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Multi-octave spanning, Watt-level ultrafast mid-infrared source
摘要： We present a source of brilliant mid-infrared radiation, seamlessly covering the wavelength range between 1.33 and 18 μm (7500–555 cm?1) with three channels, employing broadband nonlinear conversion processes driven by the output of a thulium-fiber laser system. The high-average-power femtosecond frontend delivers a 50 MHz train of 250 fs pulses spectrally centered at 1.96 μm. The three parallel channels employ soliton self-compression in a fused-silica fiber, supercontinuum generation in a ZBLAN fiber, and difference-frequency generation in GaSe driven by soliton self-compressed pulses. The total output enables spectral coverage from 1.33 to 2.4 μm, from 2.4 to 5.2 μm, and from 5.2 to 18 μm with 4.5 W, 0.22 W and 0.5 W, respectively. This spatially coherent source with a footprint of less than 4 m2 exceeds the brilliance of 3rd-generation synchrotrons by more than three orders of magnitude over 90% of the bandwidth.
关键词： intra-pulse difference frequency generation (DFG),ultrafast optics,supercontinuum generation,mid-infrared generation,ZBLAN optical fibre,nonlinear optics
更新于2025-09-23 15:19:57
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Reconstructing ultrafast energy-time-entangled two-photon pulses
摘要： The generation of ultrafast laser pulses and the reconstruction of their electric fields is essential for many applications in modern optics. Quantum optical fields can also be generated on ultrafast timescales; however, the tools and methods available for strong laser pulses are not appropriate for measuring the properties of weak, possibly entangled pulses. Here, we demonstrate a method to reconstruct the joint-spectral amplitude of a two-photon energy-time entangled state from joint measurements of the frequencies and arrival times of the photons, and the correlations between them. Our reconstruction method is based on a modified Gerchberg-Saxton algorithm. Such techniques are essential to measure and control the shape of ultrafast entangled photon pulses.
关键词： joint-spectral amplitude,quantum optical fields,energy-time entangled state,ultrafast laser pulses,Gerchberg-Saxton algorithm
更新于2025-09-23 15:19:57
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Analysis of two-color laser-induced electron emission from a biased metal surface using an exact quantum mechanical solution
摘要： Photoelectron emission from solids, as driven by high-intensity lasers, offers a platform for the coherent control of electron motion on ultrashort spatiotemporal scales. By solving the time-dependent Schr?dinger equation, we present an exact analytical solution for the nonlinear ultrafast electron emission from a dc-biased metal surface illuminated by two-color laser fields. We systematically examine the combined effects of a dc electric field and two-color laser fields. In addition to the remarkable tunability of electron emission processes due to interference from two-color laser fields, we find that a strong dc electric field not only opens up more tunneling emission channels, but also introduces intense modulation to the emission current. We find surprising results that strong current modulation (with respect to the phase difference of the two-color lasers) persists (>70%), even with a large dc bias (i.e., ratio of the electric fields for dc : fundamental laser : second-harmonic laser ～= 1 : 0.5 : 0.07). In the meantime, the average emission current level increases by about three orders of magnitude relative to the case of zero dc bias. Application of our model to time-resolved photoelectron spectroscopy is exemplified and shows that the dynamics of the n-photon excited states depends strongly on the applied dc field. Our study suggests a practical way to maintain a strong modulation to high current photoemission, by the addition of a large dc bias for two-color laser-induced electron emission.
关键词： dc electric field,two-color laser fields,ultrafast electron emission,photoelectron emission,time-dependent Schr?dinger equation
更新于2025-09-23 15:19:57
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Tunability of the Freea??Spectral Range by Microwave Injection into a Mida??Infrared Quantum Cascade Laser
摘要： The free-spectral range (FSR) of quantum cascade lasers (QCLs) emitting at 4.7 μm can be tuned through direct microwave modulation. The intrinsic short carrier lifetime of inter-subband transitions, along with impedance matched electrical packaging, allows a high-speed modulation up to more than 30 GHz. A signi?cant broadening and ?attening of the lasing spectrum is observed under radio frequency (RF) injection with frequencies close to the round-trip cavity. An accurate analysis of the high resolution spectra of the laser shows a comb-like regime for both free-running and RF modulated QCLs, if the modulation frequency is within the locking-range of the device. One of the main advantages of collecting high-resolution mid-infrared spectra, over the plain investigation of the beatnote in the microwave region, is the access to all the longitudinal modes and thus the accurate measure of the FSR over the whole optical spectrum. The use of high-resolution spectroscopy provides an in-depth and comprehensive analysis of lasing spectra under microwave modulations.
关键词： quantum devices,mid-infrared region,injection locking,tunability of the free-spectral-range,ultrafast devices
更新于2025-09-23 15:19:57
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Crack behavior in ultrafast laser drilling of thermal barrier coated nickel superalloy
摘要： Quantitative analysis is required to explore the mechanism of crack generation in ultrafast laser drilling of thermal barrier coated nickel superalloy. In this study, a simple thermo-mechanical coupled model is established to obtain temperature history, phase transformation stress and thermal stress during drilling process, in which laser beam scanning, laser intensity attenuation, the nonlinear relationship between drilling depth and drilling time are involved. The induced stress obtained from the present model is compared with the results by digital image correlation (DIC) method. According to the crack distribution around the drilled hole, the present model is used to explain the mechanism of crack behavior in drilling of multilayer materials. Finally, the strategy using low pulse repetition rate or water jet assisted method is suggested to reduce the thermal effect in ultrafast laser drilling process.
关键词： TBC,Phase transformation stress,Thermal stress,Crack behavior,Ultrafast laser,Laser drilling
更新于2025-09-23 15:19:57
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Light-induced magnetism in plasmonic gold nanoparticles
摘要： Strategies for the ultrafast optical control of magnetism have been a topic of intense research for several decades because of the potential impact in technologies such as magnetic memory, spintronics and quantum computation, as well as the opportunities for nonlinear optical control and modulation in applications such as optical isolation and non-reciprocity. Here we report experimental quantification of optically induced magnetization in plasmonic gold nanoparticles due to the inverse Faraday effect. The induced magnetic moment is large under typical ultrafast pulse excitation (<1014?W?m?2 peak intensity), with magnetization and demagnetization kinetics that are instantaneous within the subpicosecond time resolution of our study. Our results support a mechanism of coherent transfer of angular momentum from the optical field to the electron gas, and open the door to all-optical sub-wavelength strategies for optical isolation that do not require externally applied magnetic fields.
关键词： ultrafast optical control,quantum computation,inverse Faraday effect,spintronics,magnetic memory,plasmonic gold nanoparticles,light-induced magnetism
更新于2025-09-23 15:19:57
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Spectroscopic Studies of Charge-Transfer Character and Photoresponses of F <sub/>4</sub> TCNQ-Based Donora??Acceptor Complexes
摘要： F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) is used widely as a hole-doping agent in photoresponsive organic semiconducting materials, yet relatively little is known about the photoresponses of the F4TCNQ?? anion generated via doping. Furthermore, there is still relatively little systematic exploration of how the properties of the local material or chemical environment impacts the driving force for generating these charge-transfer complexes. Here we present spectroscopic and photophysical studies of F4TCNQ in charge-transfer complexes (CTCs) with the electron donor N,N′-diphenyl-N-N′-di-p-tolylbenzene-1,4-diamine (MPDA) both in dichloroethane solution and polystyrene matrices. Integer charge transfer (ICT) between donor and acceptor occurs readily in dichloroethane solvent to form F4TCNQ??:MPDA+ CTCs, due to a ～150 mV difference in MPDA+/MPDA and F4TCNQ/F4TCNQ?? reduction potentials. Ultrafast spectroscopic studies of the CTC as well as electrochemically generated F4TCNQ?? and MDPA+ reveal that the photoresponses of these CTCs are dominated by that of the dopant anion, including rapid deactivation (800 fs) after excitation to the anion D1 excited state, followed by slower (～10 ps) vibrational cooling in the anion D0 state. Excitation to the higher-lying D2 state results in a rapid relaxation to the D1 state, in contrast to direct D2 → D0 relaxation previously observed for F4TCNQ?? in the gas phase. CTCs embedded in polystyrene (PS) matrices are observed to lose their integer charge-transfer character upon evaporation of solvent, as evidenced by changes to electronic and vibrational absorption features associated with F4TCNQ??. This change is attributed to the loss of solvent stabilization of the ion pair formed through the charge-transfer reaction. Ultrafast spectral measurements reveal that the photoresponses of the partial charge-transfer (PCT) species embedded in PS are still highly similar to those of the ICT species and unlike that of neutral F4TCNQ, implying the electronic properties of the PCT state are likewise dominated by properties of the reduced acceptor molecule. We conclude that excitation of ICT or PCT states introduces optical losses for photoresponses of doped organic semiconductor materials due to the large anion absorption cross section and its rapid, dissipative deactivation dynamics.
关键词： photoresponses,ultrafast spectroscopy,charge-transfer complexes,F4TCNQ,organic semiconducting materials
更新于2025-09-23 15:19:57
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Thienyl Sidechain Substitution and Backbone Fluorination of Benzodithiophene-Based Donor Polymers Concertedly Minimize Carrier Losses in ITIC-Based Organic Solar Cells
摘要： Non-fullerene acceptor (NFA) based organic solar cells have outperformed fullerene-based devices, yet their photophysics is less well understood. Herein, changes in the donor polymer backbone side-chain substitution and backbone fluorination in benzodithiophene (BDT)-thiophene copolymers are linked to the photophysical processes and performance of bulk heterojunction (BHJ) solar cells, using ITIC as NFA. Increased geminate recombination is observed when the donor polymer is alkoxy-substituted in conjunction with faster non-geminate recombination of free charges, limiting both the short circuit current and device fill factor. In contrast, thienyl-substitution reduces geminate recombination, albeit non-geminate recombination remains significant, leading to improved short circuit current density, yet not fill factor. Only the combination of thienyl-substitution and polymer backbone fluorination yields both efficient charge separation and significantly reduced non-geminate recombination, resulting in fill factors (FFs) in excess of 60 %. Time-delayed collection field measurements ascertain that charge generation is field-independent in the thienyl-substituted donor polymer:ITIC systems, while weakly field dependent in the alkoxy-substitued polymer:ITIC blend, indicating the low FFs are primarily caused by non-geminate recombination. This work provides insight into the interplay of donor polymer structure, BHJ photophysics, and device performance for a prototypical NFA, namely ITIC. More specifically, it links the donor polymer chemical structure to quantifiable changes of kinetic parameters and the yield of individual processes in ITIC-based BHJ blends.
关键词： non-fullerene acceptor,ultrafast spectroscopy,bulk heterojunction,charge generation,organic photovoltaics
更新于2025-09-23 15:19:57
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Giant Ultrafast Optical Nonlinearities of Annealed Sb2Te3 Layers
摘要： The optimization of thin Sb2Te3 films in order to obtain giant ultrafast optical nonlinearities is reported. The ultrafast nonlinearities of the thin film layers are studied by the Z-scan technique. Giant saturable absorption is obtained, which is the highest ever reported, by means of the Z-scan technique.
关键词： Sb2Te3,Z-scan technique,ultrafast optical nonlinearities,saturable absorption
更新于2025-09-23 15:19:57
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Photo-chemically derived Plasmonic Semiconductor Nanocrystals as Optical Switch for Ultrafast Photonics
摘要： Establishing new photonic material with large optical nonlinearity in the near-infrared regime is significant for ultrafast optical science and devices. In this paper, we developed a facile photochemical approach to fabricate covellite CuS plasmonic nanocrystals (NCs) with high chemical stability and strong oxidation resistance under ambient conditions. The photo-chemically derived CuS NCs possess strong absorption in the visible-to-near-infrared optical range caused by the localized surface plasmon resonance effect (LSPR). We further demonstrate superior saturable absorption behavior of CuS NCs with large modulation depth and high damage threshold. By using CuS as an optical switch, a highly-stable mode-locked pulsed laser operating in the telecommunication band with signal-to-noise ratio over 70 dB and pulse duration of 1.57 ps has been achieved. Our results suggest that the photochemical method is an effective technique to fabricate plasmonic NCs, which can be developed as an excellent candidate for ultrafast photonic devices in the visible-to-near-infrared region.
关键词： Optical switch,CuS nanocrystals,Photochemical synthesis,Ultrafast photonics,Plasmonic semiconductor nanocrystals
更新于2025-09-23 15:19:57