Ablation Threshold Energy Research Articles

Picosecond laser-induced evolution of processing properties of 4H–SiC

The irradiation threshold of 4H–SiC under picosecond laser action was calculated, and the influence of laser parameters on the size of 4H–SiC was studied. According to the model, the evolution rule of the microgroove size was predicted. The effect of laser parameters on the mechanical properties of 4H–SiC was studied by nanoindentation. The results show that the ablation threshold energy density of the picosecond laser on 4H–SiC is 2.67 J/cm2. The effect regular of laser parameters on the size of 4H–SiC microgrooves: energy density > scanning speed > scanning interval. The error of the microgroove which is between the predicted value and measurements is within 10 %. By doing nanoindentation detection, proving that Pop-in is the elastic-plastic transition point. It shows that laser irradiation has a significant modification effect on the mechanical properties of 4H–SiC. According to the difference range of elastic modulus and hardness, showing that the influence of laser energy density on mechanical properties is dominant. The consequences of the study provide a theoretical foundation for subsequent CMP processing.

Holographic ultraviolet nanosecond laser processing using adaptive optics

Fabrication of a through hole in a polyimide film (PI) was demonstrated by holographic ultraviolet (UV) nanosecond laser processing with a computer-generated hologram displayed on a phase-only spatial light modulator (SLM). The UV laser was directly modulated into a Bessel beam by a diffractive axicon displayed on the SLM. The direct modulation contributed to improved light-utilization efficiency of the UV laser and a simplified optical setup compared to the conventional method based on a combination of an SLM and harmonic generation using a nonlinear optical crystal. The Bessel beam reduced the number of pulse shots required for through-hole fabrication to 1/5 compared to the Gaussian beam near the ablation threshold energy of the PI film. Furthermore, adaptive optics was implemented in holographic laser processing to compensate for aberrations in the optical setup. The aberration was reduced to 1/5 compared with before the compensation. The proposed method is suitable for improving the throughput and accuracy of drilling, cutting, and additive manufacturing using UV lasers with industrial requirements.

Laser ablation ignition of flammable gas

To reduce the minimum pulse energy required for laser ignition (MPE), thereby reducing the cost of the laser device and realizing multipoint ignition with the same laser energy, the ignition mechanism flammable gas using laser ablation was investigated by varying the distance between the target and the focusing lens, together with schlieren and direct color emission observation, which reveals the behavior of the ablative target material and initial flame kernel. It was found that the MPE in the ablative ignition was consistent with the ablation threshold energy of laser fluence on the target, except when the laser focal point was near the target surface. In this latter case, vortex flow induced by laser breakdown and successive collision of the initial flame kernel with the target was observed. The increase in MPE, in this case, was explained by heat loss in the initial flame kernel.

Machining characteristics of glass substrates containing chemical components in femtosecond laser helical drilling

The machining characteristics of glass substrates containing chemical components were investigated for the purpose of femtosecond laser helical drilling. A femtosecond laser of wavelength 1552 nm and pulse duration 800 fs was adopted in the laser machining system. The substrates investigated were aluminosilicate, soda-lime, and borosilicate glass. The chemical components contained in each glass substrate were quantitatively analyzed by laser ablation-induced chemical plasma mass spectrometry. The characteristics of the drilling conditions for each glass substrate were affected by its chemical components. As the wt% of Al2O3 and MgO components in the glass substrates increased, the ablation threshold energy of each substrate decreased, resulting in greater vertical speed of the laser head.

Wavelength Dependence of Poly(<i>p</i>-hydroxystyrene) Ablation by Mid-Infrared Free-Electron Laser

Ablation of polymer thin films for resists was studied using a mid-Infrared (IR) Free-Electron Laser (FEL). Irradiation fluence of the IR light in the mid-IR region (5.6 to 8.0 μm) to a thin film of poly(p-hydroxystyrene) (PHOST) on a silicon wafer increased to cause PHOST ablation. The ablated spot size was smaller than the irradiated area calculated by wave optics, because the ablation is a multiphoton absorption process. The ablation threshold energy was determined using the irradiation area calculated by the wave optics. The threshold energy depended upon the film thickness of PHOST and irradiation wavelength of FEL. The threshold energy of thin PHOST film with 61 nm increased at the wavelength of vibrational modes of phenyl ring. It associates the durability of phenyl ring to photon decomposition.

Effect of the chemical composition on the ablation characteristics of glass substrates in femtosecond laser machining

In this work, we investigated the ablation characteristics of aluminosilicate, soda-lime, and borosilicate glass substrates in femtosecond laser processing. The laser wavelength was 1,552 nm with a pulse duration of 800 fs. The ablation threshold energy of each glass substrate was estimated using the D2 method. To determine the ablation threshold energy of each glass substrate, the weight percentages of various chemical components in the glass substrates were quantitatively analyzed by laser ablation inductively coupled plasma mass spectrometry. The ablation threshold energy of the glass substrates was found to depend on the Al2O3 and MgO contents. When the weight percentages of both components were higher, the ablation threshold energy was lower. The effect of these components on the ablation threshold energy was theoretically investigated using self-trapped exciton analysis.

Silicon crystallinity control during laser direct microstructuring with bursts of picosecond pulses

Laser ablation and modification using bursts of picosecond pulses and a tightly focused laser beam are used to manufacture structures in the bulk silicon. We demonstrate precise control of the surface crystallinity as well as the structure depth and topography of the processed areas, achieving homogeneous surface properties. The control is achieved with a combination of a well-defined pulse energy, systematic pulse positioning on the material, and the number of pulses in a burst. A custom designed fiber laser source is used to generate bursts of 1, 5, 10, and 20 pulses at a pulse repetition rate of 40 MHz and burst repetition rate of 83.3 kHz allowing for a fast and stable processing of silicon. We show a controlled transition through different laser-matter interaction regimes, from no observable changes of the silicon at low pulse energies, through amorphization below the ablation threshold energy, to the ablation with either complete, partial or nonexistent amorphization. Single micrometer-sized areas of desired shape and crystallinity were defined on the silicon surface with submicron precision, offering a promising tool for applications in the field of optics.

Optical properties of the glass composites with nano dimensional films dependence on the sol disperse phase characteristics studies

It has been proved that the characteristics of sols affect the optical properties of composites with the glass surface and nanofilms. Film thickness and composite transmission are proportionally on the volume fraction of the sol disperse phase. The laser ablation threshold energy density under the irradiation of a nanosecond laser radiation pulse increases with increasing the packing density of the dispersed phase in the layer. And the ablation threshold energy density under the laser radiation microseconds pulse increases with increasing particles size of the dispersed phase and decreases with the increasing volume fraction of the dispersed phase and the particle packing density.

Study of optical and mechanical strengths of the glass composites with sol-gel films

Dependences of optical and mechanical strengths of glass composites with the drawn films upon the film thickness, particles packing density in a layer in the sol disperse phase and the particles diameter have been studied experimentally. We report that the laser ablation threshold energy density values decrease with the growth of the composites microhardness.

The influence of the silicon dioxide barrier films on the laser ablation destruction of the glass composites with the films drown from the sols

The laser ablation destruction of the composites with nano dimensional oxide one- or two-layers films drown from the sols on a glass substrate has been studied. It has been shown that the laser ablation destruction threshold energy density depends on the number and chemical composition of the layers and the drawing velocity. The ablation threshold energy density of the two-layer composites finds out mainly a tendency to decrease at the 3.8 mm/s drawing velocity, but at the 5.8 mm/s one--to increase that can be explained by the films thickness decreasing and the low-melting components from the glass substrate diffusion due to the barrier films diminishing.

Femtosecond pulsed laser ablation of polyimide at oblique angles for medical applications

We report the ablation results for surface modification of polyimide Kapton HN foils using ultrashort femtosecond laser pulses. The modification threshold fluences for 75μm thick films of polyimide were determined at different incident angles (0°, 20°, 30°, 45°, and 50°) for vertical and horizontal diameters. Ablation at oblique angles was investigated as such interactions are found during laser procedures with the eye that require scanning of the beam and are very important to know for the treatment of various eye diseases. Polyimide, in this study, was considered as a model for corneal sculpting. Use of ultrashort femtosecond laser pulses for high-precision patterning of the sample, without thermal damage to the surroundings, has been investigated. The relationship between the incidence angle with ablation threshold fluence, threshold energy, and beam radius are described. Also, threshold energies and threshold fluences for different thicknesses of polyimide were investigated.

Laser ablation studies of nanocomposites

The first experimental measurements of the threshold energy density values for the laser ablation of glass nanocomposites with nanodimensional coatings have been carried out under the action of the YAG–Nd laser power pulse radiation. The coatings in question were of different compositions and had been created by the sol–gel technology. The procedure for determining the laser ablation threshold energy density values was worked out on the base of the breakdown probability level of 0.5. The statistical processing of the measurement data over all the samples allowed obtaining the dependence of the ablation destruction threshold energy parameters on the coating physical and chemical properties such as the sample transmission in the visible region of the spectrum, coating thickness, the chemical composition of the film-forming solution, and on the pulse duration of laser radiation.

Laser ablation of the glass nanocomposites studies

The laser ablation threshold energy density of the glass nanocomposites of the different composition for the YAG-Nd laser pulse radiation experimental measurements have been fulfilled. The dependences of the laser ablation threshold parameters versus the optical and physical properties of these nanocomposites have been studied.

Rare event molecular dynamics simulations of plasma induced surface ablation.

The interaction of thermal Ar plasma particles with Si and W surfaces is modeled using classical molecular dynamics (MD) simulations. At plasma energies above the threshold for ablation, the ablation yield can be calculated directly from MD. For plasma energies below threshold, the ablation yield becomes exponentially low, and direct MD simulations are inefficient. Instead, we propose an integration method where the yield is calculated as a function of the Ar incident kinetic energy. Subsequent integration with a Boltzmann distribution at the temperature of interest gives the thermal ablation yield. At low plasma temperatures, the ablation yield follows an Arrhenius form in which the activation energy is shown to be the threshold energy for ablation. Interestingly, equilibrium material properties, including the surface and bulk cohesive energy, are not good predictors of the threshold energy for ablation. The surface vacancy formation energy is better, but is still not a quantitative predictor. An analysis of the trajectories near threshold shows that ablation occurs by different mechanisms on different material surfaces, and both the mechanism and the binding of surface atoms determine the threshold energy.

Failure of multimode optical fibers nano-structured by near ablation threshold single-shot femtosecond laser procedure

The present paper deals with the study of the failure probability of nano-structured optical fibers when submitted to uniaxial tensile loading. A nano-structuration procedure of optical fibers thanks to near ablation threshold single shot femtosecond laser has been proposed. The ablation threshold energy Ep0 for silica fiber is such that: NA2Ep0=15.5nJ, where NA is the numerical aperture of the objective to focus the laser inside the fibers. The rupture strength of the impacted fibers can be controlled through the pulse energy Ep, the numerical aperture NA, the number Nl of nano-craters depending on the step dz of the position of the fiber surface into the focal region, the interval dx between each crater and the number nl of flaw lines. An additive combination of two classical Weibull's laws allows a good representation of the failure probability of the impacted fibers. A phenomenological model for the evolutions of the Weibull's parameters (exponents and scaling stresses) has been proposed and the experimental tendencies of the failure probability curves are fairly well described by the set of the model's equations (Eq. (27)).

A new route to graphene layers by selective laser ablation

Selectively creating regions of spatially varying thickness may enable the utilization of the electronic properties of N-layer (N=1 or more) graphene and other similar layered materials (e.g., topological insulators or layered superconductors) for novel devices and functionalities on a single chip. The ablation threshold energy density increases dramatically for decreasing layer numbers of graphene originating from the dimensional crossover of the specific heat. For the 2D regime of graphite (up to N≈7) the dominant flexural mode specific heat (due to its N-1 dependence) gives rise to a strong layer number-dependence on the pulsed laser ablation threshold energy density, while for 3D regime (N>>7) the ablation threshold saturates due to dominant acoustic mode specific heat. As a result, several energy density windows exist between the minimum energy densities that are required for ablating single, bi, or more layers of graphene, allowing layer number selectivity.

Fluorinated silica glass ablated with ArF excimer laser at low fluence

Amorphous SiO 2 (a-SiO 2) was formed by liquid-phase deposition (LPD) at room temperature. As a result of one shot of ArF excimer laser irradiation, LPD-formed a-SiO 2 shows a threshold fluence for ablation of below than 200 mJ/cm 2, which is much lower than the threshold fluence (∼1 J/cm 2) of a-SiO 2 formed by thermal oxidation of silicon. Raman scattering spectroscopy revealed that two sharp lines at 495 cm −1 and 606 cm −1, respectively, labeled D 1 and D 2, had disappeared, and the main band at 430 cm −1 was sharpened in LPD-formed a-SiO 2. It is presumed that the fluorine broke the silica network, relaxing the Si–O–Si bond angle and dramatically reducing the threshold energy for ablation of a-SiO 2.

Liquid crystal alignment on periodic microstructure induced by single-beam 532 nm polarized laser illumination on poly(urethane-imide) film

After illumination by single-beam polarized pulse laser (532 nm) with energies below the ablation threshold energy, periodic microstructure was prepared on an azobenzene-containing poly(urethane-imide) (PUI) film surface. The reflective polarized IR results proved that the azobenzene group tended to be oriented perpendicular to the surface periodic microstructure. The illuminated PUI surface was used as the alignment layer of liquid crystal (LC) molecules. The experimental results indicated that the LC molecules tended to align closely along the surface microgrooves of the surface periodic microstructure. But the anchoring energy of LC molecules on the PUI film surface was smaller than that calculated based on the Berreman theory, which indicated that LC alignment on the laser-illuminated PUI film surface was controlled by the surface microgrooves and anisotropic orientation of the azobenzene group.

Trace element analysis of synthetic mono- and poly-crystalline CaF 2 by ultraviolet laser ablation inductively coupled plasma mass spectrometry at 266 and 193 nm

The analytical figures of merit for ultraviolet laser ablation-inductively coupled plasma mass spectrometry (UV-LA-ICP-MS) at 266 nm with respect to the trace element analysis of high-purity, UV-transmitting alkaline earth halides are investigated and discussed. Ablation threshold energy density values and ablation rates for mono- and poly-crystalline CaF 2 samples were determined. Furthermore, Pb-, Rb-, Sr-, Ba- and Yb-specific analysis was performed. For these purposes, a pulsed Nd:YAG laser operated at the fourth harmonic of the fundamental wavelength (λ=266 nm) and a double-focusing sector field ICP-MS detector were employed. Depending on the background noise and isotope-specific sensitivity, the detection limits typically varied from 0.7 ng/g for Sr to 7 ng/g in the case of Pb. The concentrations were determined using a glass standard reference material (SRM NIST612). In order to demonstrate the sensitivity of the arrangement described, comparative measurements by means of a commercial ablation system consisting of an ArF excimer laser (λ=193 nm) and a quadrupole-type ICP-MS (ICP-QMS) instrument were carried out. The accuracy of both analyses was in good agreement, whereas ablation at 266 nm and detection using sector-field ICP-MS led to a sensitivity that was one order of magnitude above that obtained at 193 nm with ICP-QMS.

Chemical Modification of Poly(ethylene Terephthalate) Induced by Laser Treatment

Poly(ethylene terephthalate) (PET) is modified by a 248 nm KrF excimer laser with high (above ablation threshold) and low (below ablation threshold) energy irradiation. The PET surface develops a well-oriented periodic structure of hills and grooves or a “ripple structure” with high energy treatment. However, the ripple size can be reduced to submicron level by irradiation of the sample below the ablation threshold. Chemical surface changes of the material are characterized by x-ray photoelectron spectroscopy (XPS) and contact angles, PET modified by high energy will normally exhibit the deposition of some yellow to black ionized, carbon-rich debris on the treated surface, resulting in a reduction of the O/C ratio. In contrast, a PET surface modified by low energy leads to oxidation and almost no ablation. The increased oxygen concentration on low energy modified surfaces is probably due to a subsequent reaction with atmospheric O2 during irradiation. Polar oxidized groups like carboxyls are also induced. Contact angle measurements are in good agreement with these findings.