Optodynamic energy-conversion efficiency during an Er:YAG-laser-pulse delivery into a liquid through different fiber-tip geometries

Abstract

Abstract. When an erbium-laser pulse is directed into water through a small-diameter fiber tip (FT), the absorption of the laser energy superheats the water and its boiling induces a vapor bubble. We present the influence of different FT geometries and pulse parameters on the vapor-bubble dynamics. In our investigation, we use a free-running erbium: yttrium aluminum garnet (Er:YAG) (λ ¼ 2.94 μm) laser that was designed for laser dentistry. Its pulse is directed into the water through FTs with a flat and conical geometry. Our results show that in the case of the conical FT, a spherical bubble is induced, while a channel-like bubble develops for the flat FT. The ratio between the mechanical energy of the liquid medium and the pulse energy, which we call the optodynamic energy-conversion efficiency, is examined using shadow photography. The results indicate that this efficiency is significantly larger when a conical FT is used and it increases with increasing pulse energy and decreasing pulse duration. The spherical bubbles are compared with the Rayleigh model in order to present the influence of the pulse duration on the dynamics of the bubble's expansion.

Optodynamic Phenomena During Laser-Activated Irrigation Within Root Canals

“…After the initial collapse of the bubble (700 µs), additional oscillations can occur Figure 2 shows the laser-induced vapor bubble oscillation in 50 µs time intervals. In unconstrained space, laser-induced vapor bubbles have been shown to grow in a roughly spherical shape [7,8]. The prolate spheroidal shape of the growing bubble is likely caused by the constraints of the root canal as the water displaced by the growing bubble is forced out of the canal alongside its walls.…”

“…Matija.jezersek@fs.uni-lj.si 1 Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Slovenia light penetration depth) leads to explosive boiling that generates vapor bubbles [6,7], causing mixing of liquid also at distant regions of the complex root canal anatomy. This is an important advantage over ultrasonic needle irrigation, where a significant effect occurs only in the close proximity of the instrument [8].…”

“…For this purpose, an experimental setup was developed based on two measuring principles. Shadow photography with short, 10 ns, white-light illumination flashes, and frequencydoubled Nd:YAG laser illumination is used to visualize the cavitation bubble dynamics [7] inside the root canal. Simulated debris particles within the transparent model of the root canal are used to examine liquid vorticity.…”

Review of diverse optical fibers used in biomedical research and clinical practice

“…The shape of the tip determines how the light emerging from the fiber is distributed on a tissue sample and also determines the light collection efficiency for viewing the irradiated tissue sample or examining scattered or fluorescing light emitted from the sample. [84][85][86][87][88][89][90][91][92][93][94][95][96] When deciding on the geometry of an optical fiber tip, parameters that need to be evaluated include the sizes of the illumination and light-collection areas, the collection angle (related to the fiber NA), and the fiber diameter. Another important factor to keep in mind is that biological tissue has a multilayered characteristic from both compositional and functional viewpoints.…”

Synchronized delivery of Er:YAG-laser pulses into water studied by a laser beam transmission probe for enhanced endodontic treatment

“…Due to the very high absorption coefficient (l a = 1.247 9 10 6 m -1 ) [4] of Er:YAG, light in water more than 70 % of all the pulse's light is absorbed within an only 1-lm-thick water layer. Thus, the water is locally and instantly heated over its boiling point, and a vapor bubble develops at the fiber tip's end [5][6][7][8].…”