High-power tunable femtosecond laser systems based on optical parametric amplification offer broad spectral coverage and flexible wavelength control, enabling ultrafast spectroscopy and nonlinear studies. Driven by a 100-W femtosecond pump and combining optical parametric amplification (OPA) with second-harmonic generation (SHG), we have realized a high-power source tunable from the ultraviolet to the mid-infrared. The OPA delivers continuous tuning from 630 to 2800 nm, with a maximum signal power of 12.5 W at 700 nm and a maximum idler power of 8.24 W at 1250 nm. Subsequent SHG extends the shortest wavelength to 315 nm. To support frequency-domain spectroscopy requiring smooth and rapid OPA wavelength scanning, we implement a machine-learning-assisted autonomous tuning method and develop a progressive wavelength-to-actuator calibration strategy. This combined approach reduces frequent manual calibration of multi-motor setpoints and enables automated high-resolution calibration across the tuning range, thereby improving the practicality and reproducibility of wideband operation.

Strong-field laser physics and laser-plasma interactions require femtosecond vortex pulses that simultaneously deliver high pulse energy and high spatial intensity contrast (SIC). An optical parametric amplifier (OPA) is a promising energy scaling approach for femtosecond vortex pulses. However, vortex amplification is typically pumped with Gaussian or flat-top beams that retain nonzero intensity at the vortex center. Consequently, the intensity null is partially filled and the annular profile is distorted, resulting in a marked degradation of both the SIC and the ring-shaped structure. We introduce vortex-mode-matched pumping and flat-top vortex pumping as SIC-preserving strategies. To our knowledge, this is the first systematic SIC-centered study of ultrafast vortex-pulse OPA under different pump spatial modes. Numerical results show that vortex pumping effectively mitigates SIC degradation, while flat-top vortex pumping further improves energy extraction and achieves the best overall performance. We also establish experimentally actionable design rules by matching the pump and signal topological charges and optimizing the pump-to-signal beam-waist ratio. These research results offer valuable insights for the development of high energy and high-contrast vortex sources for supporting structured-light strong-field applications.

In this investigation, effects of substituting Mo for W and temperature on lattice constants of gamma and gamma ' phases and gamma/gamma ' misfits of second generation Ni based single crystal superalloys was investigated. The lattice constants of gamma and gamma ' phases in heat-treated W-rich and Mo-rich single crystal superalloys were measured by in-situ high temperature X-ray diffraction (HT-XRD) at temperature ranged from room temperature to 1150 degrees C. Meanwhile, both thermodynamic calculation and Vegard's law (considering thermal expansion coefficient) were used to calculate lattice constants of gamma and gamma ' phases and gamma/gamma ' misfits of two experimental alloys. Both experiment and calculation results indicated that substituting Mo for W obviously increased lattice constant of gamma phase, while its influence on lattice constant of gamma ' phase was limited, and thus substituting Mo for W significantly decreased gamma/gamma ' misfit. Meanwhile, the experimental results of HT-XRD indicated that absolute value of gamma/gamma ' misfits of two experimental alloys at 1100 degrees C were higher than those of at 1150 degrees C, which was in good agreement with evolution rule of gamma/gamma ' interfacial dislocation network spacings in two experimental alloys (after creep rupture at 1100 degrees C and 1150 degrees C).

High average power broadband tunable long-wavelength infrared (LWIR) femtosecond lasers operating at fingerprint wavelengths of 7-14 mu m hold significant promise across a range of applications, including molecular hyperspectral imaging, strong-field light-matter interaction, and resonant tissue ablation. Here, a 6-12 mu m broadband tunable parametric amplifier based on LiGaS2 or BaGa4S7, generating an output power of 2.4 W at 7.5 mu m, and 1.5 W at 9.5 mu m, pumped by a simple and effective thin-square-rod Yb:YAG amplifier producing 110 W 274 fs output pulses is presented. As a proof of concept, efficient resonant ablation and microstructure fabrication on enamel are showcased at the hydroxyapatite resonant wavelength of 9.5 mu m, with a laser intensity two orders-of-magnitude lower than that required by non-resonant femtosecond lasers, which can foster more precision surgical applications with superior biosafety.

We report on the generation of the terahertz (THz) radiation from air plasma driven by a three-color femtosecond field with the fundamental pulse in the near- (1700 nm and 800 nm) and mid-infrared (3900 nm) ranges. With an inline optical setup for three-color pulse generation and relative phase control, we observed that the THz pulse energy can be enhanced up to 6 times compared with the conventional two-color excitation scheme, dependent on the incident fundamental pulse energy. The polarization of the enhanced THz pulse was found to be elliptical, with the second and third harmonics components of the three-color pump also being elliptically polarized. With the 3.9 µm driving pulses, the maximum THz pulse energy reaches 39.4 µJ with a conversion efficiency of about 1%. Based on the plasma current model, we analytically and numerically reproduced the THz energy enhancement, as well as its dependence on incident pulse energy. The THz enhancement can be attributed to the two additional ionization wave mixing channels introduced with the addition of the third harmonic.

We presented a broadband optical parametric chirped pulse amplification(OPCPA)system based on dual-crystal spectra cascading amplification in the short-wave infrared(SWIR)region.By cascading two crystals with different phase-matching angles,the impact of gain bandwidth narrowing in OPCPA is reduced.In addition,due to the different phase-matching wavelengths,the energy backflow of the idler pulses is also mitigated,thereby enhancing the overall energy conversion efficiency of the system.Ultimately,SWIR pulses with a full-width at half-maximum(FWHM)exceeding 110 nm,a near Fourier-transform limit(FTL)pulse duration of 42.15 fs,and a pulse energy of 30 mJ are obtained(25.9％pump energy conversion efficiency),corresponding to a peak power of 0.75 TW.Compared to single-crystal amplification,this configuration achieves an 80 nm expansion in FWHM,the output pulse duration is reduced by more than 40％,the pump efficiency is increased by 17.22％,and a 2.3-time enhancement in peak power is achieved.This high-energy,terawatt-class SWIR source has significant applications in strong-field physics,including high-intensity THz and water-window X-ray generation,among other areas.

In order to explore the rejuvenation processes and restoration mechanisms of a directionally solidified superalloy applied in industrial gas turbine blades, three rejuvenation treatment regimes, combined with hot isostatic pressing (HIP), were conducted to rejuvenate the damaged microstructure and extend creep life under low temperature/high stress and high temperature/low stress. After only applying a solution rejuvenation treatment, recrystallization occurred and failed to restore creep life at low temperature/high stress (750 °C/610 MPa). The introduction of HIP fulfilled multiple roles: (i) effective pore closure to delay failure; (ii) significant suppression of recrystallization through annihilation and rearrangement of dislocations; (iii) improvement of the adequacy and reliability for high temperature homogenization based on the suppression of recrystallization. An optimized rejuvenation treatment combining HIP with elevated solution temperatures was developed, achieving superior recovery efficiencies of 87.1 and 104.7 pct in creep life under 750 °C/610 MPa and 900 °C/190 MPa conditions, respectively. These results reveal a strong temperature-stress dependence in rejuvenation efficacy, with superior restoration observed under high-temperature/low-stress conditions, offering practical guidance for service-life extension of blades.

This study explores the influence of aerosol transparency on femtosecond 1 kHz laser filamentation in air. The observations suggest that transparent and opaque aerosols may be associated with distinct filamentation pathways: (1) In transparent cases, scattering appears to play a dominant role, potentially modulated by droplet fragmentation processes related to the effective radius and effective variance, which in turn influence beam propagation characteristics; (2) In opaque cases, attenuation is governed primarily by absorption, accompanied by particle agglomeration effects. These primary trends may be further shaped by secondary processes, such as spectral blue-shift, electron attachment, and plasma-induced low-density channel formation, together contributing to the overall filamentation dynamics under different aerosol conditions. The experimental findings therefore point to a transparency-dependent balance between scattering and absorption that influences filament propagation and supercontinuum generation, offering useful implications for atmospheric laser applications.

BACKGROUND:Laser keratotomy, a corneal incision technique for vision correction, has advanced with near-infrared (NIR) femtosecond (fs) lasers-ultrashort pulsed light sources in the near-infrared spectrum. However, NIR femtosecond lasers encounter challenges such as postoperative astigmatism due to scattering by edematous tissues, and endothelial cells distortion by mechanical impact. METHODS:The mid-infrared (MIR) femtosecond lasers at a central wavelength of 6.1 μm resonating with amide modes has an output power of 100 mW and a pulse width of ~200 fs. Systematic experiments of MIR fs laser keratotomy are performed on corneas of 8-week-old male C57BL/6J mice, with optical coherence tomography and fluorescein staining for evaluating corneal recovery in vivo. Electroretinography and visual cliff test are performed for evaluating potential adverse effects on retinal and visual function. Immunofluorescence and immunohistochemistry are carried out for accessing the density, morphology and function of endothelial cell, and the structure of incision and recovery condition of cornea after sacrificing the mice. RESULTS:Efficient deep keratotomy with minimal collateral damage is realized both in normal and edematous cornea, surpassing traditional NIR femtosecond lasers by experimental comparison. Histological imaging, fluorescein staining and immunofluorescence reveal that corneal incisions ablated by MIR fs laser can heal within 3 days by identifying optimal ablation parameters. Additionally, through the electrophysiology and visual cliff index evaluations, it is confirmed that no postoperative retinal and visual impairment caused, proving a good biological safety. CONCLUSIONS:Keratotomy by MIR fs laser exhibits favorable ablative efficiency and biosafety in mice, which could serve as a new tool for ophthalmic surgery and extend the applications of femtosecond laser assisted keratotomy.

The freckle formation tendencies of single-crystal superalloys with minor amounts of carbon were investigated. Carbon addition resulted in TaC-type carbide (MC) precipitation earlier than the eutectic phase in the interdendritic region, which induced Ta depletion and resulted in increases in the W and Re contents in the eutectic. The weakened density imbalance between the interdendritic region liquid in the mushy zone and the melted bulk liquid prohibits convection flow. Additionally, as the amount of carbon intentionally added to the superalloy increases, the volume fraction of the eutectic in the superalloy decreases, and the MC changes from a blocky to script-like shape in the interdendritic region. A lower volume fraction of the eutectic phase and the script-like carbide network can depress thermosolutal convection in the interdendritic region in the longitudinal direction. For these reasons, the freckle formation tendency decreased. As the carbon content of superalloys increases, the Rayleigh number decreases, resulting in a decrease in freckle formation. The Rayleigh criterion can be used to evaluate freckle formation tendency.

Laser ablation of bio-tissues is the key technology of future surgeries, owing to the merits of submicron accuracy, non-contact operation, and precision control assisted by automation and computer intelligence. Excellent efficiency, minimal collateral damage, biological safety, and tissue selectivity are the ideal parameters for delicate surgical applications. Here, by exploring the mid-infrared (MIR) resonant ablation and the femtosecond cold processing, tissue ablation with multi-millimeter depth and cellular collateral damage, enabled by a tabletop femtosecond MIR optical parametric amplifier operating at the amide-I resonant wavelength of 6.1 mu m, is demonstrated. Remarkably, the collateral damage is observed to be 15, <4, and <1 mu m in the porcine cornea, sclera, and articular cartilage, respectively, with multi-millimeter incision depth. In addition, preliminary proof-of-concept experiments of tissue-selective ablation, microchannels on cartilage for drug delivery, laser glaucoma, keratotomy, neurologic tissue incision, dentin deep crater formation, and hypertrophic scarring ablation are demonstrated, which pave the way for high-precision surgical applications with a tabletop solution.

Mid-infrared (MIR) pulsed lasers operating at 2-5 & mu;m have important applications in communication, sensing, and medicine. However, the lack of robust MIR saturable absorbers (SAs) remains a major obstacle. Here, a semiconductor material cadmium oxide (CdO) film with high laser-induced damage threshold (800 nm, 134 mJ cm-2) and broadband saturable absorption (2.0-3.9 & mu;m) is investigated. The effective tuning of the nonlinear optical response of CdO is demonstrated by adjusting the carrier concentration via a tungsten (W)-doping scheme. The saturable absorption is improved and carrier relaxation process is accelerated after increasing the W-dopant level. Based on these findings, the robust CdO-SAs with customizable parameters are realized and Q-switched lasers with decreasing pulse width from 372 to 254.3 ns are obtained at 2 & mu;m. The design flexibility provided by CdO opens up a large parameter space that enables the continuous improvement of compact and high-performance MIR ultrafast lasers. A mid-infrared CdO based saturable absorber with high laser-induced damage threshold and broadband saturable absorption is demonstrated. Based on a tungsten-doping scheme, the effective tuning of the nonlinear optical response of CdO and customizable parameters of Q-switched lasers are realized. The design flexibility provided by CdO opens up a large parameter space that enables the improvement of mid-infrared ultrafast lasers.image

We introduce a broadband tunable femtosecond laser source in the long-wave infrared (LWIR) band, covering the range of 5–13.5 μm, based on the integration of optical parametric amplification and difference frequency generation techniques. We utilize a dual-stage tuning method, combined with the high nonlinear coefficient and broadband phase matching range of the BaGa4Se7 crystal, to facilitate significant improvements in spectral coverage and energy efficiency. The laser yields a peak output energy of 43 μJ and maintains energies above 10 μJ across the entire tuning range, with an average power output exceeding 10 mW. The pulse duration at the central wavelength of 8.3 μm is measured at 72 fs full width at half-maximum using the electro-optic sampling method. This LWIR femtosecond laser can be used in many applications, such as molecular fingerprint spectral analysis, ultrafast chemical reaction spectral analysis, materials science, and ultrafast physics research, providing an important research basis for the generation and application of mid-infrared ultrafast laser sources.

The effect of the crystal orientation on freckle formation has been investigated in single crystal Ni-base superalloy heavy-plate castings. Single crystal superalloy heavy-plate castings grown along the <001> , <011> and <111> crystallographic orientations were prepared by the bottom seeding technique and Bridgman method. Optical microscopy (OM) and scanning electron microscopy (SEM) were employed to observe the microstructure, and electron backscatter diffraction (EBSD) was used to characterize the crystallographic orientation of the castings. The morphology of the mushy zone during directional solidification was simulated by ProCAST finite element software. The experimental results show that the space between primary dendrites at the (010) crystal plane of <011> oriented plate casting and the (100) crystal plane of <111> oriented plate casting is wider than that at the same corresponding crystal plane of <001> oriented plate casting. The occurrence of freckles depends not only on orientation but also on dendrite morphology. Compared with orientation, the freckle is more sensitive to dendrite morphology and the space between primary dendrites of the single crystal plates. The freckle formation tendency of the <001> orientation casting was the weakest among the three crystal orientation castings, and the reason for this tendency was discussed.

We report 13.7 mJ, 10.59 fs and 1.08 TW few-cycle 1.45 mu m vortex lasers generated in an optical parametric chirped pulse amplification and nonlinear compression system, which have important applications in vortex high field physics.

In this Letter, we present the generation of terawatt-scale few-cycle short-wave infrared (SWIR) lasers using nonlinear compression in a large-core gas-filled hollow core fiber. Through the experimental verification, we investigate the energy scaling properties and nonlinear pulse propagation in the argon-filled hollow core fiber. At static pressure, the system delivers pulses with 5.55 mJ/9.04 fs at a central wavelength of 1.45 μm, resulting in a peak power of about 0.5 TW. Subsequently, based on the chirped input pulses and pressure gradient, the system delivers terawatt-scale two-cycle SWIR pulses with 9.52 mJ/10.65 fs, resulting in a record peak power of about 0.7 TW. This study marks a crucial advancement in the field of SWIR ultra-intense, ultrashort pulse nonlinear interaction platforms. This high-energy, few-cycle SWIR source has significant applications in high-intensity THz radiation, x-ray generation, and other fields of strong-field physics.

We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification, hollow-core fiber（HCF） and second harmonic generation processes. In this setup, the spectrum of an approximately 1.8 μm laser pulse has near 1 μm full bandwidth by employing an argon gas-filled HCF. Subsequently,after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair, 9.6 fs（～3cycles） and 150 μJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated. The energy stability of the output laser pulse is excellent with 0.8%（root mean square） over 20 min, and the temporal contrast is ＞1012at-10 ps before the main pulse. The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems.

As a driving source for many nonlinear vortex phenomena, such as the generation of isolated attosecond optical vortices, terahertz vortices, etc., terawatt-class few-cycle short-wave infrared vortex lasers are now attracting widespread attention. However, because the vortex characteristics of optical vortices are difficult to maintain in the amplification and compression stages, the generation of high-intensity few-cycle vortex lasers is still in the exploratory stage. In this article, we report 20-Hz, 18.6-mJ, 60-fs, and 1.45-μm infrared vortex lasers with 1, 2, and 3 topological charges successfully generated in an optical parametric chirped pulse amplification system. A clean intensity node at the beam center is observed and highly stable propagation in free space is demonstrated. Moreover, this high-energy vortex pulse is spectrally broadened in multiple thin plates and temporally compressed to 10.59 fs (2.2 optical cycles) with chirped mirrors, corresponding to a peak power of 1.08 TW, while highly preserving the vortex information. We believe that the generated high-energy few-cycle vortex laser has important applications from vortex optics to strong-field physics.