Picosecond Laser System Research Articles

Determination of atomic hydrogen density and fluorescence decay time by 1D resolved, picosecond TALIF in the RAID linear device

Abstract We report on the first 1D resolved two-photon absorption laser-induced
fluorescence (TALIF) measurements of atomic hydrogen (H) performed in the
Resonant Antenna Ion Device (RAID) using a picosecond laser system. The
results are obtained across a cylindrical plasma column with peak electron
density 10^18 m^-3 and temperature 1 eV on axis, which decrease monotonically
to 2*10^17 m^-3 and 0.75 eV over a scale of a few cm away from the axis. TALIF
results in these conditions are compatible with a uniform H density profile across
the observed region, with a mean dissociation degree close to 3%. The small
variation of H density across regions covering a wide range of plasma parameters
suggests that transport processes and wall interactions play an important role in
determining the H density profile. The fluorescence decay time is close to 10 ns at
all observed locations, a result compatible with complete substate mixing of the
n = 3 states of H.

Non-Radiative Deactivation in Isolated Quinoline.

The photophysics of the S2 1(ππ*) state of the polycyclic aromatic nitrogen-containing hydrocarbon (PANH) quinoline is investigated in a free jet using a picosecond laser system. A [1 + 1] multiphoton ionization spectrum yields the S2 origin at around 32 200 cm-1 and reveals several vibronic bands. In time-resolved experiments, quinoline is then excited between 312.2 and 279.7 nm. Probe wavelengths of 351 and 263.5 nm are employed. The dynamics is monitored by time-resolved photoelectron imaging. The images reveal a short-lived band at high electron kinetic energies with a ps lifetime and a band at lower electron kinetic energies that shows an offset at long delay times. In comparison with previous work, the offset is assigned to ionization from the T1 state. Lifetimes decrease from 45 ps at the S2 origin to 11 ps at +3550 cm-1. Most likely, the S2 1(ππ*) state deactivates by internal conversion to the S1 1(nπ*) state, followed by intersystem crossing to the triplet manifold.

Lens Fragmentation with Picosecond Laser Pulses After Artificial Cataract Induction with Microwaves.

Objectives: In this work we demonstrate the first laboratory study results of lens fragmentation with low-energy picosecond ultrashort laser pulses after artificial induction of cataract with microwave radiation on an ex vivo animal model. Background: This method will be evaluated with regard to the further development of lens fragmentation with novel ultrashort picosecond laser systems instead of ultrasonic phacoemulsification or the significantly more complex femtosecond laser fragmentation. Methods: As samples we used postmortem porcine eyes. The lenses were dissected and then irradiated in a microwave oven for artificial cataract induction. Subsequent computer-driven lens fragmentation was performed with a 12 ps, 1064 nm pulsed laser source with 100 µJ pulse energy, and 10 kHz pulse repetition rate. Results: Both the artificial cataract induction and the lens fragmentation were demonstrated. When inducing cataract, different degrees/stages of opaqueness and hardness could be achieved with different irradiation times and methods. The fragmentation with 12 ps pulses led to good results with regard to ablation depth and rate, especially for the softer lenses. Conclusions: As could be shown, low-energy picosecond ultrashort laser pulses are feasible for cataractous lens fragmentation on an ex vivo animal model with artificial cataract induction. Thus, this technique may influence future cataract surgeries by possibly being an alternative or extension to state-of-the-art methods. This will be evaluated with further tests and studies.

Treatment of Iron-Induced Cutaneous Hyperpigmentation With Energy-Based Devices.

Iatrogenic cutaneous siderosis is a well-recognized dermatologic complication after parenteral iron infusion. The condition manifests as discrete, hyperpigmented patches near the site of injection. Most cases do not resolve spontaneously, leading to significant aesthetic and psychological distress to patients. A recent case of iatrogenic cutaneous siderosis at our institution prompted a systematic review of the efficacy of energy-based devices previously reported in the treatment of this condition. PubMed and Cochrane databases were searched for all peer-reviewed articles published using the following search terms: "iron OR heme OR hemosiderosis OR siderosis" and "hyperpigmentation OR staining OR tattoo." Articles reporting on energy-based devices in the treatment of iron-induced hyperpigmentation were included. A total of seven articles and 54 total patients were included in this review. All patients, including the patient treated at our institution, were female, with an average age of 44 years. Hyperpigmentation was most commonly associated with intravenous iron infusion (48/54, 89%), on the arm or forearm (44/54, 81%), and used for the treatment of underlying iron deficiency anemia (54/54, 100%). The application of six different nanosecond or picosecond quality-switched laser systems was reported in the treatment of cutaneous siderosis, with wavelengths ranging from 532 to 1064 nm. Spot sizes varied between 2 and 7 mm, with energy fluences spanning 0.5-40 J/cm2 depending on both the device and spot size. Outcomes were measured after an average of 5.4 laser treatments and 10.4 months, with over half of all reported patients experiencing complete clearance (27/50, 54%). Our patient received treatment inthree test areas withpicosecond alexandrite 785 nm, nanosecond Nd:YAG 532 nm, and picosecond Nd:YAG 532 nm devices. The nanosecond Nd:YAG 532 nm treated area demonstrated the greatest improvement,and the entire arm was subsequently treated with this device. Despite the often intractable nature of iatrogenic cutaneous siderosis, laser surgery is a reasonable and safe treatment modality for patients seeking cosmetic improvement of this dyschromia. Dermatologists should be aware of this entity and the efficacy of the energy-based devices currently in our armamentarium. A combination approach may need to be utilized with different wavelengths and pulsed widths to target iron pigment in both dermal and subcutaneous layers.

Compact hundred-watt level picosecond laser system based on tapered double cladding fiber-single crystal fiber hybrid amplifier

This paper introduces a compact picosecond laser system using tapered double cladding fiber-single crystal fiber hybrid amplification technology for the first time. By modifying the Ginzburg-Landau equation, we established a simulation model and designed a passive mode-locked picosecond oscillator based on a semiconductor saturable absorber mirror. The oscillator outputs laser with a pulse width of 7.75 ps, a center wavelength of 1030.55 nm, and a spectrum width of 0.58 nm. The seed laser is stretched and amplified by the all-fiber front stage, and then injected into the tapered double cladding fiber-single crystal fiber hybrid amplifier. The laser power is amplified from 820 mw to 103.1 W, obtaining a gain of 21 dB. We used zero-phonon line pumping technology in single crystal fiber amplifier to reduce the thermal effects caused by quantum loss, thereby increasing the length of the crystal and increasing the power loading capacity. We designed a single crystal fiber amplification module using Yb:YAG with 60 mm long, 1 mm diameter and a 1 at.% doping rate for the first time. Finally, a hundred-watt level picosecond laser output with a repetition frequency of 26.33 MHz, an average power of 103.1 W, a pulse width of 244.72 ps, a spectrum width of 1.16 nm, and a beam quality of M2 x = 1.368 and M2 y = 1.511 was obtained. To the best of our knowledge, this is the highest picosecond laser output power for an all-fiber front-stage combined with a single-stage single crystal fiber amplifier.

Influence of Laser Treatment of Ti6Al4V on the Behavior of Biological Cells.

This article explores the enhancement of material surface properties of Ti6Al4V, potentially applicable to dental implants, through ultra-short pulse laser systems. This study investigates potential connections between surface wettability and biocompatibility, addressing the challenge of improving variability in material properties with specific laser treatment. Several designed microstructures were manufactured using a picosecond laser system. After that, the wettability of these structures was measured using the sessile drop method. The basic behavior and growth activity of biological cells (MG-63 cell line) on treated surfaces were also analyzed. While the conducted tests did not conclusively establish correlations between wettability and biocompatibility, the results indicated that laser treatment of Ti6Al4V could effectively enlarge the active surface to better biological cell colonization and adhesion and provide a focused moving orientation. This outcome suggests the potential application of laser treatment in producing special dental implants to mitigate the issues during and following implantation.

Interface behavior and pore distribution of Ti6Al4V/CFRTP joints affected by groove profile

This study investigated the effect of groove profile on interface behavior, pore distribution, and bonding mechanism between Ti6Al4V (TC4) and carbon fiber reinforced thermoplastic (CFRTP). Using an ultraviolet picosecond laser system, grooves with varying depth-width ratios (R) and distances between adjacent grooves (T) were precisely etched on the TC4 surface. Experiment results revealed that grooves effectively impede bubble coalescence and growth, reduce pore defects at the grooves’ outer interface, and promote closer bonding between TC4 and CFRTP, thereby enhancing joint strength. In this study, grooves significantly improved joint strength by 40.2 % to 147.5 %, primarily due to increased mechanical interlocking and bonding area. Differences in joint strength among grooved joints are mainly attributed to variations in interface behavior and pore distribution caused by R and T. Appropriate R and T are crucial for inhibiting large-volume pores and reducing pores at the grooves’ outer. When R = 1/5 and T = 360 μm, the joint with small-volume pores, no pores at the grooves' outer, and the lowest porosity exhibits the highest strength (2830.3 N). Grooves showed no significant impact on chemical bonding (CTi0.42V1.58 carburization phase and TiOS). Furthermore, no significant effect of grooves on the chemical bonding (CTi0.42V1.58 carburization phase and TiOS).

Replicative Production of Multifunctional Microfluidic Polymer Films for Biomedical Disposables

Increasing demands on the reproducibility and accuracy of lab-on-a-chip systems in the life science sector require new tools for the molding of polymer films with spatially selectively functionalized surfaces. By applying local micro- and nanostructuring to the molding tools, the aim is to achieve multifunctionality of the polymer films, by setting certain wetting properties. This means that fluid-affecting properties (hydrophobic, hydrophilic) should be possible. To functionalize polymer films, the replication tools were specifically microstructured using laser-based surface functionalization. The periodic micro- and nanostructures were produced with the help of nanosecond pulsed and picosecond pulsed laser systems using Direct Laser Interference Patterning. For this purpose, complex functional microstructures in the range of 0.1 µm to 100 µm were developed based on a bionic approach. The functional properties were transferred in a one-step replicative process using UV-imprinting and were subsequently verified by determining the wetting behavior of the molded microfluidic films and the corresponding laser microstructured replication tools. This publication presents the successfully developed processes and the promising results of this series of experiments.

Ionic terahertz metasurface in ultrathin-layered conductive hydrogel by ultrafast laser tailoring

The ion-interactive semi-conductive hydrogel emerged as a promising optoelectronic material due to its desirable electrical conductivity, optical clarity, and switchable dielectric properties beyond incumbent inorganic materials. However, developing the actively modulated terahertz (THz) devices via hydrogel remained barely studied at an early stage. Herein, a scalable high-throughput picosecond laser system rapidly tailored hydrogel into ion-interactive dielectric metasurfaces (IDMs). The IDMs exhibited minus permittivity (ɛ < 0 F/m) not belonging to hydrogel, tunable time/frequency modulation, and high-consistency geometries for specific THz wave manipulations. The interplay between anions and the π-conjugated thiophene ring of hydrogel dynamically changed the dielectric properties and electrical conductivity through mixed electron/hole transportation, making IDMs change their microscale electric fields anomalously. Other as-prepared IDMs (split resonators, interleaved antennas, and their array) further confirmed the native capability of generating orbital angular momentum, spatially manipulating THz waves, or tuning frequencies. This work ushers in a new platform to customize and deploy non-metal THz meta devices in batches.

Improving the joint strength of laser-welded CFRTP/TC4 joints via appropriate groove design

Laser surface treatment can enhance the joint strength of reinforced thermoplastic composites (CFRTP) and metal joints. In this study, an ultraviolet picosecond laser system grooved the Ti-6Al-4V (TC4) surface, and the influence of grooves on the CFRTP/TC4 joints was investigated. 0° parallel, 90° parallel, 45° parallel, 0/90° crossed and ±45° crossed grooves were created on TC4 surface. Compared with the joint without grooves, the joint strength was improved by all groove patterns. The grooves improve the thermal contact resistance at the interface, and buffer the energy input of the CFRTP side, inhibiting the pyrolysis of the CFRTP and eliminating the bubble defects. Meanwhile, the groove enhances mechanical interlocking. The joint with ± 45° crossed grooves was the strongest, being 120.1 % stronger than the joint without grooves (ultimate shear force of 1552 N). Apart from the mechanical interlocking, the compound layer consisting of the CTi0.42V1.58 phase was confirmed and a novel chemical bonding, TiOS, was also discovered at the interface. However, no significant effect of the grooves on chemical bonding was found. The increase in thermal contact resistance and the mechanical interlocking reinforcement after cooling were the main strengthening mechanisms of the grooves.

Picosecond pulsed 532nm laser system for roughening and secondary electron yield reduction of inner surfaces of up to 15m long tubes.

Laser-induced surface structuring is a promising method to suppress electron mulitpacting in the vacuum pipes of particle accelerators. Electrons are scattered inside the rough surface structure, resulting in a low Secondary Electron Yield (SEY) of the material. However, laser processing of internal pipe surfaces with a large aspect ratio is technologically challenging in terms of laser beam guidance and focusing. We present a 532nm ultrashort-pulse laser setup to process the inner parts of 15m long beam vacuum tubes of the Large Hadron Collider (LHC). Picosecond pulses at a repetition rate of 200kHz are guided through an optical fiber toward an inchworm robot traveling inside the beam pipe. The system was installed, characterized, and tested for reliability. First surface treatments achieved the required scan precision. Cu2O-dominated nano-features were observed when processing at high average laser power (5 W) and slow scanning speed (5mms-1) in nitrogen flow, and the maximum SEY of copper was decreased from 2.1 to 0.7.

Fabrication of functional zirconia surfaces using a two‐beam interference setup employing a picosecond laser system with 532‐nm wavelength: Morphology, microstructure, and wettability

AbstractThe aim of this work was to evaluate the feasibility of the fabrication of microtextures in zirconia using the direct laser interference patterning (DLIP) technique. A green ultra‐short pulsed laser (532 nm, 10 ps) with a two‐beam interference setup was used to produce line‐like structures with a spatial period of 3 µm. For a fixed set of fluence and pulse‐to‐pulse overlap values (6.2 J/cm2, 81%), periodic structures were successfully created for different hatch distances. The average depth of the features ranged from 0.37 µm for a hatch distance of 14.4 µm up to 0.84 µm for a hatch distance of 12.4 µm. However, a further decrease in hatch distance did not result in an increase in depth since the region of the ridges is also ablated. Scanning electron microscopy analysis showed pores formation on the laser grooves, but no sign of micro‐cracking could be observed. Wettability tests showed an increase in hydrophobicity after DLIP. These results bring exciting perspectives on the fabrication of micro‐textures with DLIP on zirconia surface.

Targeting new ways for large-scale, high-speed surface functionalization using direct laser interference patterning in a roll-to-roll process

Direct Laser Interference Patterning (DLIP) is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm. The raw beam having a diameter of 3 mm @ 1/e 2 is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS®-L element and cylindrical telescopes. The shaped beam is split into its diffraction orders, where the two first orders are parallelized and guided into a galvanometer scanner. The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern. The DLIP spot has a line-like interference pattern with about 15 μm spatial period. Laser fluences of up to 8 J cm−2 were achieved using a maximum pulse energy of 0.6 mJ. Furthermore, an in-house built roll-to-roll machine was developed. Using this setup, aluminum and copper foil of 20 μm and 9 μm thickness, respectively, could be processed. Subsequently to current collector structuring coating of composite electrode material took place. In case of lithium nickel manganese cobalt oxide (NMC 622) cathode deposited onto textured aluminum current collector, an increased specific discharge capacity could be achieved at a C-rate of 1 °C. For the silicon/graphite anode material deposited onto textured copper current collector, an improved rate capability at all C-rates between C/10 and 5 °C was achieved. The rate capability was increased up to 100% compared to reference material. At C-rates between C/2 and 2 °C, the specific discharge capacity was increased to 200 mAh g−1, while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 mAh g−1, showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.

Sub-picosecond timing jitter between optically synchronized femtosecond and picosecond laser systems

Synchronized optical pulses are widely used. We report here characterization and measurement of synchronized femtosecond and picosecond pulses from a Ti:Sapphire laser (nominally 800 nm) and a Nd:YAG laser (1064 nm), respectively. Synchronization is achieved by utilizing soliton self-frequency shift in a photonic-crystal fiber that allows the 800 nm femtosecond oscillator to seed the third-harmonic generation (355 nm) of picosecond regenerative amplifier. The relative timing jitter between the amplified femtosecond and the third-harmonic generation of picosecond pulses is (710 ± 160) fs, which is only (1.17 ± 0.26)% of the picosecond pulse duration. This work paves way for applications in stimulated Raman scattering spectroscopy and amplification.

Femtosecond two-photon LIF imaging of atomic hydrogen in high-pressure methane-air flames

Atomic hydrogen (H) imaging studies in combustion systems have been limited thus far to atmospheric- or low-pressure flames. The commonly used excitation scheme for two-photon laser-induced fluorescence (TPLIF) of H involves 205-nm deep-ultra-violet (DUV) laser pulses generated using nanosecond (ns), picosecond (ps), or femtosecond (fs) laser systems. Ultrashort pulse, fs excitation schemes are more attractive because of the efficient two-photon excitation and interference-free kHz-rate imaging capability. In this work, we implemented a home-built, direct fourth harmonic generation (FHG) laser system to generate high-energy fs pulses for H imaging in CH4/air flames at pressures up to 10 bar. The high-energy FHG output was capable of overcoming transmission losses of DUV laser pulses through thick optical windows of the pressure vessel. Signal interferences such as photoionization, photolytic production, amplified spontaneous emission, and background chemiluminescence were avoided or minimized during data acquisition and subsequent data processing steps. A quadratic dependence of the H TPLIF signal on the laser energy was observed. The increase in the pressure from 1 to 10 bar showed a rapid decay of the fs H TPLIF signal although it should scale linearly with increasing H number density with pressure ideally at equilibrium conditions. Besides a detailed quenching correction, laser absorption and fluorescence signal trapping remain major issues at elevated pressures. The measured fluorescence signals are compared with the equilibrium H number densities and local H concentrations calculated using the Cantera (0D) and UNICORN (2D) flame codes, respectively, for a range of equivalence ratios, and possible reasons for discrepancies are discussed. Experimentally obtained 1D and 2D spatial distributions of H are well predicted by the UNICORN flame model. Steps towards quantitative single-shot H TPLIF imaging measurements in high-pressure flames are also discussed. Overall, the fs TPLIF imaging technique coupled with a high-efficiency home-built FHG system is a promising diagnostic approach for H imaging in high-pressure flames.

Efficacy of 2% Kojic Acid Containing Formulation vs Picosecond Laser for Treatment of Melasma

Background: Melasma is a frequently observed dermatological condition. The conventional therapies for melasma improvement established to date are mainly categorized into chemical peeling, topical agents and laser therapy. A new technique to reduce discomfort and post-laser discoloration induced by heat effects is the picosecond laser system. Objective: To find out efficacy of 2% kojic acid containing formulation vs picosecond laser for treatment of melasma Methodology: This was comparative randomized controlled study carried out at the department of dermatology Qazi Hussain Ahmad Medical Complex Nowshera and alshifa clinic and skin aesthetic, Nowshera for duration of one year from July 2020 to July 2021. Totally, 300 patients were included in the study. Each picosecond laser and kojic acid group comprise of 150 patients. All the information was recorded at the baseline and each following visit. Severity Index (MASI) score was calculated and color photographs were taken of all patients. Results: At baseline, the mean MASI scores for picosecond laser and kojic acid group was 10.5±3.5 and 11.2±4.1 respectively (p=0.31). In both the group significant improvement occur in the MASI scores at weeks 12 and week 20. In picosecond laser group, the most remarkable improvement rate (62%) was noted while in kojic acid containing formulation group the rate of improvement was 41.96%. Conclusion: Our study concludes that picosecond Laser device is an efficient and well-tolerated therapeutic option for melasma as compared to kojic acid containing formulation. Keywords: Efficacy; Kojic acid; Picosecond laser; Melasma

Tailoring surface properties, biocompatibility and corrosion behavior of stainless steel by laser induced periodic surface treatment towards developing biomimetic stents

Laser-Induced Periodic Surface Structures (LIPSS) holds great potential for regenerative biomedicine. Creating highly precise LIPSS enables to generate biomimetic implant surfaces with improved properties. The present study focuses on the fabrication and investigation of laser-treated stainless steel samples with applied linear LIPSS patterns with grooves made by means of a picosecond laser system using wavelengths of 1064 nm and 532 nm. To investigate properties of the laser-treated surfaces and to understand the basics of cell-surface interactions between the LIPSS and human Umbilical Cord Mesenchymal Stem Cells (UCMSC), flat stainless steel samples with various applied nanopatterns were used. Such LIPSSs demonstrated higher surface roughness, good biocompatibility, lower wettability and higher corrosion resistance compared to the untreated (polished) specimens. The surface roughness of laser-treated samples was in microscale that enabled adhesion and migration of endothelial cells, thus increasing the likelihood for endothelialisation. This thereby could reduce the chances for the development of Late Stent Thrombosis (LST) and In-Stent Restenosis (ISR). Furthermore, laser textured surfaces demonstrated an environment supportive for cell attachment, proliferation and alignment with the nanogroves. Therefore, application of the biomimetic nanopatterns could help to overcome frequent post-surgery complications after the stent implantation.

Effect of Laser Surface Texturing parameters on the texture formation in pure magnesium substrate

Magnesium and its alloys find a prominent application in bio-implant applications. However, their poor surface property like high corrosion rate has limited their wide usage. Various conversion and deposited coating methods are available to protect the magnesium surface from the rapid degradation. Recently, laser surface texturing (LST) has been identified as a unique surface treatment technique. In this work, LST experiments were conducted on a pure magnesium substrate with a picosecond laser system. The effect of laser scan speed and number of passes on the texture formation and surface roughness was investigated. Microstructure of the textures was investigated through scanning electron microscopy and surface roughness was investigated through White Light Interferometry (WLI). Results revealed that texture formation is accurate in lower laser scanning speed. Moreover, depth of the textures increases in lower scanning speed conditions. Surface roughness of the textures is governed by the formation of recast materials in and around the textures.

Amplified Spontaneous Emission from Thermally Evaporated High-Quality Thin Films of CsPb(Br1-xYx)3 (Y = I, Cl) Perovskites.

As a wavelength-tunable lasing material, perovskites are now generating a lot of scientific attention. Conventional solution-processed CsPbX3 perovskite films sometimes suffer unavoidable pinhole defects and poor surface morphology, severely limiting their performance on amplified spontaneous emission (ASE) and lasing application. Herein, a thermal evaporation approach is explored in our work to achieve a uniform and high-coverage CsPb(Br1-xYx)3 (Y = I, Cl) perovskites polycrystalline thin film. The ASE of these films was studied using a picosecond laser system. The ASE profile increases rapidly over the narrow peak in relation to the laser pump intensity, confirming the development of stimulated emission. ASE began when the energy density threshold was reached and ranged between 25 and 170 μJ/cm2 per pulse for perovskite materials when replacing I with Br and then Cl. This work emphasizes the notable optical properties of high-quality perovskite thin films, leading to possible accessible uses in optoelectronic applications.

High Power Ultranarrow Linewidth Picosecond Laser System Based on Tapered Fiber Amplifier and Gain-Switched DFB Laser Diode

We experimentally demonstrate the highest spectral brightness for the pulsed fiber lasers to the best of our knowledge in a compact high power and pulse energy laser system consisting of a DFB laser diode as a master oscillator and a high-power fiber amplifier based on a double-clad active tapered fiber (T-DCF). Due to the unique properties of T-DCF, this system provides more than 1 MW of peak power and pulse energy of more than 60 μJ at a frequency of 500 kHz while maintaining a spectral width of less than 0.1 nm. The spectrum broadening limits the further power scaling of the laser system. The system is capable of delivering up to 150 W average power at 10 MHz pulse repetition rate with 0.14 nm linewidth. We also demonstrate the second harmonic generation of 532 nm with over 30 W at 10 MHz repetition rate and 14.5 W at 500 kHz. The experimental results reveals that the narrow linewidth system based on a DFB laser diode and a T-DCF amplifier is an excellent and robust solution for material processing and Raman spectroscopy.