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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) - Achievement of Very Smooth Cavity Sidewalls by UV Picosecond Laser Micromachining
摘要： Achievement of very smooth cavity sidewalls by UV picosecond laser micromachining. As a contactless and maskless method generating a reduced heat affected zone compared to nanosecond laser, ultrafast laser micromachining is widely used for rapid prototyping and materials processing. Today, most research and development works is devoted to study and control LIPPS occurring at the surface of the cavity bottom. But for many applications, there is a strong need to produce highly smooth sidewalls like for microelectronic sample preparation, microfluidics, waveguides, etc.. A laser based technology allowing to obtain very smooth surfaces (Ra of ~3 nm) already exists but it involves melting of a significant volume of material. So far, to the best of our knowledge, no parametric study aiming at minimizing the roughness of picosecond laser micromachined sidewalls in silicon has been performed. In the present work, picosecond laser micromachining (532 nm and 343 nm) of cavity sidewalls in silicon is studied. The evolution of the surface roughness is deeply investigated experimentally and theoretically as a function of laser and scanning parameters. We demonstrate that RaX, which is measured along the scanning laser beam direction, can be minimized by increasing laser beam overlap and the crater size, in accordance with a simple geometrical model. Experimentally, the minimum RaX is obtained for a beam overlap of ~80% and the largest crater sizes. Beyond 80%, we observed a roughness degradation which is probably due to two main phenomena. The first involves the interaction between the laser beam and the debris, which deteriorates the beam quality. The second is related to the highly heterogeneous ablation occurring for large overlaps, which induces a rough surface. Along the beam propagation direction, the sidewall is characterized by a relatively high waviness which induces a more important height variation than the roughness. The waviness depends mainly on the Rayleigh length. Thus, it can be reduced by using a large focal spot radius and a short wavelength. Once the sidewall is finished, the surface topology does not vary much with the laser micromachining time. Overall, smooth and homogeneous surfaces can be produced by choosing a beam overlap close to 80%. The best results were obtained at 343 nm, which allows to extend the Rayleigh zone, to increase the laser absorption on the sidewall asperities and to improve the induced cleaning thanks to a more confined interaction. The present work demonstrates that very low roughness (< 40 nm) can be achieved on sidewalls of cavities by picosecond laser micromachining. In addition this approach allows the roughness tuning. As it is based on a geometrical model, it is extendable to other materials as long as the surface melting, which may erase the induced periodic structuring, is not significant. This tuning possibility can be useful to modify the surface properties, such as reflectivity, friction and wettability, and therefore adapt the sidewall to different applications.
关键词： smooth cavity sidewalls,waviness,silicon,UV picosecond laser,roughness,micromachining,Rayleigh length
更新于2025-09-12 10:27:22
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Successful Treatment of Cosmetic Eyebrow Tattoos in Fitzpatrick III‐IV With Picosecond (1,064, 532‐nm) Neodymium‐Doped Yttrium Aluminum Garnet Laser With a Perfluorodecalin‐Infused Patch: A Pilot Study
摘要： Background and Objectives: Nanosecond Q‐switched lasers have been used for the removal of traditional and cosmetic tattoos. Picosecond lasers utilize pulse durations of 10?12 and provide more efficient clearance of tattoos. Safe and effective removal of tattoos is especially important in cosmetically sensitive areas such as the face. We report four patients with skin types (III–IV) who have had successful removal of eyebrow tattoos with the picosecond (1,064‐, 532‐nm) laser using a perfluorodecalin‐infused patch (PFD). Study Design/Materials and Methods: Patients with eyebrow tattoos underwent treatment with dual‐wavelength picosecond Nd:YAG laser at 1,064‐nm with a 3 mm spot size and fluence of 4–4.6 J/cm2. The 532‐nm wavelength was also used during treatment #1 (patient 2 only) with a 4 mm spot size and fluence of 0.5 J/cm2. Patient 1 had a total of three treatments (6–8 weeks apart). The remaining patients, each had only one treatment. Patients were photographed prior to treatment and subsequently at each follow‐up. Results: Immediately following each laser treatment, only mild and transient localized erythema and edema was observed. Some epidermal crusting was noted for 3–5 days following each treatment. Eyebrow hair growth was not affected and no adverse events were reported. There was 75% clearance in patient 1 after three treatments over a period of 2.5 months, 75% clearance in patient 2 after one treatment, 90% clearance in patient 3 after one treatment, and 100% clearance in patient 4 after one treatment. Conclusions: The 532‐ and 1,064‐nm wavelength of the picosecond Nd:YAG laser was safely used to clear brown and black ink eyebrow tattoos in four patients, three of whom were skin type IV, and one of whom underwent eyebrow tattoo via microblading, a novel and popular technique for cosmetic tattoos. The use of picosecond laser provides several treatment advantages to Q‐switched laser when treating eyebrow tattoos. In our experience, it required less number of treatments and lower fluences. This, along with use of the perfluorodecalin‐infused patch resulted in excellent outcomes for our patients with no significant side effects.
关键词： microblading,Nd:YAG,permanent makeup,picosecond,cosmetic tattoos,eyebrow tattoo,neodymium‐doped yttrium aluminum garnet
更新于2025-09-12 10:27:22
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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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Mild accidental macular injury induced by picosecond Nd:YAG laser
摘要： Accidental laser-associated ophthalmic complications are rare disorders which were first described in 1965 by Rathkey as a ‘laser burn’ of the macula. Most reported ophthalmic complications have been induced by nanosecond neodymium-doped yttrium aluminium garnet (Nd:YAG) laser. Several studies have reported that most nanosecond Nd:YAG laser-associated ophthalmic complications are choroidal neovascularisation, macular hole, and vitreous haemorrhage. These complications also have been reported as poor prognosis of visual function. Few reports appear to have described picosecond Nd:YAG laser-associated ophthalmic complications. In this report, a case of mild ophthalmic complications of subretinal and choroidal haemorrhage due to accidental picosecond Nd:YAG laser irradiation is described.
关键词： optical coherence tomography,angiography,picosecond Nd:YAG laser,ophthalmic complications
更新于2025-09-12 10:27:22
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High-performance oil-water separation polytetrafluoroethylene membranes prepared by picosecond laser direct ablation and drilling
摘要： The membranes with special surface wettability have attracted considerable attention, especially in the practical applications of oil-water separation. Here, we presented a simple and rapid method of picosecond (ps) laser direct ablation and then drilling to fabricate high-performance oil-water separation polytetrafluoroethylene (PTFE) membrane. It was found that the as-prepared rough PTFE membranes had ca. 0° contact angle (CA) of oil in air and above 150° CAs of water in air or oil, respectively, exhibiting superoleophilicity and under-oil superhydrophobicity. The micropore size of the membranes was less than ca. 180 μm, the corresponding separation efficiencies were over 99.0% for different oil-water mixtures due to the special and rough surface microstructures. Importantly, the separation efficiencies and fluxes of the as-prepared membranes showed no obvious change with suffering heavy erosion or 40 separation cycles, indicating that the membranes had excellent stability and applicability. Additionally, the effect of the special and rough surface on oil-water separation performance was investigated. This work provides a new pathway for the rapid fabrication of high-performance separation membranes.
关键词： Picosecond laser ablation,Superoleophilicity,Polytetrafluoroethylene,Superhydrophobicity,Oil-water separation
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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Study the Effect of Changing the Surface Roughness and the Laser Focus Distance to the Aluminum Appearance using Picosecond Laser
摘要： Picosecond laser device is used to treat Aluminum samples, the appearance of the treated samples is affected by the variation of laser focus distance and the samples surface roughness. Samples with smoother surface before laser treatments show dark colors and high increase in surface roughness after laser treatments, while samples with rougher surfaces before laser treatments show brighter colors with slightly change in surface roughness after the laser treatments. The surface texture, topography, and roughness of the treated samples is characterized to identify the mechanism driving appearance change. The characterization results indicate that size and shape of laser processing induced microscale cavities on the surface may account for the differences in samples appearance.
关键词： Aluminum Appearance,Picosecond Laser,Focus Distance,Surface Roughness
更新于2025-09-12 10:27:22
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Thermal and optical performance characteristics of a spatial light modulator with high average power picosecond laser exposure applied to materials processing applications
摘要： A spatial light modulator (SLM) addressed with Computer Generated Holograms (CGH’s) can create structured light fields when an incident laser beam is diffracted by a phase CGH. The power handling limitations of SLMs based on a liquid crystal layer have always been of some concern. Now, with careful engineering of chip thermal management, we present the detailed optical phase and temperature response of a liquid cooled SLM exposed to picosecond laser average powers up to 220W at 1064nm – new knowledge critical for determining device performance at high laser powers. SLM chip temperature rose linearly with incident laser exposure, increasing by only 5°C at 220W incident power, measured with a thermal imaging camera. Thermal response time with continuous exposure was 1-2 seconds. The optical phase response with incident power approaches 2π radians with average powers up to 130W while above this power, liquid crystal thickness variations limit phase response to just over π radians. These remarkable performance characteristics show that liquid crystal based SLM technology is highly robust when efficiently cooled. High speed, multi-beam plasmonic surface micro-structuring at a coverage rate of 8cm2s-1 is achieved on polished metal surfaces at 25W exposure, while diffractive multi-beam surface ablation on stainless steel at an ablation rate of ～4mm3min-1 is demonstrated with average power 100W. Continuous exposure for many hours exceeding 100W laser power did not result in any detectable drop in diffraction efficiency hence no permanent changes in SLM phase response characteristics have been observed This research work will help to accelerate the use of liquid crystal SLMs for both scientific and ultra-high throughput laser-materials micro-structuring applications.
关键词： Spatial light modulator,active cooling,high average power picosecond laser,high power laser micro-machining
更新于2025-09-12 10:27:22
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Alopecia Totalis Treated with 1064 nm Picosecond Nd:YAG Laser: A Case Report
摘要： Alopecia areata (AA) is an autoimmune disorder causing nonscarring hair loss. Alopecia totalis (AT), the severe form of AA, is usually refractory to many ?rst-line treatments including topical and intralesional corticosteroids and topical immunotherapy. Systemic corticosteroids, ultraviolet light phototherapy, and immunosuppressants may be effective but can cause side effects and high recurrence rates after discontinuing treatment. Janus kinase inhibitors and numerous types of lasers, such as 308 nm excimer laser or light, low-level laser therapy, and fractional lasers have been explored for alternative treatment of AA over the past few years with bene?cial effects. Herein, we presented a case of AT treated with the novel 1064 nm picosecond Nd:YAG laser (ps-Nd:YAG) (Cutera, Brisbane, CA, USA) under a split-scalp study. A 25-year-old woman presenting with AT for two years was treated with topical and intralesional steroid and the 1064 nm Nd-YAG picosecond laser on the right half of the scalp. The laser treatment interval was once a month. The left half of the scalp was treated with topical and intralesional steroids alone. After treatment for six times, the right half of the scalp had greater improvement than the left half of the scalp. 1064 nm picosecond Nd:YAG laser therapy may be an effective alternative adjuvant treatment for AT.
关键词： alopecia,laser,alopecia areata,picosecond laser,alopecia totalis,hair loss
更新于2025-09-12 10:27:22