL compression of laser pulses with such a broadband spectrum and such a large chirped pulse duration simultaneously, while without using any extra dispersion compensation methods.

Journal ArticleDOI
TL;DR: In this article , the upgraded European 1MW, 170-GHz continuous wave (CW) industrial prototype gyrotron (TH1509U) was tested at the Karlsruhe Institute of Technology (KIT).
Abstract: The upgraded European 1-MW, 170-GHz continuous wave (CW) industrial prototype gyrotron (TH1509U) for electron cyclotron resonance heating and current drive in ITER was tested at the Karlsruhe Institute of Technology (KIT). In this work, we report on the major achievements during the experimental campaigns that took place intermittently between October 2020 and July 2021. The upgraded gyrotron clearly surpassed the performance of the previous TH1509 tube. In particular, TH1509U delivered (i) 0.9 MW in 180 s pulses (maximum possible pulse length with the KIT test stand) and (ii) more than 1 MW at a pulse length limited to 40 s, due to an unforeseen problem with the test stand cooling circuit at that time. In addition, it was possible to also demonstrate gyrotron operation at (iii) 0.5 MW in 1600 s pulses. The experiments will be continued at the FALCON test stand at the École Polytechnique Fédérale de Lausanne (EPFL).

Journal ArticleDOI
TL;DR: In this paper , the secondary electron yield (SEY) changes are caused by both the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures.
Abstract: Abstract Nanostructured surfaces exhibit remarkable chemical, physical and microbiological properties and have therefore various technical and industrial applications. The ultrashort laser pulse irradiation (wavelength λ = 355 nm, pulse duration Δt p = 12 ps, repetition rate f = 100 kHz) of copper samples with appropriate laser parameters results in the formation of a micro- and nanostructured surfaces. The influence of these hierarchically textured surfaces on the secondary electron yield (SEY) was studied especially with regard to their morphological and geometrical properties. Specific SEY changes are caused by both, the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures; that can be either compact flower head-like nanostructures, non-compact filament-shaped nanostructures, molten and resolidified spherical structures, or minor modified surfaces. The measured SEY as a function of the primary electron energy is correlated with the surface topography that forms upon laser irradiation. The SEY decreases with increasing accumulated laser fluence and ablated volume, respectively. Especially flower-head-like nanostructures can be produced at high laser power (P ≥ 400 mW) and low scanning velocity (v ≤ 10 mm/s) and represent a surface with strongly reduced SEY maximum as low as 0.7.

Journal ArticleDOI
TL;DR: In this article , the authors explored large area laser ablation of steel in air at ambient pressure and compared the influence of different pulse duration regimes from femtosecond to nanosecond, showing that irradiation with 70 ns long pulses induces sufficient surface heat load to damage the steel by producing a network of microcracks on the entire surface which propagate deep into the bulk.
Abstract: This paper explores large area laser ablation of steel in air at ambient pressure and compares the influence of different pulse duration regimes from femtosecond to nanosecond. It is demonstrated that irradiation with 70 ns long pulses induces sufficient surface heat load to damage the steel by producing a network of microcracks on the entire surface which propagate deep into the bulk. In stark contrast, ultrashort pulse laser ablation maintains the integrity of the steel bulk structure. The first appearance of cracks on surfaces processed at the optimal fluence occurs when the pulse duration is increased to 15 ps. The laser fluence dependence of the ablation rate in the ultrashort pulse regime with 275 fs pulses is investigated and the ablation threshold is determined at 0.25 ± 0.05 J/cm2. The optimal ablation regime in terms of volume removal is established to be an ablation efficiency of 0.20 ± 0.02 mm3/min/W at a fluence of ∼ 1.2 ± 0.3 J/cm2 . Finally, the surface roughness for fluences from the ablation threshold up to 2.5 J/cm2 is analysed and it is demonstrated that the best smoothness of the laser processed surface occurs in the same range of fluences where ablation is most efficient.

Journal ArticleDOI
TL;DR: In this paper, the dynamic response and spallation of a nano-multilayered system under different shock pulse duration are investigated by molecular dynamics, and it is shown that spallations occur only in the Cu region instead of in Ni.

Journal ArticleDOI
TL;DR: In this article , a 1 μm solid-state passively Q-switched (PQS) laser and 1, 1.5 μm mode-locked (ML) fiber lasers based on ternary chalcogenide Ta2NiS5 saturable absorber (SA) were successfully fabricated by liquid-phase exfoliation method (LPE).
Abstract: We report on the application of a 1 μm solid-state passively Q-switched (PQS) laser and 1, 1.5 μm mode-locked (ML) fiber lasers based on ternary chalcogenide Ta2NiS5 saturable absorber (SA), which were successfully fabricated by liquid-phase exfoliation method (LPE). The nonlinear absorption of the Ta2NiS5-SA was characterized by 0.32 GW/cm2 and 0.25 GW/cm2 saturation intensities with 7.3% and 5.1% modulations depths at 1 μm and 1.5 μm, respectively. A PQS solid-state laser operating at 1.0 μm has been realized with the Ta2NiS5-SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the PQS laser are 0.257 W, 180 ns, 1.265 μJ, and 7 W. Moreover, highly stable femtosecond laser centered at 1.5 μm, and picosecond centered at 1 μm, ML fiber lasers were obtained using the Ta2NiS5-SA. A 70 dB signal-to-noise ML laser with a pulse duration of 781 fs was observed in the telecommunication window, which is better than the duration of the previously reported lasers based on Ta2NiS5. The corresponding maximum single pulse energy and peak power are 0.977 nJ and 1251 W, respectively. The Ta2NiS5-SA fabricated by the LPE method was applied in near-infrared (NIR) ML fiber lasers (evanescent field interactions) and PQS bulk lasers. The results indicate that Ta2NiS5-SA prepared by the LPE method can be applied in a 1 μm bulk PQS laser and improved by the new combination mode (evanescent field interactions) for better output performance of the fiber laser.

Journal ArticleDOI
TL;DR: In this article , the authors proposed a roadmap for the design of high repetition rate Tm-doped ultrafast fiber laser with an emission wavelength above 2000 nm, which is confirmed by both theoretical simulation and experimental verification.
Abstract: We firstly propose a roadmap for thedesign of high repetition rate (∼100 MHz) Tm-doped ultrafast fiber laser with an emission wavelength above 2000 nm. This roadmap is confirmed by both theoretical simulation and experimental verification. The designed Tm-doped fiber oscillator not only operates in continuous wave regime with a broad tunable wavelength range of ∼100 nm, but also in mode-locking regime with an emission wavelength >2000 nm (up to 2020 nm). A 470-fs laser pulse with a pulse repetition rate of ∼96 MHz and the maximum average power of 50 mW are achieved at the output wavelength of 2007 nm, matching well with the theoretical prediction. In a further step, the seed laser pulse is amplified to 3.3 W, accompanied by a Raman frequency shift of the output wavelength to 2346 nm. The homogeneous intense broadband spectrum with a bandwidth of 240-nm centered at 2200 nm is also observed.

Journal ArticleDOI
TL;DR: In this paper , the secondary electron yield (SEY) changes are caused by both the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures.
Abstract: Abstract Nanostructured surfaces exhibit remarkable chemical, physical and microbiological properties and have therefore various technical and industrial applications. The ultrashort laser pulse irradiation (wavelength λ = 355 nm, pulse duration Δt p = 12 ps, repetition rate f = 100 kHz) of copper samples with appropriate laser parameters results in the formation of a micro- and nanostructured surfaces. The influence of these hierarchically textured surfaces on the secondary electron yield (SEY) was studied especially with regard to their morphological and geometrical properties. Specific SEY changes are caused by both, the shape and the depth of the microstructures, as well as the morphology of the formed nanostructures; that can be either compact flower head-like nanostructures, non-compact filament-shaped nanostructures, molten and resolidified spherical structures, or minor modified surfaces. The measured SEY as a function of the primary electron energy is correlated with the surface topography that forms upon laser irradiation. The SEY decreases with increasing accumulated laser fluence and ablated volume, respectively. Especially flower-head-like nanostructures can be produced at high laser power (P ≥ 400 mW) and low scanning velocity (v ≤ 10 mm/s) and represent a surface with strongly reduced SEY maximum as low as 0.7.

Journal ArticleDOI
TL;DR: In this paper , a complete experimental study of CALMAX machining using EDM is presented, using a Taguchi Design of Experiment (DOE) was used, using pulse-on current, pulseon time, and opencircuit voltage as control parameters.
Abstract: As a non-conventional machining technology, EDM is used extensively in modern industry, particularly in machining difficult-to-cut materials. CALMAX is a chromium-molybdenum-vanadium tool steel with exceptional toughness, ductility, and wear resistance that has a wide range of applications. Despite the fact that EDM is routinely used in CALMAX machining, the related published research is brief and limited. The current research gives a complete experimental study of CALMAX machining using EDM. A Taguchi Design of Experiment (DOE) was used, using pulse-on current, pulse-on time, and open-circuit voltage as control parameters. Material Removal Rate (MRR), Tool Material Removal Rate (TMRR), and Tool Wear Ratio (TWR) were used to evaluate machining performance, while Ra and Rz were used to estimate Surface Quality (SQ). The produced White Layer (WL) parameters were determined using optical and SEM microscopy, as well as EDX measurements and micro-hardness studies. Finally, for each of the aforementioned indexes, Analysis of Variance (ANOVA) was performed, and multi-objective optimization was based on Grey Relational Analysis (GRA). The results show that higher open-circuit voltage produces lower WL thickness, although by increasing the pulse-on time, the TWR is increased. The average hardness of the WL is increased about 400% compared to the micro-hardness of the bulk material.

Journal ArticleDOI
TL;DR: In this article , a blue LD-pumped electro-optically (EO) Q-switched Pr3+:LiYF4 (Pr:YLF) laser was used for the first time.
Abstract: We report the generation of high energy visible pulsed beam from a blue LD-pumped electro-optically (EO) Q-switched Pr3+:LiYF4 (Pr:YLF) laser for the first time. The maximum pulse energy and highest peak power in our work perform excellent in the blue LD-pumped pulse visible lasers. The shortest pulse duration of 137 ns is obtained at the repetition rate of 100 Hz, corresponding to a single pulse energy of 260 μJ and peak power of 1.90 kW. Our research results indicate that the Pr:YLF crystal could be suitable for the generation of high energy Q-switched visible lasers. Meanwhile, we pave up a new way for the practical implementation of blue LD-pumped directly generate high energy Q-switched visible laser.

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TL;DR: In this article , a transition from a filamentary propagation with extended and low energy density deposition to a localized breakdown was observed, which suggests that Kerr self-focusing plays a major role in the beam propagation dynamics.
Abstract: Experiments and simulations are performed to study filamentation and generation of acoustic waves in water by loosely focused multi-millijoules laser pulses. When the laser pulse duration is increased from femtosecond to nanosecond duration, a transition is observed from a filamentary propagation with extended and low energy density deposition to a localized breakdown, related to high energy density deposition. The transition suggests that Kerr self-focusing plays a major role in the beam propagation dynamics. As a result, the shape, the amplitude and the spectrum of the resulting pressure wave present a strong dependence on the laser pulse duration.

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TL;DR: In this paper , the three-temperature model was used to model the dynamics of the distinct quasi-temperatures for electrons, holes, and lattice, and the authors found that electron-phonon relaxation time has a significant effect on pulse duration dependence of electron emission.
Abstract: Laser excitation in silicon from femto- to pico-second time scales is studied. We assume the three-temperature model which describes the dynamics of the distinct quasi-temperatures for electrons, holes, and lattice. Numerical results for damage threshold reproduce the experimental results not only quantitatively, but qualitatively as well, showing dependence on laser pulse duration. Comparison with experimental data suggests that electron emission and thermal melting are both responsible for damage in silicon. We found that electron–phonon relaxation time has a significant effect on pulse duration dependence of electron emission.