Polymer Ablation Research Articles

Bragg gratings in a few mode microstructured polymer optical fiber in less than 30 seconds.

We report the inscription of a Bragg grating in an undoped polymethylmethacrylate based microstructured fiber in a time record. The fiber has been irradiated with a 248 nm ultraviolet radiation, through the phase mask technique using low fluence and low repetition rate. The experimental conditions were chosen to modify the core refractive index of the fiber at the incubation regime and avoiding polymer ablation. The peak reflection of the Bragg grating was centered in the infrared region with 20 dB reflection and 0.16 nm bandwidth. These spectral properties are well attractive for sensors and communications applications.

ArF Laser Ablation of CR-39 Polymer: Effect of Irradiation on Cone Structure Formation

CR-39 polymer was processed with ArF laser. Conical microstructures formed on laser-ablated CR-39. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Energy-dispersive X-ray (EDX) spectroscopy were employed for examination of the morphology and chemical composition of irradiated surface and conical structure. SEM observation show that cone shape walls are sharp tips together with interference and well defined fringe-structure around cone base. EDX analysis indicated that cone having different chemical structure compared to surface of CR-39 polymer.

Preparation of periodic surface structures on doped poly(methyl metacrylate) films by irradiation with KrF excimer laser.

In this work, we describe laser modification of poly(methyl methacrylate) films doped with Fast Red ITR, followed by dopant exclusion from the bulk polymer. By this procedure, the polymer can be modified under extremely mild conditions. Creation of surface ordered structure was observed already after application of 15 pulses and 12 mJ cm−2 fluence. Formation of grating begins in the hottest places and tends to form concentric semi-circles around them. The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity. The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure. Most regular grating structures were obtained on polymer films deposited on atomically ‘flat’ Si substrates. After laser patterning, the dopant was removed from the polymer by soaking the film in methanol.

A study of photothermal laser ablation of various polymers on microsecond time scales.

To analyze the photothermal ablation of polymers, we designed a temperature measurement setup based on spectral pyrometry. The setup allows to acquire 2D temperature distributions with 1 μm size and 1 μs time resolution and therefore the determination of the center temperature of a laser heating process. Finite element simulations were used to verify and understand the heat conversion and heat flow in the process. With this setup, the photothermal ablation of polystyrene, poly(α-methylstyrene), a polyimide and a triazene polymer was investigated. The thermal stability, the glass transition temperature Tg and the viscosity above Tg were governing the ablation process. Thermal decomposition for the applied laser pulse of about 10 μs started at temperatures similar to the start of decomposition in thermogravimetry. Furthermore, for polystyrene and poly(α-methylstyrene), both with a Tg in the range between room and decomposition temperature, ablation already occurred at temperatures well below the decomposition temperature, only at 30–40 K above Tg. The mechanism was photomechanical, i.e. a stress due to the thermal expansion of the polymer was responsible for ablation. Low molecular weight polymers showed differences in photomechanical ablation, corresponding to their lower Tg and lower viscosity above the glass transition. However, the difference in ablated volume was only significant at higher temperatures in the temperature regime for thermal decomposition at quasi-equilibrium time scales.

EUV ablation of organic polymers at a high fluence

Abstract A preliminary investigation on short-wavelength ablation mechanisms of poly(methyl methacrylate) (PMMA) and poly (1,4-phenylene ether ether-sulfone) (PPEES) by extreme ultraviolet (EUV) radiation at 13.5 nm using a table-top laser-produced plasma from a gas-puff target at LLG (Göttingen) and at 46.9 nm by a 10 Hz desktop capillary discharge laser operated at the Institute of Physics (Prague) is presented. Ablation of polymer materials is initiated by photo-induced polymer chain scissions. The ablation occurs due to the formation of volatile products by the EUV radiolysis removed as an ablation plume from the irradiated material into the vacuum. In general, cross-linking of polymer molecules can compete with the chain decomposition. Both processes may influence the efficiency and quality of micro(nano)structuring in polymer materials. Wavelength is a critical parameter to be taken into account when an EUV ablation process occurs, because different wavelengths result in different energy densities in the near-surface region of the polymer exposed to nanosecond pulses of intense EUV radiation.

Simulation of resonant microfabrication of the PLA film by single mid-infrared femtosecond laser pulse

Recently the dynamics of the resonant ablation of polymers and toluene employing mid-infrared femtosecond laser (fs laser) has been calculated by using the fluid equations. The advantages and shortcomings of the mid-infrared fs laser resonant ablation have been discussed. The results indicated that the mid-infrared fs laser is a powerful tool for removing a polymer coating on the substrate made of another polymer due to good wavelength selectivity. In this paper we studied the resonant ablation processes of polymer coatings with ultrahigh molecular weight. The influence of the initial temperature was discussed and the selection rules of laser parameters were given. We also discussed how to make hollow patterns in a polymer film, and the results demonstrated the acceleration of the ablation process caused by suspending the film.

Short-wavelength ablation of polymers in the high-fluence regime

Short-wavelength ablation of poly(1,4-phenylene ether-ether-sulfone) (PPEES) and poly(methyl methacrylate) (PMMA) was investigated using extreme ultraviolet (XUV) and soft x-ray (SXR) radiation from plasma-based sources. The initial experiment was performed with a 10 Hz desktop capillary-discharge XUV laser lasing at 46.9 nm. The XUV laser beam was focused onto the sample by a spherical mirror coated with a Si/Sc multilayer. The same materials were irradiated with 13.5 nm radiation emitted by plasmas produced by focusing an optical laser beam onto a xenon gas-puff target. A Schwarzschild focusing optics coated with a Mo/Si multilayer was installed at the source to achieve energy densities exceeding 0.1 J cm−2 in the tight focus. The existing experimental system at the Laser Laboratorium Göttingen was upgraded by implementing a 1.2 J driving laser. An increase of the SXR fluence was secured by improving the alignment technique.

聚合物飞秒激光加工的分子动力学建模与仿真

To improve the machining accuracy of the hole on the polystyrene microspheres for laser fusion, a fundamental understanding of the mechanisms of femtosecond laser ablation is required. We establish a molecular dynamics model of femtosecond laser ablation of polymers by optimally selecting the molecule representation model and related force field. Subsequent molecular dynamics simulations of femtosecond laser ablation of polyethylene and polystyrene show that the laser ablation-induced polymer material removal is caused by single chain ejection-accompanied surface evaporation and single chain motion-accompanied thermal expansion within the bulk. Furthermore, the microscopic deformation mechanisms of the single chain include inter-chain sliding and intra-chain change. It is found that the discrepancy in the molecule architecture has strong influence on the femtosecond laser ablation of polyethylene and polystyrene.

Dynamics of mid-infrared femtosecond laser resonant ablation

Resonant ablation is beneficial to avoiding uncontrollable subsurface damages in the laser ablation of polymers. In this paper the dynamics of mid-infrared laser resonant ablation of polylactic acid and toluene was calculated by using fluid dynamic equations. The merits and drawbacks of mid-infrared femtosecond laser resonant ablation of high molecular weight polymers have been discussed.

Surface ablation of transparent polymers with femtosecond laser pulses

In this work, a study of the laser ablation on the surface of poly methyl-methacrylate (PMMA) is presented. Experiments were performed with a femtosecond laser delivering 450fs pulses at a wavelength of 1027nm. The laser beam energy was controlled through a polarizer based attenuator and measured by a calibrated photodiode energy meter. A focusing method called z-scan is used to place the sample on the beam waist. This method uses a second energy meter placed behind the sample, which was used to monitor the energy transmitted across the sample in situ. Thus, the absorption was evaluated by comparing the measurements of both energy meters. The z-scan method is evaluated by studying the laser ablation in three different positions between the sample and the laser beam waist. It is found that above a threshold energy that depends on the focusing conditions, the absorbance of the samples increases with the pulse energy. After irradiation, dimensional analysis of the craters produced at different pulse energies is performed in order to determine the best focusing conditions and the ablation threshold for ablation of PMMA samples.

Resonant infrared ablation of polystyrene with single picosecond pulses generated by an optical parametric amplifier

We report on resonant infrared laser ablation of polystyrene using single 8 ps pulses at a wavelength of 3.31 μm generated by a MgO:PPLN optical parametric amplifier pumped by a Nd:YLF laser. We determined the single-pulse ablation threshold to be 0.46 J/cm2, about a factor of five smaller than in previous free-electron-laser studies. Time-resolved imaging of the laser–target interaction reveals that the detailed dynamics of the ablation process begin with thermal expansion of a large volume of hot material from which a less dense plume of polymeric material evaporates. This plume disappears on a time scale of 0.75 μs and the hot polymer material recedes back into the crater from which it was expelled. Subsequently, and on a much longer time scale, structural alterations in the ablation crater continue to evolve for at least another millisecond. Our results suggest that single picosecond pulses are effective for the ablation of polymers and exhibit dynamics similar to those observed in studies using a free-electron laser.

Surface ablation of PLLA induced by KrF excimer laser

The surface characterization of PLLA (poly-l-lactic-acid) and its ablation due to excimer laser treatment is introduced in this paper. The main focus is to determine surface wettability and morphology changes in combination with changes of surface chemistry. The ablation loss and the determination of ablation threshold were used to study the biopolymer stability when treated to different laser fluences and pulse counts. The surface polarity was estimated using goniometry. AFM (atomic force microscopy) was used to determine the polymer surface morphology and roughness. The excimer laser has a strong effect on the polymer ablation. The thickness loss is strongly dependent on the laser fluence and number of pulses. For the fluences up to 30mJcm−2 and 6000 pulses achieved ablation about 5μm. The glass transition temperature and melting point were determined for the pristine and laser treated films. The increasing pulsed laser fluence leads to the major changes in roughness and morphology. The surface chemistry depends strongly on number of laser pulses.

Prompt response and durability of polymer ablation from synthetic fibers irradiated by thermal plasmas for arc resistant clothes

Interactions between thermal plasmas and synthetic fibers such as polyamide, polyester, phenol and aramid were investigated by thermal plasma irradiation technique. Understanding the above interactions is crucial to design effective flame retardant synthetic fiber clothes with arc resistance to protect a human from arc flash accidents. To investigate the interactions, an Ar inductively coupled thermal plasma (ICTP) was used instead of the arc discharge because the ICTP has high controllability and no contamination. The ICTP irradiation raises polymer ablation in case of polyamide and polyester. Two features of the polymer ablation such as prompt response and durability were fundamentally investigated from viewpoint of shielding the heat flux. It was found that polyamide fiber has both a high prompt response and a long durability.

Clay dispersion effects on excimer laser ablation of polymer–clay nanocomposites

ABSTRACTThe ablation behavior of polystyrene‐organically modified montmorillonite (OMMT) nanocomposites was evaluated by measuring the weight loss induced by KrF excimer laser irradiation of the nanocomposite specimens under air atmosphere. The characteristic values of ablation, ablation threshold fluence, and effective absorption coefficient for polystyrene and its nanocomposites were calculated based on the weight loss data. The effects of morphology due to spatial variation in injection molded samples are also discussed in this article. Results demonstrate that both the dispersion state and the concentration of clay play important roles in excimer laser ablation. The sensitivity of threshold fluence and absorption coefficient to dispersion state of OMMT seem to depend on the clay concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2336–2344, 2013

Femtosecond laser ablation of polymethyl-methacrylate with high focusing control

The interest of laser ablation of transparent polymers with short pulses relies on the possibility of ablating the material with little thermal damage and high spatial resolution. This enables microscopic design features needed for microfluidic devices and micromachining. Laser ablation of polymethyl-methacrylate (PMMA) surface with an Yb:KYW laser beam was carried out in air environment at room temperature. The laser had a wavelength of 1027nm and the pulse duration was 450fs. An open aperture z-scan procedure was used as a method to determine with high precision and control the best focusing conditions of the laser beam on the surface of the samples For this, the transmitted energy was measured with a photodiode detector placed beyond the sample. This was possible due to the high transparency of PMMA to the laser wavelength. Ablation craters produced on the PMMA surface at different laser pulse energies after the z-scan focusing process were characterized by means of optical and scanning electron microscopies. The fluence threshold found for ablation of PMMA is 3.2J/cm2. Well-defined craters, with diameters as small as 200nm, can be obtained with pulse energies near the ablation threshold.

Assessment of thermally induced shear stress and its effect on pattern waviness in CO2 laser ablation of birefringent polymers

This article presents the application of custom-designed poledioscope for dynamic measurement of thermally induced shear stress, as a technique for monitoring waviness of the microscale patterns created using CO2 laser, directly over optically birefringent polymers. Laser ablation experiments were conducted for three optical grade polymers: ethylene vinyl acetate, poly methyl methacrylate, and allyl diglycol carbonate under varying laser power and scanning speeds. A poledioscope, customized by incorporating beam splitter in place of rotating analyzer section of conventional polariscope, was used to assess the thermally induced shear stress on the materials in real time. The waviness of the profile of groove patterns was measured using a profilometer. The shear stress mapping and the profile waviness data recorded for range of laser processing parameters were further analyzed to determine that high thermally induced shear stress results in significant damage on waviness of the lased profile.

Infra-red laser ablative micromachining of parylene-C on SiO2 substrates for rapid prototyping, high yield, human neuronal cell patterning

Cell patterning commonly employs photolithographic methods for the micro fabrication of structures on silicon chips. These require expensive photo-mask development and complex photolithographic processing. Laser based patterning of cells has been studied in vitro and laser ablation of polymers is an active area of research promising high aspect ratios. This paper disseminates how 800 nm femtosecond infrared (IR) laser radiation can be successfully used to perform laser ablative micromachining of parylene-C on SiO2 substrates for the patterning of human hNT astrocytes (derived from the human teratocarcinoma cell line (hNT)) whilst 248 nm nanosecond ultra-violet laser radiation produces photo-oxidization of the parylene-C and destroys cell patterning. In this work, we report the laser ablation methods used and the ablation characteristics of parylene-C for IR pulse fluences. Results follow that support the validity of using IR laser ablative micromachining for patterning human hNT astrocytes cells. We disseminate the variation in yield of patterned hNT astrocytes on parylene-C with laser pulse spacing, pulse number, pulse fluence and parylene-C strip width. The findings demonstrate how laser ablative micromachining of parylene-C on SiO2 substrates can offer an accessible alternative for rapid prototyping, high yield cell patterning with broad application to multi-electrode arrays, cellular micro-arrays and microfluidics.

Laser ablation at the hydrodynamic regime

Laser ablation of several metals and PVC polymer by high energy nanosecond laser pulses is investigated experimentaly. Visualization by shadowgraphy revealed the dynamics of the discontinuities in ambient air and ablation plume above the target surface, while surface profiling allowed for determination of the ablated mass.

Surface characterization of plasma treated polymers for applications as biocompatible carriers

The objective of this work was to determine surface properties of polymer surfaces after plasma treatment with the aim of further cytocompatibility tests. Examined polymers were poly(ethyleneterephthalate) (PET), high-density poly- ethylene (HDPE), poly(tetrafluoro-ethylene) (PTFE) and poly(L-lactic acid) (PLLA). Goniometry has shown that the plasma treatment was immediately followed by a sharp decrease of contact angle of the surface. In the course of ageing the contact angle increased due to the reorientation of polar groups into the surface layer of polymer. Ablation of polymer sur- faces was observed during the degradation. Decrease of weight of polymer samples was measured by gravimetry. Surface morphology and roughness was studied by atomic force microscopy (AFM). The PLLA samples exhibited saturation of wettability (aged surface) after approximately 100 hours, while the PET and PTFE achieved constant values of contact angle after 336 hours. Irradiation by plasma leads to polymer ablation, the highest mass loss being observed for PLLA. The changes in the surface roughness and morphology were observed, a lamellar structure being induced on PTFE. Selected polymer samples were seeded with VSMC (vascular smooth muscle cells) and the adhesion and proliferation of cells was studied. It was proved that certain combination of input treatment parameters led to improvement of polymer cytocompatibility. The plasma exposure was confirmed to significantly improve the PTFE biocompatibility.

Microstructuring of polymer films by femtosecond pulses through optically trapped polystyrene microspheres

We report the laser ablation of polymers by femtosecond ( and ) pulses focused by and diameter spherical microlenses, which are held by optical traps. It is shown that this technique allows one to produce surface structures with lateral dimensions up to (). It is found that the size of the structures depends on the diameter of the microlens; the highest spatial resolution is achieved by using diameter microlenses.