Single Pulse Irradiation Research Articles

Modeling the hundreds-of-nanoseconds-long irradiation of tin droplets with a 2 µm-wavelength laser for future EUV lithography

Abstract The properties of an extreme ultraviolet (EUV) source driven by hundreds-of-nanoseconds-long laser pulses of λ laser = 2 µm wavelength are investigated through radiation-hydrodynamic simulations. We show that single-pulse irradiation of 30 µm-diameter tin droplets can generate in-band energies ∼ 30 mJ directed in the 2π sr solid angle subtended by the collector mirror, yielding energies ∼100 mJ produced from 45 µm-diameter droplets. Time-integrated in-band EUV emission profiles, generated by taking Abel transforms of the local net in-band emissivity, reveal EUV source sizes in the axial (laser) direction × radial direction of ∼600 (1000) × 100 (150) µm2 for 30 (45) µm-diameter droplets. We find that approximately 74% of the total in-band emission is produced during the first half of the total propulsion distance irrespective of droplet size or laser intensity. Furthermore, we propose a one-dimensional analytical propulsion model to qualitatively explain the simulated droplet trajectory and to predict the time taken for the droplet to vaporize. These findings offer motivation for the development of high-power EUV sources based on single-pulse, hundreds-of-nanoseconds-long irradiation of tin droplets.

Infrared microlens formation on chalcogenide polymer surface via femtosecond laser pulse ablation

In this study, we introduced micro-optical surface formation via femtosecond (fs) laser pulse scanning to chalcogenide polymer (ChP), a promising material for cost-effective infrared applications. Employing this method, we successfully fabricated a large-area poly(sulfur-random-(1,3-diisopropenylbenzene)) (S-r-DIB) microlens array (MLA) component. Each micro-concave spherical surface was crafted with a single fs laser pulse, serving as a micro-concave lens surface. We achieved a quasi-periodic MLA sample with over 2 × 105 micro-lenslets within a 10 mm × 10 mm footprint. Additionally, precise locating of laser pulse irradiation enabled us to create a hexagonal MLA with a filling factor over 37 %. Morphological investigations and imaging tests confirmed the adequate surface quality of the fabricated components, with its uniformity revealed by the virtual foci grid in near infrared region. To elucidate the forming conditions and mechanisms, we studied the evolution of surface morphology under various laser irradiation conditions. Laser induced damage thresholds of S70-r-DIB30 were experimentally determined for both 800 nm and 400 nm wavelengths under single- and multi-pulse irradiation scenarios. We identified the optimal fabrication fluence window as 115–205 mJ/cm2 with 800 nm single-pulse irradiation. The bandgap of the S70-r-DIB30 was estimated as 2.06 eV, and energy band analysis confirmed distinctions in ablation morphology. Furthermore, we investigated sub-surface morphology evolution using orthogonal ultrafast pump–probe imaging, revealing diversity compared to traditional inorganic and polymeric optical materials due to differing absorption and etching mechanisms. The elastic wave velocity of 3.2 km/s in this ChP and etching velocity of 0.7 μm/pulse were experimentally determined. These findings deepen our understanding of ChP material interaction with fs lasers, offering insights for potential applications such as surface engineering, substrate cutting, and micro-structure formation.

Efficient extreme ultraviolet emission by multiple laser pulses

We demonstrated an efficient extreme ultraviolet (EUV) source at a wavelength of 13.5 nm using spatially separated multiple solid-state-laser pulse irradiation. The maximum conversion efficiency (CE) achieved was 3.8% for ±30° oblique laser pulse injection, which was about twice as high as that for single laser pulse irradiation of 1.7%, with an EUV source size of about 100 μm for two spatially separated laser pulses with a total laser energy of 500 mJ at a laser intensity of 2×1011 W/cm2. In addition, we achieved an EUV CE of 4.7% for ±60° oblique laser pulse injection, which was one of the highest values ever reported, in the case of a 1-μm solid-state laser-produced planar Sn target plasma by multiple laser pulse irradiation. This result suggests that multiple laser-pulse irradiation at high repetition rate operation could credibly provide the next technology for future high-power EUV sources and exposure tools toward future EUV technology nodes.

Unbalanced core detector (UCD): a novel direct-reading dosimeter for FLASH radiotherapy

FLASH radiotherapy (FRT) is a novel radiotherapy technique based on dose rates that are several orders of magnitude greater than those used in conventional radiotherapy (40 Gy/s vs. 0.5–5 Gy/min). FRT is still in its preclinical and early clinical stage of development. However these studies indicate that FRT is more effective in sparing normal tissues from radiation-related side effects, as compared to conventional radiotherapy. This is the so-called "FLASH effect" and was observed with multi-MeV electron beams. Before FRT is made available to humans, more basic research is needed to fully understand its radiobiology fundamentals. Meanwhile, suitable radiation sources and dosimetric tools are gradually becoming available. Within this framework, INFN-LNF developed the Unbalanced Core Detector (UCD), a novel type of electron dosimeter designed to operate in the FRT domain. UCD main characteristics are the nearly isotropic response, the independence from the electron energy, the very high radiation resistance, the linearity up to dose rates of MGy/s and the possibility to record the time evolution of a single radiation pulse. UCD was tested using 7 and 9 MeV electron beams produced with the ElectronFlash accelerator from Sordina IORT Technologies (SIT S.p.A.) in Aprilia, Italy. UCD was used to measure dose distributions in a water phantom. The results well compare to those obtained with a flashDiamond detector from PTW.

Totally Caged Type I Pro-Photosensitizer for Oxygen-Independent Synergistic Phototherapy of Hypoxic Tumors.

Activatable type I photosensitizers are an effective way to overcome the insufficiency and imprecision of photodynamic therapy in the treatment of hypoxic tumors, however, the incompletely inhibited photoactivity of pro-photosensitizer and the limited oxidative phototoxicity of post-photosensitizer are major limitations. It is still a great challenge to address these issues using a single and facile design. Herein, a series of totally caged type I pro-photosensitizers (Pro-I-PSs) are rationally developed that are only activated in tumor hypoxic environment and combine two oxygen-independent therapeutic mechanisms under single-pulse laser irradiation to enhance the phototherapeutic efficacy. Specifically, five benzophenothiazine-based dyes modified with different nitroaromatic groups, BPN 1-5, are designed and explored as latent hypoxia-activatable Pro-I-PSs. By comparing their optical responses to nitroreductase (NTR), it is identified that the 2-methoxy-4-nitrophenyl decorated dye (BPN 2) is the optimal Pro-I-PSs, which can achieve NTR-activated background-free fluorescence/photoacoustic dual-modality tumor imaging. Furthermore, upon activation, BPN 2 can simultaneously produce an oxygen-independent photoacoustic cavitation effect and a photodynamic type I process at single-pulse laser irradiation. Detailed studies in vitro and in vivo indicated that BPN 2 can effectively induce cancer cell apoptosis through synergistic effects. This study provides promising potential for overcoming the pitfalls of hypoxic-tumor photodynamic therapy.

Experimental investigation on the transient vascular thermal response to laser irradiation by a high-speed infrared thermal camera

Based on the photothermal effect, laser can be used to treat vascular diseases (VD) in clinic of dermatology and ophthalmology. Transient vascular thermal response to laser irradiation during millisecond laser pulse is the key phenomenon in treatment process, which has not been carefully investigated before. In this study, target blood vessels in dorsal skin chamber (DSC) animal model were irradiated by a pulsed 532 nm diode laser and a 1064 nm Nd:YAG laser. The directed thermal responses (temperature variation) were recorded by a high-speed infrared thermal camera with a repetition rate of 1000 Hz. The temperature variation during and after single pulse irradiation and multipulse irradiation were investigated. The variation of blood absorption coefficient was explored based on the temperature increment in each laser pulse. The thermal properties of dorsal skin, especially the thermal diffusivity, were evaluated based on the temperature decay after each laser pulse. The interfacial heat transfer between the blood and the surroundings was also calculated based on the thermal images and compared to the correlation proposed before. The results show that the blood absorption to laser will increase by a maximum of 1.9 immediately after blood temperature exceeds threshold value, e.g., 68oC in both single pulse (pulse duration >100 ms) and multi-pulse laser irradiation. The tissue optical properties (thermal diffusivity) keep almost constant after millisecond laser heating. Also, a general correlation for interfacial heating transfer between blood and surroundings was developed, in which the influences of vessel shape and laser wavelength are incorporated. The interfacial heat transfer between blood and surrounding can be accurately quantified.

Spatial extension of the transient gain drop in a microchannel plate for a single-pulse irradiation

It is widely recognized that a microchannel plate gain drops temporarily after a particle initiates an electron avalanche and that a large amount of charge is extracted from the channel. Electron multiplication is expected to deplete the charges from the microchannel and produce depleted charges (wall charges), and this gain drop is known to persist until charges are replenished. In addition, it was reported that a gain drop occurs not only in the activated channels, where the electrons are multiplied, but also in the surrounding channels. A proposed mechanism for this phenomenon is suggested that the wall charges in the activated channels change the electric field in the surrounding channels, which affects the electron multiplications. In this study, the spatial extent of the gain drop of a chevron microchannel plate detector was evaluated by measuring gains as a function of distance from an activated channel. The experiment used two ultraviolet pulses with different beam sizes, which initially activated one channel and the six neighboring channels with carefully focused laser light, and then applied another light pulse to the surrounding 900 μm × 30 μm area. The gain of each channel was measured using a charge-coupled device camera, and the change in gain as a function of the output charge for the laser pulse was analyzed. A gain drop of 20% was observed at a channel located 110 μm far from the initial activated channel when the output charge was 4 pC. The obtained relationship between the radius of gain drop area and the output charge for the laser pulse was in good agreement with that predicted from the transverse electric field due to the wall charges by computational analysis.

Fabrication of fluidic submicron-channels by pulsed laser-induced buckling of SiOx films on fused silica

Recently, considerable attention has been drawn to the field of micro/nanofluidic channels. However, current methods for fabricating micro/nanochannels are complex, costly, and time-intensive. In the present work, we successfully fabricated transparent submicron-channels on fused silica substrates (SiO2) using a straightforward laser process. To achieve this, a single-pulse excimer laser irradiation in a rear side configuration was employed to treat a thin film of UV-absorbing silicon suboxide (SiOx) through the transparent SiO2 substrate. A polydimethylsiloxane (PDMS) superstrate (coating layer) was applied over the SiOx film before laser exposure, serving as a confinement for controlled structure formation induced by the laser. Under optimal laser fluence, the thin SiOx film buckled, leading to the formation of channels with a width ranging from 10 to 20 µm and a height of 800 to 1200 nm, exhibiting a bell-like cross-sections following the so-called Euler buckling mode. Wider channels displayed morphologies resembling varicose or telephone cord modes. Subsequent high-temperature annealing led to the oxidation of SiOx, resulting transparent SiO2 channels on the fused silica substrate. The manufactured nanochannels exhibited promising potential for effectively transporting fluids of diverse viscosities. Various fluids were conveyed through these nanochannels via capillary action and in accordance with the Lucas-Washburn equation.

Spectral control of beyond extreme ultraviolet emission from a dual-laser-produced plasma

We demonstrated spectral control of beyond extreme ultraviolet (B-EUV) emission at a central wavelength of 6.76 nm from a gadolinium (Gd) laser-produced plasma. The highest spectral purity (SP) was 5.1% under dual 1-μm laser pulse irradiation. It doubled compared to a value of 2.4% attained under single laser pulse irradiation of solid density Gd because of the reduction in optical depth. The highest maximum SP was higher than that obtained using a mid-infrared laser at 10.6 μm. The SP for the 150-ps main laser was also higher than that for 6-ns main laser irradiation. Our approach can be extended to mid-infrared solid-state laser-produced plasmas (LPPs) using driving laser wavelengths ranging from 2 to 9 μm for efficient B-EUV source development.

Single Pulse Nanosecond Laser-Stimulated Targeted Delivery of Anti-Cancer Drugs from Hybrid Lipid Nanoparticles Containing 5nm Gold Nanoparticles.

Encapsulating chemotherapeutic drugs like doxorubicin (DOX) inside lipid nanoparticles (LNPs) can overcome their acute, systematic toxicity. However, a precise drug release at the tumor microenvironment for improving the maximum tolerated dose and reducing side effects has yet to be well-established by implementing a safe stimuli-responsive strategy. This study proposes an integrated nanoscale perforation to trigger DOX release from hybrid plasmonic multilamellar LNPs composed of 5nm gold (Au) NPs clustered at the internal lamellae interfaces. To promote site-specific DOX release, a single pulse irradiation strategy is developed by taking advantage of the resonant interaction between nanosecond pulsed laser radiation (527nm) and the plasmon mode of the hybrid nanocarriers. This approach enlarges the amount of DOX in the target cells up to 11-fold compared to conventional DOX-loaded LNPs, leading to significant cancer cell death. The simulation of the pulsed laser interactions of the hybrid nanocarriers suggests a release mechanism mediated by either explosive vaporization of thin water layers adjacent to AuNP clusters or thermo-mechanical decomposition of overheated lipid layers. This simulation indicates an intact DOX integrity following irradiation since the temperature distribution is highly localized around AuNP clusters and highlights a controlled light-triggered drug delivery system.

Femtosecond laser-induced damage on the end surface of double-cladding fluorotellurite fiber

In this study, the damage characteristics of double-cladding fluorotellurite glass fiber endface was conducted. Double-cladding fluorotellurite fiber was prepared with a core composition of 70TeO2-20BaF2-10Y2O3 (TBY70), an inner cladding composition of 33AlF3-9BaF2-17CaF2-12YF3-8SrF2-11MgF2-10TeO2 (ABCYSMT), and an outer cladding composition of 65TeO2-25BaF2-10Y2O3 (TBY65). It was concluded that at the wavelength of 800 nm, the laser-induced damage threshold (LIDT) of inner and outer cladding were found to be 1951.8 and 1551.8 mJ/cm2, respectively, under single-pulse laser irradiation. Then, the influence of pulse number on the LIDT was studied. As the laser pulse number increased from 1 to 200, the LIDT of outer cladding decreased from 1551.8 mJ/cm2 to 695.2 mJ/cm2 due to the cumulative effect of damage crater defects. When the pulse number reached 100, the LIDT saturated, corresponding to a damage accumulation factor of 0.84. With the pulse number increasing continuously from 50 to 5000, the damage area showed no significant change, but the damage depth increased from 40.4 μm to 73.0 μm. In addition, the damage resistance of the two materials, TBY65 and ABCYSMT, was analyzed based on the ionization rate obtained from simulations.

High-Resolution Laser Interference Ablation and Amorphization of Silicon.

The laser interference patterning of a silicon surface via UV femtosecond pulse irradiation, resulting in 350 nm periodic structures, is demonstrated. The structuring process was performed using a laser with a 450 fs pulse duration at a wavelength of 248 nm in combination with a mask projection setup. Depending on the laser fluence, single-pulse irradiation leads to amorphization, structure formation via lateral melt flow or the formation of voids via peculiar melt coalescence. Through multipulse irradiation, combined patterns of interference structures and laser-induced periodic surface structures (LIPSS) are observed.

Damage threshold of LiF crystal irradiated by femtosecond hard XFEL pulse sequence.

Here we demonstrate the results of investigating the damage threshold of a LiF crystal after irradiating it with a sequence of coherent femtosecond pulses using the European X-ray Free Electron Laser (EuXFEL). The laser fluxes on the crystal surface varied in the range ∼ 0.015-13 kJ/cm2 per pulse when irradiated with a sequence of 1-100 pulses (tpulse ∼ 20 fs, Eph = 9 keV). Analysis of the surface of the irradiated crystal using different reading systems allowed the damage areas and the topology of the craters formed to be accurately determined. It was found that the ablation threshold decreases with increasing number of X-ray pulses, while the depth of the formed craters increases non-linearly and reaches several hundred nanometers. The obtained results have been compared with data already available in the literature for nano- and picosecond pulses from lasers in the soft X-ray/VUV and optical ranges. A failure model of lithium fluoride is developed and verified with simulation of material damage under single-pulse irradiation. The obtained damage threshold is in reasonably good agreement with the experimentally measured one.

Visible Pulsed Laser-Assisted Selective Killing of Cancer Cells with PVP-Capped Plasmonic Gold Nanostars.

A new generation of nanoscale photosensitizer agents has improved photothermal capabilities, which has increased the impact of photothermal treatments (PTTs) in cancer therapy. Gold nanostars (GNS) are promising for more efficient and less invasive PTTs than gold nanoparticles. However, the combination of GNS and visible pulsed lasers remains unexplored. This article reports the use of a 532 nm nanosecond pulse laser and polyvinylpyrrolidone (PVP)-capped GNS to kill cancer cells with location-specific exposure. Biocompatible GNS were synthesized via a simple method and were characterized under FESEM, UV-visible spectroscopy, XRD analysis, and particle size analysis. GNS were incubated over a layer of cancer cells that were grown in a glass Petri dish. A nanosecond pulsed laser was irradiated on the cell layer, and cell death was verified via propidium iodide (PI) staining. We assessed the effectiveness of single-pulse spot irradiation and multiple-pulse laser scanning irradiation in inducing cell death. Since the site of cell killing can be accurately chosen with a nanosecond pulse laser, this technique will help minimize damage to the cells around the target cells.

Exploring Low-Power Single-Pulsed Laser-Triggered Two-Photon Photodynamic/Photothermal Combination Therapy Using a Gold Nanostar/Graphene Quantum Dot Nanohybrid

Combined photodynamic/photothermal therapy (PDT/PTT) has emerged as a promising cancer treatment modality due to its potential synergistic effects and identical treatment procedures. However, its clinical application is hindered by long treatment times and complicated treatment operations when separate illumination sources are required. Here, we present the development of a new nanohybrid comprising thiolated chitosan-coated gold nanostars (AuNS-TCS) as the photothermal agent and riboflavin-conjugated N,S-doped graphene quantum dot (Rf-N,S-GQD) as the two-photon photosensitizer (TP-PS). The nanohybrid demonstrated combined TP-PDT/PTT when a low-power, single-pulsed laser irradiation was applied, and the localized surface plasmon resonance of AuNS was in resonance with the TP-absorption wavelength of Rf-N,S-GQD. The TCS coating significantly enhanced the colloidal stability of AuNSs while providing a suitable substrate to electrostatically anchor negatively charged Rf-N,S-GQDs. The plasmon-enhanced singlet oxygen (1O2) generation effect led to boosted 1O2 production both extracellularly and intracellularly. Notably, the combined TP-PDT/PTT exhibited significantly improved phototherapeutic outcomes compared to individual strategies against 2D monolayer cells and 3D multicellular tumor spheroids. Overall, this study reveals a successful single-laser-triggered, synergistic combined TP-PDT/PTT based on a plasmonic metal/QD hybrid, with potential for future investigation in clinical settings.

Study on surface thermal oxidation of silicon carbide irradiated by pulsed laser using reactive molecular dynamics.

Pulsed lasers are a powerful tool for fabricating silicon carbide (SiC) that has a hard and brittle nature, but oxidation is usually unavoidable. This study presents an exploration of the oxidation mechanism of 4H-SiC in oxygen and water under different temperatures via reactive force field molecular dynamics. Single pulse irradiation experiments were conducted to study the oxygen content of the laser-affected zone through energy dispersive x-ray spectrometry. The results show that laser-induced thermal oxidation is a complex dynamic process with the interactions among H, C, O, and Si atoms. The oxidation zone includes an oxide layer, a graphite layer, and a C-rich layer. With an increase in oxygen concentration, the amorphous oxide layer changes from silicon oxide to silicon dioxide. In addition, the formation of carbon clusters at the interface between SiOx and C-rich layers promotes the desorption of the oxide layer. The mechanism revealed in this study provides theoretical guidance for high-quality processing of 4H-SiC at atomic and close-to-atomic scales.

Creation of NV centers over a millimeter-sized region by intense single-shot ultrashort laser irradiation

Recently, ultrashort laser processing has attracted attention for creating nitrogen-vacancy (NV) centers because this method can create single NV centers in spatially-controlled positions, which is an advantage for quantum information devices. On the other hand, creating high-density NV centers in a wide region is also important for quantum sensing because the sensitivity is directly enhanced by increasing the number of NV centers. A recent study demonstrated the creation of high-density NV centers by irradiating femtosecond laser pulses, but the created region was limited to micrometer size, and this technique required many laser pulses to avoid graphitization of diamond. Here, we demonstrate the creation of NV centers in a wide region using only an intense single femtosecond laser pulse irradiation. We irradiated a diamond sample with a femtosecond laser with a focal spot size of 41 µm and a laser fluence of up to 54 J/cm2, which is much higher than the typical graphitization threshold in multi-pulse processing. We found that single-pulse irradiation created NV centers without post-annealing for a laser fluence higher than 1.8 J/cm2, and the region containing NV centers expanded with increasing laser fluence. The diameter of the area was larger than the focal spot size and reached over 100 µm at a fluence of 54 J/cm2. Furthermore, we demonstrated the NV centers’ creation in a millimeter-sized region by a single-shot defocused laser pulse over 1100 µm with a fluence of 33 J/cm2. The demonstrated technique will bring interest in the fundamentals and applications of fabricating ultrahigh-sensitivity quantum sensors.

Моделирование процессов в полупроводниковых структурах при радиационном воздействии

The radiation impact of outer space has an impact on electronic equipment and their characteristics change. The paper considers the simulation of the process of motion of holes generated in the oxide, which cause local deformation of the potential field of the lattice. Jumps of polarons make the motion of holes dispersed and highly dependent on temperature and oxide thickness. The article presents the temperature dependences of the voltage shift after a single radiation pulse. When holes move to the Si/SiO2 interface, some of the holes are captured by traps. The effect of the influence of the capture cross section on the increase in holes in traps is noticeable in the electrical dependence of the increase in the number of oxide traps immediately after irradiation. The graphs of the dependence of the threshold voltage shift due to oxide traps on the electric field in the oxide are plotted in this work. Immediately after its appearance, the charge of oxide traps begins to be neutralized. To study this process, time, temperature, and electrical dependences are plotted, and the ratio of trapped electrons to the number of trapped holes is shown for dry and wet gate oxide technologies at different oxide thicknesses. Thus, the influence of temperature and radiation influences on the motions of holes and oxide traps in semiconductor structures is shown.

Three-Wavelength YAG: Nd3+ Laser System for Lidar Sounding of Marine Areas

The article presents the results of the UV, visible, and IR spectral range measurements of temporary parameters of single radiation pulses of a modernised RGB laser with an intracavity parametric light oscillator. It is proposed to transform the modernised RGB laser into a three-wave multifunctional laser system generating shorter and more powerful 532 and 452 nm single radiation pulses with quick switching between them. The laser system is designed for operation as part of a marine aviation radio metrical lidar and has an additional channel of safe for sight radiation with wavelength of 1572 nm to control flight altitude above sea level.

Design concepts of a new imaging system for a high-intensity XUV source beam by colour centres excitation in lithium fluoride crystals

Stable colour centre production in lithium fluoride (LiF) crystals can employ as a high-spatial-resolution imaging tool for extreme ultraviolet (XUV) irradiation, as well as the possibility for images of the unfocused beam and the beam focused by a multi-layer mirror.The LiF crystal sensitivity has sufficient to impress high-contrast photo-luminescent patterns with XUV single-pulse irradiation on an area up to 40mm2. The suggested imaging technique, using LiF as a detector, can contribute to reducing the lack of sufficient knowledge for XUV beam characterization and profile featurization which can open a very wide range of XUV metrology and tomography applications.The experimental results explain the concepts of detection of high-intensity source at13.5nm using a YAG:Ce scintillator crystal embedded with a CMOS camera, additionally using LiF as a 2D high-resolution detector, and the work shows investigations outcomes and improvement procedure and analysis.The results demonstrate the potential of LiF crystals as a sub-micrometre resolution two-dimensional imaging tool for XUV irradiation applications. Moreover, the research study explains the optimization sequences of the new imaging technique that will play an important role to predict the achievable spot size, geometry, beam profile and intensity distribution, as well as the characterization complexity of XUV source features.