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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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High Power Pulse Laser Reflection Sequence Combination with a Fast Steering Mirror
摘要： We propose and demonstrate a new approach for a high power pulse laser reflection sequence combination with a fast steering mirror (FSM). This approach possesses significant advantages for lasers combining with a variety of output power, wavelength, pulse duration, repetition rates and polarization. The maximum number of laser routes participating in combination principally depends on the FSM’s adjustment time of the step response, lasers’ repetition rates and pulse duration. A proof-of-principle experiment is performed with two 2-kW level pulsed beams. The results indicate that the combined beam has an excellent pointing stability with rms pointing jitter ～8.5 ??rad. Meanwhile, a high combining efficiency of 98.6% is achieved with maintaining good beam quality.
关键词： combining efficiency,fast steering mirror,high power pulse laser,reflection sequence combination,pointing stability
更新于2025-09-12 10:27:22
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Strong self-focusing of a chirped pulse laser in thermal quantum plasma under density transition
摘要： In the present manuscript, an analysis has been done on strong self-focusing of a chirped pulse laser in thermal quantum plasma under exponential plasma density transition. It is observed that the beam width parameter reduces up to great extent which in turns enhances the process of self-focusing. It is observed that in the embellishment of self-focusing of laser beam, thermal quantum plasma contributes significantly. Further, it is seen that with change in different parameters like intensity of the laser beam, chirped parameter value and plasma frequency, self-focusing is sensitive and becomes stronger at higher values of these parameters. The present work may have important applications in field of laser interaction with the quantum plasma, laser driven particle accelerators etc.
关键词： thermal quantum plasma,Chirped pulse Laser,self-focusing,exponential plasma density transition
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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[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) - Numerical and Experimental Study on the IR Femtosecond Laser and Phase Mask-Based Grating Inscription in Photonic Crystal Fibers
摘要： Femtosecond pulse laser sources enable the fabrication of fiber Bragg gratings (FBGs) in non-photosensitive fibers, allow for through coating grating inscription when working at infrared (IR) wavelengths and can provide for high temperature stable gratings. Target applications for such gratings include, but are not limited to, optical communications, fiber lasers and fiber sensing. When dealing with such grating inscription method in photonic crystal fibers (PCF) however, the presence of air holes in the fiber cladding impedes the delivery of the femtosecond laser pulse energy to the fiber core, which in its turn significantly affects the index change through non-linear absorption processes in the fiber core [1]. Our research focuses on this issue in view of understanding how the grating writing laser pulses interact with the PCF’s holey structure and of enabling more efficient femtosecond laser-based inscription of FBGs in PCFs. Here we report on the inscription of FBGs in a hexagonal lattice PCF using a femtosecond pulse laser operating at 1030 nm with a phase mask and a short focal length cylindrical lens (f=10 mm) that focuses light to the fiber core [2]. We first looked into the influence of the alignment on laser beam focusing in the cross-section of the PCF by comparing the focusing characteristics to those in standard step-index single mode fiber. As a figure of merit, we used the transverse coupling efficiency (TCE), which is defined as the ratio of the integrated core field intensities simulated (using Lumerical FDTD Solutions?) in the presence and absence of holey cladding. Fig. 1b shows how the TCE changes as the fiber is translated along the X and Y axes in the cross-sectional plane. X=0 and Y=0 corresponds to focused to the center of the core, and negative Y indicates translation of the fiber away from the lens (see Fig. 1a). For a step-index fiber we observe a typically elongated region in which we find optimal coupling with TCE=1 (no air holes) for a beam waist of 2.34 μm and a depth of focus of 15.7 μm. Fig. 1c shows an alignment map for a hexagonal lattice PCF (with structure shown in the inset of Fig. 1d), when light is incident along the ΓK axis of the hexagon. We can identify three distinct regions with a TCE around 0.6. Those appear when the fiber is shifted by around 15 μm and 30 μm further from the lens. This offset indicates that optimal coupling of the grating writing beam to the PCF core requires focusing to the edge of the holey cladding or closer to the silica cladding region of the fiber, rather than to the core center. Fig. 1 a) Fiber translational axes and translation dependence of the transverse coupling efficiency (TCE) for b) step-index fiber and c) PCF. d) Spectra of the IR femtosecond pulse inscribed FBG in the PCF (SEM image in the inset). We then inscribed FBGs in the above mentioned hexagonal lattice PCF with a commercial Yb:KGW ultrafast regenerative amplifier system Pharos 6W (Light Conversion) at 1030 nm and 190 fs duration pulses at a repetition rate of 100 Hz. We used high accuracy alignment stages to find the best coupling position by monitoring the luminescence (around 420 nm) from the Ge-doped core. The reflection and transmission spectra of the inscribed FBG are shown in Fig. 1c. We achieved an almost 4 dB strong FBG in around 4 seconds using a laser power of 450 mW. To the best of our knowledge it is the first time that the difference between regular step-index fibers and PCFs in best focusing conditions for IR femtosecond laser-based FBG writing is studied and that such a FBG is realized in a PCF using a 1030 nm source and a phase mask technique with a short focal length cylindrical lens.
关键词： phase mask,photonic crystal fibers,Femtosecond pulse laser,fiber Bragg gratings,transverse coupling efficiency
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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Nonlinear photoresponse of metallic graphene-like VSe2 ultrathin nanosheets for pulse laser generation
摘要： Vanadium diselenide (VSe2), a typical metallic behaviour material among transition metal dichalcogenides (TMDCs) family, exhibits excellent photoelectric characteristics with a zero band gap, missing applicaiotn in pulse generation. In this work, a high-quality VSe2 saturable absorber (SA) was synthesized through a liquid-phase exfoliation method. The saturable absorption of obtained VSe2-SA was characterized systematically. The measured modulation depth was 9.9%, and the saturated intensity was 533.8 μJ/cm2. By incorporating this optical modulator into a ytterbium-doped ?ber laser cavity, a stable passively Q-switched laser could be achieved. The pulse had the central wavelength of 1064.03 nm. As the pump power was increased, the repetition rate increased from 24.3 kHz to 35.6 kHz, and the pulse duration decreased from 7.21 μs to 5.27 μs. The output power had the maximum value of 28.55 mW. These results indicated that VSe2 is an e?ective candidate to generate pulse laser due to its excellent nonlinear optical properties and universal photoelectric response, which may advance the applications of VSe2-based nonlinear optics and photoelectric devices.
关键词： VSe2,?ber laser,transition metal dichalcogenides,pulse laser,saturable absorber
更新于2025-09-11 14:15:04
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Correlation between defect absorption and nano-second laser-induced damage of HfO2/SiO2 based high reflective coatings at 1064?nm
摘要： The distribution of defect weak absorption and nanosecond pulse laser induced damage characteristics of HfO2/SiO2 multilayers were investigated. A combination of in-situ measurements of defect weak absorption distribution and laser induced damage threshold (LIDT) map was proposed, whereby the evolution of defect weak absorption and the laser induced damage morphology under laser irradiation was studied. During the laser irradiation, some nodular and scalded defects can be removed or passivated by the low flux laser, and the absorption of these defect types was reduced accordingly. Besides, catastrophic destruction defects with enhanced absorption after laser irradiation would develop into catastrophic damage. Further, two-dimensional scanning of the sample surface was used to study the relationship between defects weak absorption and the LIDT. The results indicated that the correlation of defects weak absorption intensity distribution and LIDT map depended on defect evaluation properties during the laser irradiation.
关键词： Nanosecond pulse laser,HfO2/SiO2 multilayers,High reflective coatings,Laser-induced damage,Defect absorption
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