Showing papers on "Pulse duration published in 2021"
TL;DR: In this article, the authors used WxNb(1−x)Se2 nanosheets as a rising ultrafast photonic device to generate high power mode-locked and Q-switched pulses in a fiber laser.
Abstract: Ternary transition metal chalcogenides (TTMDCs), a novel type of two-dimensional (2D) three-element materials, possess multiple physical and chemical properties and have promising potentials in basic physics and devices. Herein, the usage of WxNb(1−x)Se2 nanosheets as a rising ultrafast photonic device to generate high power mode-locked and Q-switched pulses in a fiber laser is demonstrated. The WxNb(1−x)Se2 nanosheets were successfully prepared by the liquid exfoliation method with thickness less than 3 nm. The nonlinear optical absorption of the WxNb(1−x)Se2-based device was investigated with the saturable intensity of 40.93 MW cm−2 and modulation depth of 5.43%. After integrating the WxNb(1−x)Se2-based device into an Er-doped fiber (EDF) laser cavity, mode-locking and Q-switching laser pulses were formed. In the mode-locked mechanism output, the pulse width is as narrow as 131 fs and the output power is 52.93 mW. In Q-switched operation, the shortest pulse duration is 1.47 μs with the largest pulse energy of 257 nJ. Compared to recent studies, our results showed some improvements. This study suggests that 2D TTMDC-based devices could be developed as efficient ultrafast photonics candidates and widely used in nonlinear optical applications.
78 citations
TL;DR: An ultrafast laser based on coherent beam combination of four ytterbium-doped step-index fiber amplifiers is presented in this article, which delivers an average power of 35 kW and a pulse duration of 430 fs at 80 MHz repetition rate.
Abstract: An ultrafast laser based on coherent beam combination of four ytterbium-doped step-index fiber amplifiers is presented The system delivers an average power of 35 kW and a pulse duration of 430 fs at 80 MHz repetition rate The beam quality is excellent (M2<124x110) and the relative intensity noise is as low as 1% in the frequency span from 1 Hz to 1 MHz The system is turn-key operable as it features an automated spatial and temporal alignment of the interferometric amplification channels
50 citations
TL;DR: In this paper, a multipass cell for nonlinear compression to few-cycle pulse duration is introduced composing dielectrically enhanced silver mirrors on silicon substrates, achieving high output beam quality (M2 < 1.2) and high spatio-spectral homogeneity (97.5%), as well as the compressibility of the output pulses to 6.9 fs duration.
Abstract: A multipass cell for nonlinear compression to few-cycle pulse duration is introduced composing dielectrically enhanced silver mirrors on silicon substrates. Spectral broadening with 388 W output average power and 776 µJ pulse energy is obtained at 82% cell transmission. A high output beam quality (M2<1.2) and a high spatio-spectral homogeneity (97.5%), as well as the compressibility of the output pulses to 6.9 fs duration, are demonstrated. A finite element analysis reveals scalability of this cell to 2 kW average output power.
46 citations
TL;DR: In this paper, an ultrafast fiber chirped-pulse amplifier comprising 8 coherently combined amplifier channels is presented, which delivers 1 kW average power at 1 mJ pulse energy and 260 fs pulse duration.
Abstract: An ultrafast fiber chirped-pulse amplifier comprising 8 coherently combined amplifier channels is presented. The laser delivers 1 kW average power at 1 mJ pulse energy and 260 fs pulse duration. Excellent beam quality and low noise performance are confirmed. The laser has proven suitable for demanding scientific applications. Further power scaling is possible right away using even more amplifier channels
44 citations
TL;DR: In this article, the authors demonstrate all-optical modulation of second-harmonic generation in MoS2 with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration.
Abstract: Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization. Advanced functionalities are enabled by modulation of the harmonic generation efficiency, which can be achieved with electrical or all-optical triggers. Electrical control of the harmonic generation efficiency offers large modulation depth at the cost of low switching speed, by contrast to all-optical nonlinear devices, which provide high speed and low modulation depth. Here we demonstrate all-optical modulation of second-harmonic generation in MoS2 with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration. This result arises from a combination of D3h crystal symmetry and the deep subwavelength thickness of the sample, it can therefore be extended to the whole family of transition metal dichalcogenides to provide great flexibility in the design of advanced nonlinear optical devices such as high-speed integrated frequency converters, broadband autocorrelators for ultrashort pulse characterization, and tunable nanoscale holograms.
31 citations
TL;DR: To the best of the knowledge, this is the first time that optical microfiber coupler based saturable absorber (OMC-SA) for mode-locked fiber laser is demonstrated.
Abstract: We demonstrated a mode-locked fiber laser based on a novel photonic device that combined optical microfiber coupler (OMC) and saturable absorption materials. The stable ultrafast laser was formed based on the interaction between the deposited Indium Antimonide (InSb) and the evanescent field on OMC. Different from optical microfiber (OM), OMC can directly output the mode-locked laser without additional beam splitting devices, which further improves the integrated characteristics of the fiber laser. The pulse duration of the output pulse is 405 fs at the central wavelength of 1560 nm. To the best of our knowledge, this is the first time that optical microfiber coupler based saturable absorber (OMC-SA) for mode-locked fiber laser is demonstrated.
30 citations
TL;DR: In this paper, a Quasi Continuous Wave (QCW) fiber laser was used for cutting 1.3mm-thick carbon fiber reinforced plastic (CFRP) sheets with cutting speed up to 2700mm/min.
Abstract: In the present work, laser cutting of Carbon Fibre Reinforced Plastics (CFRP) is investigated by means of a Quasi Continuous Wave (QCW) fibre laser. The adoption of high pulse power (up to 4.5 kW) and short pulse duration (0.05 ms) may reduce the HAZ formation and allows high cutting speed. For the aforementioned reasons, the improvement of the laser cutting parameters is industrially relevant, especially on materials that are difficult to cut with the standard modes. To assess the influence of the process parameters on kerf geometry and Heat Affected Zone, experimental tests were carried out fixing the average power at 450W and changing the pulse power, the pulse duration, and the overlapping factor. The tests were performed adopting a full factorial design 33 according to the DoE methodology. ANalysis Of VAriance was used to determine which and how the process parameters affect the kerf geometry and HAZ extension. Results show that the laser allows cutting 1.3 mm-thick CFRP sheets with cutting speed up to 2700 mm/min. Also, by an appropriate selection of the process parameters, it is possible to obtain narrow kerfs (smaller than 200 μm) and a limited HAZ (about 0.5 mm). Besides, the correlation between the inner and the outer HAZ was found: the HAZ measured on the bottom surface can be usefully adopted as a damage index to understand the overall thermal damage since it can be correlated to section HAZ. The latter is the reference damage parameter according to UNI EN ISO 12584 standard.
26 citations
TL;DR: In this article, the influence of USP polishing on surface properties of 1.2738 tool steel including surface roughness, surface topography and microstructure of the remelted surface layer was investigated.
25 citations
TL;DR: In this paper, a dissipative soliton generation in a 1.7-μm net-normal dispersion Tm-doped fiber laser by nonlinear polarization rotation technique was reported.
Abstract: We report on the dissipative soliton generation in a 1.7-μm net-normal dispersion Tm-doped fiber laser by nonlinear polarization rotation technique. An intra-cavity bandpass filter was employed to suppress the long-wavelength emission, while the cavity dispersion was compensated by a segment of ultrahigh numerical aperture (UHNA4) fiber. The dissipative soliton with a central wavelength of 1746 nm was obtained, covering a spectral range from 1737 nm to 1754 nm. The de-chirped duration and energy of the dissipative soliton were 370 fs and 0.2 nJ, respectively. In addition, the dynamics of multiple dissipative solitons were also investigated. Through optimization of the cavity dispersion, the 50 nm broadband dissipative soliton with de-chirped pulse duration of 230 fs could be achieved. The development of dissipative soliton seed laser represents the first step in achieving the chirped pulse amplification system at the 1.7-μm wave band, which would find potential applications in fields such as biomedical imaging and material processing.
25 citations
TL;DR: In this paper, a dual-comb thin-disk laser (TDL) oscillator was used for high-resolution spectroscopy and it was shown that the frequency noise of the comb lines of both pulse trains is correlated.
Abstract: Free-running dual-comb systems based on a single laser cavity are an attractive next generation technology for a wide variety of applications. The high average power achievable by dual-comb thin-disk laser (TDL) oscillators make this technology especially attractive for spectroscopy and sensing applications in the molecular fingerprint region enabled by nonlinear frequency conversion. However, the high noise levels of TDL oscillators, e.g., induced by the turbulent water-cooling of the disk, are a severe challenge for spectroscopic applications. In this contribution, we confirm for the first time the suitability of dual-comb TDLs for high-resolution spectroscopy. Based on the novel concept of polarization splitting inside a TDL, our oscillator generates two asynchronous pulse trains of 240-fs pulse duration at 6-W and 8-W average power per pulse train and ∼97-MHz repetition rate at a central wavelength of 1030 nm. In the first detailed noise investigation of such a system, we identify the repetition frequency as the dominant noise term and show that ∼85% of the frequency noise of the comb lines of both pulse trains is correlated (integrated from 200 Hz to 20 kHz). We detect the absorption spectrum of acetylene in free-running operation within a measurement time of 1 millisecond. Being highly suitable for nonlinear frequency conversion, we believe the here presented result is an important step towards simple yet powerful mid-infrared dual-comb systems for high-resolution spectroscopy.
24 citations
TL;DR: In this article, the authors proposed a model to describe the potential change during a galvanostatic current pulse, which includes an initial, relatively long-lasting double layer charging, and analyzed the accuracy of the lithium diffusion coefficient, derived by using the Weppner-Huggins method within a suitably chosen time interval of the pulse.
Abstract: Accurate knowledge of transport properties of Li-insertion materials in application-relevant temperature ranges is of crucial importance for the targeted optimization of Li-ion batteries (LIBs). Galvanostatic intermittent titration technique (GITT) is a widely applied method to determine Li-ion diffusion coefficients of electrode materials. The well-known calculation formulas based on Weppner's and Huggins' approach, imply a square-root time dependence of the potential during a GITT pulse. Charging the electrochemical double layer capacitance at the beginning of a GITT pulse usually takes less than one second. However, at lower temperatures down to -40 °C, the double layer charging time strongly increases due to an increase of the charge transfer resistance. The charging time can become comparable with the pulse duration, impeding the conventional GITT diffusion analysis. We propose a model to describe the potential change during a galvanostatic current pulse, which includes an initial, relatively long-lasting double layer charging, and analyze the accuracy of the lithium diffusion coefficient, derived by using the Weppner-Huggins method within a suitably chosen time interval of the pulse. Effects leading to an inaccurate determination of the diffusion coefficient are discussed and suggestions to improve GITT analyses at low temperature are derived.
TL;DR: The highest energetic efficiency and precision is achieved for pulse durations below the mechanical expansion time of 3-5 ps, where the stress confinement condition is fulfilled.
Abstract: In this work, we investigate single-pulse laser ablation of bulk stainless steel (AISI304), aluminium (Al) and copper (Cu) and its dependence on the pulse duration We measured the reflectivity, ablation thresholds and volumes under the variation of pulse duration and fluence The known drop of efficiency with increasing pulse duration is confirmed for single-pulse ablation in all three metals We attribute the efficiency drop to a weakened photomechanically driven ablation process and a stronger contribution of photothermal phase explosion The highest energetic efficiency and precision is achieved for pulse durations below the mechanical expansion time of 3-5 ps, where the stress confinement condition is fulfilled
TL;DR: In this article, the role of the pulse length on topography and corrosion properties of AZ31 magnesium alloy laser-treated surfaces is presented, and three different laser sources with pulse lengths of 20ns, 800ps and 266fs were employed with a similar experimental setup.
Abstract: Despite having a whole range of applications as in weight-saving structures, biodegradable implants and rechargeable batteries, the usage of magnesium is still hindered by its high tendency to corrosion. Pulsed laser treatments are an interesting approach to modify the surface of magnesium aiming the improvement of the corrosion properties as well as the generation a controlled roughness, which is useful for improving coatings adhesion or tailoring the interactions with living cells at the surface of an implant. In this work, a novel study on the role of the pulse length on topography and corrosion properties of AZ31 magnesium alloy laser-treated surfaces is presented. Three different laser sources with pulse lengths of 20 ns, 800 ps and 266 fs were employed with a similar experimental setup. Surface topography analysis revealed a reduction of the amount of melt generated and an increase in the aspect ratio (depth/width) of the ablated features as the pulse length is reduced. All three treatments significantly improved the corrosion performance of the untreated base material. Thicker and more homogenously distributed recast material for the longer pulses of the nanosecond treatment resulted in a longer-lasting protection (11–12 fold reduction in mass loss rate vs base material) compared to the pico- and femtosecond treatments (4–5 fold reduction).
TL;DR: In this article, the effects of the pulse duration as well as the pulse energy on the melt pool size, solidification morphology and material properties have been investigated with a mode-locked fiber laser system delivering pulses from 500fs up to 800ps at a wavelength of 1030nm.
Abstract: Laser assisted powder bed fusion of Al-40 wt%Si using ultra-short laser pulses is presented. The effects of the pulse duration as well as the pulse energy on the melt pool size, solidification morphology and material properties have been investigated. The experiments have been carried out with a mode-locked fiber laser system delivering pulses from 500 fs up to 800 ps at a wavelength of 1030 nm. Comparative investigations have been performed using a continuous wave Yb-fiber laser operating at 1070 nm. The results show that the melt pool width is reduced at shorter pulse durations and higher repetition rates while maintaining the same average power. Additionally, keyhole melting is achieved in pulsed operation after exceeding the threshold fluence for single pulse ablation. In comparison to continuous wave radiation, powder bed fusion using ultra-short laser pulses leads to a more uniform melt pool shape with refined primary Si and eutectic structure that is accompanied with an improvement of the mechanical properties.
TL;DR: In this article, a fully polarization maintaining (PM) integrated laser features a chirped fiber Bragg grating (CFBG) for dispersion compensation and a fiber integrated compact non-reciprocal phase bias device, which is alignment free.
Abstract: We report a simple and compact design of a dispersion compensated mode-locked Yb:fiber oscillator based on a nonlinear amplifying loop mirror (NALM). The fully polarization maintaining (PM) fiber integrated laser features a chirped fiber Bragg grating (CFBG) for dispersion compensation and a fiber integrated compact non-reciprocal phase bias device, which is alignment-free. The main design parameters were determined by numerically simulating the pulse evolution in the oscillator and by analyzing their impact on the laser performance. Experimentally, we achieved an 88 fs compressed pulse duration with sub-fs timing jitter at 54 MHz repetition rate and 51 mW of output power with 5.5 * 10-5 [20 Hz, 1 MHz] integrated relative intensity noise (RIN). Furthermore, we demonstrate tight phase-locking of the laser's carrier-envelope offset frequency (fceo) to a stable radio frequency (RF) reference and of one frequency comb tooth to a stable optical reference at 291 THz.
TL;DR: In this article, a scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps-20 ps).
Abstract: A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps–20 ps). Maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.
25 Aug 2021
TL;DR: In this article, a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale soft X-ray isolated attosecond pulse (IAP) using high-order harmonics generation (HHG) was presented.
Abstract: Since the first isolated attosecond pulse was demonstrated through high-order harmonics generation (HHG) in 2001, researchers’ interest in the ultrashort time region has expanded. However, one realizes a limitation for related research such as attosecond spectroscopy. The bottleneck is concluded to be the lack of a high-peak-power isolated attosecond pulse source. Therefore, currently, generating an intense attosecond pulse would be one of the highest priority goals. In this paper, we review our recent work of a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale soft-X-ray isolated attosecond pulse (IAP) using HHG. By employing several stabilization methods, we have achieved a stable 50 mJ three-channel optical-waveform synthesizer with a peak power at the multi-TW level. This optical-waveform synthesizer is capable of creating a stable intense optical field for generating an intense continuum harmonic beam thanks to the successful stabilization of all the parameters. Furthermore, the precision control of shot-to-shot reproducible synthesized waveforms is achieved. Through the HHG process employing a loose-focusing geometry, an intense shot-to-shot stable supercontinuum (50–70 eV) is generated in an argon gas cell. This continuum spectrum supports an IAP with a transform-limited duration of 170 as and a submicrojoule pulse energy, which allows the generation of a GW-scale IAP. Another supercontinuum in the soft-X-ray region with higher photon energy of approximately 100–130 eV is also generated in neon gas from the synthesizer. The transform-limited pulse duration is 106 as. Thus, the enhancement of HHG output through optimized waveform synthesis is experimentally proved.
TL;DR: An ultrafast fiber chirped-pulse amplification laser system based on a coherent combination of 16 ytterbium-doped rod-type amplifiers is presented in this article.
Abstract: An ultrafast fiber chirped-pulse amplification laser system based on a coherent combination of 16 ytterbium-doped rod-type amplifiers is presented. It generates 10 mJ pulse energy at 1 kW average power and 120 fs pulse duration. A partially helium-protected, two-staged chirped-pulse amplification grating compressor is implemented to maintain the close to diffraction-limited beam quality by avoiding nonlinear absorption in air.
TL;DR: In this article, it was shown that, by virtue of the low dispersion of the group velocity, the KDP crystal has some advantages over silica: a larger pulse compression coefficient, especially at a small value of the В-integral (B = 5, …, 9), lower absolute values of chirped mirror dispersion, and also a possibility to control the magnitude of nonlinearity and dispersion by changing crystal orientation.
Abstract: The input pulse of the laser PEARL with energy of 18 J and pulse duration of about 60 fs was compressed to 10 fs after passage through a 4-mm-thick KDP crystal and reflection at two chirped mirrors with sum dispersion of −200 fs2. The experiments were performed for the В-integral values from 5 to 19 without visible damage to the optical elements, which indicates that small-scale self-focusing is not a significant issue. It was shown that, by virtue of the low dispersion of the group velocity, the KDP crystal has some advantages over silica: a larger pulse compression coefficient, especially at a small value of the В-integral (B = 5, …, 9), lower absolute values of chirped mirror dispersion, and also a possibility to control the magnitude of nonlinearity and dispersion by changing crystal orientation.
TL;DR: In this article, the impact of dual voltage pulses on the switching performance of three-terminal magnetic tunnel junctions was investigated and it was shown that the concurrent action of an SOT pulse and an MTJ bias pulse allows for reducing the critical switching energy below the level typical of spin-transfer-torque while preserving the ability to switch the MTJ on the subnanosecond time scale.
Abstract: We use three-terminal magnetic tunnel junctions (MTJs) designed for field-free switching by spin-orbit torques (SOTs) to systematically study the impact of dual voltage pulses on the switching performance. We show that the concurrent action of an SOT pulse and an MTJ bias pulse allows for reducing the critical switching energy below the level typical of spin-transfer-torque while preserving the ability to switch the MTJ on the subnanosecond time scale. By performing dc and real-time electrical measurements, we discriminate and quantify three effects arising from the MTJ bias: the voltage-controlled change of the
perpendicular magnetic anisotropy, current-induced heating, and the spin-transfer torque. The experimental results are supported by micromagnetic modeling. We observe that, depending on the pulse duration and the MTJ diameter, different effects take a lead in assisting the SOTs in the magnetization-reversal process. Finally, we present a compact model that allows for evaluating the impact of each effect due to the MTJ bias on the critical switching parameters. Our results provide input to optimize the switching of three-terminal devices as a function of time, size, and material parameters
TL;DR: In this article, the authors studied experimentally thermal single-pulse switching in Gd-Fe-Co alloys, for a wide range of system parameters, such as composition, laser power, and pulse duration.
Abstract: Many questions are still open regarding the physical mechanisms behind the magnetic switching in Gd-Fe-Co alloys by single optical pulses. Phenomenological models suggest a femtosecond scale exchange relaxation between sublattice magnetization as the driving mechanism for switching. The recent observation of thermally induced switching in Gd-Fe-Co by using both several picosecond optical laser pulse as well as electric current pulses has questioned this previous understanding. This has raised the question of whether or not the same switching mechanics are acting at the femtosecond and picosecond scales. In this work, we aim at filling this gap in the understanding of the switching mechanisms behind thermal single-pulse switching. To that end, we have studied experimentally thermal single-pulse switching in Gd-Fe-Co alloys, for a wide range of system parameters, such as composition, laser power, and pulse duration. We provide a quantitative description of the switching dynamics using atomistic spin dynamics methods with excellent agreement between the model and our experiments across a wide range of parameters and timescales, ranging from femtoseconds to picoseconds. Furthermore, we find distinct element-specific damping parameters as a key ingredient for switching with long picosecond pulses and argue that switching with pulse durations as long as 15 ps is possible due to a low damping constant of Gd. Our findings can be easily extended to speed up dynamics in other contexts where ferrimagnetic Gd-Fe-Co alloys have been already demonstrated to show fast and energy-efficient processes, e.g., domain-wall motion in a track and spin-orbit torque switching in spintronics devices.
TL;DR: In this paper, the authors reported experimental observation of multimode Q-switching and spatio-temporal mode locking in a multimode fiber laser and found that weak spatial filtering is essential to obtain stable Qswitched pulses.
Abstract: We report experimental observation of multimode Q-switching and spatiotemporal mode locking in a multimode fiber laser A typical steady Q-switching state is achieved with a 188 μs pulse duration, a 7014 kHz repetition rate, and a 2158 mW output power, corresponding to the single pulse energy of 308 μJ We find weak spatial filtering is essential to obtain stable Q-switched pulses, in contrast to the relatively stronger spatial filtering for spatiotemporal mode locking Furthermore, a reversible transition process, as well as a critical bistable state, between multimode Q-switching and spatiotemporal mode locking, is achieved with specific spatial coupling and waveplates sets We believe the results will not only contribute to understanding the complicated nonlinear dynamics in multimode, fiber-based platforms, but also benefit the development of promising high-pulse energy lasers
TL;DR: In this article, the authors demonstrate the generation of few-femtosecond extreme-ultraviolet free-electron laser pulses, whose duration is measured by autocorrelation.
Abstract: Free-electron lasers producing ultrashort pulses with high peak power promise to extend ultrafast non-linear spectroscopic techniques into the extreme-ultraviolet–X-ray regime. Key aspects are the synchronization between pump and probe, and the control of the pulse properties (duration, intensity and coherence). Externally seeded free-electron lasers produce coherent pulses that can be synchronized with femtosecond accuracy. An important goal is to shorten the pulse duration, but the simple approach of shortening the seed is not sufficient because of the finite-gain bandwidth of the conversion process. An alternative is the amplification of a soliton in a multistage, superradiant cascade: here, we demonstrate the generation of few-femtosecond extreme-ultraviolet pulses, whose duration we measure by autocorrelation. We achieve pulses four times shorter, and with a higher peak power, than in the standard high-gain harmonic generation mode and we prove that the pulse duration matches the Fourier transform limit of the spectral intensity distribution. By amplifying a soliton in a multistage cascade, few-femtosecond extreme-ultraviolet free-electron laser pulses are achieved.
TL;DR: In this article, ultrathin 2D tellurene nanosheets were harvested from bulk tellurium crystals by liquid-phase exfoliation method, and they were characterized by two-arm detection technology.
Abstract: Tellurene is a new 2D nonlayered material, which have obvious structural differences in both horizontal and vertical directions compared to layered materials. However, photonic devices related to its nonlinear optical characteristics are currently less studied. Herein, ultrathin 2D tellurene nanosheets were harvested from bulk tellurium crystals by liquid-phase exfoliation method. The low saturable intensity (1.06 MW/cm2) and the high modulation depth (35.64%) of tellurene nanosheets were characterized by two-arm detection technology. To the best of our knowledge, this is the first attempt to utilize tellurene-microfiber as a saturable absorber, and achieved a picosecond passive mode-locked erbium-doped fiber laser. Stable picosecond pulses were generated at 1558.8 nm with a pulse duration of 1.03 ps. This work highlights the promise of 2D tellurene in short pulse lasers and will promote the applications of 2D nonlayered materials in ultrafast photonics.
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TL;DR: In this paper, a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale isolated attosecond pulse (IAP) using high-order harmonics generation (HHG) is presented.
Abstract: The bottleneck for an attosecond science experiment is concluded to be the lack of a high-peak-power isolated attosecond pulse source. Therefore, currently, generating an intense attosecond pulse would be one of the highest priority goals. In this paper, we review a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale soft-x-ray isolated attosecond pulse (IAP) using high-order harmonics generation (HHG). Simultaneously, using several stabilization methods, namely, the low-repetition-rate laser carrier-envelope phase stabilization, Mach-Zehnder interferometer, balanced optical cross-correlator, and beam-pointing stabilizer, we demonstrate a stable 50-mJ three-channel optical-waveform synthesizer with a peak power at the multi-TW level. This optical-waveform synthesizer is capable of creating a stable intense optical field for generating an intense continuum harmonic beam thanks to the successful stabilization of all the parameters. Furthermore, the precision control of shot-to-shot reproducible synthesized waveforms is achieved. Through the HHG process employing a loose-focusing geometry, an intense shot-to-shot stable supercontinuum (50-70 eV) is generated in an argon gas cell. This continuum spectrum supports an IAP with a transform-limited duration of 170 as and a submicrojoule pulse energy, which allows the generation of a GW-scale IAP. Another supercontinuum in the soft-x-ray region with higher photon energy of approximately 100-130 eV is also generated in neon gas from the synthesizer. The transform-limited pulse duration is 106 as. According to this work, the enhancement of HHG output through optimized waveform synthesis is experimentally proved. The high-energy multicycle pulse with 10-Hz repetition rate is proved to have the same controllability for optimized waveform synthesis for HHG as few- or subcycle pulses from a 1-kHz laser.
TL;DR: In this paper, the authors reported a high-power pure Kerr-lens mode-locked Yb:CALYO laser based on the dual-confocal cavity delivering sub-100-fs pulses.
Abstract: We reported a high-power pure Kerr-lens mode-locked Yb:CALYO laser based on the dual-confocal cavity delivering sub-100-fs pulses. The output pulses at 81 MHz have an average power of 10.4 W and the pulse duration of 98 fs, corresponding to the peak power of 1.14 MW. This is, to the best of our knowledge, the highest average power ever reported for a Kerr-lens mode-locked Yb-bulk oscillator. Analysis of the dual-confocal cavity was also conducted, which indicates a way to achieve higher average power. We believe the result described in this Letter may pave a way to develop Kerr-lens mode-locked bulk lasers with much higher average power.
TL;DR: In this paper, the authors investigate the limits of pulse duration in a Kerr-lens mode-locked Yb:YAG thin-disk laser (TDL) oscillator.
Abstract: We experimentally investigate the limits of pulse duration in a Kerr-lens mode-locked Yb:YAG thin-disk laser (TDL) oscillator. Thanks to its excellent mechanical and optical properties, Yb:YAG is one of the most used gain materials for continuous-wave and pulsed TDLs. In mode-locked operation, its 8-nm wide gain bandwidth only directly supports pulses with a minimum duration of approximately 140 fs. For achieving shorter pulses, a Kerr-lens mode-locked TDL oscillator can be operated in the strongly self-phase modulation (SPM) broadened regime. Here, the spectral bandwidth of the oscillating pulse exceeds the available gain bandwidth by generating additional frequencies via SPM inside the Kerr medium. In this work, we study and compare different laser configurations in the strongly SPM-broadened regime. Starting with a configuration providing 84-fs pulses at 69 W average power at 17 MHz repetition rate, we reduce the pulse duration by optimizing various mode-locking parameters. One crucial parameter is the dispersion control which was provided by in-house-developed dispersive mirrors produced by ion-beam sputtering (IBS). We discuss trade-offs in average power, pulse duration, efficiency, and intra-cavity peak power. For the configuration operating at the highest SPM-broadening, we achieve a minimum pulse duration of 27 fs, which represents the shortest pulse duration directly generated by any ultrafast TDL oscillator. The corresponding full width at half maximum (FWHM) spectral bandwidth exceeds more than five times the FWHM gain bandwidth. The average output power of 3.3 W is moderate for ultrafast TDL oscillators, but higher than other Yb-based laser oscillators operating at this pulse duration. Additionally, the corresponding intra-cavity peak power of 0.8 GW is highly attractive for implementing intra-cavity extreme nonlinear optical interactions such as high harmonic generation.
TL;DR: In this paper, the room-temperature switching of 1T-TaS2 thin-film charge-density-wave devices, using nanosecond-duration electrical pulsing to construct their time-resolved current-voltage characteristics was investigated.
Abstract: We report on the room-temperature switching of 1T-TaS2 thin-film charge-density-wave devices, using nanosecond-duration electrical pulsing to construct their time-resolved current–voltage characteristics. The switching action is based upon the nearly commensurate to incommensurate charge-density-wave phase transition in this material, which has a characteristic temperature of 350 K at thermal equilibrium. For sufficiently short pulses, with rise times in the nanosecond range, self-heating of the devices is suppressed, and their current–voltage characteristics are weakly nonlinear and free of hysteresis. This changes as the pulse duration is increased to ∼200 ns, where the current develops pronounced hysteresis that evolves nonmonotonically with the pulse duration. By combining the results of our experiments with a numerical analysis of transient heat diffusion in these devices, we clearly reveal the thermal origins of their switching. In spite of this thermal character, our modeling suggests that suitable reduction of the size of these devices should allow their operation at GHz frequencies.
TL;DR: This is the first time of switchable modes for laser pulse generation are achieved by using this PdSe2 SA as a saturable absorber (SA) in an Erbium-doped fiber laser (EDFL) system, and will encourage the research community to carry out further studies with this P dSe2 material in the future.
Abstract: In-plane anisotropic two-dimensional (2D) materials have gained considerable interest in the field of research, due to having the potential of being used in different device applications. Recently, among these 2D materials, group 10 transition metal dichalcogenides (TMDs) pentagonal Palladium diselenide (PdSe2) is utilized in various sections of researches like nanoelectronics, thermoelectric, spintronics, optoelectronics, and ultrafast photonics, owing to its high air stability and broad absorption spectrum properties. In this paper, it is demonstrated that by utilizing this novel 2D layered PdSe2 material as a saturable absorber (SA) in an EDF laser system, it is possible to obtain switchable laser pulse generation modes. At first, the Q-switching operation mode is attained at a threshold pump power of 56.8 mW at 1564 nm, where the modulation range of pulse duration and repetition rate is 18.5 μs-2.0 μs and 16.4 kHz-57.0 kHz, respectively. Afterward, the laser pulse generation mode is switched to the mode-locked state at a pump power of 63.1 mW (threshold value) by changing the polarization condition inside the laser cavity, and this phenomenon persists until the maximum pump power of 230.4 mW. For this mode-locking operation, the achieved pulse duration is 766 fs, corresponding to the central wavelength and 3 dB bandwidth of 1566 nm and 4.16 nm, respectively. Finally, it is illustrated that PdSe2 exhibits a modulation depth of 7.01%, which substantiates the high nonlinearity of the material. To the best of the authors' knowledge, this is the first time of switchable modes for laser pulse generation are achieved by using this PdSe2 SA. Therefore, this work will encourage the research community to carry out further studies with this PdSe2 material in the future.
TL;DR: In this article, a combined gain media Kerr-lens mode-locked laser based on a Tm:Lu2O3 ceramic and a single crystal was presented with an average output power of 42 mW at a wavelength of 2.1 μm and a repetition rate of 93.3 MHz.
Abstract: We present a combined gain media Kerr-lens mode-locked laser based on a Tm:Lu2O3 ceramic and a Tm:Sc2O3 single crystal. Pulses as short as 41 fs, corresponding to less than 6 optical cycles, were obtained with an average output power of 42 mW at a wavelength of 2.1 μm and a repetition rate of 93.3 MHz. Furthermore, a maximum average power of 316 mW with a pulse duration of 73 fs was achieved.