COMMUNICATIONand as self-organized nanopatterns induced on a surface, [ 30 ] are among other polarization-related phenomena demonstrated recently.The infl uence of beam polarization orientation on laser processing has been thoroughly studied in the cases of conductive and dielectric solid targets. [ 31,32 ] There are known effects of polarization on the scalar parameters of laser-matter interaction, such as absorption coeffi cient and ionization rate. [33][34][35][36] It is also known that heat conduction fl ux (vector) in plasma might be dependent on the direction of the imposed fi eld. [ 37 ] In what follows, these effects are considered in succession: (i) accumulation from multiple pulses, (ii) effects of polarization under high-numerical aperture (NA) focusing, and (iii) the infl uence of the external high-frequency electric fi eld on electronic heat conduction. The latter contribution has not yet been considered in laser fabrication under tight focusing. All these photomodifi cation mechanisms occur simultaneously and affect polymerization, which takes approximately a millisecond for common photoresists [ 38 ] at a >90% voxel overlap at typical writing velocity of 100 µm s -1 for widespread laser 3D nanolithography. [ 39 ] In this paper, a systematic analysis via modeling and experiments is presented in order to reveal polarization effects, their infl uence on the feature size (resolution), and the coupling between thermal gradient and polarization in DLW.To study and demonstrate the polarization effects, 3D suspended resolution bridges at various angles, α , between the linear polarization and scanning direction were fabricated on a glass substrate ( Figure 1 inset in (a); see details in the Experimental Section). The line-width difference was 10%-20% (varying exposure) under typical polymerization conditions for the linearly polarized pulses. The largest width of a 3D bridge was observed when the scan direction was perpendicular to the orientation of linear polarization, α = π / 2 ( E ⊥ v s ). The heightto-width ratio of the suspended lines was dependent on the orientation of linear polarization and changed between 3.07 and 3.44; self-focusing was not present under our experimental conditions. [ 40 ] Detailed analysis of polarization, threshold, and heat accumulation effects, which are all important, are discussed next.For the experimental conditions used, the focal spot diameter (at 1/ e 2 ) can be calculated as d f = 1.22 λ /NA = 898 nm assuming, for simplicity, a Gaussian intensity profi le. However, at such tight focusing it is necessary to use the vectorial Debye theory (specifi cs [ 41 ] can be found in Section A, Supporting Information), which predicts an ellipsoidal focal spot with two lateral cross sections: W l = 790 nm and W s = 572 nm for long and short cross sections, respectively (or 500 and 360 nm at full width at half maximum (FWHM)) for the actual experimental
Objective: To find a correlation between the severity of enamel microcracks (EMCs) and their increase during debonding and residual adhesive removal (RAR). Materials and Methods: Following their examination with scanning electron microscopy (SEM), 90 extracted human premolars were divided into three groups of 30: group 1, teeth having pronounced EMCs (visible with the naked eye under normal room illumination); group 2, teeth showing weak EMCs (not apparent under normal room illumination but visible by SEM); and group 3, a control group. EMCs have been classified into weak and pronounced, based on their visibility. Metal brackets (MB) and ceramic brackets (CB), 15 of each type, were bonded to all the teeth from groups 1 and 2. Debonding was performed with pliers, followed by RAR. The location, length, and width of the longest EMCs were measured using SEM before and after debonding. Results: The mean overall width (W overall ) was higher for pronounced EMCs before and after debonding CB (P , .05), and after the removal of MB. Pronounced EMCs showed greater length values using both types of brackets. After debonding, the increase in W overall of pronounced EMCs was 0.57 mm with MB (P , .05) and 0.30 mm with CB; for weak EMCs, 2 0.32 mm with MB and 0.30 mm with CB. Conclusions: Although the teeth having pronounced EMCs showed higher width and length values, this did not predispose to greater EMCs increase after debonding MB and CB followed by RAR. (Angle Orthod. 2016;86:437-447.)
The objective of this in vitro study was to evaluate the effect of the enamel cracks on the tooth damage during the debonding. Measurements of the cracks characteristics (visibility, direction, length, and location) were performed utilizing a scanning electron microscopy (SEM) technique and mathematically derived formulas (x=h/30, l=n*x) before and following the removal of mechanically retained metal and ceramic brackets. The likelihood of having greater extent enamel defects was higher for the teeth with pronounced cracks (odds vatios, OR=3.728), increased when the crack was located in more than one zone of the tooth (OR=1.998), and the inclination did not exceed 30-45° (OR=0.505). Using ceramic brackets the risk of greater amount tooth structure defects raised 1.45 times (OR=1.450). Enamel crack showing all these characteristics at the beginning of the orthodontic treatment and the use of ceramic brackets might predispose to higher risk of greater extent tooth surface damage after the debonding by 20.4%.
In this paper, an overview of literature supported by original experimental results on direct laser polymerization of three-dimensional micro-/nano-structuring of various photopolymers is presented. Alternative technologies, principles of threshold based direct laser writing in polymers employing ultrafast lasers, issues of optimization of the laser structuring parameters for increasing fabrication resolution and production throughput are presented and discussed. Examples of woodpile templates and nanogratings are shown as well as an opto-fluidic sensor design for usage in lab-on-chip type devices is demonstrated and its performance is characterized. Additionally, a possibility to produce a three-dimensional electric circuit is introduced.
In this paper, an overview of literature supported by original experimental results on direct laser polymerization of three-dimensional micro-/nano-structuring of various photopolymers is presented. Alternative technologies, principles of threshold based direct laser writing in polymers employing ultrafast lasers, issues of optimization of the laser structuring parameters for increasing fabrication resolution and production throughput are presented and discussed. Examples of woodpile templates and nanogratings are shown as well as an opto-fluidic sensor design for usage in lab-on-chip type devices is demonstrated and its performance is characterized. Additionally, a possibility to produce a three-dimensional electric circuit is introduced.
We present a developed method based on direct laser writing (DLW) and chemical metallization (CM) for microfabrication of three-dimensional (3D) metallic structures. Such approach enables manufacturing of free-form electro-conductive interconnects which can be used in integrated electric circuits such as micro-opto-electro-mechanical systems (MOEMS). The proposed technique employing ultrafast high repetition rate lasers enables efficient fabrication of 3D microstructures on dielectric as well as conductive substrates. The produced polymer links out of organic-inorganic composite matrix after CM serve as interconnects of separate metallic contacts; their dimensions are: height 15 μm, width 5 μm, length 35-45 μm, and they could provide 300 nΩm resistivity measured in a macroscopic way. This proves the techniques potential for creating integrated 3D electric circuits at microscale.
We demonstrate how the coupling between (i) polarization of the writing laser beam, (ii) tight focusing and (iii) heat conduction affects the size, shape and absorption in the laser-affected area and therefore the polymerization process. It is possible to control the sizes of 3D laser-produced structure at the scale of several nanometers. Specifically we were able to tune the aspect ratio of 3D suspended line up to 20% in hybrid SZ2080 resist. The focal spot of tightly focused linearly polarized beam has an elliptical form with the long axis in the field direction. It is shown here that this effect is enhanced by increase in the electronic heat conduction when polarization coincide with temperature gradient along with the absorption. Overlapping of three effects (iiii) results in the difference of several tens of nanometers between two axes of the focal ellipse. Narrow line appears when polarization and scan direction coincide, while the wide line is produced when these directions are perpendicular to each other. The effect scales with the laser intensity giving a possibility to control the width of the structure on nanometer scale as demonstrated experimentally in this work. These effects are of general nature and can be observed in any laser-matter interaction experiments where plasma produced by using tight focusing of linear-polarized light.
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