Revealing the reason behind jet formation at the tip of laser optical
fiber

Date:
October 12, 2020
Source:
Tohoku University
Summary:
When an optical fiber is immersed in liquid, a high temperature,
high speed jet is discharged. Researchers expect this to be
applied to medical treatment in the future. Now, a research team
has explored this phenomenon further and revealed the reasons
behind the jet formation.



FULL STORY ==========================================================================
When an optical fiber is immersed in liquid, a high temperature, high
speed jet is discharged. Researchers expect this to be applied to medical treatment in the future. Now, a research team from Russia and Japan has explored this phenomenon further and revealed the reasons behind the
jet formation.


========================================================================== Lasers using a thin optical fiber and combined with an endoscope and
catheter can be easily transported into deep areas of the body or inside
blood vessels.

Traditionally, affected areas or lesions are removed by generating heat
inside the tissue through laser absorption -- a process known as the photothermal effect.

Yet, hydrodynamical phenomena, such as microbubble formation or high-speed
jet generation from the optical fiber, show immense medical promise.

The process of jet formation happens when the laser is irradiated to
the water, causing the water to boil and a vapor bubble to form at the
tip of the optical fiber. The vapor bubble grows until the laser energy absorbed in the liquid is consumed. Because of the surrounding cold
liquid, condensation suddenly shrinks the vapor bubble.

Using a numerical simulation, Dr. Junosuke Okajima from Tohoku
University's Institute of Fluid Science, along with his colleagues in
Russia, set out to clarify the jet formation mechanism. Their simulation investigated the relationship between the bubble deformation and the
induced flow field.

When the bubble shrinks, the flow toward the tip of the optical fiber
is formed. The flow deforms the bubble into the cylindrical shape. This deformation induces the collision of flow in a radial direction. This
collision generates the jet forward. As a result of collision and jet formation, the vortex is formed at the tip of the deformed bubble and
it grows larger.

"We found the jet velocity depends on the relationship between the size
of the vapor bubble just before the shrinking and the fiber radius,"
said Okajima. "We will continue to develop this study and try to find
the optimum condition which maximizes the jet velocity and temperature,
making further laser surgical techniques more effective and safer."

========================================================================== Story Source: Materials provided by Tohoku_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Roman V. Fursenko, Vladimir M. Chudnovskii, Sergey S. Minaev,
Junnosuke
Okajima. Mechanism of high velocity jet formation after a gas bubble
collapse near the micro fiber immersed in a liquid. International
Journal of Heat and Mass Transfer, 2020; 163: 120420 DOI: 10.1016/
j.ijheatmasstransfer.2020.120420 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201012120018.htm

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