The surface treatment of carbon fiber/epoxy composites with a pulsed infrared (1064 nm wavelength) nanosecond (7 ns pulse duration) laser has been investigated. It is found that single 1064 nm laser pulse can remove the polymer matrix from composite surface to expose the carbon fibers by expansion of the pyrolysis gas resulting from laser-induced polymer degradation. The influences of laser power density and scan strategy on matrix removal process have been studied. The bonding strength of laser processed, adhesion-bonded CFRP (carbon fiber reinforced plastic) increase with lower matrix residues on the fibers and a linear relation is found. The adhesion-bonding strength of CFRP surfaces, tested by lap-joint shear test, exceeds the strength measured for untreated and abrasion treated (SiC paper) samples. The main origin of fiber damage of the laser-treated surface is mechanical fracture rather than thermal damage as found by laser scanning confocal microscope and scanning electron microscope. The characteristic morphologies and failure modes of shear-tested surfaces are analyzed. The obvious improvement of adhesive strength is achieved by the laser-treated surfaces attributed to matrix removal and carbon fibers protruding. A 1 D model is established to describe temperature and internal gas pressure of the irradiated surface. The new laser treatment method needs less laser energy and low pulse numbers and prove the way to an efficient, low-cost surface treatment for preparation of high quality adhesion bonded CFRP components.

The near infrared (NIR) laser drilling of a carbon fiber reinforced polymer (CFRP) composite in the continuous wave (CW) mode and the ms pulse mode was investigated by an experiment and a numerical simulation. The relationships between the laser penetrating time, entrance hole diameter, surface heat affected zone (HAZ) width, and material ablation rate and the laser irradiation time and laser peak power densities were obtained from the experiment. For the same average power density of the laser output, 3.5 kW/cm², it was found that the ms pulse laser mode, which had a higher peak power density, had a higher drilling efficiency. When drilling the same holes, the pulse laser mode, which had the highest peak power density of 49.8 kW/cm², had the lowest drilling time of 0.23 s and had the smallest surface HAZ width of 0.54 mm. In addition, it was found that the laser penetrating time decreased sharply when the peak power density was higher than 23.4 kW/cm². After analyzing the internal gas pressure by the numerical simulation, it was considered that a large internal gas pressure appeared, which resulted from polymer pyrolysis, causing a large amount of the mechanical erosion of the composite material to improve the drilling efficiency. Therefore, the ms pulse laser showed its potential and advantage in laser drilling the CFRP composite.

CO₂ laser machining is a cost effective and time saving solution for fabricating microchannels on polymethylmethacrylate (PMMA). Due to the lack of research on the incubation effect and ablation behavior of PMMA under high-power laser irradiation, predictions of the microchannel profile are limited. In this study, the ablation process and mechanism of a continuous CO₂ laser machining process on microchannel production in PMMA in single-pass and multi-pass laser scan modes are investigated. It is found that a higher laser energy density of a single pass causes a lower ablation threshold. The ablated surface can be divided into three regions: the ablation zone, the incubation zone, and the virgin zone. The PMMA ablation process is mainly attributed to the thermal decomposition reactions and the splashing of molten polymer. The depth, width, aspect ratio, volume ablation rate, and mass ablation rate of the channel increase as the laser scanning speed decreases and the number of laser scans increases. The differences in ablation results obtained under the same total laser energy density using different scan modes are attributed to the incubation effect, which is caused by the thermal deposition of laser energy in the polymer. Finally, an optimized simulation model that is used to solve the problem of a channel width greater than spot diameter is proposed. The error percentage between the experimental and simulation results varies from 0.44% to 5.9%.

Optical beam deflection and high-speed photographic methods are employed to investigate the interaction mechanism between a laser-induced bubble and a metal target for underwater laser propulsion. A preliminary theory is proposed to reveal the step increases of the kinetic energy transferred to the target during the process of increasing the incident laser energy. This theory also helps to explain the increasing coupling efficiency with incident laser energy for underwater laser propulsion.