Largest Pulse Energy Research Articles

Passively Q-switched Yb:KLu(WO4)2 laser with 2D MoTe2 acting as saturable absorber

We report on an efficient Yb:KLu(WO4)2 laser that could be passively Q-switched with 2D MoTe2 serving as saturable absorber. Stable repetitively Q-switched operation was realized with the resonator output coupling changed over a wide range from 10 to 90%, producing a maximum output power of 2.06 W at a repetition rate of 2.18 MHz with an optical-to-optical efficiency of 35%, while the slope efficiency was 56%. The largest pulse energy, shortest duration, and highest peak power achieved were 1.3 µJ, 36 ns, and 36.1 W, respectively.

Identification and Representation of Multi-Pulse Near-Fault Strong Ground Motion Using Adaptive Wavelet Transform

In order to identify the horizontal seismic motion owning the largest pulse energy, and represent the dominant pulse-like component embedded in this seismic motion, we used the adaptive wavelet transform algorithm in this paper. Fifteen candidate mother wavelets were evaluated to select the optimum wavelet based on the similarities between the candidate mother wavelet and the target seismic motion, evaluated by the minimum cross variance. This adaptive choosing algorithm for the optimum mother wavelet was invoked before identifying both the horizontal direction owning the largest pulse energy and every dominant pulse, which provides the optimum mother wavelet for the continuous wavelet transform. Each dominant pulse can be represented by its adaptively selected optimum mother wavelet. The results indicate that the identified multi-pulse component fits well with the seismic motion. In most cases, mother wavelets in one multi-pulse seismic motion were different from each other. For the Chi-Chi event (1999-Sep-20 17:47:16 UTC, Mw = 7.6), 62.26% of the qualified pulse-like earthquake motions lay in the horizontal direction ranging from ±15° to ±75°. The Daubechies 6 (db6) mother wavelet was the most frequently used type for both the first and second pulse components.

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

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.

Anomalous passive Q-switching induced by Cr4+:YAG: with pulse repetition rate approaching up to 1 MHz

Anomalous passive Q-switching behavior was demonstrated in an Yb:KLu(WO4)2 laser, with a Cr4+:YAG crystal plate acting as saturable absorber whose initial transmission amounted to 99.3%. In stable Q-switched operation realized under high output coupling of 80%, 1.83 W of average output power was produced at a pulse repetition rate of 0.97 MHz, far beyond the upper limit imposed by the recovery time of the saturable absorber. The largest pulse energy, shortest pulse duration, and highest peak power were, respectively, 1.89 µJ, 39 ns, and 48.5 W. The high-repetition-rate passive Q-switching performance shows a close similarity to some Yb-ion lasers passively Q-switched by 2D saturable absorbers.

Passive Q-switching of an Yb:KLu(WO4)2 laser with 2D saturable absorbers of MoS2 and WS2: Scaling the output power to 2-W level

Abstract We report on a highly efficient, compact, passively Q-switched Yb:KLu(WO4)2 laser, with few-layer MoS2 or WS2 acting as saturable absorber. A maximum output power of 2.45 W was generated at a repetition rate of 2.52 MHz, with 6.49 W of pump power absorbed in passively Q-switched operation induced by MoS2; the largest pulse energy, shortest duration, and highest peak power were, respectively, 1.27 μ J, 43 ns, and 29.5 W. With WS2 as saturable absorber, the output power attainable in stable Q-switched operation was 1.87 W, produced with an optical-to-optical efficiency of 37% and a slope efficiency of 71%. The minimum pulse duration obtained was 39 ns; while the largest pulse energy and highest peak power were 1.19 μ J and 30.5 W.

Various large-energy soliton operations within an Er-doped fiber laser with bismuth selenide as a saturable absorber.

Different large-energy mode-locked operations were successfully obtained within a Bi2Se3-based Er-doped fiber laser. First, mode-locked operation with maximum pulse energy of 17.2nJ and pulse width of 187ns under a pulse repetition rate of 537.6kHz was obtained under the pump power of 680mW. In addition, the characteristics of dark solitons and soliton rains, which also exhibit large pulse energies, have been investigated experimentally. Our results fully proved that Bi2Se3 was an excellent candidate for investigating various mode-locked operations with large pulse energy due to its high nonlinear effect and high damage threshold.

Few-layer Bi2Te3: an effective 2D saturable absorber for passive Q-switching of compact solid-state lasers in the 1-μm region.

An experimental investigation was carried out to evaluate the potential of few-layer Bi2Te3 topological insulator in use as a saturable absorber for passive Q-switching of compact solid-state lasers in the 1-μm spectral region. By incorporating a sapphire-based few-layer Bi2Te3 sample into a Yb:LuPO4 laser that was formed with a 4-mm plane-parallel resonator, we realized efficient, high-power, high-repetition-rate pulsed laser operation. Depending on the output coupling utilized, single- or dual-wavelength laser action could be achieved. A maximum output power of 5.02 W at 1014.5 nm was produced at a pulse repetition rate of 1.67 MHz, with an optical-to-optical efficiency of 41% and a slope efficiency of 54%; while operating at 1004.9/1012.7 nm, the pulsed laser could produce an output power of 3.94 W at 1.38 MHz, with a pulse duration being as short as 34 ns. The largest pulse energy and highest peak power achieved were 3.0 μJ and 85.3 W. The results demonstrated in our experiment reveal the great potential of the few-layer Bi2Te3 topological insulator in the development of pulsed compact solid-state lasers in the 1-μm region.

Nonlinear optical response of a Co:ZnO epitaxial thin film for large spectral range pulse modulation

We demonstrate the large spectral range nonlinear optical response of a Co:ZnO epitaxial thin film (with single crystal structure) with the absorption range from 1.0 μm to 2.0 μm, for the first time to our knowledge. The third-order nonlinear optical properties and saturable absorption of Co0.15Zn0.85O (Co:ZnO) were studied with the modulation depth of 0.68% and saturation fluence of 1.532 μJ/cm2. Passive Q-switched lasers at the wavelengths of a 1.4 μm Nd:YGG laser and a 1.9 μm Tm:LuVO4 laser were realized with the Co:ZnO epitaxial thin film as the saturable absorber. In the case where the wavelength is 1.4 μm, we obtained the shortest pulse width, the largest pulse energy and the highest peak power, which were recorded at 89 ns, 2.3 μJ and 25.8 W, respectively. Moreover, when the laser output wavelength is 1.9 μm, we got the smallest pulse width of 274 ns. This work provides a promising saturable absorber with a large spectral range response.

Research on Surface Topography Characteristics of Laser Micro-hole Drilling

The surface of laser micro processing has great differences compared with the traditional machining surface. To research surface topography is of great significance for laser processing surface property. Combined with the laser mechanism, the surface characteristics of micro blind-hole drilled with different pulse energy and number were studied in the materials of spring steel 65Mn, stainless steel SUS301 and ceramic Al2O3. The results indicate that large pulse energy makes the hole much irregular and multi-pulse may cause the surface much rough. A large amount of molten material gathers around the hole for 65Mn and SUS301 while not for Al2O3 because of different processing mechanism. Therefore, process parameters and conditions should be explored for better surface topography of laser drilling.

High-efficiency, high-energy ytterbium-doped Q-switched fibre laser with graphene oxide-COOH saturable absorber

Employing graphene oxide (GO)–COOH film as a new saturable absorber (SA), we demonstrate a high-efficiency, high-energy Q-switched ytterbium-doped fiber (YDF) laser operating at a wavelength of 1.03 μm for the first time. GO–COOH film was prepared using a liquid-phase exfoliation method. Stable Q-switched pulses ranging from 4.5 μs to 1.35 μs with repetition rate in the range of 25 kHz–135 kHz were achieved. The maximum total output power was 82 mW, slope efficiency was 61.1% and the highest single pulse energy was 685 nJ at the repetition rate of 74 kHz—which is, to the best of our knowledge, the highest slope efficiency and largest pulse energy yet obtained from a Q-switched single-mode YDF laser with SA. The Q-switched YDF laser demonstrated in this paper confirms that GO–COOH is a cost-effective SA suitable for practical application in ∼1.0 μm Q-switched YDF lasers.

Passive Q-switching laser properties of Yb:Re3Ga5O12 (Re [formula omitted] Y, Lu, Gd) garnets with GaAs semiconductor saturable absorber

We report, for the first time to our knowledge, on the GaAs saturable absorber passive Q-switching laser properties of Yb:Y3Ga5O12, Yb:Lu3Ga5O12, and Yb:Gd3Ga5O12 gallium garnet crystals. 1.10–1.53 W of average output power at 1025–1026 nm could be generated at pulse repetition rates ranging from 19.6 to 43.5 kHz. The shortest pulse duration achieved with the three garnets proved to be very close, falling in a range of 3.3–3.5 ns. The largest pulse energy and highest peak power, obtained with Yb:Y3Ga5O12; Yb:Lu3Ga5O12; and Yb:Gd3Ga5O12, were respectively, 52.0; 82.4; and 55.0 μJ, and 12.4, 17.0, and 12.7 kW.

Er-doped Q-switched fiber laser with a black phosphorus/polymethyl methacrylate saturable absorber.

A stable Q-switched Er-doped fiber (EDF) laser is successfully obtained by using a black phosphorus (BP)/polymethyl methacrylate (PMMA) film as the saturable absorber (SA). To avoid the oxidization of nanomaterials, the BP nanoparticles are fabricated via a liquid-phase exfoliation method and then embedded into a PMMA film that possesses excellent optical transparency in the selected spectrum range. The modulation depth (MD) of the BP/PMMA film SA is 14.3% and the saturable intensity (Isat) is 6.9 MW/cm2. By inserting the BP/PMMA film into the EDF laser cavity, we achieve the stable passive Q-switching operation over the wavelength range from 1561.21nm to 1564.16nm. The repetition rate increases from 10.348kHz to 30.098kHz, and the pulse duration decreases from 25.01μs to 2.98μs by altering the pump power from 9mW to 90mW. The maximum single pulse energy is 283.91nJ. To the best of our knowledge, 283.91nJ is the largest single pulse energy among the Q-switched fiber lasers with BP as the Q-switcher at the 1.5μm wavelength region. The experimental results evidently show that the BP/PMMA film SA can work as a promising Q-switcher for large pulse energy fiber lasers.

Double Q-switched 946 nm laser with MgO:LN electro-optic crystal and MoSe2 saturable absorber

We report a double Q-switched 946 nm laser with a magnesium-oxide-doped LiNbO3 (MgO:LN) electro-optic (EO) crystal and a monolayer molybdenum diselenide (MoSe2) saturable absorber (SA). A pulsed laser diode side-pumped long neodymium-doped yttrium aluminum garnet rod (φ3×65 mm) is used as the gain medium. Large pulse energy up to 3.15 mJ and peak power up to 346 kW are generated at the repetition rate of 550 Hz, corresponding to the beam quality factors of Mx2=3.849, My2=3.868. Monolayer MoSe2 nanosheets applied in the experiment would be a promising SA for a passive Q-switching operation.

One-dimensional Bi_2Te_3 nanowire based broadband saturable absorber for passively Q-switched Yb-doped and Er-doped solid state lasers

The broad saturable absorption of topological insulator Bi2Te3 nanowires is presented for the first time, as well as the passively Q-switched pulse operations on both Yb-doped and Er-doped bulk laser with a bandwidth over about 1.7 μm. Uniform Bi2Te3 nanowires with a large aspect ratio have been synthesized using ultrathin Te nanowires as the template. The broad absorption spectrum from visible to middle infrared reveals a broad optical response. In a 1.0 μm Yb-doped laser, a pulse width of 303 ns with a pulse energy of 1.2 µJ is achieved. While at Er-doped mid-infrared 2.79 μm, the shortest pulse width and largest pulse energy are tested to be 444 ns and 5 µJ, respectively. Those results reveal the topological insulator Bi2Te3 nanowire to be a reliable broad optical switcher for solid state lasers in near- and mid-infrared bands. As far as we know, it is for the first time that TIs based solid state lasers at mid-infrared region are reported. Furthermore, this work can be extendable to explore TIs with other nanstructures for application as optoelectronic devices.

Nonlinear Pulse Compression to Sub-40 fs at $4.5~\mu$ J Pulse Energy by Multi-Pass-Cell Spectral Broadening

We report on the pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal. The compressed pulse energy is $4.5~\mu \text{J}$ , which corresponds to 84 W of average power, with a compression efficiency of 88%. This recently introduced compression scheme is suitable for a large pulse energy range and for high average power. In this paper, we show that it can achieve three times shorter pulses than previously demonstrated.

Passively Q-switched dual-wavelength green laser with an Yb:YAG/Cr4+:YAG/YAG composite crystal.

A compact dual-wavelength passively Q-switched green laser by intra-cavity frequency doubling of a Yb:YAG/Cr4+:YAG/YAG composite crystal was demonstrated for the first time to our best knowledge. The maximum green laser output power of 1.0 W was obtained under the pump power of 9.7 W, and the corresponding slope efficiency is 15.2%. The shortest pulse width, largest pulse energy, and highest peak power were achieved to be 5.54 ns, 246.1μJ, and 40.76 KW, respectively. Dual-wavelength laser oscillation simultaneously at 515 nm and 524.5 nm has been achieved. This passively Q-switched dual-wavelength green laser can be used as a laser source for Terahertz generation.

High peak power cavity dumping semiconductor lasers.

We report on the development of a nanosecond pulsed kW-class optically pumped InGaAs semiconductor laser emitting around 1020 nm, which is suitable for applications such as incoherent laser radar, nonlinear optics, and materials processing. Using an intracavity Pockels cell to cavity-dump VECSELs, we are able to access large pulse energies by storing energy in the optical cavity rather than in the gain medium. We demonstrate peak powers >1 kW and 3 μJ pulses, show the pulse length is equivalent to the photon round-trip time, and show that the wavelength can be tuned within the gain bandwidth of the semiconductor gain.

Repetition-frequency-controllable double Q-switched Ho:LuAG laser with acousto-optic modulator and Cr2+:ZnS saturable absorber

A repetition-frequency-controllable double Q-switched (DQS) Ho:LuAG laser at 2098.34 nm with acousto-optic modulator (AOM) and Cr2+:ZnS saturable absorber (SA) was investigated. The maximum output power of 5.3 W was obtained at the AOM repetition frequency (RF) of 3.72 kHz, corresponding to the slope efficiency of 29.8%. The largest pulse energy of 2.8 mJ with the shortest pulse width of 54.2 ns was observed at the AOM RF of 2.64 kHz. Compared with the passively Q-switched Ho: LuAG laser, the DQS Ho: LuAG laser could generate shorter pulse width and larger pulse energy, and its RF could be controlled by the AOM RF. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Spectroscopic properties and pulsed laser performance of thulium-doped (Lu,Y)3Al5O12 mixed crystal

In this paper, we describe a thulium-doped (Lu,Y)3Al5O12 mixed crystal that was designed and grown to achieve a large pulse energy in Q-switched laser operation. Its absorption cross-sections at 781.3 nm and 1629.2 nm were calculated to be 3.4 × 10−21 cm2 and 5 × 10−21 cm2, respectively, and the emission cross-section at 2018.3 nm was calculated to be 1.92 × 10−21 cm2. The highest single pulse energy of 1.4 mJ near 2.02 μm was realized in an actively Q-switched solid-state laser, and further power scaling was just limited by the damage of the crystal coating. Based on the calculated spectrum parameters, theoretical simulation of the single pulse energy that considering the cross-relaxation process was proposed, which was well consistent with the experimental results.

Comparative Research on the Quality of Micro Hole in Superalloy GH2135 and Stainless Steel 420J1 by Laser Processing

Both superalloy GH2135 and stainless steel 420J1 were used as test materials to be processed by LASERTEC 80 PowerDrill three-dimensional solid laser processing center. The microstructure of the hole was investigated by super depth of field microscope and laser scanning microscope. The front and back orifice diameter, orifice deposits and thermal effect of accumulation zone were studied. The single factor test method was used to study the influence of pulse energy, pulse width and repetition frequency on the quality of micro holes. The results showed that the front and back diameter of the holes all increase with the increase of pulse energy from 0.4J-3.9J. And the front and back aperture are increase with the increase of pulse width from 0.9ms-1.9ms. Meanwhile, the variation of the aperture and pore taper is more noticeable with the repetition frequency changed from 10Hz-60Hz. The results revealed that pulse energy is one of the biggest influence factors, large pulse energy can lead to small hole taper within a certain range, and short pulse width can reduce orifice debris and splash. Both the recast layer and microcrack were existed in the two kinds of metal materials. The quality of holes drilling in GH2135 is better than 420J1.