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Single-shot frequency-resolved optical gating for retrieving the pulse shape of high energy picosecond pulses
摘要： Accurate characterization of laser pulses used in experiments is a crucial step to the analysis of their results. In this paper, a novel single-shot frequency-resolved optical gating (FROG) device is described, one that incorporates a dispersive element which allows it to fully characterize pulses up to 25 ps in duration with a 65 fs per pixel temporal resolution. A newly developed phase retrieval routine based on memetic algorithms is implemented and shown to circumvent the stagnation problem that often occurs with traditional FROG analysis programs when they encounter a local minimum.
关键词： frequency-resolved optical gating,picosecond pulses,memetic algorithms,pulse shape retrieval,FROG
更新于2025-09-23 15:21:21
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Investigation of laser damage of grating waveguide structures submitted to sub-picosecond pulses
摘要： Grating waveguide structures (GWS) are reflective diffractive optical elements that operate based on the combination of sub-wavelength gratings (periodic microstructures) integrated with planar waveguides. They can be used for high-power laser applications for pulse compression, spectral stabilization, wavelength multiplexing, as well as polarization shaping. In this work, we investigate the laser-damage resistance of GWS based on Ta2O5/SiO2 multilayers at pulse durations of 500 fs and wavelength of 1030 nm. We particularly study the influence of the material of the multilayer sequence, the designed grating structure, and the operational conditions (angle of incidence and polarization of the laser beam) on the laser-damage resistance of the GWS. Comparison of measurements to simulation of the electric-field distribution in the structure reveals a good correlation between laser-induced damage threshold (LIDT) values and electric-field enhancement in the structure. Based on this work, an optimized design has been defined to increase the LIDT of the GWS. An improvement of the LIDT of a factor 2 has been obtained.
关键词： Ta2O5/SiO2 multilayers,Grating waveguide structures,Electric-field distribution,Sub-picosecond pulses,Laser-damage resistance
更新于2025-09-23 15:21:01
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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) - Efficient 2-W Average Power 206 nm Deep-Ultraviolet Generation from 100-kHz Picosecond Pulses
摘要： We report on the generation of 2 W average power pulsed deep-ultraviolet radiation at 206 nm with few-picosecond pulse duration at a repetition rate of 100 kHz. The 206 nm radiation is derived in three steps by fifth harmonic generation from a 1030-nm, 1.6-ps Yb3+:YAG laser. The steps are second harmonic generation (SHG), fourth harmonic generation (FHG) and sum frequency generation (SFG), see Fig. 1 a). A nonlinear-optical beam flattening scheme together with group velocity matching by substantial pulse front tilts enable, to the author’s best knowledge, a new world record in average output power and conversion efficiency.
关键词： harmonic generation,beam flattening,deep-ultraviolet,picosecond pulses,nonlinear optics
更新于2025-09-16 10:30:52
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Pico- to nanosecond pulsed laser-induced forward transfer (LIFT) of silver nanoparticle inks: a comparative study
摘要： Silver nanoparticle inks are among the key functional materials used in printed electronics. Depositing it by laser-induced forward transfer remains a challenging task because the non-linear rheological nature of these inks narrows the range of the laser processing parameters. Understanding, therefore, the influence of the laser parameters on the ejection dynamics and deposition quality is of critical importance. The influence of the laser pulse duration from pico- to nanosecond-laser-induced jet dynamics was investigated using time-resolved shadowgraphy imaging. Jet speed and surface area analyses showed that in the lower laser fluence level range, picosecond pulses induce higher surface area ejections which propagate at higher velocities. As the laser fluence levels were increased, the difference in jet velocity and surface area evolutions narrows. Deposition analysis showed a similar behavior with lower transfer thresholds and larger depositions at lower fluence range when picosecond-laser pulses were used.
关键词： Time-resolved shadowgraphy,Silver nanoparticle inks,Nanosecond pulses,Laser-induced forward transfer,Printed electronics,Picosecond pulses
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) - Generating Picosecond Pulses from Mid-Infrared Fiber Lasers using Frequency-Shifted Feedback
摘要： Ultrafast mode-locked ?ber lasers in the near infrared have enabled a host of key applications in a variety of ?elds such as medicine and defense. In recent years there has been signi?cant interest in pushing the emission wavelength of these ?ber laser systems to the mid infrared (MIR 3 - 5 μm) due to the presence of strong molecular absorption features in this spectral range. Various techniques to achieve this have been demonstrated, with a majority of the work focused on implementation of loss modulation via real saturable absorbers. While this has been successful in generating picosecond pulses in the mid-infrared [1], commercial availability of absorbers is currently limited, and alternatives such as nanomaterials (graphene, black phosphorous) raise questions regarding long-term stability. Virtual absorbers based on nonlinear polarization evolution have shown comparatively superior performance in terms of pulse duration [2] but this method is highly sensitive to small environmental perturbations. In this work we will present recent efforts to offer an alternative method of ‘mode-locking’ using frequency-shifted feedback (FSF) [3,4]. The method requires a frequency shifting element in the cavity, which in this case is an acousto-optic ?lter or modulator. Initial efforts are based on a dysprosium-doped ZBLAN ?ber laser pumped with an Er:ZBLAN ?ber laser (Fig. 1a). An acousto-optic tunable ?lter (AOTF) provides the requisite frequency shift and also a means of tuning the emission wavelength. The broad gain bandwith of dysprosium allows this system to be tuned over a range of 330 nm (Fig. 1b) with a pulse duration that remains consistent at 33 ps. Pulse formation dynamics are investigated numerically and will be presented with consideration to the various parameters that impact realized pulse duration. Of these it will be shown that a ?ltering effect is necessary in addition to the frequency shifting, with the AOTF providing this in the dysprosium case. Filter bandwidth is shown to in part dictate pulse duration, with a wider ?lter supporting shorter pulses. To investigate this we replace the dysprosium cavity with a similar holmium-doped system which replaces the AOTF with a simple acousto-optic modulator (AOM). The broader acceptance bandwidth of the AOM results in improved performance and a pulse duration of less than 5 ps (Fig.1 c-e), which surpasses the current record performance of mid-IR saturable absorber ?ber lasers systems.
关键词： holmium-doped system,frequency-shifted feedback,dysprosium-doped ZBLAN fiber laser,picosecond pulses,acousto-optic tunable filter,mid-infrared fiber lasers
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) - A Functional Mapping for Passively Mode-Locked Semiconductor Lasers
摘要： Passive Mode-locking (PML) of semiconductor lasers is a most promising method for the generation of low repetition rate picosecond pulses, which is of paramount importance for a number of applications. Because of the long round-trip times and fast time scales of the ?eld evolution this regime is computationally very intensive. Studying the pulse train dynamics and temporal jitter can require simulations over hundreds of thousands of round-trips. If, in addition to the longitudinal dynamics, transverse diffraction of the beam or thermal processes are considered, the problem becomes intractable. The Haus master equation [1] is a widely used approach to study PML. By considering a partial differential equation (PDE) model one can restrict the analysis of the ?eld to a small temporal interval around the pulse, making the approach computationally ef?cient. Yet this method, when applied to a particular design, provides only qualitative predictions due to the many simplifying hypothesis involved. We present a method that combines the accuracy of ?rst principle time-delayed models with the computational ef?ciency of the Haus master equation. Our method is based upon computing only the so-called fast stage in the vicinity of the pulse where stimulated emission is dominant, while using an approximate analytical solution of the dynamics during the slow stages in-between pulses. We illustrate the idea of the functional mapping (FM) using the DDE model of [2] that considers unidirectional propagation in a ring laser, however it can be used in other models as well, including approaches using delay algebraic equations (DAEs) like [3]. The equations for the ?eld amplitude A, the gain G and the absorption Q read ˙A γ = ?A +Y (t ? τ) , ˙Q = Q0 ? Q ? s (cid:2) 1 ? e (cid:3) ?Q |A|2 , (1) (3) ˙G = Γ (G0 ? G) ? e ?Q (cid:2) eG ? 1 (cid:3) |A|2 , (2) (cid:4) Y (t) = √ κ exp 1 ? iα 2 G (t) ? 1 ? iβ 2 (cid:5) Q (t) A (t) . (4) We wrote Eq. (1) in a form that makes apparent that the forcing ?eld Y (t ? τ) de?ned in Eq. (4) is a nonlinear function that is known over a whole interval of duration τ. Since gain G and losses Q are functions of A, Y involves only the past values of the ?eld, i.e., Y (t ? τ) = g [A (t ? τ)]. Knowing the forcing term Y, Eq. (1) can be solved for A over an interval of duration τ. Integrating Eqs. (1-4), not over the whole round-trips, but only in a selected time interval in the pulse vicinity, is at the core of the functional mapping (FM) method. The speedup of the FM is equal to the ratio of the actual integration domain 2δ and of the full round-trip τ, i.e., m = τ/ (2δ ). Taking a domain of duration 2δ = 5τp, a pulse with of τp = 1 ps at a repetition rate of τ ?1 = 1 GHz, yields a speedup m = 200, i.e., a 24 hours simulation with, e.g., slow thermal effects or transverse diffraction could potentially be achieved in a few (～ 7) minutes.
关键词： picosecond pulses,semiconductor lasers,Passive Mode-locking,computational efficiency,functional mapping
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) - Passively Mode-Locked High-Repetition Rate Er:YLF Laser at 2.81 μm Generating 72 ps Pulses
摘要： The erbium-doped active media allow to generate laser radiation in spectral range 2.7-2.94 μm if the laser transition 4I11/2→4I13/2 is used. Since the laser radiation in this spectral range is strongly absorbed in the water these lasers can be used in medicine (surgery, ophthalmology, urology). Nowadays, there are many papers deal with erbium-doped bulk active media operating in free-running or Q-switched regime, nevertheless, the passively mode-locked lasers are mainly built with Er-doped fibres. However, the compact passively mode-locked erbium-doped bulk lasers could offer a higher repetition rate and smaller dimensions. To date, the shortest laser pulses (1.78 ns) generated with erbium bulk laser (Er:CaF2-SrF2) was obtained in Q-switched mode-locked regime. In this paper, the SESAM mode-locked compact Er:YLF laser with the picosecond pulses and GHz repetition rate for the first time, according to the author’s knowledge, is presented.
关键词： mode-locked,GHz repetition rate,picosecond pulses,laser,erbium-doped
更新于2025-09-11 14:15:04
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Resonance Enhancement in Laser-Produced Plasmas (Concepts and Applications) || Resonance Processes at Different Conditions of Harmonic Generation in Laser-Produced Plasmas
摘要： Resonance Processes at Different Conditions of Harmonic Generation in Laser-Produced Plasmas
关键词： resonance enhancement,laser-produced plasmas,picosecond pulses,high-order harmonic generation,harmonic generation
更新于2025-09-11 14:15:04