Study on the influence of side-blown airflow velocities on plasma and combustion wave generated from fused silica induced by combined pulse laser

This study examines the impact of variations in side-blowing airflow velocity on plasma generation,combustion wave propagation mechanisms,and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser.The airflow rate and pulse delay are the main experimental variables.The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing.The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the sideblowing airflow at different airflow rates(0.2 Ma,0.4 Ma,and 0.6 Ma).As the flow rate of the sideblow air stream increases,the initial expansion velocities of the plasma and combustion wave gradually decrease,and the side-blow air stream increasingly suppresses the plasma.It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action.Therefore,the side-blown airflow alone cannot completely clear the plasma.Depending on the delay conditions,the pressure of the side-blowing airflow,the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser.Both simulation and experimental results are consistent,indicating the potential for further exploration of fused silica targets in the laser field.

Study on the effect of focal position change on the expansion velocity and propagation mechanism of plasma generated by millisecond pulsed laser-induced fused silica

In this work, by controlling the positional relationship between the target and the focal point, the surface damage, shock wave phenomenon and propagation mechanism involved in the plasma generation of fused silica by millisecond pulsed laser irradiation at different focal positions were studied. Laser energy is an important experimental variable. The dynamic process of plasma was detected by optical shadow method, and the influence of surface film damage on plasma propagation and the propagation mechanism at different focal positions were discussed. The study found that the plasma induced by the pulsed laser at the focus position within 0–20 μs exploded, the micro-droplets formed around 20 μs. At the same time, a shock wave is formed by the compressed air, the micro-droplets are compressed under the action of the shock wave recoil pressure, and the micro-droplets channel phenomenon is observed in the micro-droplets. The peak velocities of plasma and combustion wave appear earlier in the pre-focus position than in the post-focus position. This research provides a reference for the field of laser processing using fused silica as the substrate.

Theoretical and experimental studies on high-power laser-induced thermal blooming effect in chamber with different gases

High-power laser induced thermal blooming effects in a closed chamber with three different gases are investigated theoretically and experimentally in this work. In the theoretical treatment, an incompressible gas turbulent model is adopted.In the numerical simulation the gas refractive index as a function of both the temperature and pressure is taken into consideration. In the experimental study the pump-probe technology is adopted. A high-power 1064-nm fiber laser with maximum output power of 12 k W is used to drive the gas thermal blooming, and a 50-m W high-beam-quality 637-nm laser diode(LD)is used as a probe beam. The influences of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality are analyzed for three different gases of air, nitrogen, and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in good agreement with the simulated results.

High-Efficiency Spectral-Beam-Combined 930 nm Diode Laser Source

Spectral beam combining is an effective way to achieve high-brightness direct diode laser output.We present an experimental study on spectral beam combining with external cavity based on transmission grating.Using a series of cylindrical transform lenses with different focal lengths,spectral beaming combining efficiency is greatly improved,and the results of wavelength intervals are consistent with the theoretical calculations.With the injection current of 90 A,a 75.1 W cw 930 nm output power with wavelength span of 18.6 nm and spectral beam combining efficiency of 92.7%is achieved,the beam parameter product is 5.77 mm·mrad.

The 5.2 kW Nd：YAG Slab Amplifier Chain Seeded by Nd：YVO4 Innoslab Laser

A high power Nd：YAG end-pumped slab amplifier chain with a Nd：YVO4 innoslab laser as the master oscillator is demonstrated. A chain output power of 5210 W with beam quality of 4 times the diffraction limit is achieved by double-passing the first amplifier stage and single-passing the second stage with an optical efficiency of 29% while working at a frequency of 1kHz and pulse width of 200 μs.

The acceleration mechanism of shock wave induced by millisecond-nanosecond combined-pulse laser on silicon

The velocity variation law of shock wave induced by millisecond-nanosecond combined-pulse laser has been investigated experimentally. The pulse delay and laser energy are important experimental variables. The method of laser shadowgraphy is used in the experiment.Experimental results show that when the pulse delay is 2.4 ms, the ms and ns laser energy density is 301 J cm^(-2) and 12 J cm^(-2), respectively, the velocity of shock wave is 1.09 times faster than that induced by single ns pulse laser. It is inferred that the shock wave propagates in the plasma is faster than that in air. When the ms and ns laser energy density is 414.58 and 24 J cm^(-2), the velocity of shock wave shows rising trend with pulse delay in a range of 1.4 ms>Δt> 0.8 ms. It is indicated that with the increase of ns laser energy, the laser energy absorbed by laser-supported absorption wave increases. The mechanism of inverse bremsstrahlung absorption acts with target surface absorption simultaneously during the ns laser irradiation. Thus, the phenomenon of the double shock wave is induced. The numerical results of the phenomenon were accordance with experiment. The results of this research can provide a reference for the field of laser propulsion.

A 117-W 1.66-Times Diffraction Limited Continuous-Wave Nd:YVO4 Zigzag Slab Laser with Multilayer Amplified-Spontaneous-Emission Absorbing Coatings

We report a continuous-wave end-pumped Nd:YVη4 zigzag slab laser with multilayer amplified spontaneous emission(ASE)absorbing coatings.The coatings are deposited on the slab faces.A five-layer structure consists of SiO2-Ti-SiO2-Ti-Au,and the thicknesses are 2520 nm,10 nm,160 nm,24 nm and 200 nm,respectively.The designed coatings show good performance for the ASE control in the experimental tests.A stable-unstable hybrid laser oscillator along orthogonal directions in the slab aperture is further configured,achieving the 117 W output at a pump of 328 W.The beam quality factors M2 in the unstable direction and stable direction are 1.57 and1.66,respectively.

High-energy picosecond single-pass multi-stage optical parametric generator and amplifier

We demonstrate a new management of multi-stage optical parametric generator(OPG)and amplifier(OPA)to obtain high-energy picosecond sources with high beam quality.The setup of multi-stage OPG-OPA requires mode-matching between the pump beam and the stable mode of the OPG-OPA.In a proof-of-principle experiment,the single-pass multi-stage OPG-OPA consists of three walk-off compensated KTP crystal pairs and two lenses,pumped by an 86 ps,1064 nm 10 kHz picosecond laser.The signal light at~1.77μm has an average output power of 502 mW with record energy up to 50.2μJ.The beam quality factor of the signal light can be improved toM^(2)_(x) ×M^(2)_(y)after filtering out about 40%signal power.To the best of our knowledge,it is the first picosecond single-pass multi-stage OPG-OPA pumped at kHz regime.

A 45-μJ,10-kHz,burst-mode picosecond optical parametric oscillator synchronously pumped at a second harmonic cavity

A novel high-energy picosecond optical parametric oscillator(OPO)was realized by placing an OPO in a secondharmonic(SH)cavity.In a proof-of-principle experiment,we demonstrated excellent burst energy of 45μJ for the OPO signal at 900 nm that operates at a pulse repetition rate of 10 k Hz and a pulse width of 46.8 ps.The beam quality was measured as M_(x)^(2)=1.44 and M_(y)^(2)=1.40 in the orthogonal directions,corresponding to an average beam factor M^(2)=1.42.So far,this study is the first to investigate high-energy ps OPO synchronously pumped in a second-harmonic cavity.

Investigation of laser diode face-pumped high average power heat capacity laser

The three-dimensional （3D） pump intensity distribution in medium of the laser diode （LD） pumped high average power heat capacity laser is simulated by the ray tracing method, and the divergence characteristics of fast axis and slow axis of LD are simultaneously considered. The transient 3D temperature and stress distributions are also simulated by the finite dement method （FEM） with considering the uneven heat source distribution in medium. A LD face-pumped Nd：GGG heat capacity laser is designed. The average output power is 1.49 kW with an optical-optical efficiency of 24.1%. OCIS codes： 140.3480, 140.6810, 120.6810, 000.4430.

Continuous-waveπ-polarized 1084 nm laser based on Nd:MgO:LiNbO_(3)under 888 nm thermally boosted pumping

A continuous-wave(CW)π-polarized 1084 nm laser based on Nd:MgO:LiNbO_(3)under 888 nm thermally boosted pumping is reported.According to the absorption spectrum and energy level structure of Nd:MgO:LiNbO_(3),the 888 nm laser diode(LD)is used for thermally boosted pumping.This pumping method eliminates the quantum defect caused by the nonradiative transition in Nd:MgO:LiNbO_(3)under the traditional 813 nm pumping and effectively improves the serious thermal effect of the crystal.The unmatched polarized 1093 nm laser is completely suppressed,and theπ-polarized laser output of1084 nm in the whole pump range is realized by the 888 nm thermally boosted pumping.In the present work,we achieved the CWπ-polarized 1084 nm laser with a maximum output power of 7.53 W and a slope efficiency of about 46.1%.

High-energy,hundred-picosecond pulsed 266 nm mid-ultraviolet generation by a barium borate crystal

We present a high-energy,hundred-picosecond(ps)pulsed mid-ultraviolet solid-state laser at 266 nm by a direct second harmonic generation(SHG)in a barium borate(BaB_(2)O_(4),BBO)nonlinear crystal.The green pump source is a 710 mJ,330 ps pulsed laser at a wavelength of 532 nm with a repetition rate of 1 Hz.Under a green pump energy of 710 mJ,a maximum output energy of 253.3 mJ at 266 nm is achieved with 250 ps pulse duration resulting in a peak power of more than 1 GW,corresponding to an SHG conversion efficiency of 35.7%from 532 to 266 nm.The experimental data were well consistent with the theoretical prediction.To the best of our knowledge,this laser exhibits both the highest output energy and highest peak power ever achieved in a hundred-ps/ps regime at 266 nm for BBO-SHG.

High-power 1560 nm single-frequency erbium fiber amplifier core-pumped at 1480 nm

High-power continuous-wave single-frequency Er-doped fiber amplifiers at 1560 nm by in-band and core pumping of a 1480 nm Raman fiber laser are investigated in detail.Both co-and counter-pumping configurations are studied experimentally.Up to 59.1 W output and 90%efficiency were obtained in the fundamental mode and linear polarization in the co-pumped case,while less power and efficiency were achieved in the counter-pumped setup for additional loss.The amplifier performs indistinguishably in terms of laser linewidth and relative intensity noise in the frequency range up to 10 MHz for both configurations.However,the spectral pedestal is raised in co-pumping,caused by cross-phase modulation between the pump and signal laser,which is observed and analyzed for the first time.Nevertheless,the spectral pedestal is 34.9 dB below the peak,which has a negligible effect for most applications.

Machine learning-accelerated discovery of novel 2D ferromagnetic materials with strong magnetization

Two-dimensional ferromagnetic(2DFM)semiconductors(metals,half-metals,and so on)are important materials fornext-generation nano-electronic and nano-spintronic devices.However,these kinds of materials remain scarce,“trial anderror”experiments and calculations are both time-consumingand expensive.In the present work,in order to obtain theoptimal 2DFM materials with strong magnetization,a machinelearning(ML)framework was established to search the 2Dmaterial space containing over 2417 samples and identified 615compounds whose magnetic orders were then determined viahigh-throughput first-principles calculations.With the adoptionof ML algorithms,two classification models and a regressionmodel were trained.The interpretability of the regressionmodel was evaluated through Shapley Additive exPlanations(SHAP)analysis.Unexpectedly,it is found that Cr2NF2 is apotential antiferromagnetic ferroelectric 2D multiferroic material.More importantly,60 novel 2DFM candidates werepredicted,and among them,13 candidates have magnetic moments of>7μB.Os2Cl8,Fe3GeSe2,and Mn4N3S2 were predictedto be novel 2DFM semiconductors,metals,and half-metals,respectively.With the adoption of the ML approach in thecurrent work,the prediction of 2DFM materials with strongmagnetization can be accelerated,and the computation timecan be drastically reduced by more than one order ofmagnitude.

All-fiber-based photonic microwave generation with 10^(-15) frequency instability

We demonstrate an all-fiber-based photonic microwave generation with 10^(-15) frequency instability.The system consists of an ultra-stable laser by optical fiber delay line,an all-fiber-based"figure-of-nine"optical frequency comb,a high signal-tonoise ratio photonic detection unit,and a microwave frequency synthesizer.The whole optical links are made from optical fiber and optical fiber components,which renders the whole system compactness,reliability,and robustness with respect to environmental influences.Frequency instabilities of 3.5×10^(-15) at 100 s for 6.834 GHz signal and 4.3×10^(-15) at 100 s for9.192 GHz signal were achieved.