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We demonstrate a dual-wavelength, compact femtosecond optical parametric oscillator (OPO) with high-repetition-rate, which is harmonically pumped by a ~101 MHz Yb-doped fiber laser system. The dual-wavelength output is realized by exploiting the bidirectional off-axis pumping technique, and the multiplication of repetition rate is derived by placing a nonlinear crystal in a miniaturized V-type cavity with only 16.5 cm length. By adjusting the detuning degree of the pump at one end, the maximum dual-wavelength gap is 66 nm from 1497 to 1563 nm. The time interval between the dual wavelengths can be adjusted freely. This is the first report on a dual-wavelength with the high-repetition-rate of GHz-level, femtosecond OPO system.

This study explored the influence of biochar (BC) on anaerobic digestion (AD) of swine manure under various tetracycline (TC) pressures. It was found that both low (0.5 mg/L) and high (50 mg/L) TC pressures inhibited AD performance, while BC mitigated it in multi-facets. Under high TC pressure, BC accelerated syntrophic methanogenesis by boosting direct interspecies electron transfer pathway. The TC removal efficiencies were enhanced by 24.3-158.2% with BC assistance, which were attributed to the enhanced biological degradation rather than BC’s physiochemical adsorption. Moreover, BC possibly acted as a protective role to alleviate intensive extracellular polymeric substances secretion under TC pressures. Integrated microbial community, metabolic function predicting, and antibiotic resistance genes (ARG) analysis revealed that BC addition not only enriched Anaerolineceae, which likely responsible for the 24.2-41.9% higher level expression of organics metabolic pathways and xenobiotics biodegradation, but also reduced ARG abundance by controlling the potential ARG host (Firmicutes) proliferation.

This study explored the performances, and associated mechanisms of biochar promoting volatile fatty acids (VFA) oxidation via extracellular electron transfer (EET) pathway. It was found that in a bioelectrochemical system, adding biochar suspension remarkably enhanced electricity generation whatever acetate or propionate used as an electron donor. The maximum current density in biochar-assisted groups reached 1.6–2.2 A/m2, which were 69.2–220.0% higher than that of control groups. The lower electrical resistance of anode in biochar-assisted groups was potentially attributed to the formed biofilm dominated by electro-active Geobacteraceae, and the electron donor type depending on dominant genus. In specific, with biochar assistance, Desulfuromonas enriched from 1.1% to 25.0% when acetate as an electron donor, and the relative abundance of Geobacter increased from 4.6% to 31.7% as dominant genus in propionate-added group. Electrochemical analysis uncovered that biochar hardly elevated sludge electrical conductivity, while the excellent redox-based electron exchange transfer capacity likely made biochar as a transient electron acceptor, which was more accessible than anode to support the metabolism of electroactive bacteria in the initial stage. Meanwhile, the porous surface area of biochar particle likely provided a “bridge” between suspended sludge and anode, to support a more directional evolution of electroactive bacteria on anode. This dual-function of biochar achieved a sustainable VFA oxidation via EET-based pathway.

In this letter, we propose and demonstrate a practically compact 1-GHz repetition-rate femtosecond optical parametric oscillator (OPO) based on MgO:PPLN crystal, which is harmonically pumped by a 53 MHz Yb-doped fiber laser. The multiplication of the repetition rate is derived by placing the nonlinear crystal in a miniaturized V-type cavity with 13.9 cm length. The near-infrared signal output pulses are tunable from 1350 nm to 1650 nm. The signal pulse duration across the complete tuning range is measured to be around 125 fs. Thanks to the high repetition rate, broadband tenability, and simplicity of the optical setup, this type of OPO holds promise for many applications.

We numerically and experimentally investigate the multi-pulsing mechanism in a dispersion-managed mode-locked Yb-doped fiber laser. Multi-pulsing occurs primarily owing to the inherent filtering effect of the chirped fiber Bragg grating. The spectral filtering effect restricts the spectral broadening induced by self-phase modulation and causes extra loss, leading to a decreased pump power threshold for the multi-pulsing state. Numerical simulations show that multi-pulsing emerges at a lower pump power when the spectral filter bandwidth becomes narrower. In the experiment, the spectral width increases as the net cavity dispersion approaches zero. Pulses with wider spectral widths experience more loss from the spectral filtering effect, leading to a decreased pump power threshold for multi-pulsing. Therefore, the net cavity dispersion also has an impact on the multi-pulsing threshold. Based on this conclusion, we devise a strategy to obtain single-pulsing operation with the shortest pulse width and the highest pulse energy.

We report a compact femtosecond optical parametric oscillator (OPO) with a tunable repetition rate that is harmonically pumped using a 52.5 MHz Yb-doped fiber laser system. By reducing the OPO cavity length, the repetition rate can be adjusted successively from 1.935 to 2.95 GHz at 52.5 MHz intervals. The multiplication of the repetition rate is achieved by placing a nonlinear crystal in a compact linear cavity, and the minimum cavity length is 47.8 mm. The maximum signal power (205.2 mW) at 2.04 GHz is obtained at an input pump power of 2.35 W and a central wavelength of 1472 nm. The central wavelength of the signal pulses can be tuned from 1383 to 1596 nm. To the best of our knowledge, 2.95 GHz is the highest repetition rate achieved using a femtosecond OPO based on an ultrashort cavity with a length that is N times (N is an integer) shorter than that of the pump cavity.

We propose a high-efficiency and compact 910-MHz femtosecond optical parametric oscillator, which is harmonically pumped by a ∼101 MHz Yb doped fiber laser system. The OPO is capable of delivering watt-level, power-enhanced signals across the telecommunication waveband. The signal power enhancement is realized by exploiting the bidirectional pumping technique. A maximum signal power of 1.04 W at 1502 nm is obtained for an input pump power of 3.8 W. Tunable near-infrared signal pulses with a wavelength range between 1350 and 1610 nm are measured, and the pulse durations vary from 193 to 464 fs. This compact and economic design provides a solution for efficient high repetition rate pulse generation over a large wavelength span, which will be beneficial for a variety of practical applications.

In this study, we successfully demonstrate the achievement of 1.37 W average power for a picosecond deep ultraviolet (DUV) laser at 213 nm with a 1 MHz repetition rate using β-BaB2O4 (BBO) crystals, which is the highest output power of a 213 nm picosecond laser system with an all-solid-state setup so far. The laser system generates over 1.3 μJ 213-nm pulse energy. The fifth harmonic is generated by sum-frequency generation of the 532 and 355 nm beams based on a “2 + 3” scheme. BBO crystals with lengths of 6, 8, and 10 mm are investigated. Furthermore, the DUV laser system produces a high-beam quality and narrow linewidth output. The DUV system can be stably maintained over 100 h with expanded beam sizes of 532 and 355 nm at 800 mW, and without requiring a change in the positions and temperatures of nonlinear crystals.

On the basis of a home-made femtosecond Yb-doped fiber laser, we designed a compact and efficient third harmonic generation scheme by a simple compensation plate of β-BaB2O4 crystal. The compensation plate is optimized through its thickness and cutting angle to reverse both spatial and temporal walk-off. By optimizing the parameters of the compensation plate and incident light intensity, a maximum output of 2.23 W with a repetition rate of 1 MHz at 345 nm is obtained, which implies a conversion efficiency of 23% from the infrared to ultraviolet.

We demonstrate a femtosecond optical parametric oscillator that can generate orthogonally polarized dual-wavelength femtosecond pulses. Two periodically poled lithium niobate (PPLN) crystals with mutually orthogonal crystal axes are pumped by a single femtosecond fiber laser. The central wavelength of the two orthogonally polarized signal pulses can be continuously tuned from 1387 to 1588 nm with a maximum frequency separation of 27 THz. Because of the orthogonal dual-crystal scheme, the system is immune to the coherent coupling effect, thus overcoming the limitation of minimum frequency separation.

We demonstrate a high average power, widely tunable, dielectric-mirror-less optical parametric oscillator (OPO) based on MgO:PPLN (MgO-doped periodically poled lithium niobate), which is synchronously pumped by a 1040 nm femtosecond fiber laser. The OPO does not require any dielectric coating mirrors. By exploiting the four-prism sequence system, combined with the gold mirrors, the oscillating laser pulses could span the spectral regions in both the signal and idler, and the output pulses of OPO can be tuned across 1367–1914 nm in the signal, and 2152–4480 nm in the idler as well. This device can deliver as much as 1.2 W of average power at 1482 nm in the signal and up to 411 mW at 3487 nm in the idler, respectively. The ultrabroad-band spectra tunability, along with the high average output property, makes the dielectric-mirror-less OPO an attractive alternative to conventional OPOs.

Transverse parasitic lasing (PL) in large-aperture Ti:sapphire (Ti:S) crystals is a critical factor that limits the energy achievable with the chirped-pulse amplification (CPA) technique. We propose a method to suppress PL effects in large-aperture Ti:S amplifiers by using a temporal dual-pulse pump. Theoretical simulations based on the experimental parameters in 2.0 PW Ti:S laser system are performed to predict the transverse gain as a function of pumping time and output energy. By optimizing the temporal profile of the pump beam as well as the time delay between the input seed and pump pulses, we can minimize PL effects in Ti:S crystals. This method is applicable to larger-aperture Ti:S crystals pumped at higher pump fluence and energy, and is potential to develop a ~10 PW laser system.

We report a hybrid femtosecond laser system based on a femtosecond Yb-doped fiber laser and a Yb-doped potassium gadolinium tungstate (Yb:KGW) regenerative amplifier. To match the central wavelength of the seed source, a Yb:KGW crystal is used in the regenerative amplifier for Np polarization. We study and optimize the dynamics of nonlinear amplification to alleviate the gain narrowing effect. With optimization, the system can output 270 fs pulses with 21 μJ pulse energy at a 60 kHz repetition rate.

The latest progress towards a 10PW ultra-intense femtosecond laser at SIOM was reported. The energy of 192.3J was achieved with Ti: sapphire amplifiers, which could support a peak power of 5.13PW.

Based on the polarized-dependent absorption characteristic of Ti:S crystals, we propose a method to reduce the absorption coefficient of Ti:S by using a σ-polarized pump. For Ti:S crystals, the absorption cross section of σ-polarized pump light is approximately half that of π-polarized pump light, which reduces the excited state density near the surface of the amplifier crystal, resulting in reduced transverse parasitic lasing and amplified spontaneous emission. The experimental results based on a diameter of 80 mm Ti:S confirmed the proposed method with different index-matched cladding materials [ethanol and bromonaphthalene (BN)]. In the case of an ethanol cladding, the maximum amplified output energies for π- and σ-polarized pumping are 20.8 J and 26.8 J, respectively—corresponding to 28.8% energy improvement achieved by the σ-polarized pump. In the case of a BN cladding, the maximum amplified output energies achieved by π- and σ-polarized pumping are 40 J and 44 J, respectively; this result corresponds to about 10% energy improvement achieved by the σ-polarized pump. This method can be used in larger size Ti:S amplifiers.

We report on a 2.0 PW femtosecond laser system at 800 nm based on the scheme of chirped pulse amplification using Ti:sapphire crystals, which is the highest peak power ever achieved from a femtosecond laser system. Combining the index-matching cladding technique and the precise control of the time delay between the input seed pulse and pump pulses, the parasitic lasing in the final booster amplifier is effectively suppressed at the pump energy of 140 J at 527 nm. The maximum output energy from the final amplifier is 72.6 J, corresponding to a conversion efficiency of 47.2% from the pump energy to the output laser energy. The measured spectral width of the amplified output pulse from the final amplifier is 60.8 nm for the full width at half-maximum (FWHM) by controlling the spectral evolution in the amplifier chain, and the recompressed pulse duration is 26.0 fs. The technology of cross-polarized wave (XPW) is applied in a broadband front-end, and the pulse contrast is improved to ~1.5 × 10−11 (−100 ps before the main pulse) which is measured at 83 TW power level with a repetition rate of 5 HZ.

Based on technologies of chirped pulse amplification and optical parametric chirped pulse amplification, the peak power of petawatt femtosecond laser was upgraded. The hybrid scheme was confirmed to be an approach for ten patawatt laser.

We reported a hybrid chirped pulse amplification (CPA) and optical parametric chirped pulse amplification (OPCPA) laser system with peak power of 0.61PW. The conversion efficiency of LBO-OPCPA reached 25.38% with output energy of 28.68 J. The compressed pulse width of hybrid laser was 33.8fs.

A hybrid chirped pulse amplification and optical parametric chirped pulse amplification laser was reported. The amplified energy of LBO-OPCPA was 28.68 J with conversion efficiency of 25.38%. After compression, 0.61 PW peak power was produced.

The optical parametric-chirped pulse amplification (OPCPA) based on large-aperture nonlinear optical crystals is promising for implementation of an ultrahigh peak-power laser system of 10 PW and beyond. We demonstrated the highest energy broadband OPCPA at 800 nm, to the best of our knowledge, by using an 80 mm in diameter LiB(3)O(5)(LBO) amplifier, with an output energy of 28.68 J, a bandwidth of 80 nm (FWHM), and conversion efficiency of 25.38%. After compression, a peak power of 0.61 PW with 33.8 fs pulse duration is produced.

We report on the generation of 192.3 J centered at 800 nm wavelength from a chirped-pulse amplification (CPA) Ti:sapphire laser system. The experimental results demonstrate that parasitic lasing can be suppressed successfully in the final amplifier based on a Ti:sapphire crystal of 150 mm in diameter. An over 50% pump-to-signal conversion efficiency was measured for the final amplifier by optimizing the time delay of two pump pulses and enhancing the injected seed energy. With 72% compressor throughput efficiency and 27 fs long compressed pulse duration obtained at a lower energy level, this laser could potentially support a compressed laser pulse of 5.13 PW peak power. The experimental results represent notable progress regarding the CPA laser.

In this Letter, we present a study of high-energy and high-conversion-efficiency broadband optical parametric chirped-pulse amplification (OPCPA) system with a 100 mm×100 mm×17 mm LBO crystal near 800 nm. The results showed that the back-conversion was sensitively affected by the pump intensity and the injected signal intensity. It occurred when the injected signal was above 0.82 J with a pump energy of 170 J, and this effect also reshaped the amplified spectrum. After optimization, an amplified energy of 45.3 J was achieved with a conversion efficiency of 26.3% by the OPCPA. The peak power of the hybrid CPA-OPCPA laser system reached 1.02 PW with a compressed duration of 32 fs, which is the first reported OPCPA peak power higher than 1 PW, to the best of our knowledge.

We provide a tunable temporal shaping method of a laser pulse to compensate pulse distortion in saturated laser amplifiers. The solutions of our computer programs, which express pulse distortion because of saturation effects in pulse laser amplifiers, determine the optimum input pulse shape required to produce a top-hat target pulse shape at the output of the saturated laser amplifier. With the tuning ability of the method provided here, the top-hat target pulse shape can be maintained at different output characteristic energies relative to the saturation energy of the amplifier. Moreover, the relation is experimentally verified using a solid-state laser amplifier chain. The method will prove useful in applications of high-energy laser amplifier systems that require a top-hat pulse shape to be efficient, such as the pump laser pulse of optical parametric chirped pulse amplification.

Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992, optical parametric chirped pulse amplification (OPCPA) became the most promising method for the amplification of broadband optical pulses. In the meantime, we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers. The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level. Meanwhile, the output pulse duration based on optical parametric amplification has entered the range of few-optical-cycle field. In this paper, we overview the basic principles, trends in development, and current state of the ultrashort and laser systems based on OPCPA, respectively.