The role of incidence angle in the laser ablation of a planar target

Starting point of this paper is photopolymer printing plate used for flexographic printing. It is used for transfer of the printing ink onto the printing surface during the reproduction process. Photopolymer printing plate consists of several layers: polyester basis, photo sensitive polymer material and LAMS - Laser Ablation Mask. In the platemaking process the photosensitive material, which will form a printing plate, has to be several time exposed to different radiation in order to obtain a functional printability performance. LAMS layer has a role of masking in the exposure process. Upon pre-exposure, LAMS layer has to be removed by laser ablation only at the surfaces where photopolymer printing plate needs to be exposed. After ablation the exposures to UV lights follows and the plate will be finished with chemical removal of the unexposed parts of the polymer. Functionality of the finished printing plate has to be characterised and monitored in every procedure step because the formed image element on the printing plate has a major influence on the quality of the finished printed product. In this paper observing of the changes in the polymer material which is caused by exposure through LAMS layer will be performed. The aim is to measure the surface openings on the LAMS mask and to measure surface coverage (image elements) on the polymer material formed by exposure through the LAMS. Measuring will be made by image analysis software based on microscopic images of the control fields of differing halftone values. It is assumed that there will be a correlation between the LAMS openings and formed image elements on the printing plates. Preliminary results indicate that certain differences in image elements can be detected and are probably the consequence of the different amount of irradiated surface of the polymer material. Since the polymer material which forms the printing plate should be stable in the graphic reproduction process, results of the paper will explain the influence of UV exposures on polymerisation process and on the functional printability performance of the plates.

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The role of secondary mesenchyme cells during sea urchin gastrulation studied by laser ablation

Development ◽

10.1242/dev.103.2.317 ◽

1988 ◽

Vol 103 (2) ◽

pp. 317-324 ◽

Cited By ~ 1

Author(s):

J. Hardin

Keyword(s):

Laser Ablation ◽

Sea Urchin ◽

Normal Rate ◽

Common Mechanism ◽

Gastrula Stage ◽

Mechanical Tension ◽

Lytechinus Pictus ◽

Final Length ◽

Mesenchyme Cells

It has long been thought that traction exerted by filopodia of secondary mesenchyme cells (SMCs) is a sufficient mechanism to account for elongation of the archenteron during sea urchin gastrulation. The filopodial traction hypothesis has been directly tested here by laser ablation of SMCs in gastrulae of the sea urchin, Lytechinus pictus. When SMCs are ablated at the onset of secondary invagination, the archenteron doubles in length at the normal rate of elongation, but advance of the tip of the archenteron stops at the 2/3 gastrula stage. In contrast, when all SMCs are ablated at or following the 2/3 gastrula stage, further elongation does not occur. However, if a few SMCs are allowed to remain in 2/3-3/4 gastrulae, elongation continues, although more slowly than in controls. The final length of archenterons in embryos ablated at the 1/3-1/2 gastrula stage is virtually identical to the final length of everted archenterons in LiCl-induced exogastrulae; since filopodial traction is not exerted in either case, an alternate, common mechanism of elongation probably operates in both cases. These results suggest that archenteron elongation involves two processes: (1) active, filopodia-independent elongation, which depends on active cell rearrangement and (2) filopodia-dependent elongation, which depends on mechanical tension exerted by the filopodia.

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Holmium-YAG Laser ablation characteristics in calvarial lamellar and cortical bone: The role of water and tissue micro-architecture

Lasers in Medical Science ◽

10.1007/bf02133329 ◽

1995 ◽

Vol 10 (3) ◽

pp. 181-188 ◽

Cited By ~ 5

Author(s):

Brian Jet -Fei Wong ◽

Vivian Sung ◽

Michael W. Berns ◽

Lars O. Svaasand ◽

Joseph Neev

Keyword(s):

Laser Ablation ◽

Cortical Bone ◽

Yag Laser ◽

Ablation Characteristics

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The Metal-Dielectric Transition in Short-Pulse Laser Ablation of Metals

Volume 4 ◽

10.1115/ht-fed2004-56645 ◽

2004 ◽

Author(s):

Cristian Porneala ◽

David A. Willis

Keyword(s):

Laser Ablation ◽

Absorption Coefficient ◽

Phase Change ◽

Pulse Laser ◽

Pulse Laser Ablation ◽

Short Pulse ◽

Phase Explosion ◽

Short Pulse Laser ◽

Dielectric Transition

Phase explosion is an explosive liquid-vapor phase change that occurs during short pulse laser ablation. Phase explosion results from homogenous vapor nucleation in a superheated liquid phase as the surface temperature approaches the thermodynamic critical temperature, Tc. For a metastable liquid, the upper limit of superheating is approximately 0.9Tc, above which the rate of homogeneous nucleation rises dramatically. Prior to reaching the superheat limit however, a “dielectric transition” is expected to occur at approximately 0.8Tc. The dielectric transition is the transition of an electrically conductive material to a non-conducting state due to large fluctuations in material properties. One consequence of the dielectric transition is that the material will become semi-transparent. Until now, little work has been performed to understand the role of the dielectric transition in laser ablation, and many questions remain about how the surface will rise above 0.8Tc if the surface is semitransparent and only weakly absorbing. This work investigates the role of the dielectric transition with a one-dimensional numerical model for heat transfer and phase change and includes the effect of the metal to dielectric transition. The model is used to simulate heating of aluminum by a Nd:YAG laser with a 7 nanosecond pulse width (FWHM) at the fundamental wavelength of 1064 nm. Calculations of the transient temperature field, melt depth, and depth of the dielectric layer are obtained. Estimates of the absorption coefficient of a metal surface above the metal-dielectric transition are made from correlations found in the research literature. The value of the absorption coefficient is shown to be a critical parameter for determining the energy density required to reach 0.9Tc.

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