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Ultrashort laser based two-photon phase-resolved fluorescence lifetime measurement method
摘要： This paper presents a two-photon phase-resolved fluorescence-lifetime measurement method based on the use of an ultrashort pulse laser. The proposed method also involves the use of a lock-in amplifier to control the phase difference between the reference and fluorescence signals, thereby facilitating the use of an alternative method for determining fluorescence lifetimes. Verification of the fluorescence lifetimes as measured in this study was performed using rhodamine B and a cellular thermoprobe as samples. In this study, we assume that the fluorescence decay was monoexponential in all cases. Rhodamine B was observed to exhibit an average fluorescence lifetime of 2.15 ns, whereas a temperature sensitivity of 1.39 ns/°C over a temperature range of 33.79–37.2 °C was demonstrated for the cellular thermoprobe. These results validate the feasibility of the proposed method for accurate measurement of fluorescence lifetimes using a simple laser configuration.
关键词： rhodamine B,ultrashort pulse laser,temperature sensor,phase-resolved fluorescence-lifetime,two-photon microscopy,cellular thermoprobe
更新于2025-09-19 17:13:59
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X-ray radiation protection aspects during ultrashort laser processing
摘要： Ultrashort pulse laser processing of materials allows for precise machining with high accuracy. By increasing the repetition rate to several 100 kHz, laser machining becomes quick and cost-effective. Ultrafast laser processing at high repetition rates and peak intensities above 1013 W/cm2 can cause a potential hazard by generation of unwanted x-ray radiation. Therefore, radiation protection must be considered. For 925 fs pulse duration at a center wavelength of 1030 nm, the x-ray emission in air at a repetition rate of 400 kHz was investigated up to a peak intensity of 2.6 × 1014 W/cm2. Based on the presented measurements, the properties of potential shielding materials will be discussed. By extending our previous works, a scaling of the x-ray radiation emission to higher peak intensities up to 1015 W/cm2 is described, and emitted x-ray doses are predicted.
关键词： laser-induced x-ray emission,ultrashort pulse laser processing,laser ablation,radiation protection
更新于2025-09-16 10:30:52
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Study on nonthermala??thermal processing boundary in drilling of ceramics using ultrashort pulse laser system with variable parameters over a wide range
摘要： Quality and throughput of laser material processing are influenced by multiple laser parameters as well as material properties. Since material degradation due to laser processing is generally related to heat-affected zone, quick optimization and realization of nonthermal process is one of the most important issues for higher-grade laser processing. In this work, we developed various parameter-controlled ultrashort pulse laser system that can control various laser parameters over a wide range, such as pulse duration over three orders of magnitude. Using this laser system (wavelength: 1033 nm, pulse duration: 0.4 to 400 ps, repetition: up to 1 MHz), we have investigated nonthermal–thermal processing boundary in drilling of ceramics: aluminum nitride (AlN) and yttria-stabilized zirconia (YSZ), with high and low thermal conductivity, respectively. As a result, the AlN ceramic exhibited strong dependence of ablation rate on fluence: low-, mid- and high-fluence regimes appeared with different logarithmic correlations. Further, the nonthermal–thermal process boundaries appeared, depending on the pulse duration. On the other hand, the ablation behavior of YSZ was much different from AlN; the ablation rate did not show distinct three regimes. Further, there were no nonthermal process windows for the YSZ. Therefore, the nonthermal–thermal process boundaries were governed by the laser parameters like pulse duration as well as the material thermal conductivity.
关键词： Ultrashort pulse laser,Ceramics,Drilling
更新于2025-09-16 10:30:52
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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) - Controllable Generation of Ultrashort Multi-Bound Solitons in a Mode-Locked Erbium-Doped Ring Laser with a Highly-Nonlinear Resonator
摘要： Mode-locked (ML) ultrashort pulse (USP) fiber lasers can be treated as an ideal platform to expand future applications due to a complex nonlinear dynamics with a presence of a high value of a group velocity dispersion and a third-order dispersion in the laser resonator. Up to now a series of novel ML regimes have been investigated e.g. self-similar pulses, noise-like pulses, multi-bound solitons, and a soliton rain generation. Multi-bound solitons (MBS) generation regime, also known as soliton molecules, is of considerable interest in various fields of applications. For example, the investigation of a MBS generation is very attractive for increasing the data transfer capacity in telecommunications due to coding alphabet extension. The coding concept of MBS suggests a data stream using more than two symbols (2?N symbols, where N is the number of generated solitons in a bound state) [1]. And also, recent research shows that using ultrafast bursts of pulses can improve the quality of laser ablation for medical applications [2]. Moreover, MBS generation can be also used in a coherent pulse staking amplification scheme increasing an amplification efficiency along with a formation of high-energy solitons at a high-repetition-rate [3]. Previously we have obtained a generation of stable low-noise ultrashort multi-bound solitons in a passive mode-locked all-fiber erbium-doped ring laser with a highly-nonlinear resonator [4]. Fig. 1 shows autocorrelation traces and spectrums of MBS generation obtained by pump power variation at a wavelength of 980 nm. The output spectrums are evidently showing high-contrast intensity fringes (up to ~20 dB) and autocorrelation traces having symmetrical form without additional intensity peaks that indicates a stable and strong coherent connection between ultrashort pulses and fixed coherent phase difference in the temporal domain between several identical pulses. It is known that the highest energy of a fundamental soliton in a laser resonator with duration τp is limited by the soliton area theorem Es ~ |β2|/(γ · τp), where γ is the net nonlinear coefficient and β2 is the total cavity dispersion [1]. Soliton energy quantization results in pulse splitting at operation powers higher than the fundamental limit. Here we experimentally demonstrate the formation multi-bound solitons with the controllable number of bound states 7 < N < 17 by pump power variation in the range from ~160 mW to ~377 mW obtained in a highly-nonlinear fiber ring cavity.
关键词： ultrashort pulse,laser ablation,fiber lasers,Mode-locked,coherent pulse staking amplification,soliton molecules,telecommunications,multi-bound solitons
更新于2025-09-12 10:27:22
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Fabrication of a ball end nose micro milling tool by tangential laser ablation
摘要： The general trend towards miniaturization of components is leading to an increasing demand for micro cutting tools. Such tools are found in a variety of applications like optics manufacturing, mold machining or medical technology. Indeed, micromachining exhibits a high efficiency, accuracy and low cost in comparison to other micro processing technologies. Micro cutting tools are mostly produced by grinding, a mechanical process, which might damage the tool due to induced forces, vibrations and heat. These detrimental effects cause the high scrap rate in the manufacturing of micro cutting tools and limited geometrical flexibility. A new approach for the manufacturing of micro cutting tools is given by the ultrashort-pulsed laser technology: it enables material removal, which is independent of the hardness of the workpiece material and with only a negligible heat-affected zone. In most cases, laser ablation is disadvantaged in contrast to grinding because of its relatively low material-removal rate. When it comes to the manufacturing of micro cutting tools the small amount of material to be removed makes the ultra-short pulsed laser an interesting alternative to grinding. Furthermore, the laser ablation is a force and wear-free process, which ensures high precision. In this paper, a commercially available micro ball end mill geometry is measured by micro X-ray tomography and 3D microscopy. The movement of the mechanical axes and the path of the laser beam for manufacturing the desired tool are determined based on these measurements. The milling tools with a diameter of 100 μm are produced from cemented carbide blanks, on a 8-axis laser machining center. After machining, the tools are analyzed by SEM and using FIB: By creating a cross section perpendicular to the cutting edge the heat-affected zone is examined. Finally, the cutting tool is successfully applied for the manufacturing of micro electrodes in copper for an EDM process while recording the cutting forces.
关键词： ultrashort pulse laser ablation,tangential laser ablation,ball end nose micro milling tool
更新于2025-09-12 10:27:22
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Investigations on energy deposition in polycarbonate by picosecond laser pulses for welding applications
摘要： Over the past decade, much research has been done on micro welding of glass by ultrashort lasers pulses. Due to the nonlinear absorption process, the material modification is only confined to the focal volume which enables precise processing at low thermal stress. However, only few articles are available on welding of transparent polymers by ultrashort laser pulses. In this paper, a new approach is used on local melting of polycarbonate by focusing 10 ps laser pulses with up to 400 kHz frequency as preliminary work for welding applications. The influence of different parameters and irradiation strategies on the shape of the modifications were investigated.
关键词： absorber-free,nonlinear absorption,Ultrashort pulse laser,polymer welding,picosecond
更新于2025-09-12 10:27:22
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Simulation of laser ablation mechanism of silicon nitride by ultrashort pulse laser
摘要： A mathematical model is developed to find the depth of laser ablation and laser-material interaction in laser processing of Si3N4 (SL200-BG) by an ultrashort (picosecond) pulse laser. The model is verified with experiments which were carried out at different laser scan speeds from 1 mm/s to 100 mm/s. Experimental validation shows a model accuracy of 85%. Additionally, the results show that in laser intensities (IL) higher than 1.5 × 109 W/cm2, the laser-material interaction is “Multi Photon Ionization” (MPI) with no effects of thermal reaction while in lower values of IL, there are effects of thermal damages adjacent to the laser cut.
关键词： Ultrashort pulse laser,Simulation,Silicon nitride
更新于2025-09-12 10:27:22
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Surface functionalization under water using picosecond and femtosecond laser pulses – first observations and novel effects
摘要： Functionalization by changing the topography of workpiece surfaces is interesting for many applications. Lasers – especially ultrashort pulse lasers – are flexible tools for this kind of tasks. Besides deterministic structures they allow for processing surfaces in a way that stochastic structures appear. Ripple and spike structures can be fabricated in air. In liquids, however, there are only a few investigations and many open questions. The idea of this paper is to check how water in contact to the workpiece surface affects femtosecond laser surface processing and what kind of structures appear. Results obtained with a picosecond laser are presented for comparison.
关键词： ultrashort pulse laser,surface functionalization,spike structures,material processing in liquids
更新于2025-09-12 10:27:22
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Highly-efficient laser ablation of copper by bursts of ultrashort tuneable (fs-ps) pulses
摘要： Ultrashort pulse laser, capable of varying pulse duration between 210 fs and 10 ps and producing a burst of pulses with an intra-burst pulse repetition rate of 64.5 MHz (time distance between pulses 15.5 ns), was used to investigate the ablation efficiency of the copper. The study on ablation efficiency was done for various numbers of pulses per burst between 1 and 40. The increase in the ablation efficiency by 20% for 3 pulses per burst compared to a non-burst regime was observed. The comparison was made between the beam-size optimised regimes. Therefore, the real advantage of the burst regime was demonstrated. To the best of our knowledge, we report the highest laser milling ablation efficiency of copper of 4.84 μm3/μJ by ultrashort pulses at ~1 μm optical wavelength.
关键词： ultrashort pulse laser,laser milling,ablation efficiency,copper ablation,burst mode
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) - Build-Up of Bidirectional Ultrashort Pulse Laser Generation: From Q-Switched Instabilities to Mode-Locking
摘要： Development of new technologies in electronics has made it possible to observe real-time spectral evolution of ultrashort pulses via time-stretching techniques [1]. These experimental methods complement the theoretical completed work on the rich build-up dynamics of solitons in ultrafast lasers [2, 3]. In this work, we have obtained the formation dynamics of counter-propagating solitons in a bidirectional hybrid mode-locked erbium-doped fibre laser using the dispersive Fourier transform (DFT) technique [4]. The bidirectional ring Erbium-doped fibre laser, adopted from [5] is mode-locked via the co-action of single-walled carbon nanotube and non-linear polarization rotation. The laser generates near transform-limited 790 and 570 fs soliton pulses at 14.78 MHz repetition rate with ~1 mW output power. Real-time dynamics were evaluated using a pair of 50-GHz fast photodetector and a 33 GHz real-time digital storage oscilloscope. The DFT is realised in the dispersion compensated fibre (DCF) with overall dispersion of D = -1200 ps/nm. DFT resolution is determined by the total accumulated dispersion and limited by the fundamental Fourier limit to Δλ = 0.28 nm [4]. We have observed soliton formation in frequency domain for both clockwise (CW) and counter-clockwise (CCW) directions. The whole bidirectional pulses formation takes almost 62000 roundtrips from first modulation instabilities until stable ultrafast bidirectional regime is established. Fig. 1a shows real-time spectrum formation for both pulses from 60100 to 62900 roundtrips, when the stable mode-locking is established in both directions. The whole formation dynamics differ from the earlier demonstrated in unidirectional lasers in [2, 3]. The generation starts from characteristic modulation instabilities, which spectral bandwidth rapidly increase, transforming to Q-switched generation (Fig. 1b). Bound soliton formation and unstable mode-locking generation observed before stable mode-locking regime is occurred (Fig. 1e) from unstable Q-switched generation. We believe that obtained results would constitute a basis for the further investigations of counter-propagating soliton dynamics and interactions in bidirectional fibre laser cavities and the role of Q-switched instabilities in mode-locking regime formation.
关键词： mode-locking,bidirectional,ultrashort pulse laser,Q-switched instabilities,soliton dynamics
更新于2025-09-11 14:15:04