Glass Ablation Research Articles

Shock-induced concentric rings in femtosecond laser ablation of glass

Both the single and multiple pulse ablation of dielectrics with high-intensity femtosecond lasers have been well studied. Additionally, the “pulse-shaping” regime, in which temporal peaks are separated by picoseconds, has also been investigated. In this paper, we show that a “prepulse configuration”—where one pulse is followed several nanoseconds later by a much stronger pulse—is qualitatively different from any of the previously investigated regimes. In particular, it leads to the recently discovered “concentric rings” feature in glass. We show that the damage pattern produced in glass is very different for two pulses separated by nanoseconds than for two pulses separated by either milliseconds or picoseconds. For nanosecond separations, the second pulse interacts with the shock wave created by the first, significantly altering the damage pattern. In addition to producing novel structures, this pump-probe technique provides a new way of studying ablation plume and shockwave dynamics.

Nanostructures synthesis by femtosecond laser ablation of glasses

In this article, we investigate the variations in ablation dynamics that result in diverse nanostructures on SiO2 based glass samples. A three-dimensional fibrous nanoparticle agglomerate was observed on sodalime glass when exposed to femtosecond laser irradiation. The fused nanoparticles have diameters ranging from 30 nm to 70 nm. Long continuous nanofibers of extremely high aspect ratio (certain fibers up to 100 000:1) were obtained by exposing silica glass surface to femtosecond laser irradiation at MHz repetition rate in air. A nanostructure assembly comprising of nanofiber and nanoparticle agglomerates was also observed by ablating silica glass. From our experimental analysis, it was determined that variation in bandgap and material composition alters ablation dynamics and dictates the response of glass to femtosecond laser irradiation, ultimately leading to the formation of structures with varying morphology on silica and sodalime glass. The possible underlying mechanisms that produce such nanostructures on glass specimens have also been explored.

TGV Microfabrication Technology for 3D Packaging

Glass is expected to be applied to a core material for panel size interposer for 3D package system nowadays. The most important challenge for glass as an interposer is the development of through hole formation with cost-effective and high-throughput. Several through hole drilling technologies such as wet etching, deep reactive-ion etching, sandblasting, laser ablation and the use of photosensitive glass have been studied and reported so far. However, the glass microfabrication technology combining both high-throughput and large area processability have not been reported yet. This study explored the new glass fabrication method by means of electrical discharge to realize high throughput and fine pitch hole drilling. An alkali-free glass substrate was used. Focused and controlled electrical discharge induced dielectric breakdown of glass material and also created Joule heat induced ablation and ejection of glass. Approximately 50 – 60 micron in diameter through hole was made. The result shows, even serial process can have a potential for high high-throughput solution, because this phenomenon can complete as an ultrashort process time of 1msec or less. In terms of fine pitch processability, 100um pitch hole drilling was confirmed. In this study, several glass fabrication technologies were compared by SEM and optical microscope observation for hole shape characteristic. Additionally a potential of industrialization and fine pitch hole drilling were considered. This study pointed out necessary development subjects towards an application, glass core material for 3D interposer substrate.

Cost effective 3D Glass Microfabrication for Advanced Packaging Applications

Interposer technologies are gathering more importance in IC packaging as the industry continues miniaturization trends in microfabrication nodes and IC packaging to meet design and utility needs in consumer electronics. Furthermore, IC packaging is widely seen as a method to prolong Moore's law. Historically, silicon has been the material of interest for interposer materials given its prevalence in IC production, but it presents many technical and costs hurdles. In contrast, glass interposer technology presents a low cost alternative, yet attempts at producing advanced through glass vias (TGVs) arrays using traditional methods, such as laser ablation, have inherent process flaws, such as reduced interposer mechanical strength and debris sputtering among others. In this extended abstract we present 3D Glass Solutions' efforts in using our proprietary APEX™ Glass ceramic to create various interposer technologies. This extended abstract will present on the production of large arrays of 10 micron diameter TGVs, with 20 micron center-to-center pitch, in 100 micron thick APEX™ Glass ceramic and the comparisons of wet etching of APEX™ Glass vs. laser ablation.

Ablation of silica glass induced by laser plasma soft X‐ray irradiation

AbstractSilica glass can be ablated using focused laser plasma soft X‐rays. The ablation technique enables us to fabricate trenches with a width as narrow as 50 nm. In the present paper, we have investigated the nano‐ablation process. The soft X‐ray irradiation causes a silica surface broken into almost atomic species. Ionic species have kinetic energies higher than that gained by heating to the boiling point. We measured the ablation depth as a function of the soft X‐ray fluence. The depth analysis revealed that soft X‐rays are absorbed in a silica surface with an effective absorption depth of 10 nm. The result indicates that the energy density of the soft X‐rays per unit volume at the threshold fluence is comparable to that required for breaking silica glass into atomic species. Further, the results suggest that ablation occurs before diffusion of absorbed energy into the surrounding region. In addition to energy absorption, repulsive forces between ionic species may cause ablation of the silica surface by soft X‐ray irradiation. These properties of soft X‐ray ablation may make possible the nano‐ablation of silica glass. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(9): 30–35, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10354

Nanofibre fabrication by femtosecond laser ablation of silica glass

This article presents a fabrication technique for generating densely populated and randomly oriented silica nanofibres by direct ablation of silica glass using a femtosecond laser with 12.4 MHz repetition rate and a pulse width of 214 fs, under ambient conditions. Four types of nanofibres with diameters ranging from a few tens of nanometers to a few hundreds of nanometers were formed. Some fibers reach lengths of 10 mm. The possible mechanisms for fibre formation have been explored.

High-fluence femtosecond laser ablation of silica glass: effects of laser-induced pressure

A pump-probe technique is employed to investigate the dynamic process of femtosecond laser ablation of silica glass, and three stress waves are observed inside the silica glass in the time-resolved shadowgraphs at a fluence of 40 J cm−2. It is believed that the first stress wave is a thermoelastic wave generated by thermal expansion, while the second and the third are generated subsequently by the mechanical expansions as a result of the extremely high pressure induced by the laser. By employing digital holography, the ablation crater is investigated to identify the ablation results, and high-density silica glass is found beneath the ablation crater, which is also the result of the laser-induced pressure. Furthermore, it is found that more stress waves will be generated at a higher fluence, and the thresholds for the generation of the first, second and third stress wave are measured to be about 2 J cm−2, 6 J cm−2 and 31 J cm−2, respectively. The theoretical calculation result shows that the laser-induced pressure increases with the increase in fluence and can be on the scale of TPa, and we believe a higher pressure will induce more mechanical expansions and therefore more stress waves.

Time-resolved optical diagnosis of intense femtosecond laser ablation of silica glass

The dynamic process of femtosecond laser pulse ablation of silica glass has been experimentally investigated by ultrafast time-resolved optical diagnosis. The digital holograms of material ejections outside the silica glass are recorded, and two-dimensional phase difference maps at different delay times are obtained, from which the composition and the structure of the ejected materials are deduced. Besides, the time-resolved shadowgraphs of the phenomena inside the silica glass are also recorded, and the evolution process of two stress waves inside the silica glass is observed in the shadowgraphs, which are believed to be related to two material ejections outside the target.

Iodine as an elemental marker for imaging of single cells and tissue sections by laser ablation inductively coupled plasma mass spectrometry

A new laser ablation (LA)-ICP-MS method for single cell and cell nucleus imaging was developed. Therein, iodine was employed as an elemental dye for fibroblast cells and for thin tissue sections. At an incubation time of 60 s, iodine is located mainly within the cell nuclei. This effect was illustrated in fibroblast cells, and iodine signal within the cell nucleus was as high as 5 × 104 cps at 4 μm laser spot size. The surrounding cytoplasm was iodinated as well, but to a lesser extent. The spatial resolution attained was sufficient to detect even smaller cell nuclei within a liver biopsy tissue. Furthermore, iodine was successfully employed for biomolecule labeling and we demonstrated that iodine signal increased with increasing thickness of a palatine tonsil tissue. Thus, the use of iodine as an internal standard to correct for tissue inhomogeneities in LA-ICP-MS was investigated for the simultaneous detection of two tumor markers (Her 2 and CK 7) in breast cancer tissue. Additionally, lanthanide background resulting from glass ablation can be corrected for by Eu standardization.

Comparison of separation performance of laser-ablated and wet-etched microfluidic devices

Laser ablation of glass allows for production of microfluidic devices without the need for hydrofluoric acid and photolithography. The goal of this study was to compare the separation performance of microfluidic devices produced using a low-cost laser ablation system and conventional wet etching. During laser ablation, cracking of the glass substrate was prevented by heating the glass to 300 °C. A range of laser energy densities was found to produce channel depths ranging from 4 to 35 μm and channel widths from 118 to 162 μm. The electroosmotic flow velocity was lower in laser-ablated devices, 0.110±0.005 cm s(-1), as compared to wet-etched microfluidic chips, 0.126±0.003 cm s(-1). Separations of both small and large molecules performed on both wet- and laser-ablated devices were compared by examining limits of detection, theoretical plate count, and peak asymmetry. Laser-induced fluorescence detection limits were 10 pM fluorescein for both types of devices. Laser-ablated and wet-etched microfluidic chips had reproducible migration times with ≤ 2.8% relative standard deviation and peak asymmetries ranged from 1.0 to 1.8. Numbers of theoretical plates were between 2.8- and 6.2-fold higher on the wet-etched devices compared to laser-ablated devices. Nevertheless, resolution between small and large analytes was accomplished, which indicates that laser ablation may find an application in pedagogical studies of electrophoresis or microfluidic devices, or in settings where hydrofluoric acid cannot be used.

Generation of multiple stress waves in silica glass in high fluence femtosecond laser ablation

Shadowgraphs of dynamic processes outside and inside transparent target during the intense femtosecond laser ablation of silica glass are recorded. Two material ejections outside the target and two corresponding stress waves inside the target are observed at different energy fluences. In particular, a third stress wave can be observed at energy fluence as high as 40 J/cm2. The first wave is a thermoelastic wave, while the second and the third may be generated subsequently by the mechanical expansions. In addition, the magnitudes of the three stress waves decrease sequentially based on our analysis.

Effect of nonionic surfactant addition on Pyrex glass ablation using water-assisted CO2 laser processing

Pyrex glass etching using laser ablation is an important technology for the microfluid application to lab-on-a-chip devices but suffers from the formation of surface crack. In this article, the addition of nonionic surfactant to water for glass ablation using water-assisted CO2 laser processing (WACLAP) has been investigated to enhance ablation rate and to eliminate conventional surface defects of cracks in air. WACLAP for Pyrex glass ablation can reduce thermal-stress-induced crack with water cooling and hydrophilic nonionic surfactant to water can enhance ablation performance. Compared to pure water, the 15% weight percent Lauramidopropyl Betaine surfactant solutions for WACLAP can enhance ablation rate from 13.6 to 25 μm/pass of Pyrex glass ablation at a linear laser energy density of 2.11 J/cm, i.e., 24 W power, 114 mm/s scanning speed, and obtain through-wafer etching at 3.16 J/cm for 20 passes without cracks on the surface. Effect of surfactant concentration and linear energy density on WACLAP was also examined. The possible mechanism of surfactant-enhanced phenomenon was discussed by the Newton’s law of viscosity of surfactant solution.

Structuring by field enhancement of glass, Ag, Au, and Co thin films using short pulse laser ablation

Single pulse laser ablation of glass, Ag, Au, and Co thin films was experimentally investigated with a laser pulse width of 400 ps at a wavelength of 532 nm both in the far and near fields. In the far-field regime, the electromagnetic field results from a focused laser beam, while the near-field regime is realized by a combination of the focused laser beam incident on a spherical colloidal particle. For the near-field experiments we have used polystyrene colloidal particles of 700 nm diameter self-assembled or spin coated on top of the surfaces. Laser fluences applied are in the range of 0.01–10 J/cm2. The diameter and the morphologies of the ablated holes were investigated by optical microscopy, profilometry, scanning electron microscopy, and atomic force microscopy. The dependence of the shape of the holes reflects the fluence regime and the thermophysical properties, i.e., melting temperature and thermal diffusivity of the surfaces involved in the experiments. We give quantitative data about the fluence threshold, diameter, and depth ablation dependence for the far and near fields and discuss their values with respect to the enhancement factor of the intensity of the electromagnetic field due to the use of the colloidal particles. Theoretical estimations of the intensity enhancement were done using the finite-difference time-domain method by using the RSOFT software. The application of near fields allows structuring of the surfaces with structure dimension in the order of 100 nm and even below.

The influence of substrate temperature on femtosecond laser micro-processing of silicon, stainless steel and glass

We report the influence of substrate temperature on femtosecond laser ablation of silicon, stainless steel, and glass. Remarkable decrease in surface roughness was observed under high substrate temperature for silicon and stainless steel. While the ablation efficiency of glass as a typical wide band-gap material is scarcely altered at 900 K, the efficiency for stainless steel as a conductor apparently increased about 20% accompanied to the elevation of substrate temperature from 300 to 900 K. Silicon wafer results in slight increase of the ablation efficiency with decreasing the ablation threshold. Considering that the melting temperature of glass is much lower than those of silicon and steel, the observations from this work suggests that the material ablation caused by the ultrafast laser irradiation could not be explained in term of only laser-induced thermal excitation.

Ultraviolet laser ablation of polycarbonate and glass in air

The fundamental physical processes that follow ultraviolet laser ablation of polycarbonate and borosilicate glass in air have been investigated using photodeflection as a function of the distance from the surface to probe laser. Four features were observed in the data sets for each material. Two of these features correlate well with gas dynamical predictions for the expansion of the shock wave and gas plume. The third feature is consistent with the propagation of the popping sound of the laser ablation event. The final feature, which occurs at very early times and does not shift significantly in time as the surface to probe distance is increased from 0 to greater than 6 mm, has been tentatively ascribed to the ejection of fast electrons. The final significant observation is complete blocking of the probe laser, only observed during borosilicate ablation, which is attributed to scattering of the probe laser light by macroscopic SiOx particles that grow in the final stages of plume expansion and cooling.

Active glass nanoparticles by ultrafast laser pulses

The authors have successfully demonstrated a method employing pulsed-laser ablation of active glass to produce nanoparticles exhibiting upconversion, pumped by near-infrared wavelengths and emitting visible light. A high repetition rate ultrashort pulsed laser was used to ablate glass under atmospheric conditions. Ejected particles collected were analysed by electron microscopy to determine particle size and characterise the morphology. The measured mean particle diameter was ~17~nm. A bright upconversion green emission was observed from the nanoparticles almost in a similar fashion as from the bulk specimen. The upconversion photoluminescence characteristics have been investigated to explore potential applications for efficient bioimaging and light-emitting devices.

High-Speed Photographic Observation of Shock-Pressure Pulses in Water Induced by Laser Energy Absorption at Roughened Surface

Absorption enhancement of laser energy at roughened surface was discovered by our group years ago. Laser ablation threshold apparently decreases by intentional roughening of the surface. Another important condition of threshold reduction is found for transparent material surface, if the pulse laser beam is irradiated from the rear side through the transparent plate. Several examples of the shock pulse induced in water and in air by pulse laser ablation of ground glass, roughened PMMA plates and fiber has been observed in detail by high-speed photography. Simple preliminary experiments to study the physical mechanism of enhanced absorption of laser energy have also been planned and demonstrated.

Structural and optical properties of annealed W-dopedBaTiO3 thin films prepared by pulsed laser deposition

Tungsten-doped barium titanate thin films have been prepared on glass and silicon substratesby laser ablation. The films were compositionally, structurally and optically characterized.Rutherford backscattering spectroscopy simulation gave the composition to beBa0.85W0.05Ti0.94O3.2 with acationic ratio (Ba+W)/Ti of 0.95. All the films without annealing were amorphous. The calculated lattice constantsthrough the diffraction patterns on the silicon substrate indicated the high probability ofthe film having a cubic symmetry. Atomic force microscopy results showed the film surfaceto be smooth with a maximum roughness of 5 nm, varied grain size distributionand average grain size of 50 nm. Through the Swanepoel envelope method, therefractive index dispersion was obtained. Maximum and minimum refractive indices of2.6 and 2.32 at 475 and 812 nm, respectively, were calculated. Analysis of thedependence of the refractive index and the dielectric constant on wavelength led to thedetermination of the high-frequency dielectric constant and the carrier density effective mass ratio(Nc/m*). The single-oscillator model proved to be adequate for describing the dispersion behaviour.Through this model, the dispersion parameter, average oscillator parameter and strengthwere determined. The optical band gap obtained on annealed sample was 3.8 eV byassuming a direct transition.

Pulse laser ablation of ground glass

We have studied pulse laser ablation of ground glass surface. Ablation process in air and in vacuum has been observed by high speed framing camera. Burst of small fragments of glass has been observed in the present experiment, when ground glass surface is laser ablated through glass plate from rear side. Production of macro particles by laser ablation is an inherent characteristic of ground glass, and no similar phenomena have been observed in case of ablation of other transparent materials. By using ns-duration Nd:YAG laser of 100–400 mJ/pulse, observed maximum particle velocity ranges from 0.5 to 1.5 km/s. In order to understand the particle generation process, scanning electron micrograph observation of the ground surface in the region of no laser irradiation and also in the damaged region, has been made. Cleavage surface structure has been evidenced in the damaged surface area, which stems from plenty of micro cracks covering the virgin glass surface. Effects of surface roughness on the particle generation were studied by using ground glass of quartz with different surface roughness. Produced glass particles were captured in vacuum by a polymethylmetacrylate (PMMA) plate. Size distribution was obtained by analysing the trapped particles on the PMMA plate and revealed that most probable particles size has almost no dependence on the initial surface roughness. Finally, we applied the phenomena to ignite pentaerithritoltetranitrate (PETN) powder explosive, and succeeded in igniting (PETN) powder only by laser ablation of ground glass.

Thermal and fluid processes of a thin melt zone during femtosecond laser ablation of glass: the formation of rims by single laser pulses

We study the formation mechanism of rims created around femtosecond laser ablated craters on glass. Experimental studies of the surface morphology reveal that a thin rim is formed around the smooth craters and is raised above the undamaged surface by about 50–100 nm. To investigate the mechanism of rim formation following a single ultrafast laser pulse, we perform a one-dimensional theoretical analysis of the thermal and fluid processes involved in the ablation process. The results indicate the existence of a very thin melted zone below the surface and suggest that the rim is formed by the high pressure plasma producing a pressure-driven fluid motion of the molten material outwards from the centre of the crater. The numerical solutions of pressure-driven fluid motion of the thin melt demonstrate that the melt can flow to the crater edge and form a rim within the first nanoseconds of the ablation process. The possibility that a tall rim can be formed during the initial stages of the plasma is suggestive that the rim may tilt outwards towards the low pressure region creating a resolidified melt splash as observed in the experiments. The possibility of controlling or suppressing the rim formation is discussed also.