Development and optimization of Laser Shock Repeated Dense Peening (LSRDP) using most advanced laser architectures.

The laser shock peening process (LSP), used to reinforce metals, currently has two major configurations with limitations. (1) Laser irradiation with large spot sizes, but with the need to use a thermal protective coating to avoid detrimental thermal damage (which increases the overall cost of the process) or (2) laser irradiation without thermal coating but with very small spot sizes and high overlap ratios, thus increasing the amount of time required to treat a given surface. In this study, we develop a new faster configuration for the LSP process, which can be applied without a thermal coating, but is still effective regarding surface treatment time. A new laser system has been developed for this faster configuration and has been used to perform the LSP treatment of aluminum alloys at a high-repetition rate. This new DPSS Q-switched Nd:YAG laser, delivers 1 J of energy with a pulse duration from 7 to 21 ns at a very high frequency of 200 Hz. We also studied the laser/matter interaction, according to the laser pulse duration, energy, and its wavelength. The water confinement (ejection and renewing) was monitored while an air-blowing system was implemented to manage water issues identified with this new configuration. Altogether, we demonstrated that such a configuration is fully operational.

Impact of the Curve Diameter and Laser Settings on Laser Fiber Fracture.

OBJECTIVE: To analyze the risk factors for laser fiber fractures when deflected to form a curve, including laser settings, size of the laser fiber, and the fiber bending diameter. MATERIALS AND METHODS: Single-use 272 and 365 µm fibers (Rocamed®, Monaco) were employed along with a holmium laser (Rocamed). Five different fiber curve diameters were tested: 9, 12, 15, 18, and 20 mm. Fragmentation and dusting settings were used at a theoretical power of 7.5 W. The laser was activated for 5 minutes and the principal judgment criterion was fiber fracture. Every test for each parameter, bending diameter, and fiber size combinations was repeated 10 times. RESULTS: With dusting settings, fibers broke more frequently at a curved diameter of 9 mm for both 272 and 365 µm fibers (p = 0.037 and 0.006, respectively). Using fragmentation settings, fibers broke more frequently at 12 mm for 272 µm and 15 mm for 365 µm (p = 0.007 and 0.033, respectively). Short pulse and high energy were significant risk factors for fiber fracture using the 365 µm fibers (p = 0.02), but not for the 272 µm fibers (p = 0.35). Frequency was not a risk factor for fiber rupture. Fiber diameters also seemed to be involved in the failure with a higher number of broken fibers for the 365 µm fibers, but this was not statistically significant when compared with the 272 µm fibers (p > 0.05). CONCLUSION: Small-core fibers are more resistant than large-core fibers as lower bending diameters (<9 mm) are required to break smaller fibers. In acute angles, the use of small-core fibers, at a low energy and long-pulse (dusting) setting, will reduce the risk of fiber rupture.

Do We Really Need to Wear Proper Eye Protection When Using Holmium:YAG Laser During Endourologic Procedures? Results from an Ex Vivo Animal Model on Pig Eyes.

PURPOSE: We sought to evaluate the effect of holmium:yttrium-aluminum-garnet (Ho:YAG) laser exposure on ex vivo pig eyes and to test the protective action of different glasses in preventing eye lesions in case of accident. MATERIALS AND METHODS: We pointed the tip of a Ho:YAG laser fiber from different distances (0, 3, 5, 8, 10, and 20 cm, respectively) toward the center of the pupil of the pig eye. The Ho:YAG laser was activated for 1 or 5 seconds at three different settings (0.5 J-20 Hz, 1 J-10 Hz, and 2 J-10 Hz, respectively). The experiment was repeated using laser safety glasses and eyeglasses. A total of 78 pig eyes were used. The effects of the Ho:YAG laser on pig eyes were assessed by histopathology. Comparable laser emission experiments were performed on thermal paper at different distances using different pulse energies. RESULTS: Ho:YAG laser-induced corneal lesions were observed in unprotected eyes, ranging from superficial burning lesions to full-thickness necrotic areas, and were directly related to pulse energy and time of exposure and inversely related to the distance from the eye. When the laser was placed 5 cm or more, no corneal damage was observed regardless of the laser setting and the time of exposure. Similar distance/energy level relationships were observed on thermal paper. No damage was observed to the lens or the retina in any of the Ho-YAG laser-treated eyes or in any of the eyes protected by laser safety and eyeglasses. CONCLUSIONS: Ho:YAG lasers can cause damage when set to high energy, but only to the cornea, from close distances (0-5 cm) and in the absence of eye protection. Eyeglasses are equally effective in preventing laser damage as laser safety glasses.