Glass Ablation Research Articles

Comparative analysis of microlens array formation in fused silica glass by laser: Femtosecond versus picosecond pulses

The growing demand for flexible, high-quality fabrication of free-form micro-optics drives the development of laser-based fabrication techniques for both the shape formation and surface polishing of optical elements. In this paper, we performed a thorough and systematic study on fused silica glass ablation using 10 ps and 320 fs duration pulses. Ablation processes for both pulse durations were optimized based on the measurements of the removed material layer thickness and surface roughness, and by analyzing the topographies of ablated cavities to remove material layers as thin as possible with minimum surface damage. Our findings demonstrate higher process resolution and surface quality for femtosecond pulses. Ablation of pre-roughened glass reduced the minimal removable glass layer thickness well below the 1 μm mark for both pulse durations, improving the process resolution. The minimal removable glass layer thickness was 14 times smaller for the femtosecond pulses, with up to 4.5 times lower surface roughness compared to samples processed with picosecond pulses. On the other hand, results revealed faster glass removal rates with picosecond pulses. In the end, arrays of microlenses were fabricated with both pulse durations and subsequently polished with a CO2 laser. Results revealed higher performance of microlenses fabricated with femtosecond pulses, providing better focusing capabilities and lesser beam scattering. Finally, this study demonstrated the successful fabrication of free-form optical elements with femtosecond and picosecond pulses, demonstrating the versatility and the potential of laser-based techniques.

One-second regeneration of superhydrophilicity and antifog performance of laser induced tungsten based micro-nano structure by flame treatment

In this study, hierarchical micro-nano structured glass surfaces were produced by a cost effective laser marker ablation of tungsten-coated glass. The treated surface demonstrated a water contact angle of 0°, achieved and maintained remarkable antifog performance over 13 months without apparent degradation, which had rarely been reported. Remarkably, a one-second flame treatment fully restored the superhydrophilicity and antifog properties, an intervention not previously reported. Such structure also showcased exceptional self-cleaning property. Wenzel model could not explain the suboptimal hydrophilicity of highly rough surfaces, underscoring the necessity for a new model. The area density of capillary force used to estimates water spreading capability on a surface was proposed as a criterion for assessing the strength of hydrophilicity, aligning with preliminary experimental results.

Durable self-cleaning anti-fog and antireflective titanium-based micro-nano structures on glass by laser marker ablation

Hierarchical micro-nano structured glass surfaces were produced by a low-cost laser marker ablation of Titanium-coated glass. The samples were systematically analyzed in terms of composition, structure, morphology, transparency, and anti-fog performance. The influences of varying laser scan hatch distance and Titanium (Ti) coating thickness on the resulting surface properties were studied. The results showed that the surface exhibited a 30 μm-sized periodic hillock-hollow micro-structure, with widely dispersed nanoparticles of approximately 50 nm in diameter all over the micro-structure. The most favorable surface characteristics were achieved with a 250 nm Ti coating and a 0.03 mm hatch distance, resulting in a notable enhancement of the average transmission of the glass by 1.29 % over a wide spectral range spanning from 400 nm to 1100 nm. Additionally, the treated surface exhibited super-hydrophilicity, evidenced by a contact angle of 0°, thereby demonstrating excellent anti-fog performance in fog tests that remained effective for an impressive duration of 318 days. It also exhibits exceptional anti-fouling and self-cleaning attributes, which remain effective over a span of 459 days. This outstanding antifog self-cleaninng performance and broadband transmission enhancement was, for the first time, co-achieved for laser treated glass. These accomplishments hold substantial practical relevance in diverse applications.

Durable self-cleaning anti-reflective and antifog micro-nanostructures fabricated by laser ablation of vanadium-coated glass surfaces

In this study, low-cost laser marker ablation of vanadium-coated glass was adopted to prepare self-cleaning, anti-reflective, and anti-fog micro-nano structures on its surface. The surface had a hierarchical micro-nano structure composed of a quasi-periodic microstructure and ∼100 nm-sized worm-like clusters interspersed with dispersed nanoparticles. The solar spectrum (AM 1.5) weighted average transmission of treated glass was enhanced by 3.87% over control glass in the wavelength range of 400–1100 nm. Importantly, the water contact angle of the laser-treated samples achieved and maintained 0° for a duration of 25 days, and the laser-treated samples achieved and maintained excellent anti-fog performance for 150 days. The antifog performance degraded substantially afterward, though was still noticeable compared to the reference even after 428 days of storage in the laboratory. Furthermore, co-achievement of exceptional self-cleaning anti-fog performance and broadband transmission enhancement through laser treatment of glass has rarely been previously reported.

Laser writing of parabolic micromirrors with a high numerical aperture for optical trapping and rotation

On-chip optical trapping systems allow for high scalability and lower the barrier to access. Systems capable of trapping multiple particles typically come with high cost and complexity. Here, we present a technique for making parabolic mirrors with micrometer-size dimensions and high numerical apertures (NA > 1). Over 350 mirrors are made by simple CO2 laser ablation of glass followed by gold deposition. We fabricate mirrors of arbitrary diameter and depth at a high throughput rate by carefully controlling the ablation parameters. We use the micromirrors for three-dimensional optical trapping of microbeads in solution, achieving a maximum optical trap stiffness of 52 pN/μm/W. We, then, further demonstrate the viability of the mirrors as in situ optical elements through the rotation of a vaterite particle using reflected circularly polarized light. The method used allows for rapid and highly customizable fabrication of dense optical arrays.

Effect of electrical erosion on composite insulator core rod under acidic environment

Silicone rubber housings crack under the combined internal and external factors and expose the core rod. The exposed core rod deteriorates or breaks under electric fields and electrical current. Based on the main characteristics and mechanism of the core rod corrosion, this paper performs an electrical erosion test in an acid-fog environment and analyzes the core rod's macroscopic results and physicochemical properties. The results indicate the following. First, the discharge on core rod during the electrical erosion process contains four consecutive stages. The electrical current, partial discharge, temperature increase, and macroscopic morphology show regular changes at different stages. The arc usually occurs in the carbonization channel, making the channel have the maximum heat. The area of the core rod heating constantly changes but mainly at the high-voltage side and presents as a regional temperature increase. Second, the fracture of glass fiber and ablation of epoxy resin matrix are related to the continuous action of nitric acid. The generation, expansion, and release of pyrolysis gas form bubbles and pores on the epoxy resin matrix. Erosion and pyrolysis cause the loss of the epoxy resin matrix. Third, the combined effect of electrical current, nitric acid, and heat damage the core rod axially and radially. The study provides support for the subsequent core rod deterioration and fracture mechanism.

Time-resolved Spectroscopy of Glass Ablation during Micro-via Processing using 248 nm Excimer Laser for Semiconductor Interposer Packaging

Time-resolved Spectroscopy of Glass Ablation during Micro-via Processing using 248 nm Excimer Laser for Semiconductor Interposer Packaging

Direct Laser Ablation of Glasses with Low Surface Roughness Using Femtosecond UV Laser Pulses

Direct Laser Ablation of Glasses with Low Surface Roughness Using Femtosecond UV Laser Pulses

Numerical simulation of femtosecond laser ablation of quartz glass and silicon nitride.

The ablation threshold and depth models were established based on the electron density evolution equation of dielectric and ionization theory. The volume model was then deduced, and the models were validated. For quartz glass and silicon nitride, the dependences of the threshold with pulse duration, ablation depth, and volume with fluence were analyzed. Also, the relations of scallop height and scanning velocity were predicted. The results show that the thresholds of quartz glass at durations of 12, 35, and 220 fs were 3.3, 2.9, and 2.3J/cm2, respectively, while the thresholds of silicon nitride at the same durations were 2.0, 1.8, and 1.4J/cm2, respectively. The ablation depth of quartz glass decreased with the increase of duration when the fluence deviated from the threshold. The depth of silicon nitride was opposite to it, and the ablation volume of silicon nitride was larger than that of quartz glass in the same condition. When the scanning velocity and fluence were determined, the scallop height decreased with the increase of duration. However, when the velocity and duration were determined, the scallop height increased with the increase of fluence. The shorter the duration was, the greater the variation of the scallop height.

Temperature field simulation of chalcogenide glass ablation by nanosecond pulsed laser-based on pump–probe technology

Chalcogenide glass (ChG) is one of the best candidate materials for the fabrication of micro-nano resolution photonic devices by laser direct writing (LDW). In this work, the thermodynamics and the surface structures evolution of As2S3 by nanosecond pulse are investigated by the dual-laser pump–probe system. Above the ablation threshold (124, 157, 196 mJ/cm2), the descend duration of sample surface reflectivity was observed to be 25, 48, and 80 ns, respectively. Furthermore, to research the effects of pulse irradiation and surface thermal energy diffusion on the sample surface temperature, the dual-temperature model is applied. At the lowest laser fluence, the temperature drops rapidly to the melting point in a short time (23 ns), which results in the formation of a crater in the pulse action area. At the highest fluence, the surface temperature decreases slowly to the melting point (77 ns). And during this period, the material surface is continuously heated, which leads to the deepening of melting depth. So, a deep crater (294 nm) is formed on the surface, and the reflectivity declines the slowest. Secondly, due to the highest temperature in the central region and the diffusion movement of heat energy, the rim structure and the small droplet structures will appear at a higher fluence.

Low-cost SERS substrate featuring laser-ablated amorphous nanostructure

In this work, we aimed at fast and scalable manufacturing of low-cost SERS substrates using ultrashort-pulse laser-induced plasma-assisted ablation (LIPAA) of soda-lime glass. A two-step approach of amorphous nanostructure formation on the glass surface and subsequent deposition of 170 nm silver layer resulted in homogenous SERS-active substrates covered with nanostructures of around 100 nm in diameter, forming 1–3 μm size dendrimers. The average enhancement factor (EF) evaluated using thiophenol was 3.0 × 105, while the surface activity was found to be consistent at any given point of substrates. Relatively modest EF was explained by amorphous, rounded-shaped features on soda-lime glass formed during the LIPAA-induced melting and subsequent solidification. That resulted in a lesser amount of hot spots but increased surface homogeneity. The use of soda-lime glass to fabricate SERS substrates promises a cheaper and scalable alternative to more widely used sapphire and other material substrates opening prospects for low-cost routine SERS testing with high reproducibility in chemistry, medical, forensic, and environmental sciences.

Heat accumulation and surface roughness evolution in CO2 nanosecond laser ablation of quartz glass

Quartz glass is frequently used for optical components, but traditional machining methods, particularly for aspherical optics, are often associated with long process times and high costs. One possible approach to achieve higher efficiencies and higher speeds in contactless processing is laser ablation using CO2 laser radiation. This study investigates the evolution of surface topography during laser ablation of quartz glass using nanosecond pulses from a Q-switched CO2 laser beam source. The special focus of a broad empirical study lay on ablation depth, ablation rate, ablation efficiency and resulting surface roughness for an ablation process using 300 ns laser pulses at a maximum laser power of 115 W and pulse frequencies up to 150 kHz. Ablation efficiency shows a characteristic logarithmic dependency on laser fluence. It was revealed that local heat accumulation significantly affects the optical penetration depth, which reduces the threshold fluence for multi-pulse laser ablation down to approx. 0.37 J/cm2. Ablation rates of up to 1.48 mm3 min−1 W−1 were achieved, which exceeds results achieved for laser ablation using cw laser radiation or ultra-short pulses. An ablation rate of up to 170 mm3/min is a particularly noteworthy result. Therein, a maximum ablation efficiency of approx. 64% shows that the largest part of the incident laser energy was used for material ablation. Finally, based on a simplified model, numerical calculations and experimental results, pulse stability was identified to have a decisive impact on the evolution of the resulting surface roughness. The resulting surface roughness Sa is typically increased in pulsed laser processing and depends linearly on standard deviation of ablation depth and the square root of the number of ablation layers.

Efficient milling and cutting of borosilicate glasses through a thin flowing water film with a picosecond laser

Direct laser ablation allows high-quality processing, precision, and cutting of complex shapes. Unfortunately, this technology is usually not considered as the primary candidate for cutting and milling of glasses due to low processing speeds. Thus, laser-based rear side drilling and crack generation techniques are chosen instead. However, we report on the milling and cutting of borosilicate glass plates with high average power and high pulse repetition rate picosecond laser. We optimised laser processing parameters for the efficient direct material ablation and employed water-assisted ablation to improve the ablation efficiency and the cutting speed of borosilicate glasses. The laser process was realised through a thin flowing water film, which was formed by spraying water mist on the surface of the workpiece. Firstly, we characterised thin water film parameters, such as film thickness, flow velocity, and defined a working area with constant processing conditions. Next, we optimised laser processing parameters for both processing environments: ablation through the thin water film and in air. Under optimal parameters, ablation through the thin water film was much more effective, increasing the cutting speed of 420 μm thick glass plates nearly ten times – from 0.52 to 5 mm/s. Furthermore, the morphology of the cuts was improved as well: cut wall roughness and edge chipping were reduced, spatter deposition was avoided in the vicinity of the cut. We investigated the milling of 130 to 1700 μm wide and 50 to 500 μm deep grooves with a maximum depth-to-width ratio of 3.8. Findings revealed that the ablation efficiency increase provided by the water layer did not depend on the depth or the width of the groove and remained constant. Therefore, it became possible to predict the ablation efficiency through the thin water film by knowing the ablation efficiency in air and an absolute ablation efficiency difference between two processing environments. • Efficient borosilicate glass milling and cutting in the air and through the water film was conducted with a picosecond laser. • Optimal laser fluence for efficient glass ablation was 40% higher than in air. • An absolute change in ablation efficiency between two environments did not depend on the transverse dimensions of the groove. • Water film improved ablation efficiency significantly, resulting in nearly 10 times higher cutting speed than in air.

Nanosecond laser ablation of a metallic glass in water: a high time-resolved imaging study

ABSTRACT We use a state-of-the-art, ultrafast camera to probe the nanosecond pulse laser ablation of a metallic glass target in water. The laser-induced plasma of metallic glass is captured for the first time. We further observe a series of shock waves in water and the cavitation bubble on the target surface. The shock waves inherit the rapid expansion of the plasma, satisfying the momentum conservation. But the cavitation bubble stems from the nucleation of the surrounding water due to the heating of the plasma. We find that the bubble growth deviates from the Rayleigh-Plesset theory. The primary reason for this deviation is the effect of ablation products due to the temporal overlap between the explosive boiling and the bubble dynamics. Our findings provide a fundamental understanding of underwater laser ablation of metallic glasses, which is an important step to forward such ablation-related applications.

Picosecond laser ablation on glass using wavelength of 1064, 532, and 355 nm

The process of removing transparent material such as glass by means of laser ablation is widely performed in the industry. In many cases, the ultrashort pulse laser is used as the laser source, but the laser wavelength is diverse. The ablation mechanism of the transparent material generally is considered nonlinear absorption, but it is known that the absorption coefficient depends on the wavelength. However, there are few examples that discuss the ablation mechanism for multiwavelengths. We performed laser ablation of glass with a 15-ps pulse width and 1064, 532, and 355 nm wavelengths and constructed a unified understanding of the principle by numerical calculation using combined rate equation and beam propagation method. In addition, we measured the three-dimensional profile of the processing traces using a microscope and investigated the dependence of ablation volume to the wavelength. As a result, we acquired the results of ablation efficiency, laser fluence threshold, and inverse absorption coefficient of fused silica glass using various wavelengths in a single set-up. We were able to explain the ablation diameter and depth by numerical calculation considering the multiphoton ionization process and avalanche ionization process. In addition, the calculated laser efficiency indicated that the wavelength suitable for ablation on glass was 355 nm.

Interference-based laser-induced micro-plasma ablation of glass

AbstractGlass is one of the most important technical surfaces for numerous applications in automotive, optical, and consumer industries. In addition, by producing textured surfaces with periodic features in the micrometre range, new functions can be created. Although laser-based methods have shown to be capable to produce structured materials in a wide amount of materials, due to its transparency large bandgap dielectrics can be only processed in a controlled manner by employing high-power ultra-short pulsed lasers, thus limiting the employable laser sources. In this article, an interference-based method for the texturing of soda-lime glass using a 15 ns pulsed (1 kHz repetition rate) infrared (1053 nm) laser is proposed, which allows fabricating different periodic patterns with micrometre resolution. This method consists on irradiating a metallic absorber (stainless steel) put in direct contact with the glass sample and inducing locally an etching process on the backside of the glass. Then, the produced plasma at the interference maxima positions leads to the local fabrication of well-defined periodic line-like and dot-like surface patterns. The produced patterns are characterised using white light interferometry and scanning electron microscopy.

Ablation in Externally Applied Electric and Magnetic Fields.

To harness light-matter interactions at the nano-/micro-scale, better tools for control must be developed. Here, it is shown that by applying an external electric and/or magnetic field, ablation of Si and glass under ultra-short (sub-1 ps) laser pulse irradiation can be controlled via the Lorentz force , where is velocity of charge e, is the applied electrical bias and is the magnetic flux density. The external electric E-field was applied during laser ablation using suspended micro-electrodes above a glass substrate with an air gap for the incident laser beam. The counter-facing Al-electrodes on Si surface were used to study debris formation patterns on Si. Debris was deposited preferentially towards the negative electrode in the case of glass and Si ablation. Also, an external magnetic field was applied during laser ablation of Si in different geometries and is shown to affect ripple formation. Chemical analysis of ablated areas with and without a magnetic field showed strong chemical differences, revealed by synchrotron near-edge X-ray absorption fine structure (NEXAFS) measurements. Harnessing the vectorial nature of the Lorentz force widens application potential of surface modifications and debris formation in external E-/B-fields, with potential applications in mass and charge spectroscopes.

Submicron bubbles/voids formation in the subsurface region of soda-lime glass by single pulse fs laser-induced spallation

The formation of bubbles near the surface of soda-lime glass induced by single pulse irradiation with Ti: Sapphire laser of a wavelength of 775 nm and 150 fs pulse duration below the laser ablation threshold is reported. The bubbles with a diameter of 0.3–3 µm are much smaller than the spot size of ~12 µm and exhibit a semi-spherical surface, an ellipsoidal void and an upper shell thickness of approx. 100 nm. The bubbles are formed in a narrow energy range between bulk glass modification and glass ablation. The bubbles formation is accomplished with some changes of the glass morphology around the bubbles. Damaged bubbles occur near the upper laser energy limit for bubbles formation that show nanoholes or slits in the bubbles shell and opened shells exposing the bottom of the void. It is suggested, that the bubble forming mechanism is related to nonlinear processes of laser photon absorption, laser-induced spallation processes, materials heating after electron relaxation, and thermal driven, viscoplastic-mechanical processes. Mainly the material composition gradient of the soda-lime glass near the surface that affects photon absorption, melting, ablation and material expansion processes enable the formation of these bubbles. The void inside the bubble is formed first by pre-spallation resulting in a detached layer that is lifted further forming the bubbles shell by subsurface laser ablation/evaporation processes of the bulk glass. The upper shell of the bubble is formed by a thermally stable crust of corroded soda-lime glass. The results may have valuable impact to laser ablation processes for high precision fabrication. Further, the fast fabrication of such 3D submicron structures due to the single pulse interaction with the glass enables new technical processes for potential applications in sensing, photonic or microfluidic.

Laser-induced plasma-assisted ablation (LIPAA) of glass: Effects of the laser fluence on plasma parameters and crater morphology

This paper reports the fabrication of micro-craters on the soda lime glass substrate by laser-induced plasma-assisted ablation (LIPAA) using a Q-switched Nd-YAG laser (wavelength = 1064 nm, pulsed width = 6 ns). The objectives were to investigate the effects of laser fluence and target-to-substrate distance on the morphology of micro-craters, and to relate the observed effects with the plasma parameters. The incident laser fluence at the sacrificial aluminium target was in the range of 27–870 J/cm2 and target-to-substrate distance was in the range of 0 to 600 μm. The micro-craters were analyzed with the help of optical microscope and profilometer. And the plasma parameters were measured using the optical emission spectroscopy. Our results showed that the diameter and depth of micro-craters increases with the laser fluence and seems to reach saturation at higher fluence levels. However, the diameter and depth of the micro-craters were found to decrease linearly with the increase of target-to-substrate distance. The electron temperature and density of the aluminium plasma estimated using Boltzmann plot and Stark broadening methods were in the range of 6320–11450 K and 7.78 × 1016–2.0 × 1017 cm−3, respectively. The variation of plasma parameters as a function of the laser fluence was quite identical to the change in the size of micro-craters. The experimental results are discussed on the basis of LIPAA models and plasma shielding of the laser radiation.

Study of silica-based intrinsically emitting nanoparticles produced by an excimer laser.

We report an experimental study demonstrating the feasibility to produce both pure and Ge-doped silica nanoparticles (size ranging from tens up to hundreds of nanometers) using nanosecond pulsed KrF laser ablation of bulk glass. In particular, pure silica nanoparticles were produced using a laser pulse energy of 400 mJ on pure silica, whereas Ge-doped nanoparticles were obtained using 33 and 165 mJ per pulse on germanosilicate glass. The difference in the required energy is attributed to the Ge doping, which modifies the optical properties of the silica by facilitating energy absorption processes such as multiphoton absorption or by introducing absorbing point defects. Defect generation in bulk pure silica before nanoparticle production starts is also suggested by our results. Regarding the Ge-doped samples, scanning electron microscopy (SEM) and cathodoluminescence (CL) investigations revealed a good correspondence between the morphology of the generated particles and their emission signal due to the germanium lone pair center (GLPC), regardless of the energy per pulse used for their production. This suggests a reasonable homogeneity of the emission features of the samples. Similarly, energy dispersive X-ray spectroscopy (EDX) data showed that the O, Ge and Si signals qualitatively correspond to the particle morphology, suggesting a generally uniform chemical composition of the Ge-doped samples. No significant CL signal could be detected in pure silica nanoparticles, evidencing the positive impact of Ge for the development of intrinsically emitting nanoparticles. Transmission electron microscope (TEM) data suggested that the Ge-doped silica nanoparticles are amorphous. SEM and TEM data evidenced that the produced nanoparticles tend to be slightly more spherical in shape for a higher energy per pulse. Scanning transmission electron microscope (STEM) data have shown that, regardless of size and applied energy per pulse, in each nanoparticle, some inhomogeneity is present in the form of brighter (i.e., more dense) features of a few nanometers.