We experimentally showed that the π/2-period oscillation of femtosecond laser ablation threshold with laser polarization orientation can be observed in calcium fluoride (CaF2). While the lowest single pulse ablation threshold, 5.3 J/cm2, was observed when laser polarization is along the 010-crystal axis, the highest one, 5.8±0.1 J/cm2, was found when angle between polarization and the 010-crystal axis were π/4 or 3π/4. The π/2-period oscillation of ablation threshold tends to be eliminated (yet still detectable) at high pulse fluence. The anisotropic ablation is possibly resulted from the different rate of avalanche ionization in different crystal axes.
Fiber-Reinforced Plastics/Polymers (FRPs) are widely used in the astronautic industry as the material of spacecrafts’ structural, thermal control, and satellite payload system. Ultrafast laser processing is a non-contact, versatile or efficient tool for reduced, equal, or additive material processing, which has very recently been put into use for manufacturing spacecrafts made of fiber-reinforced polymer composites. We analyzed the fitness between ultrafast laser manufacturing technology and astronautic manufacturing demand. Special attention was paid on the progress related to ultrafast laser processing of fiber-reinforced polymers used in spacecrafts, such as cutting, milling, laser marking and surface roughening for preparation of high adhesion coatings, with carbon- FRP and glass-FRP involved. Typical machining results via traditional manufacturing techniques were demonstrated for comparisons. The study may shed light on the practical application of ultrafast laser processing of FRP products used in the astronautic industries.
In this paper, ultrafast laser ablation of Aramid Fiber Reinforced Plastic (AFRP) and its application in satellite reflector antenna was studied. Intrinsic properties for transmission spectrum were measured. For material processing the influence of pulse energy fluence, pulse overlapping rate and laser wavelength (from the NIR to the NUV) on appearance qualities (namely the blackening of cutting edge) were studied. It was shown that the wavelength played an important role in controlling the machining defects such as blackening. While NUV wavelength long pulse (10 ps) laser generated a smooth cutting cross-section with material’s intrinsic colors, the NIR wavelength resulted in a carbonization-prone ablation, even if the femtosecond laser was considered. The possible mechanisms involved were discussed. The application of laser trimming of satellite antenna was demonstrated.
The near-infrared picosecond laser ablation characteristics (threshold, heat-affected zone (HAZ) and morphology) for graphitized carbon fiber-reinforced cyanate ester resin (M55/BS-4), a mesoscopically heterogeneous composite, were studied. The ablation threshold and its incubation effect for the composite were measured based on the diameter-regression method, with the single-pulse threshold derived from the incubation model. The influence of incident laser fluence (0.6-26J/cm2) and beam scanning speed (0.8-5m/s) on the ablation quality were analyzed. It was show that the ablation threshold, morphology and thickness of HAZ can be controlled by processing parameters for the composite. Well-defined groove with clear edge and minor HAZ, probably an indication of mesoscopically uniform removal for the material’s heterogeneous structure, was obtained by using a proper combination of scanning speed and incident fluence. A satellite-used carbon-fiber skin as large as 1m2 based on laser cutting was demonstrated by using further optimized processing parameters.
We carried out a comparative study on ablation threshold behavior of femtosecond laser twin double-pulse processing of typical transparent material, semiconductors and metallic materials. Based on the change of ablation area with pulse temporal separation (100 fs-15ps) under the same spatially distributed Gaussian beam, influence of pulse-separation on normalized double-pulse ablation threshold (which is normalized to the single-pulse ablation threshold) was demonstrated qualitatively. Special attention paid on the variation characteristics of normalized double-pulse ablation threshold in the sub-picosecond pulse-separation range, as well as its value in pulse-separations comparable or larger than the electron-phonon (or ion) coupling time. We show that the ablation threshold behavior of femtosecond laser twin double-pulse is strongly material-specie dependent, however, can be summarized in to several ones. The difference in ionization and/or deionization mechanisms for the non-metal compared is possibly the physical origins for the contrasted behavior of double-pulse ablation threshold.
Carbon fiber reinforced polymer(CFRP) is a typical hard to machine material. High modulus CFRP is one of the most widely used types in spacecraft structures. In this paper, the ultrafast laser precision cutting technology for two kinds of high modulus materials with different thermal conductivity is studied. The single factor ablation experiments are carried out on two kinds of plates with the thickness of 1mm. The threshold value of the two materials and the influence law of different laser fluence and scanning speed parameters on the entrance cutting size and heat-affected zone are obtained, and the physical mechanism of the above laws is described. The results show that the huge difference in the thermal conductivity of the two materials has a certain influence on the difficulty of processing the material and the selection of process parameters.
We carried out a comparative study on laser cutting of fiber-reinforced plastic and its honeycomb sandwich structure widely used in aeronautic industry. The influence of pulse duration (CW, ns, ps and fs), wavelength (MIR, NIR, and NUV) on cutting quality (characterized by the HAZ) and productivity was experimentally studied. It was demonstrated that for either the aramid fiber reinforced plastics/polymers (AFRPs) or high-modulus carbon fiber reinforced plastics/polymers (CFRPs) and its honeycomb sandwich structure, tradition laser cutting was unable to satisfy the requirements of the appearance qualities in the astronautic industry due to the thermal damage induced discoloration, in spite of the less extension of damage than the contact machining used currently. The pulse duration effects on HAZ, the wavelength effects on cutting quality and productivity, the differences and similarities for low-HAZ cutting of AFRPs and high-modulus CFRPs, was studied, and the possible physical origins was discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.