Showing: 1 - 3 of 3 RESULTS

Achieving distributed directional listening with fiber acoustic sensing

Distributed directional listening with distributed fiber acoustic sensing and directionally coherent enhancement
Experiment results of multiple targets. Credit: SIOM

Recently, a research team from the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (CAS) proposed multi-source aliasing suppression for distributed fiber acoustic sensing (DAS) with directionally coherent enhancement technology. The results were published in Optics Letters.


DAS has some unique advantages, including large coverage, high spatial-and-temporal resolution, and strong ambient adaptability, so it is widely applied in many fields.

At present, DAS is still troubled by the aliasing problem from multiple adjacent sources due to its physical mechanism. On the one hand, weak target signals may be submerged by intense broadband environmental noise; on the other hand, multiple target signals are challenging to detect individually.

The solving of multi-source aliasing is helpful to individually detect multi-source signals, the identification ability and reliability of DAS will be improved, and the large-scale application process can be promoted.

The researchers proposed a new DAS detection scheme based on distributed directional coherence enhancement for multi-source interference suppression.

With the unique continuously spatially detection characteristic and array signal processing idea, the spatial correlation of multi-dimension detection data was explored, the distributed directional coherence enhancement was realized, signals from specific directions could be enhanced or suppressed, and multi-source aliasing could be suppressed.

In experiments, they found the proposed method can extract weak target signals from intense broadband ambient noise. The same-frequency signals from different adjacent targets can also be separated from each other with the directional listening method.

In the proposed method, the array signal processing idea was successfully utilized into DAS, and distributed directional listening was realized. Many common problems from multi-source aliasings, such as low recognition accuracy and robustness, can be resolved, and the proposed method is expected to promote the large-scale implementation of DAS.


Scientists propose neural network for multi-class arrhythmia detection


More information:
Zhaoyong Wang et al. Multi-source aliasing suppression for distributed fiber acoustic sensing with directionally coherent enhancement technology, Optics Letters (2020). DOI: 10.1364/OL.404736
Provided by
Chinese Academy of Sciences

Citation:
Achieving distributed directional listening with fiber acoustic sensing (2020, October 14)
retrieved 14 October 2020
from https://phys.org/news/2020-10-fiber-acoustic.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

Source Article

Ultrafast fiber laser produces record high power

lasertag
Credit: Pixabay/CC0 Public Domain

Researchers have developed an ultrafast fiber laser that delivers an average power more than ten times what is available from today’s high-power lasers. The technology is poised to improve industrial-scale materials processing and paves the way for visionary applications.


Michael Müller, a Ph.D. student of Prof. Jens Limpert from the Friedrich Schiller University’s Institute of Applied Physics and the Fraunhofer Institute of Institute for Applied Optics and Precision Engineering in Jena, Germany, will present the new laser at the all-virtual 2020 OSA Laser Congress to be held 12-16 October. The presentation is scheduled for Tuesday, 13 October at 14:30 EDT.

High power without the heat

In lasers, waste heat is generated in the process of light emission. Laser geometries with a large surface-to-volume ratio, such as fibers, can dissipate this heat very well. Thus, an average power of about 1 kilowatt is obtained from today’s high-power lasers. Beyond this power, the heat load degrades the beam quality and poses a limit.

To circumvent this limitation, the research team around Müller and Limpert created a new laser that externally combines the output of 12 laser amplifiers. They showed that the laser can produce 10.4 kW average power without degradation of the beam quality. Thermographic imaging of the final beam combiner revealed a marginal heating. Thus, power scaling to the 100-kW level could be accomplished by adding even more amplifier channels.

“In the future, high-power combined lasers not only will accelerate industrial processing, but also enable formerly visionary applications such as laser-driven particle acceleration and space debris removal,” said Müller.

The investigation of novel applications at that power level as well as the transfer of the laser technology to commercial systems is ongoing within the frame of the Fraunhofer Cluster of Excellence Advanced Photon Sources (CAPS), which foremost involves engineering of the laboratory setup into a rugged design. On the research side, the team in Jena now focuses on multicore fibers that offer the potential to deliver even superior performance in simpler and smaller systems.


New ultrafast yellow laser poised to benefit biomedical applications


More information:
OSA Laser Congress: www.osa.org/en-us/meetings/osa … ings/laser_congress/
Provided by
The Optical Society

Citation:
Ultrafast fiber laser produces record high power (2020, October 13)
retrieved 13 October 2020
from https://phys.org/news/2020-10-ultrafast-fiber-laser-high-power.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

Source Article

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

Revealing the Reason Behind Jet Formation at the Tip of Laser Optical Fiber
The observation of water jets in experiments and the schematics of the jet formation mechanism. Credit: Junnosuke Okajima, Tohoku University

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.

  • Revealing the Reason Behind Jet Formation at the Tip of Laser Optical Fiber
    The numerical simulation results of bubble deformation at the tip of optical fiber and the induced flow field. Credit: Roman Fursenko
  • Revealing the Reason Behind Jet Formation at the Tip of Laser Optical Fiber
    The observation of water jets in experiments. Credit: Junnosuke Okajima, Tohoku University

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 vortexis 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.”


Researchers use laser-generated bubbles to create 3-D images in liquid


More information:
Roman V. Fursenko et al. 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). DOI: 10.1016/j.ijheatmasstransfer.2020.120420
Provided by
Tohoku University

Citation:
Revealing the reason behind jet formation at the tip of laser optical fiber (2020, October 12)
retrieved 12 October 2020
from https://phys.org/news/2020-10-revealing-jet-formation-laser-optical.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

Source A