Femtosecond Laser Research Articles

High Sensitivity Fiber Bragg Grating Humidity Sensors Made With Through-the-Coating Femtosecond Laser Writing and Polyimide Coating Thickening

High Sensitivity Fiber Bragg Grating Humidity Sensors Made With Through-the-Coating Femtosecond Laser Writing and Polyimide Coating Thickening

Studying the viabilityand growth kinetics of vancomycin-resistant Enterococcus faecalis V583 following femtosecond laser irradiation (420-465 nm).

Enterococcus faecalis is among the most resistant bacteria found in infected root canals. The demand for cutting-edge disinfection methods has rekindled research on photoinactivation with visible light. This study investigated the bactericidal activity of femtosecond laser irradiation against vancomycin-resistant Enterococcus faecalis V583 (VRE). The effect of parameters such as wavelength and energy density on the viability and growth kinetics of VRE was studied to design an optimized laser-based antimicrobial photoinactivation approach without any prior addition of exogenous photosensitizers. The most effective wavelengths were 430nm and 435nm at a fluence of 1000J/cm2, causing a nearly 2-log reduction (98.6% and 98.3% inhibition, respectively) in viable bacterial counts. The colony-forming units and growth rate of the laser-treated cultures were progressively decreased as energy density or light dose increased at 445nm but reached a limit at 1250J/cm2. At a higher fluence of 2000J/cm2, the efficacy was reduced due to a photobleaching phenomenon. Our results highlight the importance of optimizing laser exposure parameters, such as wavelength and fluence, in bacterial photoinactivation experiments. To our knowledge, this is the first study to report an optimized wavelength for the inactivation of VRE using visible femtosecond laser light.

Predicting and probing the local temperature rise around plasmonic core-shell nanoparticles to study thermally activated processes.

Ultrafast spectroscopy can be used to study dynamic processes on femtosecond to nanosecond timescales, but is typically used for photoinduced processes. Several materials can induce ultrafast temperature rises upon absorption of femtosecond laser pulses, in principle allowing to study thermally activated processes, such as (catalytic) reactions, phase transitions, and conformational changes. Gold-silica core-shell nanoparticles are particularly interesting for this, as they can be used in a wide range of media and are chemically inert. Here we computationally model the temporal and spatial temperature profiles of gold nanoparticles with and without silica shell in liquid and gas media. Fast rises in temperature within tens of picoseconds are always observed. This is fast enough to study many of the aforementioned processes. We also validate our results experimentally using a poly(urethane-urea) exhibiting a temperature-dependent hydrogen bonding network, which shows local temperatures above 90 ◦C are reached on this timescale. Moreover, this experimentally shows the hydrogen bond breaking in such polymers occurs within tens of picoseconds.

Enhanced Wear Resistance of Microstripe-Textured Water-Lubricated Materials Fabricated via Hot Embossing

Water-lubricated material is the fundamental ingredient of a water-lubricated bearing (WLB), of which the friction and wear properties directly affect the working performance and service life of a WLB. We designed a micron-scale stripe texture and fabricated a negative microtexture mold by femtosecond laser etching. The microtextures were fabricated onto the surface of Thordon and polyurethane water-lubricated materials by a precision thermoforming machine. Tribological tests showed that the microstripe texture on water-lubricated materials had lower friction and wear properties than that on pristine surface materials. The results demonstrated that the presence of the microstripe texture effectively improved the friction and anti-wear properties of the water-lubricated materials. This study provides a new idea for the design and preparation of water-lubricated materials with good water-lubricating and anti-wear properties.

Dual Infrared 2‐Photon Microscopy Achieves Minimal Background Deep Tissue Imaging in Brain and Plant Tissues

AbstractTraditional deep fluorescence imaging has primarily focused on red‐shifting imaging wavelengths into the near‐infrared (NIR) windows or implementation of multi‐photon excitation approaches. Here, the advantages of NIR and multiphoton imaging are combined by developing a dual‐infrared two‐photon microscope that enables high‐resolution deep imaging in biological tissues. This study first computationally identifies that photon absorption, as opposed to scattering, is the primary contributor to signal attenuation. A NIR two‐photon microscope is constructed next with a 1640 nm femtosecond pulsed laser and a NIR PMT detector to image biological tissues labeled with fluorescent single‐walled carbon nanotubes (SWNTs). Spatial imaging resolutions are achieved close to the Abbe resolution limit and eliminate blur and background autofluorescence of biomolecules, 300 µm deep into brain slices and through the full 120 µm thickness of a Nicotiana benthamiana leaf. NIR‐II two‐photon microscopy can also measure tissue heterogeneity by quantifying how much the fluorescence power law function varies across tissues, a feature this study exploits to distinguish Huntington's Disease afflicted mouse brain tissues from wildtype. These results suggest dual‐infrared two‐photon microscopy can accomplish in‐tissue structural imaging and biochemical sensing with a minimal background, and with high spatial resolution, in optically opaque or highly autofluorescent biological tissues.

Programmable quantum emitter formation in silicon.

Silicon-based quantum emitters are candidates for large-scale qubit integration due to their single-photon emission properties and potential for spin-photon interfaces with long spin coherence times. Here, we demonstrate local writing and erasing of selected light-emitting defects using femtosecond laser pulses in combination with hydrogen-based defect activation and passivation at a single center level. By choosing forming gas (N2/H2) during thermal annealing of carbon-implanted silicon, we can select the formation of a series of hydrogen and carbon-related quantum emitters, including T and Ci centers while passivating the more common G-centers. The Ci center is a telecom S-band emitter with promising optical and spin properties that consists of a single interstitial carbon atom in the silicon lattice. Density functional theory calculations show that the Ci center brightness is enhanced by several orders of magnitude in the presence of hydrogen. Fs-laser pulses locally affect the passivation or activation of quantum emitters with hydrogen for programmable formation of selected quantum emitters.

Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties

Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties

Three-Dimensional Directional Assembly of Liquid Crystal Molecules.

The precise construction of hierarchically long-range ordered structures using molecules as fundamental building blocks can fully harness their anisotropy and potential. However, the three-dimensional (3D), high-precision, and single-step directional assembly of molecules is a long-pending challenge. Here, we propose a 3D directional molecular assembly strategy via femtosecond laser direct writing (FsLDW) and demonstrate the feasibility of this approach using liquid crystal (LC) molecules as an illustrative example. The physical mechanism for femtosecond (fs) laser-induced assembly of LC molecules has been investigated, and precise 3D arbitrary assembly of LC molecules has been achieved by defining the discretized laser scanning pathway. Additionally, an LC-based Fresnel zone plate array with polarization selection and colorization imaging functions has been fabricated to further illustrate the potential of this method. This study not only introduces a 3D high-resolution alignment method for LC-based functional devices but also establishes a universal protocol for the precise 3D directional assembly of anisotropic molecules. This article is protected by copyright. All rights reserved.

Sensitive detection and imaging of H2O density through Rydberg resonant femtosecond laser induced photofragmentation fluorescence.

A femtosecond laser induced photofragmentation fluorescence (fs-LIPF) scheme for the sensitive detection and imaging of water vapor is presented. Two photons of 244.3nm excite water to the D̃ state and produce hydroxyl radicals in the fluorescing à state. Two more photons promote electrons from the D̃ state to a neutral Rydberg state of the (1b2)-1 ionic core through a 2 + 2 doubly resonant process. The resulting high-lying Rydberg state undergoes neutral dissociation, and the energetic hydrogen fragments are detected from their Balmer series fluorescence. These channels (in the low-pressure limit) have detection sensitivities around 1012 molecules per cubic centimeters, orders of magnitude more sensitive than laser-induced fluorescence based approaches, allowing for sensitive non-invasive detection and imaging of water density for many important processes.

Femtosecond laser-induced nanoparticle implantation into flexible substrate for sensitive and reusable microfluidics SERS detection

Surface-enhanced Raman spectroscopy (SERS) microfluidic system, which enables rapid detection of chemical and biological analytes, offers an effective platform to monitor various food contaminants and disease diagnoses. The efficacy of SERS microfluidic systems is greatly dependent on the sensitivity and reusability of SERS detection substrates to ensure repeated use for prolonged periods. This study proposed a novel process of femtosecond laser nanoparticle array (NPA) implantation to achieve homogeneous forward transfer of gold NPA on a flexible polymer film and accurately integrated it within microfluidic chips for SERS detection. The implanted Au-NPA strips show a remarkable electromagnetic field enhancement with the factor of 9 × 108 during SERS detection of malachite green (MG) solution, achieving a detection limit lower than 10 ppt, far better than most laser-prepared SERS substrates. Furthermore, Au-NPA strips show excellent reusability after several physical and chemical cleaning, because of the robust embedment of laser-implanted NPA in flexible substrates. To demonstrate the performance of Au-NPA, a SERS microfluidic system is built to monitor the online oxidation reaction between MG/NaClO reactants, which helps infer the reaction path. The proposed method of nanoparticle implantation is more effective than the direct laser structuring technique. It provides better performance for SERS detection, robustness of detection, and substrate flexibility and has a wider range of applications for microfluidic systems without any negative impact.

Neoclassical tearing mode stabilization by electron cyclotron current drive in EAST tokamak experiments

The stabilization of the m/n= 2/1 neoclassical tearing mode (NTM) by electron cyclotron current drive (ECCD) has been carried out in EAST H-mode discharges, where m/n is the poloidal/toroidal mode number. The experimental results are reported for the first time in this paper. To facilitate the experimental study, the magnetic island (NTM) is generated by a sufficiently large amplitude of the externally applied resonant magnetic perturbation (RMP). After switching off the RMP, the NTM exists due to the bootstrap current perturbation, with the magnetic island width being about 5 cm for the local equilibrium bootstrap current fraction being larger than 10%. By applying the localized ECCD later, the NTM is fully suppressed if the radial misalignment between the magnetic island and the ECCD location is sufficiently small. The stabilizing effect depends on both the radial misalignment and the applied electron cyclotron wave power. More importantly, it is found that the NTM can be avoided when applying ECCD earlier during the ramp-up phase of the RMP amplitude, if ECCD is localized around the O-point of the magnetic island, indicating an efficient way for avoiding locked modes that can lead to the major disruptions of tokamak plasmas.

The Interaction of Femtosecond Laser with Perovskites for Advanced Photonics

Halide perovskites have attracted increasingly attention as “rising star” materials for advanced photonics and optoelectronics. Construction micro‐/nano‐architecture of perovskites will provide a good platform to investigate and optimize the fundamental photon–matter–structure interaction. It will also improve the properties, pixelate and miniaturize the integration of versatile optoelectronic devices for emerging applications. In this regard, femtosecond (fs) laser processing technique has been widely used to fabricate micro‐/nano‐architecture with high spatial resolution, limitless flexibility, and unrestricted three‐dimensional structuring capability at a large‐scale, low‐cost way. Concurrently, it is reported that the high refractive index, low thermal conductivity and ultrafast thermalization rate of perovskites are beneficial for the processing by fs laser into micro‐/nano‐architecture without the degradation of their optoelectronic properties. This review systematically summarizes the interaction of fs laser with perovskites, including the mechanisms, and phenomena. Besides the traditional optoelectronics and applications of halide perovskites, the novel properties and applications from optical structures generated by fs laser processing of perovskites are also discussed. The challenges and outlooks for fs laser processed perovskite materials and devices are highlighted. This review will promote the relevant fundamental research on light–matter–structure interaction, and facilitate the integration of perovskite micro‐/nano‐architecture‐based optoelectronic devices.

Ultra‐High Proportion of Grain Boundaries in Zinc Metal Anode Spontaneously Inhibiting Dendrites Growth

Aqueous Zn‐ion batteries are an attractive electrochemical energy storage solution for their budget and safe properties. However, dendrites and uncontrolled side reactions in anodes detract the cycle life and energy density of the batteries.Grain boundaries in metals are generally considered as the source of the above problems but we present a diverse result. This study introduces an ultra‐high proportion of grain boundaries on zinc electrodes through femtosecond laser bombardment to enhance stability of zinc metal/electrolyte interface.The ultra‐high proportion of grain boundaries promotes the homogenization of zinc growth potential, to achieve uniform nucleation and growth, thereby suppressing dendrite formation. Additionally, the abundant active sites mitigate the side reactions during the electrochemical process. Consequently, the 15‐μm‐Fs‐Zn||MnO2 pouch cell achieves an energy density of 249.4 Wh kg–1 and operates for over 60 cycles at a depth‐of‐discharge of 23%. The recognition of the favorable influence exerted by UP‐GBs paves a new way for other metal batteries.

Ultra-High Proportion of Grain Boundaries in Zinc Metal Anode Spontaneously Inhibiting Dendrites Growth.

Aqueous Zn-ion batteries are an attractive electrochemical energy storage solution for their budget and safe properties. However, dendrites and uncontrolled side reactions in anodes detract the cycle life and energy density of the batteries.Grain boundaries in metals are generally considered as the source of the above problems but we present a diverse result. This study introduces an ultra-high proportion of grain boundaries on zinc electrodes through femtosecond laser bombardment to enhance stability of zinc metal/electrolyte interface.The ultra-high proportion of grain boundaries promotes the homogenization of zinc growth potential, to achieve uniform nucleation and growth, thereby suppressing dendrite formation. Additionally, the abundant active sites mitigate the side reactions during the electrochemical process. Consequently, the 15-μm-Fs-Zn||MnO2 pouch cell achieves an energy density of 249.4 Wh kg-1 and operates for over 60 cycles at a depth-of-discharge of 23%. The recognition of the favorable influence exerted by UP-GBs paves a new way for other metal batteries.

Improving Three-Photon Fluorescence of Near-Infrared Quantum Dots for Deep Brain Imaging by Suppressing Biexciton Decay.

Three-photon fluorescence microscopy (3PFM) is a promising brain research tool with submicrometer spatial resolution and high imaging depth. However, only limited materials have been developed for 3PFM owing to the rigorous requirement of the three-photon fluorescence (3PF) process. Herein, under the guidance of a band gap engineering strategy, CdTe/CdSe/ZnS quantum dots (QDs) emitting in the near-infrared window are designed for constructing 3PF probes. The formation of type II structure significantly increased the three-photon absorption cross section of QDs and caused the delocalization of electron-hole wave functions. The time-resolved transient absorption spectroscopy confirmed that the decay of biexcitons was significantly suppressed due to the appropriate band gap alignment, which further enhanced the 3PF efficiency of QDs. By utilizing QD-based 3PF probes, high-resolution 3PFM imaging of cerebral vasculature was realized excited by a 1600 nm femtosecond laser, indicating the possibility of deep brain imaging with these 3PF probes.

Femtosecond laser ultrafast photothermal exsolution

Abstract Exsolution, as an effective approach to construct particle-decorated interfaces, is still challenging to yield interfacial films rather than isolated particles. Inspired by in vivo near infrared laser photothermal therapy (PTT), using 3 mol.% Y2O3 stabilized tetragonal zirconia polycrystals (3Y-TZP) as host oxide matrix and iron-oxide (Fe3O4/γ-Fe2O3/α-Fe2O3) materials as photothermal modulator and exsolution resource, femtosecond laser ultrafast exsolution approach is presented enabling to conquer this challenge. The key is to trigger photothermal annealing behavior via femtosecond laser ablation to initialize phase transition into tetragonal zirconia (t-ZrO2) and induce columnar crystal growth, where Fe-ions rapidly segregate along grain boundaries and diffuse towards the outmost surface, becoming “frozen” there, highlighting the potential to use photothermal materials and ultrafast heating/quenching behaviors of femtosecond laser ablation for interfacial modification via exsolution. Triggering interfacial iron-oxide coloring exsolution is composition and concentration dependent, indicating photothermal materials themselves and corresponding photothermal transition capacity play a crucial role, initializing at 5wt%, 2wt%, and and 3wt% for Fe3O4-/γ-Fe2O3/α-Fe2O3 embedded 3Y-TZP samples. Due to different photothermal effects, exsolution states of ablated 5wt% Fe3O4-/γ-Fe2O3/α-Fe2O3-embedded 3Y-TZP samples are completely different, complete coverage, exhaustion (ablated away) and partial exsolution (rich in the crystal boundaries of sublayers). This novel exsolution is uniquely featured by up to now the deepest microscale (10 μm from 5 wt%-Fe3O4-3Y-TZP sample) Fe-elemental deficient layer for exsolution and the whole coverage of exsolved materials rather than formation of isolated exsolved particles by other methods. It is believed that femtosecond laser ultrafast photothermal exsolution may pave a good way to modulate interfacial properties for extensive applications in the fields of biology, optics/photonics, energy, catalysis, environment, etc.

High‐Quality Micropattern Printing by Complex‐Amplitude Modulation Holographic Femtosecond Laser

AbstractHolographic femtosecond laser printing technology is widely used in the fabrication of micropatterns because of its high efficiency and flexibility. However, speckle noise and energy fluctuations limit the quality of the printed structure. In this study, an improved complex‐amplitude modulation holographic femtosecond laser printing method for high‐quality micropattern fabrication is proposed. The holographic light field is divided into a signal area and a surrounding noise area. To improve laser uniformity, phase modulation is applied in the signal region to eliminate the speckle noise caused by unconstrained phase interference, and weighted amplitude modulation is introduced in the signal area to improve the calculation accuracy. To precisely control laser energy density, weighted energy efficiency modulation is introduced in the noise region to disperse the energy that exceeds the material damage threshold. Under the synergistic control of laser uniformity and energy density, high‐quality micro‐pattern structures are printed efficiently. A high‐quality millimeter‐sized multifocal zone plate with micron accuracy is fabricated with the splicing printing method, demonstrating the potential of micropattern processing and the fabrication of functional devices such as binary optics.

Nonlinear dynamics of femtosecond laser interaction with the central nervous system in zebrafish

Understanding the photodamage mechanism underlying the highly nonlinear dynamic of femtosecond laser pulses at the second transparent window of tissue is crucial for label-free microscopy. Here, we report the identification of two cavitation regimes from 1030 nm pulses when interacting with the central nervous system in zebrafish. We show that at low repetition rates, the damage is confined due to plasma-based ablation and sudden local temperature rise. At high repetition rates, the damage becomes collateral due to plasma-mediated photochemistry. Furthermore, we investigate the role of fluorescence labels with linear and nonlinear absorption pathways in optical breakdown. To verify our findings, we examined cell death and cellular responses to tissue damage, including the recruitment of fibroblasts and immune cells after irradiation. These findings contribute to advancing the emerging nonlinear optical microscopy techniques and provide a strategy for inducing precise, and localized injuries using near-infrared femtosecond laser pulses.

Nanopatterning and nanostructure formation with femtosecond laser: Revolutionizing surface engineering on soda-lime glass

Glass, due to its high transparency and chemical stability, has found extensive use in electrical, electronic, and optoelectronic devices. This study presents a novel approach to modify the morphological features of laser-generated tracks and produced nanoparticles in soda-lime glass using the accuracy of micro processing by femtosecond laser pulses. The investigation has meticulously examined how variations in the incident laser pulse energy and scanning velocity dictate the formation of distinct morphological characteristics on the glass surface. FESEM has revealed three distinct morphological formations, including particulate, self-ordered periodic surface structures, and a combination of the two. Additionally, TEM analysis has shown the generation of both spherical and irregular-shaped nanoparticles with diameters ranging from 10 nm to less than 2 μm, and an amorphous structure confirmed by SAED patterns. The periodicity of the LIPSS was found to be 550±25 nm, and they were oriented perpendicular to the laser polarization vector.

Design of an ultrafast plasmonic nanolaser for high-intensity broadband emission operating at room temperature

We propose a plasmonic nanolaser based on a metal–insulator–semiconductor–insulator–metal (MISIM) structure, which effectively confines light on a subwavelength scale (∼λ/14). As the pump power increases, the proposed plasmonic nanolaser exhibits broadband output characteristics of 20 nm, and the maximum output power can reach 20 µW. Furthermore, the carrier lifetime at the upper energy level in our proposed structure is measured to be about 400 fs using a double pump-probe excitation. The ultrafast characteristic is attributed to the inherent Purcell effect of plasmonic systems. Our work paves the way toward deep-subwavelength mode confinement and ultrafast femtosecond plasmonic lasers in spaser-based interconnected, eigenmode engineering of plasmonic nanolasers, nano-LEDs, and spontaneous emission control.