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Micro/nano processing of natural silk fibers with near-field enhanced ultrafast laser; ?????¨è????o?￠???oè????????????ˉ1?¤????è?????è??è??????o3????·￥;
摘要： Silkworm silk fiber is an attractive material owing to its remarkable mechanical characteristics, excellent optical properties, and good biocompatibility and biodegradability. However, nano-processing of the silk fiber is still a challenge limiting its applications in nanoengineering and related fields. Herein, we report localized near-field enhancement-assisted ablation with an ultrafast laser to break this bottleneck. Localized processing of silk fiber, including nano-holing, nano-grooving, and cutting could retain the key molecular structure building blocks and the pristine functionality of the silk fiber. An extremely narrow nanohole with a width of ~64 nm was successfully achieved. The processed silk fiber can be used to transfer micro/nanoparticles and drugs, showing potential for biomedical engineering. The processing strategy developed in this study can also be extended to other materials, paving a new way for fabricating functional nanostructures with precisely controlled size and morphology.
关键词： nano-processing,ultrafast laser,drug delivery,silk fiber,laser ablation
更新于2025-09-23 15:21:01
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An Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu2Zn1-xCdxSnS4 Heterointerface for Photovoltaic Applications
摘要： To improve the constraints of kesterite Cu2ZnSnS4 (CZTS) solar cell, such as undesirable band alignment at p?n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu2Zn1-xCdxSnS4 through cost-effective solution-based method without post-annealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of Cu2Zn1-xCdxSnS4 materials. Tunable direct band gap energy ranging from 1.51 eV to 1.03 eV with high absorption coefficient was demonstrated for the Cu2Zn1-xCdxSnS4 nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu2Zn1-xCdxSnS4 helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation photo-excited charge carriers in Cu2CdSnS4 (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point towards efficient separation of photoexcited carriers across the p?n junction in the ultrafast time scale and highlight a route to improve device performances.
关键词： grain boundary,photovoltaic,cation substitution,Earth-abundant material,interfacial engineering,band offset,ultrafast carrier dynamics
更新于2025-09-23 15:21:01
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Terahertz electromagnetic waves radiated from coherent longitudinal optical (LO) phonons and LO-phonon plasmon coupled modes in (001)-, (110)-, and (111)-oriented semi-insulating GaAs single crystals
摘要： We report on terahertz electromagnetic waves from coherent longitudinal optical (LO) phonons and coherent LO-phonon plasmon coupled (LOPC) modes in (001)-, (110)-, and (111)-oriented semi-insulating GaAs single crystals. The coherent LO phonons and coherent LOPC modes are observed in the three samples. In contrast, coherent transverse optical (TO) phonons are not observed in the (110)- and (111)-oriented samples in spite of that the TO phonon is the Raman active mode. We conclude that only the coherent longitudinal oscillating polarization such as coherent LO phonons and coherent LOPC modes radiate the terahertz wave and that the Raman selection rule does not contribute to the terahertz-wave-radiation process. The photogenerated electron-density dependence of the frequencies of the coherent LOPC mode is almost the same in the three samples. This ?nding indicates that the coupling of the LO phonon with the plasmon is not in?uenced by the surface orientations of the three samples.
关键词： coherent LO-phonon plasmon coupled mode,coherent longitudinal optical (LO) phonon,terahertz time-domain spectroscopy,coherent transverse optical phonon,ultrafast phenomena,Raman scattering effect
更新于2025-09-23 15:21:01
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Environmentally Stable 1.56-??m Femtosecond Laser System With Discontinuous Selectable Repetition Rate
摘要： We demonstrate here an environmentally stable and compact Er-doped fiber laser system capable of delivering sub-100-fs pulse duration with discontinuous selectable repetition rate from 10 to 70 MHz. This laser source employs a SESAM harmonic mode-locked soliton laser to facilitate tunable repetition rate. A single-mode-fiber (SMF) amplifier and a double-cladding-fiber (DCF) amplifier (both with double-pass configuration) bridged by a three-stage YVO4-based divider are used to manage the dispersion map and boost the seed pulses. With the help of ×8 replicas, the seed pulses are simultaneously amplified and compressed with 90% recombining efficiency, generating 4.60-nJ pulse energy at 10 MHz and 6.13-nJ pulse energy at 70 MHz. The main advantage of the proposed laser system is that when pulse repetition rate is switched on-demand, the pulse duration can be kept almost unchanged only by simply adjusting the pump powers of the fiber amplifiers, instead of changing any optical device (the spacing between gratings or the length of fibers).
关键词： fiber amplifiers,Mode-locked Laser,ultrafast laser,tunable repetition rate
更新于2025-09-23 15:21:01
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Quantum-memory-enabled ultrafast optical switching in carbon nanotubes
摘要： Optical nonlinearities can be engineered into high-speed optical gates when a probe signal is switched coherently and fast by an optical control pulse through various nonlinear effects for switching. In semiconductors, strong light–matter interaction can also excite many electrons to interact with each other, which can deteriorate switching through Coulomb-induced dephasing. Here, we demonstrate that optical transmission of carbon nanotubes can be switched reversibly hundreds of times via detuned Rabi splitting, faster than 200 fs via nonresonant but strong control pulses. Our detailed experiment–theory analysis identifies that quantum memory in Coulombic scattering restores reversibility whilst simultaneously reducing undesirable pure dephasing of coherences. This capability creates new possibilities for ultrafast quantum optoelectronic processing in quantum materials.
关键词： carbon nanotubes,Ultrafast switching,quantum memory of many-body nonlinearilties,excitonic Stark shift,quantum optoelectronics
更新于2025-09-23 15:21:01
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Highly Conjugated, Fused-Ring, Quadrupolar Organic Chromophores with Large Two-Photon Absorption Cross-Sections in the Near-Infrared
摘要： The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as non-fullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 103 GM) in the near infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (7 rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement and their moderate magnitudes (ca. 10-21 m2) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.
关键词： pump-probe spectroscopy,Nonlinear optics,Z-scan,organic optoelectronics,ultrafast spectroscopy,two-photon absorption
更新于2025-09-23 15:21:01
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Ultrafast fiber laser delivering conservative, dispersion-managed, and dissipative solitons
摘要： A thulium-doped ?ber laser, delivering the temporal solitons, has been proposed with a carbon nanotubes saturable absorber. By adjusting the dispersion design in the laser cavity, the proposed laser can generate three types of solitons, which are conservative soliton (CS), dispersion-managed soliton (DMS), and dissipative soliton (DS), respectively. The experimental results show that, for the ?rst time to the best of our knowledge, the autocorrelation traces of CS, DMS, and DS are in good agreement with hyperbolic secant curve, Gaussian curve, and super-Gaussian curve, respectively. DS with the broad spectral bandwidth of 45.3 nm is emitted from the cavity while the dispersion is adjusted to 0.005 ps2.
关键词： Mode-locking,soliton.,ultrafast ?ber laser
更新于2025-09-23 15:21:01
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Bis(4-methylthio)phenyl)amine-based hole transport materials for highly-efficient perovskite solar cells: insight into the carrier ultrafast dynamics and interfacial transport
摘要： Hole transport layers (HTLs) play a significant role in the performance of perovskite solar cells. A new class of linear small-molecules based on bis(4-methylthio)phenyl)amine as an end group, carbon, oxygen and sulfur as the center atoms for the center unit (denoted as MT-based small-molecule), respectively, have been applied as HTL, and two of them presented the efficiency over 20% in the planar inverted perovskite solar cells (PSCs), which demonstrated a significant improvement in comparison with the widely used HTL, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (known as PEDOT:PSS), in the planar inverted architecture. The ultrafast carrier dynamics show that the excited hot carrier cooling process of MT-based small-molecule HTL samples is faster than that of PEDOT:PSS samples. The kinetic analysis of photo-bleaching peaks of femtosecond transient absorption spectra reveals that the traps at the interface between MT-based small-molecule HTLs and MAPbI3 can be filled much quicker than that at PEDOT/MAPbI3 interfaces. Moreover, the hole injection time from MAPbI3 to MT-based small-molecule HTLs is around 10 times quicker than that to PEDOT:PSS. Such quick trap filling and hole extraction bring a significant enhancement in photovoltaic performances. These findings uncover the carrier transport mechanisms and illuminate a promising approach for the design of new HTLs for highly-efficient perovskite solar cells.
关键词： hole transport layer,perovskite solar cell,ultrafast carrier dynamics
更新于2025-09-23 15:21:01
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The laser beamline in SULF facility
摘要： In this paper, we report the recent progress on the 1 PW/0.1 Hz laser beamline of Shanghai Superintense Ultrafast Laser Facility (SULF). The SULF-1 PW laser beamline is based on the double chirped pulse ampli?cation (CPA) scheme, which can generate laser pulses of 50.8 J at 0.1 Hz after the ?nal ampli?er; the shot-to-shot energy ?uctuation of the ampli?ed pulse is as low as 1.2% (std). After compression, the pulse duration of 29.6 fs is achieved, which can support a maximal peak power of 1 PW. The contrast ratio at ?80 ps before main pulse is measured to be 2.5 × 10?11. The focused peak intensity is improved by optimizing the angular dispersion in the grating compressor. The maximal focused peak intensity can reach 2.7 × 1019 W/cm2 even with an f /26.5 off-axis parabolic mirror. The horizontal and vertical angular pointing ?uctuations in 1 h are measured to be 1.89 and 2.45 μrad, respectively. The moderate repetition rate and the good stability are desirable characteristics for laser–matter interactions. The SULF-1 PW laser beamline is now in the phase of commissioning, and preliminary experiments of particle acceleration and secondary radiation under 300–400 TW/0.1 Hz laser condition have been implemented. The progress on the experiments and the daily stable operation of the laser demonstrate the availability of the SULF-1 PW beamline.
关键词： lasers,ultrafast lasers,titanium,laser ampli?ers
更新于2025-09-23 15:21:01
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Deep and high precision cutting of alumina ceramics by picosecond laser
摘要： Ceramics possess high thermal and chemical resistance, low density, and high compressive strength; however, the machining complications imposed by their inherent brittleness limit their range of applications. Laser cutting technology can offer an automated manufacturing technique for machining these brittle materials. In this paper, a laser cutting method, so-called wobbling, was developed for performing deep, high precision, and defect-free laser cutting of industrial grade alumina ceramics. This work explored picosecond laser process parameters such as focal position, linear speed, and wobble amplitude in order to control cut depth and optimize cut quality in terms of kerf width, kerf taper, surface cleanness, while avoiding crack formation. The morphology and cut quality were evaluated using 3D laser scanning microscopy and scanning electron microscopy (SEM). Picosecond laser cutting process parameters were optimized, achieving a maximum material removal rate of ~10 mm3/min. It was shown that the laser cutting process developed via these experiments represents an effective and efficient manufacturing tool that can be incorporated in engineered net shaping systems.
关键词： Laser cutting,Material removal rate,Ablation,Ultrafast laser micromachining,Alumina ceramics
更新于2025-09-23 15:21:01