Measurement of Ablation Threshold for Interaction between Tissue and Excimer Laser

2019 ◽  
Author(s):  
Jana Urzova
Keyword(s):  
Excimer Laser ◽  
Ablation Threshold

Corneal crosslinking by an argon-fluorine excimer laser

2021 ◽  
pp. 35-38
Author(s):  
I.M. Kornilovskiy ◽  
Keyword(s):  
Excimer Laser ◽  
Ablation Threshold ◽  
Objective Assessment ◽  
Corneal Stroma ◽  
Radiation Energy ◽  
Secondary Radiation ◽  
Cross Linking ◽  
Negative Effects ◽  
Corneal Crosslinking ◽  
Clinical Observations

Purpose. To substantiate the expediency of using ablative and subablative energy densities of an argon-fluorine excimer laser for corneal crosslinking. Material and methods. In the period from 1 month to 6 years, the results of more than 500 photorefractive and phototherapeutic operations with saturation of the cornea with riboflavin and the effect of crosslinking were analyzed. To activate riboflavin, secondary radiation was used, induced by the use of ablative and subablative energy densities of an argon-fluorine excimer laser. For an objective assessment of the effect of excimer laser crosslinking, we used the techniques of computed keratotopography, aberrometry, optical coherence tomography, and densitometry. Results. Clinical observations have shown that in most cases of photorefractive surgery of the cornea for the prevention of keratoectasias, it is sufficient to carry out ablation after saturation of the corneal stroma with 0.25% isotonic riboflavin solution for 3-10 minutes, depending on the degree of ametropia and the volume of tissue removed. This provided photoprotective protection of deeper stromal structures from the negative effects of ablation-induced secondary radiation. At the same time, upon completion of ablation, secondary radiation initiated the effect of crosslinking in the adjacent layers, which did not violate the elastic properties of the cornea. In a number of cases, the cross-linking effect was enhanced by additional exposure to energy densities below the ablation threshold and the formation of a Bowman-like membrane structure on the ablation surface. For keratoconus and corneal pathology, without and in combination with keratoectasia, the technology of therapeutic cross-linking was used. This technology provided for the saturation of the stroma with 0.1% or 0.25% isotonic riboflavin solution and its activation by subablative radiation energy densities of an argon-fluorine excimer laser. During therapeutic crosslinking, according to OCT and densitometry, all the classic signs of traditional corneal crosslinking were revealed. Conclusion. The radiation of an argon-fluorine excimer laser with the use of ablative pulse energy densities can be recommended for prophylactic crosslinking in all cases of corneal thinning during photorefractive surgeries, while the use of energy densities below the ablation threshold allows for therapeutic crosslinking in keratoconus and corneal ectasias of various etiology. Key words: excimer laser crosslinking, cornea, keratoconus, photorefractive ablation, riboflavin.

Fabrication of High Density Silicon Nano-Dots by Excimer Laser Irradiation on Block Copolymer Masks

2007 ◽  
Author(s):  
Dae Up Ahn ◽  
Erol Sancaktar
Keyword(s):  
Laser Ablation ◽  
Block Copolymer ◽  
Laser Irradiation ◽  
Excimer Laser ◽  
Ablation Threshold ◽  
Laser Intensity ◽  
Selective Etching ◽  
Time Duration ◽  
Excimer Laser Ablation ◽  
Excimer Laser Irradiation

We report easy and fast fabrication methods to prepare densely packed polystyrene (PS) and silicon nano-dots using one-step excimer laser irradiation on cylindrically nanopatterned block copolymer materials, without any additional selective etching steps before a non-selective etching. Preferential etching in more ultraviolet (UV)-sensitive block component, and non-selective removal of all block components allowed transferring nanopatterns in block copolymer masks to inorganic silicon substrates, when an appropriate laser intensity was used. Surface melt flows of block components, which severely undermine the initial orders of nanopatterns in a block copolymer mask, were observed at the laser intensity near the ablation threshold of the less UV-sensitive component. Thus, in order to obtain mask-image-like topographic nanopatterns on the target material surfaces, the intensity of excimer laser radiation should be sufficiently lower than the ablation threshold of the less UV-sensitive component as long as the intensity is higher than that of the more UV-sensitive component. Numerical analyses on the photothermal excimer laser ablation in binary mixture systems predicted the presence of a matrix-assisted excimer laser ablation in the less UV-sensitive component at the laser intensity lower than its ablation threshold, owing to the heat conduction from the more UV-sensitive component during the nanoscopic level of time duration.

Investigation of excimer laser ablation threshold of polymers using a microphone

2002 ◽  
Vol 197-198 ◽  
pp. 800-804 ◽  
Author(s):  
Jörg Krüger ◽  
Hiroyuki Niino ◽  
Akira Yabe
Keyword(s):  
Laser Ablation ◽  
Excimer Laser ◽  
Ablation Threshold ◽  
Excimer Laser Ablation

Physico-Chemical Modifications and Biological Improvements of Biomedical PET as a Consequence of Excimer LASER Irradiation

2005 ◽  
Vol 288-289 ◽  
pp. 347-350
Author(s):  
G. Mayer ◽  
N. Blanchemain ◽  
C. Dupas-Bruzek ◽  
M. Traisnel ◽  
D. Derozier ◽  
...  
Keyword(s):  
Excimer Laser ◽  
Ablation Threshold ◽  
Surface Profile ◽  
Irradiation Intensity ◽  
Cell Vitality ◽  
Physico Chemical ◽  
Irradiation Energy ◽  
Modify Surface ◽  
Excimer Laser Irradiation ◽  
Different Origins

LASER Excimer irradiation can modify surface properties for biocompatibility improvement of a medical device. The PETs from 3 different origins were used in this study. The samples have been irradiated by excimer LASER with 10 different energies. The surface profile, the surface energy and the materials crystallinity have been assessed. Biological characterizations were made with human embryonic epithelial cells L132: proliferation, vitality, viability, adhesion with the p-NPP, and morphology. - The profile measurements allowed to establish the ablation threshold, which was 36 mJ/cm². The surface hydrophilic state increased reciprocally with the irradiation intensity. The gain is 13 %. The irradiated and non-irradiated product has identical cristallinity. PET was shown not to be toxic for L132 cells. Cell proliferation and cell vitality showed dose-dependant increases reciprocal to the irradiation energy (from 88 to 138% with respect to control). The correlation was highly significant (R² = 0,8). SEM micrographs show that the cells are better spread on the surface of irradiated PET than on untreated PET.

scholarly journals New Possibilities of Refractive Modeling of the Cornea by the Radiation of an Argon-fluorine Excimer Laser

2021 ◽  
pp. 7-18
Author(s):  
I. M. Kornilovskiy
Keyword(s):  
Excimer Laser ◽  
Clinical Studies ◽  
Ablation Threshold ◽  
Objective Assessment ◽  
Corneal Stroma ◽  
Strength Properties ◽  
Secondary Radiation ◽  
Total Radiation Dose ◽  
Corneal Nerves ◽  
Negative Effect

Purpose: To consider new possibilities of refractive modeling of the cornea by the radiation of an argon-fluorine excimer laser in ablative and subablative modes after saturation of the stroma with riboflavin. Materials and Methods: Experimental (20 pork, 90 rabbit eyes) and clinical studies on photorefractive and phototherapeutic operations with saturation of the corneal stroma with riboflavin (610 operations) were analyzed. To activate riboflavin, secondary radiation induced by exposure to ablative and subablative energy densities was used. A quick transition to energy densities below the ablation threshold without additional calibrations was carried out using a “Microscan Visum-500” excimer laser (Optosystems, Russia). An objective assessment of the refractive keratomodelling effect and visual results was carried out according to the data of complex optometric studies. Results: Experimental and clinical studies have shown the advantages of refractive keratomodeling by theradiation of an argon-fluorine excimer laser in ablative and subablative modes after saturation of the stroma with riboflavin. Isotonic 0.25% riboflavin solution did not affect the accuracy of refractive ablation and blocked the negative effect of induced secondary radiation on keratocytes and corneal nerves. This reduced the aseptic inflammatory response and the risk of developing an irreversible form of fibroplasia. Ablation with riboflavin initiated a damped crosslinking effect, which increased the photoprotective and strength properties of the thinned cornea. A refractive keratomodelling effect was found when energy densities were applied below the stromal ablation threshold. The magnitude of this refractive effect depended on the total radiation dose and the topography of the affected area. This approach made it possible to implement laser-induced refractive keratomodeling without ablation of the corneal stroma. Conclusion: Refractive modeling of the cornea by the radiation of an argon-fluorine excimer laser in ablative and subablative modes after saturation of the stroma with riboflavin opens up new possibilities in laser correction of ametropia.

Excimer laser ablation of aluminum nitride

1997 ◽  
Vol 12 (1) ◽  
pp. 218-225 ◽  
Author(s):  
Janet K. Lumpp ◽  
Susan D. Allen
Keyword(s):  
Aluminum Nitride ◽  
Excimer Laser ◽  
Ablation Threshold ◽  
Statistical Design ◽  
Ablation Rate ◽  
Data Sets ◽  
Statistical Design Of Experiments ◽  
Excimer Laser Ablation ◽  
High Fluences ◽  
Processing Variables

Excimer laser wavelengths ablate aluminum nitride at rates up to 0.2 μm/pulse where the rate increases with decreasing background pressure and increasing fluence. The ablation threshold for AlN at 248 nm is approximately 2 J/cm2. Blind vias are produced with flat bottoms, straight walls, and a decomposed metallic layer remaining on the surface. Ablation rate dependence on fluence saturates at high fluences due to absorption by the ablation plume. The influence of processing variables on ablation rate and ablation mechanisms are discussed. Statistical design of experiments is used to compare data sets.

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