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- 实验方案
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Hollow Core Optical Fibers for Industrial Ultra Short Pulse Laser Beam Delivery Applications
摘要： Hollow core ?bers were introduced many years ago but are now starting to be used regularly in more demanding applications. While ?rst experiments mainly focused on the characterization and analysis of the ?bers themselves, they are now implemented as a tool in the laser beam delivery. Owing to their different designs and implementations, different tasks can be achieved, such as ?exible beam delivery, wide spectral broadening up to supercontinuum generation or intense gas-laser interaction over long distances. To achieve a constant result in these applications under varying conditions, many parameters of these ?bers have to be controlled precisely during fabrication and implementation. A wide variety of hollow core ?ber designs have been analyzed and implemented into a high-power industrial beam delivery and their performance has been measured.
关键词： hollow core ?ber,ultrafast lasers,beam delivery
更新于2025-09-11 14:15:04
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Ultrafast Terahertz Frequency and Phase Tuning by All‐Optical Molecularization of Metasurfaces
摘要： The integration of photoactive semiconductors exhibiting strong light–matter interactions into functional unit meta-atoms facilitates effective approaches to dynamically manipulate terahertz (THz) waves. Here, a new metaphotonic modulator is proposed and comprehensively studied, which demonstrates extensive tunability of the resonant frequency and phase with the merit of ultrafast photoswitching. Specifically, parallel silicon (Si) bridges are embedded in metasurfaces to reinforce the connection ability, achieving ultrafast optical molecularization from a magnetic quadrupole into an electric dipole. Under femtosecond pulse excitation, the demonstrated resonant frequency tuning range is as high as 40% (from 1.16 to 0.7 THz) and can be further promoted up to 48% (from 1.56 to 0.81 THz) by varying the Si bridge length. Meanwhile, the phase delay at given frequencies can be controlled up to 53.3° without significantly changing the high transmission. Furthermore, the transient frequency switching and phase shifting dynamics are systematically investigated for the first time, showing a full recovery time within 2 ns. By optically molecularizing metasurfaces, extended tuning ranges with regard to the resonant frequency and phase, as well as an ultrafast switching speed, are simultaneously acquired in the proposed metamodulator, which provides deeper insight into the multifunctional active-tuning systems.
关键词： silicon microstructures,ultrafast photoswitching,terahertz metamaterials,molecularization
更新于2025-09-11 14:15:04
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Reconstruction of coherent anti‐Stokes Raman scattering signals generated by means of laser pulses with asymmetric amplitude and phase
摘要： Time and frequency asymmetries in ultrashort chirped laser fields might appear as a consequence of dispersive propagation, pulse shaping techniques, or generation of auxiliary light pulses needed in nonlinear optics. Here, we try to find an answer to the question of how to solve analytically coherent anti‐Stokes Raman scattering (CARS) under asymmetric conditions of chirped femtosecond laser pulses. The approach breaks in two parts. One for the field amplitudes and the other for the phases. The former revolves around Gaussian dependences that, besides being rather common in ultrashort laser physics, can be arranged and mixed to reproduce spectrally asymmetric laser amplitudes. The latter is limited to field phases with cubic frequency dependence (i.e., second‐order chirp) whose asymmetry is simulated by adding a linear term to the quadratic phase. Both approximations for amplitudes and phases of the three laser pulses are mandatory to guarantee the solution to the complexity posed by the CARS problem. Comparisons with known experimental and numerical results support the validity of the model.
关键词： laser spectroscopy,coherent anti‐Stokes Raman scattering,ultrafast laser physics
更新于2025-09-11 14:15:04
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Characterization and laser-induced degradation of a medical grade polylactide
摘要： In this study, we carried out the structural and thermal characterization of a medical-grade poly (lactide) (PLA) by SEC, TGA, DSC, NMR, ICP-MS and Py-GC/MS. Moreover, we investigated the laser-induced degradation occurring when ultrashort laser pulses (ULP) were employed to cut extremely thin polymer films prepared by solvent-casting. ULP polymer cutting technology is an interesting manufacturing process for its advantages in potential medical applications. In fact, heat transmission to the region surrounding the cuts is limited, so that the incisions are precise and the effects on the regions around them are small. In this way, the need for post-processing is reduced and ULP cutting becomes interesting for industrial applications. However, degradation induced by ULP may occur and compromise the properties of the polymer samples. To investigate this possibility, portions of PLA films, ultrashort laser cut (ULC) and uncut, were analysed by SEC, DSC, NMR and FTIR. Furthermore, PLA oligomers were studied by ESI-MS. Both SEC and NMR showed a decrease in the molecular weight. FTIR, ESI-MS and NMR spectra revealed the presence of olefin end groups originated from a b-H transfer mechanism, induced by heat and/or light (Norrish II mechanism). Additionally, the inspection of the ESI mass spectra highlighted the cleavage of ester bonds related to the Norrish I type mechanism, undetected by the other techniques.
关键词： Polymer degradation,Ultrafast laser sources,Norrish mechanisms,Biodegradable polymers,Polylactide,Micro-cutting
更新于2025-09-11 14:15:04
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Ultrafast transport and relaxation of hot plasmonic electrons in metal-dielectric heterostructures
摘要： Owing to the ultrashort timescales of ballistic electron transport, relaxation dynamics of hot nonequilibrium electrons is conventionally considered local. Utilizing propagating surface plasmon-polaritons (SPs) in metal-dielectric heterostructures, we demonstrate that both local (relaxation) and nonlocal (transport) hot electron dynamics contribute to the transient optical response. The data obtained in two distinct series of pump-probe experiments demonstrate a strong increase in both nonthermal electron generation ef?ciency and nonlocal relaxation timescales at the SP resonance. We develop a simple kinetic model incorporating a SP excitation, where both local and nonlocal electron relaxation in metals are included, and analyze nonequilibrium electron dynamics in its entirety in the case of collective electronic excitations. Our results elucidate the role of SPs in nonequilibrium electron dynamics and demonstrate rich perspectives of ultrafast plasmonics for tailoring spatiotemporal distribution of hot electrons in metallic nanostructures.
关键词： metal-dielectric heterostructures,hot plasmonic electrons,surface plasmon-polaritons,nonequilibrium electron dynamics,ultrafast transport
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Optical Soliton Molecular Complexes in Ultrafast Fiber Lasers
摘要： Optical soliton molecules are under intense research focus, owing in particular to the interesting analogies between their self-assembly and internal dynamics, and those of matter molecules. Two interacting dissipative solitons can form a soliton-pair molecule, which can behave as a robust entity traveling around the cavity for an indefinite time [1]. The internal oscillatory dynamics of soliton molecules can be compared to molecular vibrations, though they are fundamentally different [2,3]. The recent experimental investigations in Refs. [2,3] have been enabled by the dispersive Fourier transform (DFT) technique, which allows recording spectral measurements at multi-MHz frame rates. They showed the existence of various oscillatory dynamics among soliton-pair and soliton-triplet basic molecules. Following the analogy between light and matter molecules, we now consider the experimental possibility of forming a “soliton molecular complex” (SMC), namely, a higher-order pattern obtained by the stable bonding of several soliton molecules, and investigating its complex internal dynamics. Such structure implies two different bond types, a strong one within each soliton molecule, and a weaker one to maintain the overall structure. We here report the first real-time recording and analysis of several internal dynamics of SMCs, which support this new structural concept. We shall describe our results concerning the dynamics of the fundamental SMC, made of two soliton-pair molecules, or (2+2)-SMC. The experimental configuration is based on an erbium-doped fiber ring laser, which is mode-locked by means of nonlinear polarization evolution (NPE), and its output spectrum analyzed in real-time through DFT [4]. The formation of various SMC is controlled by the laser output power and the tuning of NPE through the orientation of intracavity waveplates, in an experimental procedure which utilizes the hysteretic laser behavior in the multi-pulse regime. SMCs with sliding-phase and oscillating-phase dynamics have been characterized by real-time spectral interferometry measurements, thus revealing the dynamics of the major internal degrees of freedom of the complexes, namely the dynamics of the relative temporal and phase separations between the different soliton constituents. Numerical simulations confirm the experimental observations and offer an additional insight into the understanding of the complex dynamics of SMCs. By showing that soliton molecules can form various bonds according to the distance between soliton constituents, which we can manipulate, this work opens the way to the manipulation of large-scale optical- soliton complexes, which can be extended to other photonic platforms, such as microresonators.
关键词： soliton molecular complex,Optical soliton molecules,nonlinear polarization evolution,ultrafast fiber lasers,dispersive Fourier transform
更新于2025-09-11 14:15:04
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All-Fiber Saturable Absorbers for Ultrafast Fiber Lasers
摘要： The past decade has witnessed tremendous achievements of ultrafast ?ber laser technologies due to rapid developments of saturable absorbers (SAs) based on, in particular, nanomaterials such as 0D quantum dot, 1D carbon nanotubes, 2D layered materials, and 3D nanostructures. However, most of those nanomaterials-based SAs are inevitably absence of the high damage threshold and all-?ber integration, therefore challenging their applications on highly integrated and high-energy pulse generations. Recently, the real all-?ber SAs based on the nonlinear multimodal interference (NLMMI) technique using multimode ?bers are demonstrated to overcome the above limitations. In this review, a detailed summary of the recent advances in NLMMI-based all-?ber SAs is provided, including the fundamental theory, implementation scenarios, and ultrafast ?ber lasers of the all-?ber SAs, covering wide wavelength range of 1, 1.55, and 2 μm. In addition to the state-of-the-art overview, optical rogue waves in the all-?ber SA-based ultrafast ?ber laser are extensively analyzed, which reveals the laser physics behind the dynamics from low-energy to high-energy pulses and directs the design of high-energy ultrafast ?ber lasers. The conclusions and perspectives of the all-?ber SAs are also discussed at the end.
关键词： nonlinear multimode interference effect,high-energy pulse generation,saturable absorber,Ultrafast ?ber laser,optical rogue wave
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Ultrafast Dynamics in Quantum Dot Doped Nanocomposites at Low Temperatures: Study by Means of Site-Selective Spectroscopy
摘要： Study of the dynamics and luminescence properties of nanocomposite materials based on semiconductor quantum dots is an important and urgent trend of modern physics and materials science. Semiconductor quantum dots have a number of unusual photophysical and spectral properties, which are determined by their structure, size and microscopic features of interaction with the local environment. Considerable efforts are aimed to search for and study new luminescence labels [1] and suitable matrices for functional quantum-dot-based materials, e.g., liquid crystals [2]. In this paper we discuss the new data on ultrafast dynamics in nanocomposites doped with semiconductor colloidal nanocrystals (quantum dots, QDs) revealed by two types of site-selective spectroscopy techniques. Optical dephasing in a thin film of double-coated CdSe/CdS/ZnS QDs was studied in a wide range of cryogenic temperatures using a method of the photon echo. Experiments were performed using unique incoherent photon echo spectrometer (see e.g. [3]). We measured the decay curves of 2-pulse incoherent photon echo signals in ensemble of QDs and obtained very short relaxation times (about hundreds of femtoseconds) in a temperature range from 4.5 K to 50 K [4]. These results are extremely different from the data obtained in the ensembles of impurity organic dye molecules for which the relaxation times are about nanoseconds at this very temperature. Possible reasons for such ultrafast optical dephasing can be associated: (1) with structural inhomogeneities of QDs themselves; (2) with the features of internal dynamics of the emitting core (e.g., blinking of QDs); (3) with the surface states in a QDs shells. Furthermore, the size variance and strongly inhomogeneous local environment (local fields in a solid matrix) can lead to fast relaxation in the QDs ensemble. In order to separate the contributions to the optical dephasing of the processes of interaction of quantum dots with the matrix from the processes inside the QDs themselves, we measured the temperature dependences of the luminescence spectra of nanocomposites. Generally, with the temperature decrease, the maxima of the exciton bands in a luminescence spectra shift to the UV spectral range. Such phenomenon can be described taking into account the electron-phonon (exciton-phonon) interaction. The temperature shift of the exciton luminescence spectrum can be described using the modified Varshni equation [5]. Theoretical model that takes into account the electron-phonon interaction made it possible to quantitatively describe the temperature dependences of the exciton luminescence spectra of QDs, as well as to determine the values of the Huang-Rhys factor and the average energy of phonons in nanocrystals. In our experiments no noticeable temperature changes in the exciton maxima widths have been observed, which is related, on the one hand, to the resolution of used experimental technique and, on the other hand, to the occurrence of significant inhomogeneous broadening of the spectra caused by a large dispersion of QD sizes. Describing the temperature behavior of the position and width of the luminescence spectra of QDs one should take into account an interaction of the electronic transition of the impurity with vibrational excitations, e.g. with local or quasi-local phonons in a solid matrix. In this connection, we have studied the influence of the matrix on luminescence properties of QD-doped nanocomposites. The combination of the photon echo and luminescence spectroscopy is a powerful method to study the ultrafast processes of interaction of the impurity ensemble of QDs with a solid matrix as well as the intrinsic dynamics of quantum dots themselves.
关键词： ultrafast dynamics,luminescence,quantum dots,photon echo,nanocomposites,site-selective spectroscopy
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Ghz-Bursts and Ultrafast External Modulation of Femtosecond Fiber Lasers with kW Average Power Levels
摘要： State-of-the-art ultrafast materials processing applications impose strong requirements on the driving laser systems. For novel ablation schemes GHz-bursts are necessary to operate ideally [1,2]. Additionally, fast modulation and control of these pulse trains is required allowing for both high-power operation (kW of average powers and mJ pulse energies) and, ideally, pulse-to-pulse amplitude control. Here we present novel solutions to address these demands based on fiber-laser technology and coherent beam combination. A standard approach to generate GHz-pulse bursts is to use a seed oscillator with a GHz repetition rate emitting a continuous pulse train and employ a pulse picker to generate the burst afterwards. Although this approach is easy to implement, it is relatively inflexible and imposes strong requirements on the pulse picker. The approach presented herein bases on a state-of-the-art MHz-level oscillator followed by a standard pulse picker. The pulse burst is generated using cascaded fiber-based delay lines (see Fig. 1). This method allows for intra-burst repetition rates >10GHz with variable pulse numbers at flexible repetition rates. Furthermore, the implementation of ultra-fast switches into high-power material processing devices is of high demand. Although there has been progress in recent years, switching and modulation of high-power laser systems is still an extreme technological challenge. Typical solutions for fast switching up to the GHz level force a trade-off between speed and high-power capability. The novel approach presented herein bases on the coherent combination of at least two parallelly working amplifier channels that are coherently combined prior the CPA compressor. Coherent combination technology has been used so far as a power-scaling concept [3] allowing to increase average power and output energy of a laser system linearly with the number of combined channels. However, it also enables fast switching of the output port by changing the phase between the two interferometrically combined amplifier channels. The advantage of this approach is that the switching element (such as an fiber-coupled electro-optical modulator) can be integrated at an early low-power stage of the system, while it actually performs as an external modulator placed at the system output. However, at the output position, only a power-scalable beam combining element has to be employed.
关键词： kW average power levels,GHz-bursts,ultrafast external modulation,femtosecond fiber lasers
更新于2025-09-11 14:15:04
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[IEEE 2019 International Conference on Electronics Packaging (ICEP) - Niigata, Japan (2019.4.17-2019.4.20)] 2019 International Conference on Electronics Packaging (ICEP) - An Investigation of Compound Machining of Ceramic-LPM Package by Ultrafast Laser
摘要： It is well known that ceramic substrates provide excellent electrical insulation and protection from oxidation/ corrosion in addition to idea heat dissipation while allowing heat dissipation through controlled paths, e.g. integrated heat sinks. Low pressure molding (LPM) with polyamide and polyolefin (hot- melt) materials is a process typically used to injection molding for waterproof, to encapsulate and environmentally to protect electronic components. The purpose than epoxy encapsulation is to protect electronic components with finer pitch against moisture, dust dirt and vibration. There is a special need for SiP (System in Package) application utilizing both ceramic substrate and LPM package materials where ceramic serves as mechanical structure and thermal dissipation path and LPM for high density SMT (Surface Mount) package. The research of this paper is to apply nano UV (Ultraviolet) laser to machine the LPM and ceramic substrate (sapphire, Al2O3) and compare the results with nano green laser. The interactions of these two materials with laser are quite different and even conflicting for machining (LPM is ductile and hot-melt while ceramic is brittle), thus proper strategy has to be taken to satisfy needs for both materials. One of the major problem is the re-solidification of LPM material as temperature elevated during laser irradiation. It is necessary to provide a delay time between each laser pulsing. The laser ablation threshold (LAT) of green and UV laser for both materials is also investigated in this paper. The best parameters for processing ceramic substrates are speed 200 mm/s, frequency 95 kHz, delay time 450 ms, when processing LPM speed 700 mm/s, frequency 40 kHz, delay time 250 ms.
关键词： Low Pressure Mold (LPM) compound,laser ablation threshold (LAT),ceramic substrate,ultrafast Laser
更新于2025-09-11 14:15:04