Ablation area

For EPy-doped PMMA film, a 308 nm excimer laser (Lumonics TE 430T-2, 6ns) was used as as exposure source. We used a tine-correlated single photon counting systen (18) for measuring fluorescence spectra and rise as well as decay curves of a snail ablated area. The excitation was a frequency-doubled laser pulse (295 nm, lOps) generated from a synchronously punped cavity-dumped dye laser (Spectra Physics 375B) and a CW mode-locked YAG laser (Spectra Physics 3000). Decay curves under a fluorescence microscope were measured by the same systen as used before (19). 

Fluorescence Rise and Decay Curves. Both monomer and excimer fluorescence decay curves of the unirradiated film are nonexponential and the excimer fluorescence shows a slow rise component. This behavior is quite similar to the result reported for the PMMA film doped with pyrene. (23) A delay in the excimer formation process was interpreted as the time taken for the two molecules in the ground state dimer to form the excimer geometry. Dynamic data of the ablated area observed at 375 no (monomer fluorescence) and 500 nm (exciner fluorescence) are shown in Figure 5. When the laser fluence increased, the monomer fluorescence decay became slower. The slow rise of the excimer fluorescence disappeared and the decay became faster. 

It is confirmed that the polymer matrix around ablated area was also affected strongly by laser ablation. The change of the matrix properties are brought about over a few tens of pin. This type of information is basically important and indispensable for practical applications such as excimer laser lithography. The time-resolved fluorescence spectroscopy is one of the powerful characterization methods for ablated polymer matrix. 

In LA-ICP-MS, the sample is placed inside a sample holder or laser cell where ablation takes place. The ablated area varies in size depending on the sample matrix but is usually smaller than 1000 X 1000 pm and less than 30 pm deep. The ablated material is flushed from the laser cell using a 1.1-1.3 liter/minute flow of argon or an argon/helium-mixed carrier gas through Tygon... 

C. F. Boutron, M. Leclerc, N. Risler, Atmospheric trace elements in Antarctic prehistoric ice collected at a coastal ablation area, Atmos. Environ., 18 (1984), 1947-1953. 

The diameters D of the laser-damaged (ablated) areas are determined with a microscope. The laser fluence sufficient to ablate the material (for a fixed pulse duration r and number of pulses per spot N) is named threshold fluence Fth-... 

Fig. 9 Diagram of laser-induced ablation on the samples (top) and corresponding Gaussian fluence profile along x-axis (bottom). D marks the diameter of the ablated area...

The method applied to measure the depth of the ablated area or the removed mass can also have an influence on the ablation parameters. If profilometric measurements (optical interferometry, mechanical stylus [34], or atomic force microscopy [35]) are used to calculate the ablation rate, a sharp ablation threshold can be defined. This is also supported by reflectivity [36] and acoustic measurements [37], In mass loss measurements, such as mass spectrometry or with a quartz crystal microbalance (QCM), the so-called Arrhenius tail [38] has been observed for certain conditions. The Arrhenius tail describes a region in the very low fluence range, where a linear increase of detected ablation products is observed, which is followed by a much faster increase, that coincides with removal rates of the profilometric measurements [39]. 

A more pronounced photochemical part is preferable for material structuring, as it leads to a more uniform decomposition of the polymer and results in less debris. In additional, large quantities of gaseous products are produced and less material is redeposited in and around the ablated area. The designed polymers such as the TP show a clear advantage over commercially available polymers. 

The blue ice areas are of great interest because they expose old ice that formed in the central accumulation area that may be up to 1,000 km distant in the up-ice direction. Moreover, meteorites, cosmic spherules, fly-ash, and other kinds of object or particles that fell on the surface of the ice sheet in the area of accumulation emerge from the ice in the ablation area and can be recovered for scientific study (Chapter 18). Blue ice is typically slippery and rippled by the katabatic winds which polish its surface. Many unwary travelers have slipped on the ice and fallen unexpectedly, sometimes with painful consequences. 

The model of Whillans and Cassidy (1983) in Fig. 18.5 assumes that meteorites that fall in the accumulation area of the East Antarctic ice sheet west of the Transantarctic Mountains, are buried and are then transported by the flow of the ice sheet until they emerge in the ablation zone adjacent to the Transantarctic Mountains. The flow lines of the Whillans-Cassidy model in Eig. 18.5 predict that the age of the ice in the ablation area decreases with increasing distance west of the Transantarctic Mountains. Therefore, the terrestrial ages of meteorite specimens (i.e., the time that has elapsed since the fall of a meteorite) should also decrease with increasing distance from the western slope of the mountains. 

Fig. 18.5 Cross-section of the East Antarctic ice sheet west of the Allan HiUs in southern Victoria Land according to the ice-flow model of Whilltins and Cassidy (1983). The model predicts that the terrestrial ages of meteorite specimens that are transported by the ice sheet tmd tire released when the ice sublimates in the ablation area should decrease with increasing distance west of the Allan Hills. Adapted from Whillans and Cassidy (1983). The view is to the north with west on the left and east on the right. The vertical exaggeration is lOOx (Adapted from WhUlans and Cassidy 1983)...

Experience has shown that ablation areas that expose bare ice occur in many places on the East Antarctic ice sheet adjacent to the entire length of the Transantarctic Mountains. Many of these areas have yielded a wide variety of meteorite specimens including rocks from the Moon and from Mars listed in Appendices 18.12.3 and 18.12.4. The ongoing search for meteorites by the personnel of ANSMET is one of the most successful programs of the United States Antarctic Program operated by the National Science Foundation. Several summary reports have been published by past and current participants in this enterprise, including especially the book by Cassidy (2003) and reports by Harvey (2003), Cassidy et al. (1992), Cassidy (1991), Cassidy and Harvey (1991), Koeberl (1988a), Marvin and Mason (1980, 1982, 1984), Marvin (1981, 1984, 1989), Marvin and McPherson (1989), Cassidy and Rancitelli (1982), and Cassidy et al. (1977). 

Display of assistive information AR can also be used to render operation information, such as cutting paths or ablation areas planned graphically. This is the case, for example, of the computer-assisted laser microsurgery system presented by Mattos and Caldwell [54]. In this system, laser trajectories defined intraop-eratively enable subsequent automatic laser control and precise execution of the planned action [54]. 

The Finnigan LTQ linear ion trap mass spectrometer equipped with the vMALDI source (ThermoFisher, San Jose, CA, USA) was used for all imaging mass spectrometry experiments. The instrument has been described in detail previously (6), but briefly, the source consists of a N2 laser (337 nm) directed to the vacuum chamber using fiber optics. The laser spot size for these experiments was 120 xm. The spot size was evaluated by ablating a small piece of photosensitive paper and then measuring the size of the ablated area with a microscope. The source is maintained at a pressure of 0.17 Torr using N2. 

Speakman and his colleagues describe the application of inductively coupled plasma mass spectrometry (ICP-MS) to the elemental analysis of obsidian, chert, pottery and painted and glazed surfaces. Only a very small area is affected in the laser ablation sampling, usually 1000 pm by 1000 pm by 30 pm. Their method is virtually nondestructive since the ablated area is not visible to the naked eye. Because ICP-MS has a lower detection limit than other... 

Unlike INAA, XRF, or ICP-MS of solutions which produces a bulk elemental characterization of the entire matrix, LA-ICP-MS provides a point specific characterization of the ablated area of the sarrqrle. On one hand, attenqrts... 

Fig. 5.1.11a-f. Typical course of a cavitating lesion, a Small initial lesion, b RFA, c central cavitation within the ablated area, exceeding the initial lesion volume by at least 200% 1 month post RFA, d resorption of cavitation at 3 months post RFA, e residual pleural-based thickening 6 months post RFA, f complete resolution... 

A transient hyperechoic zone is seen at US within and surrounding a tumor during and immediately after ablation. However, this finding can be used only as a rough guide to the extent of tumor destruction. Contrast-enhanced US performed after the end of the procedure may allow an initial evaluation of treatment effect. Residual viable tumor can be easily identified in hypervascular lesions, such as hepatocellular carcinoma (HCC), as it stands out in the arterial phase against the unenhanced ablated area. However, interpretation of contrast-enhanced US findings is more difficult in hypovascular lesions. 

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