Laser-induced Plasma Ablation Research Articles

Femtosecond laser-induced plasma-assisted backward deposition of robustly adherent porous carbon films on glass substrates

The simple and rapid production and transfer of high-quality carbon materials are crucial for the flexible and efficient fabrication of carbon-based electronic devices. Recently, a laser-assisted transfer method combining laser-induced carbonization and transfer printing was demonstrated for the one-step preparation and transfer of patterned laser-induced carbon films to transparent substrates. However, this method is limited by insufficient robustness and weak adhesion of the carbon film post-transfer. Herein, we developed a non-contact laser-induced plasma-assisted deposition method to deposit robustly adherent porous carbon films on glass substrates. By well-adjusting the laser parameters and inserting spacers with adjustable thickness, laser-induced plasma ablation replaced direct laser ablation during femtosecond laser scanning of the substrate-polyimide-carrier sandwich structure, resulting in micro-channels with a carbon-glass recast layer instead of easily peelable flakes on the glass substrate. This hierarchical structure significantly enhances the adhesion between the laser-induced carbon film and the glass substrate, ensuring outstanding stability of the deposited carbon film under various adhesion tests. Furthermore, compared to carbon films prepared by the laser-assisted transfer method, the obtained carbon films are hydrophilic, low-resistance, and porous, facilitating the fabrication of energy storage devices. To demonstrate its practical application, a planar carbon-based micro-supercapacitor was fabricated on glass, exhibiting excellent electrochemical and cycling performance.

High-Precision and Low-Damage Microchannel Construction via Magnetically Assisted Laser-Induced Plasma Ablation for Micro-Thermoelectric Devices.

Thermoelectric devices are developing toward high density and miniaturization with a large filling factor for new applications in chip thermal management and microenergy harvesting. Pulsed laser etching has become one of the most effective tools for the patterning construction of highly integrated micro-thermoelectric devices. However, the laser spot size and Gaussian laser energy distribution restrict the processing size and accuracy of microchannels. Moreover, the rapid temperature rise caused by laser energy injection would also raise serious problems such as element volatilization, cracks, and recast layers. Herein, a liquid-assisted nanosecond laser ablation technology with magnetically controlled plasma is proposed to etch microchannels on thermoelectric thick films. By evaluating the size and shape of microchannels, we theoretically investigated the influence of cavitation bubbles on the laser optical path and surface roughness in laser-induced plasma ablation. In addition, the energy criterion for high-precision ablation is revealed, and the effect of magnetic field on ablation threshold is explained by magnetic constraint on energy and kinetic properties of the laser-induced charged plasma plume. Finally, the high-precision and low-damage microchannels are achieved on Bi2Te3 thermoelectric thick films with a minimum line width of 19.12 μm and a small sidewall inclination degree of tan θ = 0.085. This work provides a promising alternative for the fabrication of high-density three-dimensional (3D) patterning in semiconductor microdevices.

Target holder as a specific sensor for laser-induced plasma ablation

We have used grounded and isolated targets to measure currents of electrons escaping the pulsed laser-produced plasma. Presented experiments show that the laser-produced plasma is dominated by three phases such as the ignition phase, active and afterglow phases. The last two phases occurring after laser-plasma interaction are influenced by whether the target is isolated from the vacuum chamber or grounded. The voltage arising on the isolated target, which acts as a capacitor, mainly affects the active phase, where collisions of particles still form the plasma. This can cause reduction in ion emissions, as observed for heavier elements. The target charging accompanying the laser ablation was driven by nanosecond laser radiation with fluence ranging between 1–4 J/cm2.

Microchannel Fabrication in Fused Quartz by Backside Laser-Induced Plasma Ablation Using 248 nm KrF Excimer Laser

Laser-induced plasma ablation (LIPA) using a 248 nm KrF excimer laser was investigated for microchannel fabrication. Examination of the morphology in relation to ablation performance was emphasized, and a synthetic LIPA mechanism model was proposed based on the results. Backside LIPA with a metal target on the bottom can be attributed to a combination of two phenomena: laser-induced plasma vaporization thermal ablation from the metal target below and enhanced laser–glass direct interaction from the plasma residuum. The laser absorption enhancement of quartz substrate resulting from the metal residuum was validated clearly using absorption spectrum measurements. The influence of laser parameters on the etching quality during LIPA was also analyzed for processing optimization. Finally, fused quartz glass microchannels of outstanding surface quality and dimension uniformity were implemented. The channel depth was 28 μm, and the bottom surface roughness was better than several hundred nanometers.

Evaluation of laser-induced plasma ablation focusing on the difference in pulse duration.

A pulsed laser cause vaporization of tissue by plasma if a laser can provide high-density energy within a very short pulse duration. Such phenomena are called laser-induced plasma ablation. The influence of the laser-induced plasma ablation for tissue is unclear because the ablation mechanism is differing regardless of two lasers provide almost the same power density. The two kinds of lasers' vaporization mechanism (Nanosecond laser output could cause an optical breakdown in the air depending on power density and pulse duration of the laser and Femtosecond laser output could cause a breakdown only on solids surface since pulse irradiation time is shorter than energy transfer time) are evaluated by using thermal damage and destruction of tissue. The experimental results show that nanosecond laser caused vaporization without thermal damage and destruction at the tissue approximant 300 μm away from the ablation area. The pulsed laser which has high power density and longer pulse duration than energy transfer time is suitable for plasma ablation not depending on thermal process.

飞秒脉冲激光对硅基多层膜损伤特性

In order to understand the ultrafast laser-induced damage mechanisms of typical imaging sensor's film structures, the damage characteristics of Si-based multi-layer films irradiated by a femtosecond pulsed laser were investigated, and the laser pulse fluence ranges and threshold conditions corresponding to various damage phenomena were evaluated. Si-based multi-layer films that were similar in structure of CCD were prepared by electron beam deposition. The damage characteristics of these films irradiated by a femtosecond pulsed laser with wavelength of 800 nm and pulse width of 100 fs under different pulse fluences and numbers were investigated using a metallurgical microscope. Experimental results showed that the laser-affected zone size increased linearly with pulse fluence in the range of 1.01 to 24.7 J/cm2. Surface damage caused by oxidation/amorphization, non-thermal ablation, and laser-induced plasma ablation could be observed in the laser irradiated zone, which tightly depended on the pulse fluence. Multi-layer damage could be observed and the damage probability increased from 1% to 51% in the pulse fluence range from 2.42 to 24.7 J/cm2. Irradiated by sequent pulses at a fluence of 1.01 J/cm2, the laser affected zone remained almost unchanged and the ablated depth increased with the pulse number. From the single pulse damage experiment data, the femtosecond pulse laser-induced surface damage threshold was evaluated to be 0.543 J/cm2 and laser-induced multi-layer stress damage threshold was linearly fitted to be 2.16 J/cm2. Sequent pulse irradiation with low fluence(≤ 1.01 J/cm2) also could lead to deep damage on the multi-layer film.

Effect of hydrocarbon molecular decomposition on palladium-assisted laser-induced plasma ablation.

The Q-switched Nd:YAG laser is focused on a palladium target in the control chamber filled with various hydrocarbon atmospheres (C1-C4) to investigate their effect on the palladium ablated mass, gas reaction products, and corresponding plasma parameters (such as electron density Ne and plasma temperature Te) during molecular decomposition. The plasma parameters arise mainly from the Pd nanocatalytic activity during the laser-induced plasma process. We compare synthetic air atmosphere to hydrocarbon media to understand how the latter generates excess heat via oxygen-free exothermic (recombination) reactions. Subsequently, this gives rise to more energetic plasma and higher temperature, regarding the large amount of nanoparticles released into the plasma. The dynamics of the decomposition/recombination events accompany the nanocatalyst activity, leading to soot deposition all over the chamber.

A fiber-optic diagnostic technique for mechanical detection of the laser–metal interaction underwater

A new fiber-optic force sensor based on optical beam deflection for the investigation of the mechanical effects during laser–metal interaction underwater is developed. This sensor is applied to detect the laser-induced plasma ablation force and liquid-jet impact during the cavitation bubble collapse near a solid boundary when a Q-switched laser is focused on a metal in water. The experimental results indicate the liquid-jet effect outweighs the well-known laser-induced plasma ablation force. This technique has the advantages of high-frequency response, simple structure, and nondestructive examination.