Investigation on single-pulse 266 nm nanosecond laser and 780 nm femtosecond laser ablation of sapphire was carried out. Diameter, depth and volume of ablated holes varying with laser density is studied. The results show that 266 nm nanosecond laser ablation of sapphire is caused by photochemical and photothermal effects. 780 nm femtosecond laser ablation of sapphire is due to “cooling”ablation. As energy density increases, thermal effect still exists, yet being much less significant, while ablation mass is greater than that by nanosecond laser. In nanosecond and femtosecond laser ablation, the ablation efficiency increase first and then decrease due to plasma shielding. Ablation efficiency is higher by nanosecond laser than by femtosecond laser at the same laser density. The ablation efficiency reaches the maximum at the energy density of 55.32 J/cm2 to 68.43J/cm2. However, 780 nm femtosecond laser could machine a microstructure with larger depth diameter ratio at lower density.
In this paper, investigation on fiber laser cutting of CFRP was carried out through establishing a multi-physical finite element model and cutting experiment. A multi-physical field model of laser cutting of CFRP was established. Experiments on 1 kW fiber laser cutting of 1 mm CFRP was performed. The relationship between cutting quality (slit width, notch taper, and HAZ width) and laser process parameters such as laser power and cutting speed was investigated. The results show that the transfer of laser energy in CFRP is mainly along the direction of fiber laying, and the heat transfer speed in carbon fiber is much faster than that in resin. The width of the slit, HAZ and the notch taper all increase with the increasing of laser power. However, the width of slit and HAZ decrease as the cutting speed increase and the notch taper increased first and then decreased. When the laser power is 150 W and the cutting speed is 1 m/min, the cutting quality is better.
In this paper, 266 nm nanosecond solid-state laser machining of SiC was experimentally investigated. Atomic force microscope and optical microscopy are used to detect the ablation morphology of specimens. The changes in the diameter of the ablated holes and depth of single and multi-pulse laser ablation of SiC were studied and the removal mechanism was analyzed. The results show that in the single-pulse ablation experiment, as the laser energy density increases, the diameter of the ablated holes gradually increases, and the ablation depth increases first and then decreases. In the multi-pulse machining experiment, the average depth per pulse increases as the laser density increasing when the number of the laser pulse is less than 125 pulses. When the number of laser pulses is more than 125 pulses, the average depth per pulse increases as the laser density at lower laser density; whereas, the average depth per pulse keeps a constant value at higher laser density.
Laser cutting is considered as an effective tool to process the carbon fiber reinforced plastics (CFRP), but it is still a problem how to eliminate the heat affected zone (HAZ). In this paper, numerical simulation of laser cutting CFRP with different resin contents is carried out in order to investigate the formation mechanism and the effect of resin content on the HAZ. The energy distribution characteristics and heat transmission mechanism during laser cutting CFRP was studied through a finite element method. A model of laser-cutting of single-layer CFRP with different resin content was established by COMSOL multi-physics software to analyze the temperature field. The simulation results show that the absorbed laser energy is mainly transmitted along the direction of the carbon fiber laying. The maximum temperature of the surface carbon fiber in CFRP increases as the resin content increases. However, the width of HZA was decreases as the resin content increasing.
Ultraviolet (UV) solid-state laser has become an effective tool of processing hard and brittle materials due to its short wavelength, small spot and better beam quality. In this paper, experiment on the microgroove of hard and brittle sapphire wafers was carried out using a solid-state nanosecond laser with a wavelength of 266 nm. Samples were detected by scanning electron microscope(SEM) and optical microscope. The microgrooves on sapphire wafers were fabricated with different laser parameters through linear scanning experiments. The effects of laser energy, number of laser scans, and scanning speed on groove width and depth were investigated.
In this research, the formation of laser-induced periodic surface structures (LIPSS) on the nickel surface by femtosecond laser pulses was investigated. In the experiment, we used a commercially available amplified Ti:sapphire laser system that generated 164 fs laser pulses with a maximum pulse energy (Ep) of 1 mJ at a 1 kHz repetition rate and with a central wavelength λ= 780 nm. To obtain a fine periodic ordering of surface nanostructures, the laser beam, through a 0.2 mm pinhole aperture positioned near the 10× objective lens, was focused onto the sample. The samples were mounted on an XYZ-translation stage and irradiated in static and line-scanning experiment. The morphology of the induced periodic structure was examined by scanning electron microscopy. The surface profile was measured by atomic force microscopy. LIPSS with a period of around 700 nm entirely covered the irradiated area. Large area of LIPSS in the nickel surface was produced in line-scanning experiment. The mechanism of the formation of LIPSS in the entire irradiated area in static irradiation was discussed. The function of a 0.2 mm pinhole aperture was studied. The regular LIPSS on the nickel surface changed the optical property of the surface. The regular LIPSS on nickel surface could be also applied on the micro-mould fabrication.
In this research, the formation of laser-induced periodic surface structures (LIPSS) on the stainless steel surface by
femtosecond laser pulses was investigated under static irradiation and line-scanning experiment. In the experiment, we
used a commercial amplified Ti:sapphire laser system that generated 164 fs laser pulses with a maximum pulse energy
(Ep) of 1 mJ at a 1 kHz repetition rate and with a central wavelength λ = 780 nm. To obtain a fine periodic ordering of
surface nanostructures, the laser beam, through a 0.2 mm pinhole aperture positioned near the 5× objective lens, was
focused onto the sample. The samples were mounted on an XYZ-translation stage and irradiated in static and
line-scanning experiment. The morphology of the induced periodic structure was examined by scanning electron
microscopy. The surface profile was measured by atomic force microscopy. High-spatial-frequency LIPSS (HSFL) with
a period of 255 ± 21 nm were obtained over the entire ablated area. HSFL were found to form on low-spatial-frequency
LIPSS (LSFL). From our results we elucidated the relationship between the formation of LSFL and HSFL to obtain an
enhanced understanding of the mechanism of HSFL formation by femtosecond laser pulses. A large number of
applications have been proposed, such as improvement of the optical properties of the surface, new cutting tool
development and hard diamond. More applications could be found as the spatial period of HSFL on different materials
comes into sub-100 nm.
This paper provides an investigation of the ablation behavior of single crystal 4H-SiC and 6H-SiC wafer to improve the
manufacturability and high-temperature performance of SiC using laser applications. 266nm pulsed laser
micromachining of SiC was investigated. The purpose is to establish suitable laser parametric regime for the fabrication
of high accuracy, high spatial resolution and thin diaphragms for high-temperature MEMS pressure sensor applications.
Etch rate, ablation threshold and quality of micromachined features were evaluated. The governing ablation mechanisms,
such as thermal vaporization, phase explosion, and photomechanical fragmentation, were correlated with the effects of
pulse energy. The ablation threshold is obtained with ultraviolet pulsed laser ablation. The results suggested ultraviolet
pulsed laser’s potential for rapid manufacturing. Excellent quality of machined features with little collateral thermal
damage was obtained in the lower pulse energy range. The leading material removal mechanisms under these conditions