Velocity difference measurement with a fiber-optic coupler.
Two single-mode fibers collect light with the same scattered wave vector from two spatially separated regions in a sample. These regions are illuminated by a single coherent laser beam, so that the collected signals interfere when combined by means of a fiber-optic coupler, before they are directed to a photomultiplier tube. The fibers and the coupler are polarization preserving to guarantee a high signal-to-noise ratio. The measured intensity fluctuations are used to determine the velocity difference omega v(L) for spatial separations L in the sample. Specifically, an intensity autocorrelation function is calculated theoretically for rigid body rotation and is tested experimentally. Experimental results span two orders of magnitude in L and agree with theoretical predictions with an error of less than 5%. This new technique will be very useful in the study of turbulent flow and particle settling dynamics.
Du
Y
Y
Department of Physics, Oklahoma State University, Stillwater 74078, USA.
Ackerson
B J
BJ
Tong
P
P
D005336:Fiber Optic Technology / Q000295:instrumentation* / Q000379:methods*; D008027:Light; D008962:Models, Theoretical; D055100:Optical Fibers; D012542:Scattering, Radiation; D013997:Time Factors