Fiberooptic Laser Doppler Velocimeter

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SUMMARY

The discussion focuses on the operational principles of a Fiberoptic Laser Doppler Velocimeter (LDV), specifically how light is utilized to measure particle velocity in a fluid flow. The system employs a laser light source, a 3 dB coupler, and a detector to analyze the frequency shifts of scattered light due to the Doppler effect. Key questions raised include the light division process after passing through the coupler and the behavior of returning light post-scattering. Understanding these mechanisms is crucial for effectively utilizing LDV technology in fluid dynamics applications.

PREREQUISITES
  • Understanding of Laser Doppler Velocimetry principles
  • Familiarity with 3 dB coupler functionality
  • Knowledge of the Doppler effect in light scattering
  • Basic concepts of fiber optics and light propagation
NEXT STEPS
  • Research the design and operation of Fiberoptic Laser Doppler Velocimeters
  • Learn about the principles of light scattering in fluid dynamics
  • Explore the mathematical modeling of the Doppler effect in LDV systems
  • Investigate the applications of LDV in various scientific fields
USEFUL FOR

Engineers, researchers, and students in fluid dynamics, optical engineering, and measurement technology will benefit from this discussion, particularly those interested in the practical applications of Laser Doppler Velocimetry.

Zokisa
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Hi,

I have problem understanding some things about this particular LDV system(a Laser Dopler velocimeter).

google.jpg

Source is a light source - laser. On the right there is a flow seeded with particles that scatters the light.

So here we have a simple directional 3DB coupler. Light goes thought it, part of light goes thought the all fiber's length and on the distant end it comes out, scatters on a particle inside the flow and then it goes back to the fiber, comes thought the coupler and then reaches the detector. Detector determines particle velocity thought difference of frequencies of the light because of the Doppler-effect in the process of scattering.

Providing this is a 3 db counter, how is the light divided after passing thought it?
When the light comes back from the fiber after the scattering(in different direction than the laser light) how is it divided?

I hope somebody learned in school about such LDV's.
 
Last edited:
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Your picture link appears to be broken. At least to me.
 

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