Largest Pulse Energy Research Articles

Further Development of a High Pulse-Energy LED at 4 kHz for Volumetric Particle Tracking Velocimetry and a Demonstration Using 32 Such LED Units

In 2022, we reported at the 20th Lisbon symposium on the development of 460 nm LED specifically designed for illumination in volumetric Particle Tracking Velocimetry (PTV). At that time, our pulsed LED unit emitted light with a 6 ◦ divergence beam and a top-hat power cross section, producing 20 µ s pulses at a 4 kHz repetition rate and a 0.15 mJ pulse energy. Since then, we have been improving the efficiency of this LED. Currently, our LED unit emits a beam with similar specifications but with a pulse energy up to 0.65 mJ , which is 4.3 times more than the previous LED unit. We improved the efficiency of the electrical driver by further decreasing the footprint of the SMD circuitry and by using higher quality electronic components. Additionally, we replaced the aluminium pin fin heat sink with a copper pin fin heat sink and we characterized the thermal dissipation. Using SolidWorks, we integrated the electric driver, the copper heat sink and the collimating optics into a compact mechanical casing. These improvements resulted in an LED unit with greater overall efficiency, a larger pulse energy and a volume footprint that is half the the size of the previous design. Furthermore, we constructed four batteries of these LEDs, with each battery containing eight LED units. Here, we report on our improvements to the LED unit and our considerations in its development. Additionally, we describe preliminary results of a 3D-PTV experiment with Helium Filled Soap Bubbles (HFSB), which were illuminated by the four LED batteries.

Secondary cavitation bubble dynamics during laser-induced bubble formation in a small container.

We investigated secondary cavitation bubble dynamics during laser-induced bubble formation in a small container with a partially confined free surface and elastic thin walls. We employed high-speed photography to record the dynamics of sub-mm-sized laser-induced bubbles and small secondary bubble clouds. Simultaneous light scattering and acoustic measurements were used to detect the oscillation times of laser-induced bubbles. We observed that the appearance of secondary bubbles coincides with a prolonged collapse phase and with re-oscillations of the laser-induced bubble. We observed an asymmetric distribution of secondary bubbles with a preference for the upstream side of the focus, an absence of secondary bubbles in the immediate vicinity of the laser focus, and a migration of laser-induced bubble toward secondary bubbles at large pulse energies. We found that secondary bubbles are created through heating of impurities to form initial nanobubble nuclei, which are further expanded by rarefaction waves. The rarefaction waves originate from the vibration of the elastic thin walls, which are excited either directly by laser-induced bubble or by bubble-excited liquid-mass oscillations. The oscillation period of thin walls and liquid-mass were Twall = 116 µs and Tlm ≈ 160 µs, respectively. While the amplitude of the wall vibrations increases monotonically with the size of laser-induced bubbles, the amplitude of liquid-mass oscillation undulates with increasing bubble size. This can be attributed to a phase shift between the laser-induced bubble oscillation and the liquid-mass oscillator. Mutual interactions between the laser-induced bubble and secondary bubbles reveal a fast-changing pressure gradient in the liquid. Our study provides a better understanding of laser-induced bubble dynamics in a partially confined environment, which is of practical importance for microfluidics and intraluminal laser surgery.

Generation of dual large energy pulses in Er3+-doped fiber lasers based on ZrTe2 saturable absorber via polarization manipulation

We report on the generation of dual large energy pulses in a passively mode-locked Er-doped fiber laser based on ZrTe2 as saturable absorber. When the pump power is 100.4 mW, dissipative soliton resonance mode-locked operation with an output power of 9.1 mW is generated. With the increase of pump power, its average output power increased from 9.1 to 52 mW, and its corresponding fundamental repetition rate and maximum single-pulse energy are 1.22 MHz and 42.6 nJ, respectively. By properly adjusting the polarization controller, stable large energy mode-locked pulse is obtained at the same pump power. At the maximum pump power of 617.5 mW, the maximum average output power, and single-pulse energy are 55.8 mW and 45.7 nJ, respectively. Our experimental results proved that ZrTe2 has good performance in obtaining large energy pulse operations, which promotes the development of ZrTe2 nanosheets as an effective saturable absorber in the future.

Investigation of high beam quality methane Raman laser

Although lasers generated by stimulated Raman scattering (SRS) were reported to have better beam quality in comparison with pump laser; once pump laser intensity exceeded the threshold of laser-induced-breakdown (LIB), Raman laser beam quality was deteriorated dramatically. In this study, the backward SRS (BSRS) process of methane pumped by 532 nm laser was applied to produce high beam quality seed Raman laser beam, and stimulated Raman amplification with configuration of collimated seed laser and pump laser counter-propagation (BSRA) was used to increase the pulse energy of Raman laser. With a seed Raman laser of 51.4 mJ, ∼127.2 mJ Raman laser could be produced by BSRA process. Raman laser beam quality achieved Mx2 = 2.52 and My2 = 2.40, which were better than pump laser. The technique could be applied repeatedly; pulse energy and peak power of Raman laser could be further improved. This work provides of possible method to achieve high peak power (large pulse energy) Raman lasers with excellent beam quality.

Spatiotemporal dissipative soliton resonances in multimode fiber lasers

Spatiotemporal mode-locking in multimode fiber lasers is intriguing for the complex nonlinear dynamics and the increase of theoretical energy limit. In this paper, we enrich spatiotemporal mode-locking with dissipative soliton resonances, a kind of solitons which is characterized by large pulse energy in single mode fiber lasers, and demonstrate their emergence in multimode fiber lasers by employing the reverse saturable absorption effect from real saturable absorbers. The spatiotemporal dissipative soliton resonances are expected to raise the energy limit further by the locking of dissipative soliton resonances in different transverse modes, whose energy is about twice the maximum single-mode energy in our results. Moreover, properties of spatiotemporal dissipative soliton resonances are investigated by tailoring parameters of the multimode fiber laser, where evolution and transformation of the proposed pulses including shaping and broadening are disclosed. The spatiotemporal dissipative soliton resonances in multimode fiber lasers may open up new avenue for high-power and spatiotemporally engineered coherent light fields in laser dynamics and nonlinear optics.

350-2500 nm supercontinuum white laser enabled by synergic high-harmonic generation and self-phase modulation

Supercontinuum white laser with large bandwidth and high pulse energy would offer incredible versatility and opportunities for basic science and high technology applications. Here, we report the generation of high-efficiency 2.8-octave-spanning ultraviolet-visible-infrared (UV-Vis-IR) (with 350-2500 nm 25 dB bandwidth) supercontinuum white laser from a single chirped periodically poled lithium niobate (CPPLN) nonlinear crystal via synergic high-harmonic generation (HHG) and self-phase modulation (SPM). The CPPLN exhibits multiple controllable reciprocal-lattice bands to simultaneously support the quasi-phase matching (QPM) for simultaneous broadband 2nd-10th HHG via cascaded three-wave mixing against a broadband fundamental pump laser. Due to the efficient second-order nonlinearity (2nd-NL) up-conversion and significant 3rd-NL SPM effect both in the pump and HHG laser pulses, 350-2500 nm supercontinuum white laser is eventually obtained with 17 μJ per pulse under pump of 45 μJ per pulse mid-infrared femtosecond laser corresponding to an average high conversion efficiency of 37%. Our work opens up a route towards creating UV-Vis-IR all-spectrum white lasers through engineering the synergic action of HHG and SPM effects in nonlinear crystals for applications in ultrafast spectroscopy, single-shot remote sensing, biological imaging, and so on.

Multimode dissipative-soliton-resonance pulses in a Yb-doped fiber laser

Experimental observation of mode-locked dissipative-soliton-resonance (DSR) pulses, including single-mode DSR pulses and multimode DSR pulses, in a Yb-doped fiber laser is reported. DSR pulses in single-mode state and multi-mode state can exist at the same time and can be output stably. The multi-mode DSR pulses exhibit same linearly broadening characteristics and bell-shaped spectral shape as single-mode DSR pulses. The results would be beneficial for expanding the knowledge of nonlinear dynamics to multimode fiber lasers and provide new insights for DSR pulse output with a fully multimode structure to get larger pulse energy.

Efficient Raman pulse fiber laser pumped by a dissipative soliton resonance pulse near 2 µm.

A high-efficiency Raman conversion from 1.987 µm to 2.177 µm is demonstrated experimentally in 45 m GeO2-doped silica fiber, adopting a dissipative soliton resonance (DSR) rectangular pulse as the pump. Over the entire spectral distribution, the spectral purity of the first-order Raman pulse is up to 96.8%, suggesting a nearly complete pump depletion before the onset of cascaded Raman shifts. The corresponding pump-to-Raman conversion efficiency of 67.4% is the highest up to date in this spectral region. Meanwhile, a large Raman pulse energy of 1.03 µJ was obtained at the repetition rate near MHz level, corresponding to 0.893 W average power. In the total output, the Raman-dominated spike has a Full Width Half Maximum (FWHM) of 1.18 ns far narrower than DSR's pulse duration of 10.25 ns. The results indicate that DSR is a promising candidate for developing efficient Raman nanosecond pulse fiber laser in mid-infrared (MIR) region.

Efficient continuous-wave and passively Q-switched operation of an Yb:YPO4 microchip laser

We report on the performance of an Yb:YPO4 microchip laser that could be efficiently operated in both continuous-wave (CW) and passive Q-switching mode, with a 2D WS2 acting as the saturable absorber. With 6.30 W of pump power absorbed, a CW output power of 3.81 W was generated, leading to an optical conversion efficiency of 60.5%, while the slope efficiency amounting to 71%. In passively Q-switched operation, a pulsed output power of 1.67 W was produced at 660 kHz of repetition frequency, with a slope efficiency of 52%; the largest pulse energy, minimum pulse width, and highest peak power, which were achievable with different output mirrors, were respectively 2.52 μJ, 67 ns, and 31.7 W. The results demonstrated in this work represent a significant improvement in CW and passive Q-switching performance of Yb:YPO4 microchip lasers.

Combined effects of polarization and secondary ablation on precision machining of microgrooves by laser-induced microjet-assisted ablation.

In this study, we propose a polarization-modulated laser-induced microjet-assisted ablation method for machining microgrooves with controllable cross-sections. A novel mathematical model is presented to accurately predict the cross-sections by considering the combined effects of polarization and secondary ablation. The simulation and experimental results reveal that the effect of secondary ablation becomes more obvious when steeper grooves are ablated with higher repetition frequency and larger pulse energy. The polarization effect and secondary ablation of target material result in asymmetric ablation of linearly polarized laser beam. To avoid the asymmetric ablation, we present the cylindrical vector beams to achieve scanning-path independent laser micromachining with various cross-sections. Based on the prediction model, the cross-sectional characteristics are precisely designed and fabricated by tuning laser processing parameters. Our work provides a reliable approach for the controllable fabrication of microgrooves at the scale of tens of micrometers.

Energy scaling beyond the gas ionization threshold with divided-pulse nonlinear compression.

We demonstrate how pulse energy in hollow-core fiber can be scaled beyond gas-ionization limitations using divided-pulse nonlinear compression. With one pulse, ionization limits our fiber's output pulse energy to 2.7 mJ at an input of 4 mJ. By dividing the pulse to four low-energy pulses before the fiber, we eliminated the ionization and scaled the pulse energy 2.5× to 6.6 mJ at an input energy of 10 mJ. Larger energy scaling is possible, as our maximum pulse energy has not reached the new gas ionization threshold. Our results motivate applying the method to state-of-the-art systems for large pulse energy scaling without prohibitive system size increases.

Hydrazone organics with third-order nonlinear optical effect for femtosecond pulse generation and control in the L-band

Dissipative solitons are generalized solitons with much larger pulse energy and width than conventional solitons, and the pulse characteristics will be changed dramatically during transmission. Nonlinear photonic absorption device in nonlinear optical resonator can provide saturable absorption effect to generate ultrashort pulses. However, most of the nonlinear photonics devices are based on inorganic materials such as two-dimensional materials with complex production process, and there are relatively few such researches on organics. In this paper, nonlinear photonics absorption device based on hydrazone organics with high molecular polarizability and significant third-order optical nonlinearity generate ultrashort pulses. The dissipative soliton pulses are obtained by controlling the dispersion, and the pulses are compressed to the near-transformation limit of 408 fs with a compression ratio of 44.6. More importantly, the extra-cavity transport properties of dissipative solitons are discussed. Dissipative noise-like soliton pulses are discovered after additional anomalous dispersion fiber, further demonstrating that the physical laws and optical properties of dissipative solitons are completely different from those of traditional optical pulses. We expect that these experimental advances can provide some experimental basis and support for the propagation of dissipative solitons.

High Power and Large-Energy Pulse Generation in an Erbium-Doped Fiber Laser by a Ferromagnetic Insulator-Cr2Si2Te6 Saturable Absorber.

Large-energy mode-locked fiber lasers are extensively studied due to their indispensable use in various fields and applications. Recently, ferromagnetic insulators have attracted tremendous research interest in ultra-fast photonics because of their unique ferromagnetic properties and typical layered structure. In our work, Cr2Si2Te6 nanosheets are prepared and utilized as a saturable absorber (SA) in a large-energy mode-locked erbium-doped fiber (EDF) laser. With a total cavity length of 240 m, a stable mode-locked operation characterized by maximum pulse energy as high as 244.76 nJ with a repetition rate of 847.64 kHz is achieved. When the cavity length is extended to 390 m, the output maximum pulse energy is successfully scaled up to 325.50 nJ. To our knowledge, this is the largest pulse energy and highest output power level to be achieved in mode-locked fiber lasers by two-dimensional (2D) material saturable absorbers (SAs) so far. This work not only makes a forward step to the investigation of the generation of large-energy pulses in mode-locked fiber lasers but also fully proves that the ferromagnetic insulator-Cr2Si2Te6 possesses an excellent nonlinear absorption property, antioxidant capacity in ambient conditions, as well as outstanding thermal stability, which enriches our insight into 2D materials.

Pulsed fiber laser with MoyV1-ySe2-based saturable absorber

Exploring a new nonlinear material is important for ultrafast optics. Ternary transition metal chalcogenides are coming into view as a prospective kind of optoelectronic materials because of the unique physical and chemical properties. Herein, the MoyV1-ySe2 nanosheets were made by using the liquid phase exfoliation method, and their application in Q-switched Er-doped fiber (EDF) laser was studied. It was found that MoyV1-ySe2 materials has the remarkable nonlinear saturable absorption properties. By incorporating the MoyV1-ySe2-microfiber SA into an EDF cavity, the Q-switched operation was obtained. The narrowest pulse duration and largest pulse energy were 1.8 μs and 121.9 nJ. A large average output power of 26.84 mW was reached at pump power of 900 mW. The large signal-to-noise ratio of 75 dB verifies the superb stable property of Q-switched state. These results confirm that as a Q-switcher, MoyV1-ySe2-microfiber possesses a fine performance on good stability and high power pulsed fiber lasers.

Intense Two-Octave Ultraviolet-Visible-Infrared Supercontinuum Laser via High-Efficiency One-Octave Second-Harmonic Generation.

Intense ultrabroadband laser source of high pulse energy has attracted more and more attention in physics, chemistry, biology, material science, and other disciplines. We report design and realization of a chirped periodically poled lithium niobate nonlinear crystal that supports ultrabroadband second-harmonic generation covering 350-850 nm by implementing simultaneously up to 12 orders of quasiphase matching against ultrabroadband pump laser covering 700-1700 nm with an average high conversion efficiency of about 25.8%. We obtain a flat supercontinuum spectrum with a 10 dB bandwidth covering more than one octave (about 375-1200 nm) and 20 dB bandwidth covering more than two octaves (about 350-1500 nm) in the ultraviolet-visible-infrared regime and having intense energy as 0.17 mJ per pulse through synergic action of second-order and third-order nonlinearity under pump of 0.48 mJ per pulse Ti:sapphire femtosecond laser. This scheme would provide a promising method for the construction of supercontinuum laser source with extremely broad bandwidth, large pulse energy, and high peak power for a variety of basic science and high technology applications.

Large-energy mode-locked Er-doped fiber laser based Cr2Si2Te6 as a modulator

Ultrafast photonic devices based on two-dimensional (2D) materials attract the attentions of researchers. In order to expand the range and diversity of ultrafast lasers and advanced photonics, it is necessary to explore new 2D materials with excellent nonlinear absorption properties. Ferromagnetic insulators (FIs) have the suitable band structure and they can be stripped into single layer structure easily, however, few related works have been reported. In this work, Cr2Si2Te6 (CST) thin film modulator was prepared through the method of liquid-phase exfoliation (LPE) and investigated its nonlinear optical properties and application in obtaining large energy mode-locking pulse output. The modulation depth and saturable intensity of the CST were 4.40% and 12.51 MW/cm2, respectively. Transferring it into the ring cavity, the all-fiber laser can generate a large energy pulse with a center wavelength of 1558.53 nm and a repetition frequency of 1.61 MHz. The energy of single pulse was 53.03 nJ. The maximum average output power was 85.54 mW under the pump power of 1659 mW. To our knowledge, the energy of single pulse is the highest among the reported all-fiber lasers with FIs saturable absorbers (SAs). Our experimental results proved that CST-SA has excellent modulation properties, which provides a basis for future research.

Experimental study of atmospheric pressure single-pulse nanosecond discharge in pin-to-pin configuration

We present an experimental study of nanosecond high-voltage discharges in a pin-to-pin electrode configuration at atmospheric conditions operating in a single-pulse mode (no memory effects). Discharge parameters were measured using microwave Rayleigh scattering, laser Rayleigh scattering, optical emission spectroscopy enhanced with a nanosecond probing pulse, and fast photography. Spark and corona discharge regimes were studied for electrode gap sizes of 2–10 mm and a discharge pulse duration of 90 ns. The spark regime was observed for gaps <6 mm using discharge pulse energies of 0.6–1 mJ per mm of the gap length. Higher electron number densities, total electron number per gap length, discharge currents, and gas temperatures were observed for smaller electrode gaps and larger pulse energies, reaching maximal values of about 7.5 × 1015 cm−3, 3.5 × 1011 electrons/mm, 22 A, and 4000 K (at 10 μs after the discharge), respectively, for a 2 mm gap and 1 mJ/mm discharge pulse energy. An initial breakdown was followed by a secondary breakdown occurring about 30–70 ns later and was associated with ignition of a cathode spot and transition to a cathodic arc. A majority of the discharge pulse energy was deposited into the gas before the secondary breakdown (85%–89%). The electron number density after the ns-discharge pulse decayed with a characteristic time scale of 150 ns governed by dissociative recombination and electron attachment to oxygen mechanisms. For the corona regime, substantially lower pulse energies (∼0.1 mJ/mm), peak conduction current (1–2 A), electron numbers (3–5 × 1010 electrons per mm), and gas temperatures (360 K) were observed.

White Laser Realized via Synergic Second- and Third-Order Nonlinearities.

White laser with balanced performance of broad bandwidth, high average and peak power, large pulse energy, high spatial and temporal coherence, controllable spectrum profile, and overall chroma are highly desirable in various fields of modern science. Here, for the first time, we report an innovative scheme of harnessing the synergic action of both the second-order nonlinearity (2nd-NL) and the third-order nonlinearity (3rd-NL) in a single chirped periodically poled lithium niobate (CPPLN) nonlinear photonic crystal driven by a high-peak-power near-infrared (NIR) (central wavelength~1400 nm, energy~100 μJ per pulse) femtosecond pump laser to produce visible to near infrared (vis-NIR, 400-900 nm) supercontinuum white laser. The CPPLN involves a series of reciprocal-lattice bands that can be exploited to support quasiphase matching for simultaneous broadband second- and third-harmonic generations (SHG and THG) with considerable conversion efficiency. Due to the remarkable 3rd-NL which is due to the high energy density of the pump, SHG and THG laser pulses will induce significant spectral broadening in them and eventually generate bright vis-NIR white laser with high conversion efficiency up to 30%. Moreover, the spectral profile and overall chroma of output white laser can be widely modulated by adjusting the pump laser intensity, wavelength, and polarization. Our work indicates that one can deeply engineer the synergic and collective action of 2nd-NL and 3rd-NL in nonlinear crystals to accomplish high peak power, ultrabroadband vis-NIR white laser and hopefully realize the even greater but much more challenging dream of ultraviolet-visible-infrared full-spectrum laser.

Influence of Electrical Discharge Machining on Thermal Barrier Coating in a Two-Step Drilling of Nickel-Based Superalloy

The influence of electrical discharge machining (EDM) on thermal barrier coating (TBC) in a two-step drilling of nickel-based superalloy has been studied. The TBC was coated on the superalloy using electron beam physical vapor deposition (EB-PVD). Simulation result shows that the temperature at TBC/metal interface increases with pulse-on time and peak current. The temperature will exceed the melting point of the coating material when using relatively large pulse energy. Experimental result reveals that large pulse-on time or high peak current caused defect such as cracking at coating sidewall and delamination at the TBC/metal interface. For EDM drilling holes with inclined angle, the leading edge had worse condition of debris evacuation, and consequently caused secondary discharge which resulted in melt and spalling of the coating material. In addition, relatively larger pulse-on time and greater peak current might result in greater thermal stress gradient at the interface and subsequently lead to cracking or spalling at the coating layer. Therefore, process conditions of short pulse-on time, longer pulse-off time, and small peak current are recommended for EDM drilling of the EB-PVD coated nickel-based superalloy.

CVD-Bi2Te3 as a saturable absorber for various solitons in a mode-locked Er-doped fiber laser

In this work, we report about high energy and various solitons' operation by using high-efficiency topological insulator bismuth telluride (Bi2Te3) nanofilms as broadband saturable absorbers in the passively mode-locked Er-doped fiber laser. The Bi2Te3 film was successfully synthesized by chemical vapor deposition (CVD). Excellent characteristics of the dark-bright pulse pairs, bright pulses, and multiharmonics have been investigated experimentally by adjusting the polarization state. At the same time, the maximum average output power was 40.18 mW, and the single-pulse energy was 20.91 nJ. As we all know, it is the various solitons of the first generation with large pulse energy in an Er-doped fiber laser with Bi2Te3 as saturable absorber. The experimental results show that CVD Bi2Te3 can be used as an excellent candidate in mode-locked fiber lasers.