Showing papers on "Pulse duration published in 2019"

Tunable Isolated Attosecond X-ray Pulses with Gigawatt Peak Power from a Free-Electron Laser

Abstract: The quantum mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs and of sufficient intensity to interact with their target with high probability. Probing these dynamics with atomic-site specificity requires the extension of sub-femtosecond pulses to the soft X-ray spectral region. Here we report the generation of isolated GW-scale soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energy that is six orders of magnitude larger than any other source of isolated attosecond pulses in the soft X-ray spectral region, with a peak power in the tens of gigawatts. This unique combination of high intensity, high photon energy and short pulse duration enables the investigation of electron dynamics with X-ray non-linear spectroscopy and single-particle imaging.

SnSe2 Nanosheets for Subpicosecond Harmonic Mode-Locked Pulse Generation.

Abstract: Tin diselenide (SnSe2 ) nanosheets as novel 2D layered materials have excellent optical properties with many promising application prospects, such as photoelectric detectors, nonlinear optics, infrared photoelectric devices, and ultrafast photonics. Among them, ultrafast photonics has attracted much attention due to its enormous advantages; for instance, extremely fast pulse, strong peak power, and narrow bandwidth. In this work, SnSe2 nanosheets are fabricated by using solvothermal treatment, and the characteristics of SnSe2 are systemically investigated. In addition, the solution of SnSe2 nanosheets is successfully prepared as a fiber-based saturable absorber by utilizing the evanescent field effect, which can bear a high pump power. 31st-order subpicosecond harmonic mode locking is generated in an Er-doped fiber laser, corresponding to the maximum repetition rate of 257.3 MHz and pulse duration of 887 fs. The results show that SnSe2 can be used as an excellent nonlinear photonic device in many fields, such as frequency comb, lasers, photodetectors, etc.

Large-energy passively Q-switched Er-doped fiber laser based on CVD-Bi2Se3 as saturable absorber

Abstract: In our work, Bi2Se3 was successfully used for demonstrating a large-energy passively Q-switched erbium-doped fiber laser. Bi2Se3 nanosheets were fabricated by a catalyst-free chemical vapor deposition method. Based on a pyrolysis tape transfer method, the Bi2Se3 thin film on the SiO2 substrate was transferred to the end of the optical connector for constructing the fiber-integrated saturable absorber. The saturation intensity and modulation depth of the Bi2Se3 saturable absorber were 81.1 MW/cm2 and 15.7%, respectively. A stable Q-switched operation at 1549.99 nm with a maximum average output power of 23.61 mW was achieved. The minimum pulse duration and the largest pulse energy were 1.34 μs and 224.5 nJ, respectively. In comparison with previous works, the single pulse energy (224.5 nJ) obtained in our experiment was improved significantly. Our experimental results fully proved that CVD-Bi2Se3 has good performance in obtaining large energy pulse operations and will promote the applications of 2D CVD-materials in the field of pulse laser.

Few-layer bismuthene for femtosecond soliton molecules generation in Er-doped fiber laser

Abstract: Bismuthene, a mono-elemental two-dimensional material with a novel kind of few-layer structure purely consisting of bismuth, has been predicted to have a prominent optical response and enhanced stability in theory. In this paper, few-layer bismuthene is employed as the saturable absorber. The mode-locker is fabricated by dropping bismuthene on a microfiber in a passively mode-locked, Er-doped fiber laser. The single pulse can be obtained at 122.1 mW, with 621.5 fs pulse duration at 1557.5 nm central wavelength, 10.35 nm spectral width and fundamental repetition of 22.74 MHz. Thanks to the outstanding nonlinear effect and semimetal of the bismuthene, dual-pulses, octonary-pulses and fourteen-pulses soliton molecules with tightly and loosely temporal separation can be achieved for the first time, to the best of our knowledge. The preceding indicates that bismuthene will have wide potential in many applications, such as optical fiber communications, optical logical gate, and laser materials processing, etc.

Spatiotemporal self-similar fiber laser

Abstract: Spatiotemporal mode-locked fiber lasers are a type of ultrafast lasers for which the longitudinal and transverse modes of the multimode fiber cavities are locked via nonlinear interaction in the cavity. Here we report the experimental realization of a spatiotemporally mode-locked fiber laser with self-similar pulse evolution. The multimode fiber oscillator generates parabolic pulses at 1030 nm with 90 mW average power, a near-Gaussian beam quality (M2≤1.4), and 2.3 ps (192 fs externally dechirped) pulse duration. Numerical simulations confirm the experimental observations of self-similar pulse propagation. These results will enable further investigation of nonlinear dynamics in spatiotemporal mode-locked fiber lasers.

Cu2S nanosheets for ultrashort pulse generation in the near-infrared region

Abstract: 2D metal chalcogenide materials have received enormous attention due to their extraordinary bio-chemical, electronic, magnetic, thermal and optical properties. Compared with the typical two-dimensional transition metal dichalcogenides (TMDs) and topological insulators, cuprous sulfide (Cu2S) has very different two-dimensional lattice structures, along with excellent electro-catalysis and high conductivity. However, the nonlinear optical properties of Cu2S have never been studied until now. Here, the nonlinear photonics characteristics of Cu2S and its application in ultrafast lasers have been systematically studied for the first time. Through optical deposition of Cu2S nanosheets on a tapered fiber, the nonlinear optical properties of Cu2S nanosheets are measured through the interaction with the evanescent field. The results indicate that superior nonlinear saturable absorption properties with a modulation depth of 0.51% are achieved. An erbium-doped fiber (EDF) laser is constructed to verify the performance of the Cu2S saturable absorber (SA). The results show that an output pulse with 8.06 MHz repetition rate, 1.04 ps pulse duration, 1530.4 nm central wavelength and 3.1 nm spectral width without an obvious Kelly sideband is obtained. Considering the diversity of the metal chalcogenide family, various engineering applications may be developed from the nonlinear saturable absorption characteristics of Cu2S, including optical fiber communication/sensing, precision optical metrology, material processing and nonlinear optics.

Amplitude noise and coherence degradation of femtosecond supercontinuum generation in all-normal-dispersion fibers

Abstract: Supercontinuum (SC) generation via femtosecond (fs) pumping in all-normal-dispersion (ANDi) fiber is predicted to offer completely coherent broadening mechanisms, potentially allowing for substantially reduced noise levels in comparison to those obtained when operating in the anomalous dispersion regime. However, previous studies of SC noise typically treat only the quantum noise, typically in the form of one-photon-per-mode noise, and do not consider other technical noise contributions, such as the stability of the pump laser, which become important when the broadening mechanism itself is coherent. In this work, we discuss the influence of the amplitude and pulse length noise of the pump laser, both added separately and combined. We show that for a typical mode-locked laser, in which the peak power and pulse duration are anticorrelated, their combined impact on the SC noise is generally smaller than in isolation. This means that the supercontinuum noise is smaller than the noise of the mode-locked pump laser itself, a fact that was recently observed in experiments but not explained. Our detailed numerical analysis shows that the coherence of ANDi SC generation is considerably reduced on the spectral edges when realistic pump laser noise levels are taken into account.

MoTe 2 Saturable Absorber With High Modulation Depth for Erbium-Doped Fiber Laser

Abstract: Transition metal dichalcogenides have recently been considered the candidates for saturable absorption materials due to their advantages in both electronic and optoelectronic. Compared with MoS2 and WS2, MoTe2 exhibits smaller bandgap. As a result, MoTe2 owns inherent advantages in the near-infrared applications. In this paper, the MoTe2 saturable absorber (SA) were prepared by the magnetron sputtering deposition method. Owing to the enhanced light-materials interaction between MoTe2 and evanescent field from the microfiber, the modulation depth of the MoTe2 SA was up to 26.97%. By assembling the MoTe2 SA into the erbium-doped fiber laser, the mode-locked fiber laser at 1.5 μm was demonstrated. The pulse duration of 111.9 fs was proved to be the shortest in the fiber lasers based on transition metal dichalcogenides. Moreover, the mode-locked fiber laser maintains the long-term stability. Our results suggest that the proposed MoTe2 SA is promising for the ultrashort pulse generation and stable system operation.

Highly-efficient laser ablation of copper by bursts of ultrashort tuneable (fs-ps) pulses.

Abstract: Ultrashort pulse laser, capable of varying pulse duration between 210 fs and 10 ps and producing a burst of pulses with an intra-burst pulse repetition rate of 64.5 MHz (time distance between pulses 15.5 ns), was used to investigate the ablation efficiency of the copper. The study on ablation efficiency was done for various numbers of pulses per burst between 1 and 40. The increase in the ablation efficiency by 20% for 3 pulses per burst compared to a non-burst regime was observed. The comparison was made between the beam-size optimised regimes. Therefore, the real advantage of the burst regime was demonstrated. To the best of our knowledge, we report the highest laser milling ablation efficiency of copper of 4.84 µm3/µJ by ultrashort pulses at ~1 µm optical wavelength.

8.8 GHz Q-switched mode-locked waveguide lasers modulated by PtSe 2 saturable absorber.

Abstract: We demonstrate high-repetition-rate fundamentally Q-switched mode-locked Nd:YAG waveguide laser modulated by platinum diselenide (PtSe2) saturable absorber. The laser operation platform is a femtosecond laser-written monolithic Nd:YAG waveguide, and the saturable absorber is large-area few-layer PtSe2 that possesses relatively lower saturation intensity and higher modulation depth in comparison with graphene. With the superb ultrafast nonlinear saturable absorption properties of as-synthesized PtSe2, the waveguide laser could operate at ~8.8 GHz repetition rate and ~27 ps pulse duration, while maintaining a relatively high slope efficiency of 26% and high stability with signal-to-noise ratio (SNR) up to 54 dB. Our work indicates the promising applications of laser-written Nd:YAG waveguides and atomically thin PtSe2 for on-chip integration of GHz laser sources toward higher repetition rates and shorter pulse duration.

The pure-quartic soliton laser

Abstract: The generation of ultrashort pulses hinges on the careful management of dispersion. Traditionally, this has exclusively involved second-order dispersion, while higher-order dispersion was treated as a nuisance to be minimized. Here we show that high-order dispersion can be strategically leveraged to access an uncharted regime of ultrafast laser operation. In particular, we demonstrate a mode-locked laser, with an intra-cavity spectral pulse-shaper, that emits pure-quartic soliton pulses, which arise from the interaction of the fourth-order dispersion and the Kerr nonlinearity. Using phase-resolved measurements we demonstrate that the energy of these pulses is proportional to the third power of the inverse pulse duration. This implies a dramatic increase in the energy of ultrashort pulses compared to those emitted by soliton lasers to date. These results not only demonstrate a novel approach to ultrafast lasers, but more fundamentally, they clarify the use of higher-order dispersion for optical pulse control, opening up a plethora of possibilities in nonlinear optics and its applications.

High-efficiency femtosecond ablation of silicon with GHz repetition rate laser source.

Abstract: We report on silicon ablation with a 20 W GHz amplified femtosecond laser source. This novel laser delivers burst energies up to 400 μJ, providing flexible intra-pulse repetition rates of 0.88 or 3.52 GHz, up to 200 pulses with ∼350 fs pulse duration. High-efficiency, high-quality ablation can be achieved through optimally determining the number of pulses, intra-pulse repetition, and average pulse energy within a burst. Due to such optimization, we demonstrate a specific ablation rate of 2.5 mm3/min/W with a burst containing 200 pulses at 0.88 GHz, which is the highest one reported so far for fs laser ablation, to the best of our knowledge. GHz ablation is sensitive to the selection of laser parameters. We conceptually discuss the contributions of the pulses within a burst to heat-accumulation-based incubation and material ablation.

Passively Q-switched and mode-locked Tm-Ho co-doped fiber laser using a WS2 saturable absorber fabricated by chemical vapor deposition

Abstract: We demonstrate a passively Q-switched and mode-locked Tm-Ho co-doped fiber laser based on a WS2 saturable absorber (SA) fabricated by chemical vapor deposition method. When the pump power increases from 0.32 W to 0.38 W, the repetition rate of the Q-switched laser pulse increases 47.1 kHz to 90.1 kHz and the pulse width decreases from 6.2 μs to 1.7 μs. In addition, the mode-locking operation can also be observed by adjusting the polarization controller (PC) and mode-locked laser pulses at 1883.2 nm can be achieved at a high pump power between 0.5 W and 0.64 W. The pulse duration is 1.07 ns and repetition rate is 23.8 MHz and the pulse is the longest mode-locked pulse with WS2-SA ever reported.

On the Interplay of DLIP and LIPSS Upon Ultra-Short Laser Pulse Irradiation

Abstract: Controlling laser induced surface morphology is essential for developing specialized functional surfaces. This work presents novel, multi-scale periodic patterns with two-dimensional symmetry generated on stainless steel, polyimide and sapphire. The microstructures were realized by combining Direct Laser Interference Patterning with the generation of Laser Induced Periodic Surface Structures in a one-step process. An industrial, fiber femtosecond laser source emitting at 1030 nm with a pulse duration of 500 fs was utilized for the experiments. In the case of stainless steel, it was possible to create line-like or pillar-like surface patterns by rotating the polarization orientation with respect to the interference pattern. In the case of polyimide and sapphire, the absorption of the laser radiation was promoted by a multiphoton mechanism. In polyimide, grooves and pillars of several microns in depth were produced over an area much larger than the spot size. Finally, for sapphire, the simultaneous generation of interference-like pattern and laser induced periodic surface structures was realized. The results reported here provide valuable data on the feasibility to combine two state-of-the-art techniques with an industrial apparatus, to control the induced surface morphology.

Characteristics of micro-hole formation during fibre laser drilling of aerospace superalloy

Abstract: High aspect ratio micro-holes are nowadays increasingly used in various applications including aerospace, medical and automotive. This research investigates the characteristic of quasi-CW fibre laser micro-hole drilling (∼100 μm) of nickel superalloy using experimentation and numerical modelling. Micro-holes of diameter around 100 μm was drilled using percussion technique over a 2 mm thick nickel superalloy material. The main investigation focuses on understanding the micro-hole formation during the laser interaction with the material. Finite element modelling tool and high-speed imaging camera had been used to assist in understanding the basic-fundamentals of micro-hole formation during the millisecond laser drilling process. During the micro-hole drilling process, irrespective of the laser parameters, the melt ejections start after around 80 μs, and the total melt ejection duration depends on laser energy and pulse duration. The experimental results showed that it takes 15 ms to drill a micro-hole of diameter around 100 μm using a laser pulse duration of 0.1 ms, laser pulse energy of 1 J and 15 number of percussion pulses.

High-energy dissipative soliton resonance and rectangular noise-like pulse in a figure-9 Tm fiber laser

Abstract: We experimentally demonstrate a direct generation of high-energy dissipative soliton resonance (DSR) and rectangular noise-like pulse (NLP) in a figure-9 thulium-holmium-doped mode-locked fiber laser. The pulse duration and average output power of the DSR can be tuned from 33.5 ns to 144.6 ns, and from 100.25 mW to 677.5 mW, respectively. The maximum of pulse energy is 713.2 nJ without wave breaking at pump power of 6.7 W, which is the highest energy of DSR in the region of 2 μm, to the best of our knowledge. In addition, the rectangular NLP with 452 nJ pulse bunch energy is also obtained.

Nonlinear dynamic response of a tall building to near-fault pulse-like ground motions

Abstract: The objective of this study is to determine the effects of near-fault ground motions with large, medium and small pulse periods on a core-wall tall building. Three near-fault and one far-field ground motion sets, each with 11 different records, are rotated to the maximum pseudo-velocity spectrum directions. The mean transition periods of each set are obtained by the smoothed tripartite spectrum, which illustrates that the acceleration–sensitive region extends with increasing pulse duration. A 40-story core-wall building is subjected to 44 different record pairs, and the analysis results show that the ratio of pulse duration to first mode period (Tp/T1), governs the nonlinear response. It is demonstrated that higher mode effects increase while the first mode sensitive region moves away from the second mode sensitive region. The distribution profiles of the story drift, tension strain, and beam rotation demands along the height of the building are substantially different depending on the Tp/T1 ratio. In the large and medium pulses records, the core-wall reaches the flexural yielding capacity above the podium level, and this phenomenon increases the story drift ratio and flexural beam rotation demands depending on the displacement demands at the end of the acceleration-sensitive region. On the contrary, near-fault with small pulses and far-field ground motions induce yielding of core-wall at upper stories due to higher mode effects. Thus, post-yield story shear force distributions significantly change compared to the large and medium pulses ground motions.

Femtosecond fiber Mamyshev oscillator at 1550 nm.

Abstract: We investigated the possibility of reaching nanojoule-level pulse energies in a femtosecond erbium-doped fiber Mamyshev oscillator. In experiments, lasers generate stable pulse trains with energy up to 31.3 nJ, which is comparable to the highest achieved by prior ultrafast erbium fiber lasers. The pulse duration after a grating compressor is around 100 fs. However, as the pulse energy increases, the pulse quality degrades significantly, with a substantial fraction of the energy going into a picosecond pedestal. Numerical simulations agree with the experimental observations, and allow us to identify the gain spectrum and the nonlinearity of the erbium-doped fibers as challenges to the operation of such oscillators at high pulse energy.

Generation of deep ultraviolet sub-2-fs pulses

Abstract: We demonstrate the generation of few-cycle deep ultraviolet pulses via frequency upconversion of 5-fs near-infrared pulses in argon using a laser-fabricated gas cell. The measured spectrum extends from 210 to 340 nm, corresponding to a transform-limited pulse duration of 1.45 fs. We extract from a dispersion-free second-order cross-correlation measurement a pulse duration of 1.9 fs, defining a new record in the deep ultraviolet spectral range.

Optical Nonlinearity of ZrS₂ and Applications in Fiber Laser.

Abstract: Group VIB transition metal dichalcogenides (TMDs) have been successfully demonstrated as saturable absorbers (SAs) for pulsed fiber lasers. For the group comprising IVB TMDs, applications in this field remain unexplored. In this work, ZrS2-based SA is prepared by depositing a ZrS2 nanostructured film onto the side surface of a D-shaped fiber. The nonlinear optical properties of the prepared SA are investigated, which had a modulation depth of 3.3% and a saturable intensity of 13.26 MW/cm2. In a pump power range of 144–479 mW, the Er-doped fiber (EDF) laser with ZrS2 can operate in the dual-wavelength Q-switching state. The pulse duration declined from 10.0 μs down to 2.3 μs. The single pulse energy reached 53.0 nJ. The usage of ZrS2 as a SA for pulse generation in fiber lasers is presented for the first time. Compared to the experimental results of dual-wavelength Q-switched fiber lasers with two-dimensional (2D) materials, our laser performance was better. Our work indicates that the group comprising IVB TMD ZrS2 has bright prospects for nonlinear optical applications.

Few-layer bismuthene for robust ultrafast photonics in C-Band optical communications

Abstract: The ultrafast photonics of different conventional two-dimensional (2D) materials have been studied intensively. Few-layer structure bismuthene has been reported as a new type of 2D material with high efficient electronics, strong mechanics and outstanding photonics properties. In this paper, a robust ultrafast pulse generation in communications-Band (C-Band) based on few-layer bismuthene has been reported. The characteristics and the ultrafast optical nonlinear properties of few-layer bismuthene have been investigated experimentally. The optical induced deposition method is employed to fabricate the saturable absorber based on bismuthene (BiSA). Most importantly, we also utilize BiSA for the ultrafast photonics, which demonstrates that a high-splitting-threshold robust ultrafast fiber laser with 1.3-ps pulse duration at 1531 nm has been obtained in the experiments. Even though we increase the pump power from the self-starting threshold (i.e. 86 mW) to 314 mW, the soliton pulse does not split. Moreover, the high-splitting-threshold laser operation can be achieved stably even if the lasers are exposed in air for at least half a year. It is demonstrated that the proposed bismuthene nonlinear components can be potentially applied to the optical communications with C-Band (i.e. 1530-1565 nm wavelength) to broaden the communications window.

Efficient Generation of Extreme Ultraviolet Light From Nd: YAG-Driven Microdroplet-Tin Plasma

Abstract: We experimentally investigate the emission of EUV light from a mass-limited laser-produced plasma over a wide parameter range by varying the diameter of the targeted tin microdroplets and the pulse duration and energy of the 1-mu m-wavelength Nd:YAG drive laser. Combining spectroscopic data with absolute measurements of the emission into the 2% bandwidth around 13.5 nm relevant for nanolithographic applications, the plasma's efficiency in radiating EUV light is quantified. All observed dependencies of this radiative efficiency on the experimental parameters are successfully captured in a geometrical model featuring the plasma absorption length as the primary parameter. It is found that laser intensity is the pertinent parameter setting the plasma temperature and the tin-ion charge-state distribution when varying laser pulse energy and duration over almost 2 orders of magnitude. These insights enabled us to obtain a record-high 3.2% conversion efficiency of laser light into 13.5-nm radiation and to identify paths towards obtaining even higher efficiencies with 1-mu m solid-state lasers that may rival those of current state-of-the-art CO2-laser-driven sources.

From Multiple- to Single-Pulse All-Optical Helicity-Dependent Switching in Ferromagnetic Co /Pt Multilayers

Abstract: All-optical helicity-dependent switching in ferromagnetic Co/Pt multilayers is investigated using magneto-optical microscopy and anomalous Hall effect measurements. A state diagram is built by studying the effect of pulse duration, fluence, and spot size. We use numerical solutions of the three-temperature model to explain that the all-optical helicity-dependent switching mechanism relies on the spin bath reaching temperatures close to the Curie point. Further insights into the reversal process are provided by the experimental demonstration of significant helicity-dependent reversal after a single laser pulse that reveals the involvement of direct angular momentum transfer. Moreover, based on the observation that longer pulse durations and larger spot sizes lead to enhanced reversal efficiency, we identify experimental conditions that lead to saturated magnetization reversal after just a few tens of laser pulses.

Ultrafast Laser Pulses Generation by Using 2D Layered PtS 2 as a Saturable Absorber

Abstract: Platinum disulfide (PtS2) has recently drawn extensive research interest due to its excellent electronic properties, controllable bandgap over a broad range, and high air stability. Herein, we demonstrate the generation of mode-locked ultrafast laser pulses by using PtS2 nanosheets for the first time, which were fabricated by ultrasonic exfoliation followed by the centrifugation process. The fabricated PtS2 saturable absorber (SA) was used within two different fiber laser systems. Ultrafast laser pulses with pulse duration of 2.1 ps, 3-db bandwidth of 2.5 nm, and repetition rate of 15.04 MHz were produced from an Er-doped fiber laser system with an operational wavelength of 1.572 μm. Additionally, a mode-locking pulse train with repetition rate of 11.2 MHz was obtained by using the fabricated PtS2 SA within Yb-doped fiber laser system with operational wavelength of ∼1 μm. It is expected that these results will trigger further research with wide potential applications of PtS2 in the field of nonlinear optics and ultrafast photonics.

Highly efficient continuous-wave and ReSe2Q-switched ∼3 μm dual-wavelength Er:YAP crystal lasers

Abstract: We report on continuous-wave (CW) and rhenium diselenide (ReSe2) Q-switched dual-wavelength mid-infrared (MIR) laser performances of Er:YAP crystal in this Letter. Under an absorbed pump power of 5.5 W, a maximum CW Er:YAP laser output power of 1.02 W is obtained, corresponding to a slope efficiency of 25.3%. With multilayer ReSe2 material as a saturable absorber, a stable Q-switched Er:YAP crystal laser with dual-wavelength output of 2.73 and 2.80 μm is realized for the first time, to the best of our knowledge. The nonlinear optical measurements of the multilayer ReSe2 reveal efficient saturable absorption properties around 3 μm showing a modulation depth of 7.5% and a saturation intensity of 14.5 μJ/cm2. The maximum Q-switching output power reaches 526 mW, and the corresponding laser power jitter is around 3% in 1 h. The shortest pulse duration and the highest pulse repetition rate are 202.8 ns and 244.6 kHz, respectively. These results prove that Er:YAP crystal could be a reliable laser crystal for MIR solid-state lasers.