Examinando por Materia "Laser"
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- PublicaciónAcceso abiertoLaser in situ keratomileusis to correct post-keratoplasty astigmatism : 1-Step versus 2-step procedure(2004-11) Alió, Jorge L.; Javaloy, Jaime; Osman, Amr A.; Galvis, Virgilio; Tello, Alejandro; Haroun, Hazem E.Purpose: To investigate the correction of post-penetrating keratoplasty (PKP) astigmatism using laser in situ keratomileusis (LASIK). Visual and refractive outcomes were evaluated after LASIK was performed in 1 step (lamellar cut and ablation in 1 procedure) or 2 steps (lamellar cut then ablation in 2 successive procedures). Setting: Department of Cornea and Refractive Surgery, Vissum–Instituto Oftalmológico de Alicante, University of Miguel Hernández, Alicante, Spain. Methods: In this prospective observational study, 22 consecutive eyes were divided into 2 groups depending on the LASIK procedure performed to correct post-PKP astigmatism. Group 1 (1-step LASIK) included 11 eyes and Group 2 (2-step LASIK), 11 eyes. The patients were followed for 6 months. Results: A statistically significant improvement was obtained in Group 2 with a mean vector analysis result of the cylinder of –4.37 diopters (D) ± 1.79 (SD) (P = .018). In Group 1, the mean astigmatism correction was 2.38 ± 1.71 D. The number of reoperations and residual refractive defects were significantly better in Group 2. Conclusion: The 2-step technique improved the accuracy of excimer laser correction of post-PKP astigmatism.
- PublicaciónAcceso abiertoMulti-wavelength emission through self-induced second-order wave-mixing processes from a Nd3+ doped crystalline powder random laser(2015-09-03) Moura, André L.; Jeréz, Vladimir; Maia, Lauro J. Q.; Gomes, Anderson S. L.; De Araújo, Cid B.Random lasers (RLs) based on neodymium ions (Nd3+) doped crystalline powders rely on multiple light scattering to sustain laser oscillation. Although Stokes and anti-Stokes Nd3+ RLs have been demonstrated, the optical gain obtained up to now was possibly not large enough to produce self-frequency conversion. Here we demonstrate self-frequency upconversion from Nd3+ doped YAl3(BO3)4 monocrystals excited at 806 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. Besides the observation of the RL emission at 1062 nm, self-converted second-harmonic at 531 nm, and self-sum-frequency generated emission at 459 nm due to the RL and the excitation laser at 806 nm, are reported. Additionally, second-harmonic of the excitation laser at 403 nm was generated. These results exemplify the first multi-wavelength source of radiation owing to nonlinear optical effect in a Nd3+ doped crystalline powder RL. Contrary to the RLs based on dyes, this multi-wavelength light source can be used in photonic devices due to the large durability of the gain medium.