Femtosecond Ablation Research Articles

Ultrasonic vibration-assisted femtosecond laser submerged ablation process for the preparation of titanium-based crack-free hydroxyapatite

Titanium alloy-based hydroxyapatite (HAp) coating materials are beneficial for reducing stress shielding and improving the biocompatibility of implants. However, the significant disparity in thermal conductivity between titanium alloy and hydroxyapatite results in the material being highly susceptible to cracking during preparation, which diminishes the mechanical properties of the material and predisposes the implant to aseptic loosening. To obtain coatings of HAp that are free of cracks, this study proposes a process method of ultrasonic-assisted femtosecond laser under-liquid ablation of a Ca/P solution to synthesize HAp by a one-step process and apply coatings on the surface of TC4 titanium alloy. The relationship between the laser process parameters and the resulting surface morphology, coating spatial distribution, elemental composition, chemical state of the elements, phase, coating thickness, coating bonding, friction coefficient, corrosion resistance and the number of cells was investigated through a series of analytical techniques, including high-speed photographic observation, scanning electron microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), scratch testing, Tafel plot and cell adhesion assays. The findings demonstrate that titanium-based HAp coatings with a thickness of 42.5 μm, a bonding force of 55 N, a polarization resistance of 10 Ω.cm2, the absence of cracks defects, and notable bioactivity can be produced with ultrasonic-assisted submerged laser ablation in a highly concentrated Ca/P solution. The proposed method represents a novel approach to the preparation of multifunctionalized implants.

Discrete Illumination-Based Compressed Ultrafast Photography for High-Fidelity Dynamic Imaging.

Compressed ultrafast photography (CUP) can capture irreversible or difficult-to-repeat dynamic scenes at the imaging speed of more than one billion frames per second, which is obtained by compressive sensing-based image reconstruction from a compressed 2D image through the discretization of detector pixels. However, an excessively high data compression ratio in CUP severely degrades the image reconstruction quality, thereby restricting its ability to observe ultrafast dynamic scenes with complex spatial structures. To address this issue, a discrete illumination-based CUP (DI-CUP) with high fidelity is reported. In DI-CUP, the dynamic scenes are loaded into an ultrashort laser pulse train with controllable sub-pulse number and time interval, thus the data compression ratio, as well as the overlap between adjacent frames, is greatly decreased and flexibly controlled through the discretization of dynamic scenes based on laser pulse train illumination, and high-fidelity image reconstruction can be realized within the same observation time window. Furthermore, the superior performance of DI-CUP is verified by observing femtosecond laser-induced ablation dynamics and plasma channel evolution, which are hardly resolved in the spatial structures using conventional CUP. It is anticipated that DI-CUP will be widely and dependably used in the real-time observations of various ultrafast dynamics.

Ultra-sensitive axial strain and magnetic field sensor based on three reflection surface interference and harmonic vernier effect

A high-sensitivity fiber optic strain and magnetic field (MF) sensor is designed by two Fabry-Perot interferometers (FPI) cascading and harmonic Vernier effect. Two cascaded FPIs consist of an intrinsic FPI1 and an extrinsic FPI2. FPI1 is fabricated by femtosecond laser pulse ablation on the single-mode fiber core. Then, FPI1 and another single-mode fiber are inserted into a quartz capillary from both sides to form FPI2. By adjusting the cavity length of FPI2, the cascaded FPI1 and FPI2 can form a harmonic Vernier effect sensor. Due to FPI1 being a cantilever beam, it is not subjected to axial strain. The strain of the sensor acts on a longer capillary, resulting in an extension of the effective length of the strain and a many fold increase in the strain sensitivity of the sensor. Due to the compact cascading of FPI1 and FPI2, this strain sensor has a very small structural size. The sensor average strain sensitivity obtained from the experiment reached 260.05 pm/με. Due to the extremely high axial strain sensitivity of this strain sensor, adhering it to the magnetostrictive material results in the average MF sensitivity of 6.82 nm/mT, and the minimum MF intensity detected by the MF sensor is 0.1 mT. The temperature crosstalk of the MF sensor is 0.3 mT/°C.

THz active modulation device by electric field turned modulation characteristics of titanium sulfide nanofilm device

AbstractAn effective approach to manipulate terahertz (THz) waves involves the utilization of a device structure. In this particular investigation, we have successfully fabricated a SnS2 nanofilm device using femtosecond laser direct ablation. The passive and active polarization‐sensitive characteristics of the SnS2 nanofilm device were examined within the THz frequency range, employing different line spaces of 500, 600, and 700 μm. The combination of the device effect and SnS2 absorption led to an enhanced passive polarization modulation. Moreover, when an external electric field was applied to the SnS2 nanofilm device along the device line, persistent switching and linear modulation of THz wave transmission were observed. These findings indicate that the integration of material properties and device structure in this SnS2 device renders it highly suitable for applications in ultrafast THz switches, filters, and modulation devices.

Real-Time Monitoring of Thermal Phenomena during Femtosecond Ablation of Bone Tissue for Process Control.

Femtosecond (fs) laser technology is currently being considered in innovative fields such as osteotomy and treatment of hard tissue thanks to the achievable high resolution and ability to prevent tissue damage. In a previous study, suitable process parameters were obtained to achieve competitive ablation rates on pork femur processing. Nevertheless, a better control of thermal accumulation in the tissue during laser ablation could further improve the postoperative regeneration of the treated bone compared with conventional procedures and push forward the exploitation of such technology. This study presents methods for real time analyses of bone tissue temperature and composition during fs laser ablation and highlights the importance of implementing an efficient cooling method of bone tissue in order to achieve optimized results. Results show that it is possible to achieve a larger process window for bone tissue ablation where bone tissue temperature remains within the protein denaturation temperature in water-based processing environment. This is a key outcome towards a clinical exploitation of the presented technology, where higher process throughputs are necessary. The effects of process parameters and environments on bone tissue were confirmed by LIBS technique, which proved to be an efficient method by which to record real-time variation of bone tissue composition during laser irradiation.

A hybrid process technology of SiC die separation

ABSTRACT Silicon carbide (SiC) is ideal for making powerful, high-frequency chips for 5 G and electric vehicles due to its wide band gap and resistance to high voltage. However, its powerful chemical bond strength and extreme hardness make it difficult for die separation in the post-wafer process. A hybrid process technology is proposed, where die scribing is performed on SiC wafer using a femtosecond pulsed laser-assisted ablation. The extremely short energy pulses forced the ablation of traces of SiC at extreme speed, breaking chemical bonds and thereby reducing strength and hardness for easy high-speed cutting along the scribed lanes with a polycrystalline diamond wheel. The experiment showed that the average stage current dropped from 0.90 A to 0.45 A and kerf chipping ratio from 11.7 to 4.1 during die separation, proving that the process removed materials along the separation lanes using a wheel tool at low grinding force, creating separation lanes of outstanding straightness and minimal kerf chippings and SiC dies of high integrity. Furthermore, thanks to the on-line rotational machining and dressing of the wheel tool, the blunt diamond abrasive cutting edge could be redressed to expose chip pockets of appropriate depth and protruding grinding edges with a favorable negative rake angle. The established grinding regime utilizing a pressure-grinding force in cutting and material removal reduced cracking at the SiC surface. In this paper, the laser energy density, scanning speed, number of ablations, focus position, as well as the speed, feed-rate and grinding depth of the wheel tool are also discussed in detail.

Polarization sensitive electronically tuned microgroove array THz active modulator

The 6G technology has identified the frequency range of 0.1 to 1 THz as the communication band, with a particular focus on ultrafast modulation and multi-dimensional resolution coding technology. To advance the applications of THz photonics, there is a critical need for high-performance active optoelectronic THz devices. One potential solution involves the utilization of electrically controlled semi-metallic based THz modulators, which can provide suitable modulation depth and a wide modulation bandwidth. In this research, a semi-metallic TiS2 nanofilm device was developed using femtosecond laser direct ablation. The combination of structural effects and TiS2 absorption has significantly improved active modulation. These findings indicate that TiS2-based devices are well-suited for applications in THz photonics.

Investigation of laser wavelength effect on the ablation of enamel and dentin using femtosecond laser pulses

We investigated the effect of femtosecond (fs) laser ablation of enamel and dentin for different pulse wavelengths: infrared (1030 nm), green (515 nm), and ultra-violet (343 nm) and for different pulse separations to determine the optimal irradiation conditions for the precise removal of dental hard tissues with the absence of structural and compositional damage. The ablation rates and efficiencies were established for all three laser wavelengths for both enamel and dentin at room temperature without using any irrigation or cooling system, and the surfaces were assessed with optical and scanning electron microscopy, optical profilometry, and Raman spectroscopy. We demonstrated that 515 nm fs irradiation provides the highest rate and efficiency for ablation, followed by infrared. Finally, we explored the temperature variations inside the dental pulp during the laser procedures for all three wavelengths and showed that the maximum increase at the optimum conditions for both infrared and green irradiations was 5.5 °C, within the acceptable limit of temperature increase during conventional dental treatments. Ultra-violet irradiation significantly increased the internal temperature of the teeth, well above the acceptable limit, and caused severe damage to tooth structures. Thus, ultra-violet is not a compatible laser wavelength for femtosecond teeth ablation.

Dual-wavelength femtosecond laser-induced single-shot damage and ablation of silicon

An experimental and theoretical study of laser-induced damage and ablation of silicon by two individual femtosecond pulses of different wavelengths, 1030 and 515 nm, is performed to address the physical mechanisms of dual-wavelength ablation and reveal possibilities for increasing the ablation efficiency. The produced craters and damaged areas are analyzed as a function of laser fluence and time separation between the pulses and are compared with monochromatic irradiation. The order of pulses is demonstrated to be essential in bi-color ablation with higher material removal rates when a shorter-wavelength pulse arrives first at the surface. Simulations based on the two-temperature model show that the visible pulse is profitable for the generation of the electron-hole plasma while the delayed IR pulse is efficiently absorbed in the plasma enhancing energy coupling to the target. At long delays of 30–100 ps, the dual-wavelength ablation is found to be particularly strong with formation of deep smooth craters. This is explained by the expansion of a hot liquid layer produced by the first pulse with a drastic decrease in the surface reflectivity at this timescale. The results provide insight into the processes of dual-wavelength laser ablation offering a better control of the energy deposition into material.

Mimicking acute airway tissue damage using femtosecond laser nanosurgery in airway organoids.

Airway organoids derived from adult murine epithelial cells represent a complex 3D in vitro system mimicking the airway epithelial tissue's native cell composition and physiological properties. In combination with a precise damage induction via femtosecond laser-based nanosurgery, this model might allow for the examination of intra- and intercellular dynamics in the course of repair processes with a high spatio-temporal resolution, which can hardly be reached using in vivo approaches. For characterization of the organoids' response to single or multiple-cell ablation, we first analyzed overall organoid survival and found that airway organoids were capable of efficiently repairing damage induced by femtosecond laser-based ablation of a single to ten cells within 24h. An EdU staining assay further revealed a steady proliferative potential of airway organoid cells. Especially in the case of ablation of five cells, proliferation was enhanced within the first 4h upon damage induction, whereas ablation of ten cells was followed by a slight decrease in proliferation within this time frame. Analyzing individual trajectories of single cells within airway organoids, we found an increased migratory behavior in cells within close proximity to the ablation site following the ablation of ten, but not five cells. Bulk RNA sequencing and subsequent enrichment analysis revealed the differential expression of sets of genes involved in the regulation of epithelial repair, distinct signaling pathway activities such as Notch signaling, as well as cell migration after laser-based ablation. Together, our findings demonstrate that organoid repair upon ablation of ten cells involves key processes by which native airway epithelial wound healing is regulated. This marks the herein presented in vitro damage model suitable to study repair processes following localized airway injury, thereby posing a novel approach to gain insights into the mechanisms driving epithelial repair on a single-cell level.

Acoustic and plasma sensing of laser ablation via deep learning.

Monitoring laser ablation when using high power lasers can be challenging due to plasma obscuring the view of the machined sample. Whilst the appearance of the generated plasma is correlated with the laser ablation conditions, extracting useful information is extremely difficult due to the highly nonlinear processes involved. Here, we show that deep learning can enable the identification of laser pulse energy and a prediction for the appearance of the ablated sample, directly from camera images of the plasma generated during single-pulse femtosecond ablation of silica. We show that this information can also be identified directly from the acoustic signal recorded during this process. This approach has the potential to enhance real-time feedback and monitoring of laser materials processing in situations where the sample is obscured from direct viewing, and hence could be an invaluable diagnostic for laser-based manufacturing.

Single-step fabrication of hybrid germanium-gold/silver nanoentities by femtosecond laser ablation and applications in SERS-based sensing

We present a simple, fast, and single-step approach for fabricating hybrid semiconductor-metal nanoentities through liquid-assisted ultrafast (∼50 fs, 1 kHz, 800 nm) laser ablation. Femtosecond (fs) ablation of Germanium (Ge) substrate was executed in (i) distilled water (ii) silver nitrate (AgNO3—3, 5, 10 mM) (iii) Chloroauric acid (HAuCl4—3, 5, 10 mM), yielding the formation of pure Ge, hybrid Ge-silver (Ag), Ge-gold (Au) nanostructures (NSs) and nanoparticles (NPs). The morphological features and corresponding elemental compositions of Ge, Ge-Ag, and Ge-Au NSs/NPs have been conscientiously studied using different characterization techniques. Most importantly, the deposition of Ag/Au NPs on the Ge substrate and their size variation were thoroughly investigated by changing the precursor concentration. By increasing the precursor concentration (from 3 mM to 10 mM), the deposited Au NPs and Ag NPs’ size on the Ge nanostructured surface was increased from ∼46 nm to ∼100 nm and from ∼43 nm to ∼70 nm, respectively. Subsequently, the as-fabricated hybrid (Ge-Au/Ge-Ag) NSs were effectively utilized to detect diverse hazardous molecules (e.g. picric acid and thiram) via the technique of surface-enhanced Raman scattering (SERS). Our findings revealed that the hybrid SERS substrates achieved at 5 mM precursor concentration of Ag (denoted as Ge-5Ag) and Au (denoted as Ge-5Au) had demonstrated superior sensitivity with the enhancement factors of ∼2.5 × 104, 1.38 × 104 (for PA), and ∼9.7 × 105 and 9.2 × 104 (for thiram), respectively. Interestingly, the Ge-5Ag substrate has exhibited ∼10.5 times higher SERS signals than the Ge-5Au substrate.

Randomized whispering-gallery-mode microdisk laser arrays via cavity deformations for anti-counterfeiting labels

Optical physical unclonable functions (PUFs) have emerged as a promising strategy for effective and unbreakable anti-counterfeiting. However, the unpredictable spatial distribution and broadband spectra of most optical PUFs complicate efficient and accurate verification in practical anti-counterfeiting applications. Here, we propose an optical PUF-based anti-counterfeiting label from perovskite microlaser arrays, where randomness is introduced through vapor-induced microcavity deformation. The initial perovskite microdisk laser arrays with regular positions and uniform sizes are fabricated by femtosecond laser direct ablation. By introducing vapor fumigation to induce random deformations in each microlaser cavity, a laser array with completely uneven excitation thresholds and narrow-linewidth lasing signals is obtained. As a proof of concept, we demonstrated that the post-treated laser array can provide fixed-point and random lasing signals to facilitate information encoding. Furthermore, different emission states of the lasing signal can be achieved by altering the pump energy density to reflect higher capacity information. A threefold PUF (excited under three pump power densities) with a resolution of 5×5 pixels exhibits a high encoding capacity (1.43×1045), making it a promising candidate to achieve efficient authentication and high security with anti-counterfeiting labels.

Spectrum diagnosis and temperature monitoring of femtosecond laser laminectomy

Orthopedic diseases are increasingly becoming a prominent problem threatening human health. Traditional mechanical osteotomy causes mechanical and thermal damages, which are believed to increase the safety risk of orthopedic surgery. Femtosecond lasers provide a safe and efficient method for laminectomy. In this study, the experiments were conducted on femtosecond laser ablation operations aided by convolutional neural network and collaborative control. The various spectra during femtosecond laser bone ablation were detected by using isolated porcine ribs. An optical fiber spectrometer was used to monitor the spectrum, which was proved to reflect the laser ablation process. The spectral composition during femtosecond laser bone ablation was analyzed. The second harmonic was related to the penetration. The temperature distribution indicated that 15 W with cooling was the best parameter for preventing carbonization. Defocusing the laser improved safety because the ablated effect was very limited when the defocus distance was 4 mm. Although large energy input resulted in better efficiency, it also caused carbonization due to overheating.

Femtosecond laser regulatory focus ablation patterning of a fluorescent film up to 1/10 of the scale of the diffraction limit.

Patterned quantum dots (QDs) and perovskites have attracted a great deal of attention in the fabrication of optoelectronic device arrays for transistors, image sensors and displays. However, the resolution of current patterning technologies is insufficient for nanopatterned QDs and perovskites to be integrated in advanced optoelectronic and photonic applications. Herein, we demonstrate a femtosecond laser regulatory focus ablation (FsLRFA) patterning technique of a fluorescent film involving both semiconductor core-shell QDs and perovskite up to 1/10th of the scale of the diffraction limit. Annular lines with a 200 nm-width are obtained after the irradiation of the femtosecond laser. Moreover, the combination of ablated different geometries enables the laser focal spot as brushes for FsLRFA patterning technology to fabricate delicate and programmable patterns on the fluorescent film. This technology with nanoscale resolution and patterning capability paves the road toward highly integrated applications based on QDs and perovskites.

Rapid Fabrication of Wavelength-Scale Micropores on Metal by Femtosecond MHz Burst Bessel Beam Ablation.

The preparation of the wavelength-scale micropores on metallic surfaces is limited by the high opacity of metal. At present, most micropores reported in the literature are more than 20 µm in diameter, which is not only large in size, but renders them inefficient for processing so that it is difficult to meet the needs of some special fields, such as aerospace, biotechnology, and so on. In this paper, the rapid laser fabrications of the wavelength-scale micropores on various metallic surfaces are achieved through femtosecond MHz burst Bessel beam ablation. Taking advantage of the long-depth focal field of the Bessel beam, high-density micropores with a diameter of 1.3 µm and a depth of 10.5 µm are prepared on metal by MHz burst accumulation; in addition, the rapid fabrication of 2000 micropores can be achieved in 1 s. The guidelines and experimental results illustrate that the formations of the wavelength-scale porous structures are the result of the co-action of the laser-induced periodic surface structure (LIPSS) effect and Bessel beam interference. Porous metal can be used to store lubricant and form a lubricating layer on the metallic surface, thus endowing the metal resistance to various liquids' adhesion. The microporous formation process on metal provides a new physical insight for the rapid preparation of wavelength-scale metallic micropores, and promotes the application of porous metal in the fields of catalysis, gas adsorption, structural templates, and bio-transportation fields.

Analysis of stresses and shape changes in thin substrates with stressed film patterning using femtosecond laser micromachining

The accurate, high-throughput fabrication of light weight optical systems for applications like next-generation space telescopes and semiconductor wafers is both crucial and challenging. A potential solution is to first fabricate thin substrates with traditional methods, then apply surface stress to bend them into desired shapes to correct residual height errors. We have developed a stress-based figure correction method for thin silicon mirrors using a femtosecond laser micromachining technique to generate patterned stress fields, through the removal of selective stressed film regions and adjacent substrate regions. In this paper, we present an in-depth analysis for the laser-induced stresses and resulting shape changes of thin mirrors due to the periodic patterning of a stressed film (silicon oxide) on silicon substrates using femtosecond laser surface ablation. Experimental results are presented, and a 3D finite element model (FEM) is developed to study the substrate curvature in directions parallel and perpendicular to the patterned troughs in the substrates. We simulate the stress relief process in the thin-film/substrate system, and the numerical predictions compare reasonably well with curvature measurements for several different geometrical combinations of depth, width and spacing of the patterned troughs, achieving >82% quantitative agreement with the experiments. It is also shown in the simulations that certain geometries of patterned troughs induce more dramatic shape changes and counter-intuitive reversals of curvature in the direction perpendicular to the troughs, and a qualitative explanation involving the Poisson effect is presented. The 3D finite element methods and findings of this paper can be used to determine the optimal parameters of the stressed film patterns for figure correction of thin telescope mirrors and other types of thin substrates used in the semiconductor industry.

Comparison of Submillimeter Spot Ablation of Copper and Nickel by Multipulse Picosecond and Femtosecond Laser

The current transmission and reflection laser ablation micropropulsion modes have the problem of a complex working medium supply system in engineering. Therefore, we propose large-spot laser ablation with a one-dimensional supply mode. In order to verify this ablation mode, a multipulse ablation experiment of submillimeter-scale light spots was carried out on the surface of pretreated copper and nickel under the atmosphere using an ultrafast laser with a pulse width of 290 fs and 10 ps. The results show that femtosecond laser multipulse ablation (FLMA) leads to the grain refinement of copper, the crater quality of the two metals under FLMA is better, and picosecond laser multipulse ablation (PLMA) causes the crater of nickel to form a dense remelting bulge that affects laser absorption; both metals have obvious heat-affected zones after FLMA and PLMA, the heat-affected zones of nickel are 5–10% larger than those of copper, and the ablation depth of copper is deeper. Under the same conditions, the ablation mass of copper is smaller than that of nickel, and the specific impulse performance of laser ablation micropropulsion is better.

Ultrafast laser ablation, intrinsic threshold, and nanopatterning of monolayer molybdenum disulfide

Laser direct writing is an attractive method for patterning 2D materials without contamination. Literature shows that the ultrafast ablation threshold of graphene across substrates varies by an order of magnitude. Some attribute it to the thermal coupling to the substrates, but it remains by and large an open question. For the first time the effect of substrates on the femtosecond ablation of 2D materials is studied using MoS2 as an example. We show unambiguously that femtosecond ablation of MoS2 is an adiabatic process with negligible heat transfer to the substrates. The observed threshold variation is due to the etalon effect which was not identified before for the laser ablation of 2D materials. Subsequently, an intrinsic ablation threshold is proposed as a true threshold parameter for 2D materials. Additionally, we demonstrate for the first time femtosecond laser patterning of monolayer MoS2 with sub-micron resolution and mm/s speed. Moreover, engineered substrates are shown to enhance the ablation efficiency, enabling patterning with low-power ultrafast oscillators. Finally, a zero-thickness approximation is introduced to predict the field enhancement with simple analytical expressions. Our work clarifies the role of substrates on ablation and firmly establishes ultrafast laser ablation as a viable route to pattern 2D materials.

Investigation of the optical properties of monocrystalline silicon with a deposited layer of spherical zinc sulfide nanoparticles

In the present work zinc sulfide (ZnS) nanoparticles (NPs) were synthesized on silicon wafer by femtosecond pulsed ablation processing of ZnS bulk target using an electrostatic field in argon gas atmosphere. The morphology, size distribution and structural characterization of obtained ZnS NPs were investigated using scanning electron microscope (SEM), dynamic light scattering (DLS) technique and X-ray diffraction (XRD). Dominant size of obtained NPs lies in the range 10-20 nm, NPs are in spherical shape, particles of other shape and agglomerates of particles are absent. XRD investigation of synthesized NPs identified hexagonal wurtzite structure. There is a structural phase transition from the sphalerite ZnS bulk (target) structure to the structural phase of wurtzite (obtained NPs).The optical characterization of synthesized by laser ablation ZnS NPs was carried out using a photoluminescence (PL) measurement. ZnS NPs show a strong broad PL emission spectra covering the entire visible electromagnetic spectra region (range from 380 to 800 nm) centered at 513.7 nm.