Excimer laser ablation procedure

Surgery to correct refractive errors for the improvement of visual acuity generally aims at changing the corneal curvature. Corneal tissue is mainly constituted of a network of natural collagen polymer with the void volume filled with a special type of aqueous saline solution. A wide variety of laser and nonlaser procedures, such as laser-assisted in situ keratomileusis (LA-SIK), laser-cut channels for intracorneal ring segment (ICRS) implantation, femtosecond lamellar keratoplasty (FLK), intrastromal vision correction, and corneal transplantation have been developed for refractive surgical correction [83, 84]. They include removal of corneal tissue from the surface, removal of corneal tissue from the interior or stroma, and alteration of the corneal mechanical properties to produce a refractive effect. The most popular by far are procedures based on excimer laser ablation of the corneal surface and/or stroma [85]. 

An interesting method was presented for the analysis of perfluorinated polyethers (PFPE) by Cromwell et al. The fluorinated polymers are commonly used as lubricants because of their low vapor pressures, chemical inertness, and thermal stability. Samples were examined in a cubic trap FTMS-2000 system using a 4.3 T magnetic field. Both a Kr/F excimer laser and a Nd/YAG laser were used for infernal LD. The fwo-step procedure involved using the 248-nm excimer laser for desorption of the polymer and, immediately following, a second more tighfly focused 532 nm laser ablation pulse to ablate metal cations from fhe surface beneath the polymer sample. Thus, cationization could be controlled, and the dynamics of the process are discussed. Mass spectra extended up to 10,000 Da are shown. 

For any true microspectrochemical analysis a microscope and a dispersing instrument are needed. An essential feature of a laser microscope is that the objectives for both the observation of the specimen and for focusing the laser radiation must be suitable for ablation, vaporisation, and excitation of the material. The defining attribute of LMMS is the use of a high power pulsed UV laser ultimately focused down to the dil action-limited spot (0.5 ixm at 266 nm) to vaporise, atomise, and ionise a microvolume of a solid specimen in a one-step procedure. Laser microprobe mass analysers are typically equipped with Nd YAG lasers (1064 and 266 nm 5-15 ns pulses) or excimer lasers (XeF, 351 nm XeCl, 308 nm KrF, 248 nm with about 7-30 nm pulses). Power densities of up to 10 Wcm 2 are quite common organic compounds require attenuation to about 10 -10 W cm . By adjusting the laser power, desorption and ionisation can, to some extent, be selected over ablation and dissociation in the microplasma. 

Faraggi et al. [785] demonstrated fabrication of a CP-LED pixel microarray having the CP sandwiched between ITO and Al, with pixel size as small as 20 /im X 20 /im and claimed extendable to the nm-range. A photo-ablation method employing a 193 nm excimer laser was used. A schematic representation of the procedure is shown... 

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