TY - JOUR

T1 - On coherent radiation scattered by random ensembles

AU - Yu, Guoyao

AU - Newhouse, V. L.

AU - Censor, D.

N1 - Funding Information:
Pivotal to the present discussion are two ideas. The first involves the separation of coherent and incoherent radiation scattered by random media, for the purpose of remote sensing of local particle density. It is well known \[1-3\] that the total intensity of a scattered radiation field produced by non-uniformly distributed, non-interacting (no multiple scattering) and uneorrelated scatterers, can be presented as the sum of two components: (1) the incoherent intensity, which is proportional to the particle volume density n, and (2) the coherent intensity which is proportional to n 2. Glotov \[4, 5\] showed that by separating these two terms and forming their ratio, the particle density n should be obtainable. (It is clear, intuitively as well as from analysis \[6, 7\], that the simple dependence on n, n 2 as mentioned above, holds only when multiple scattering effects are insignificant.) This leads to the second aspect of the problem. Is it possible, for incident coherent radiation of suitable temporal and spatial dependence, to produce coherent and incoherent signals from an unbounded region of homogeneously distributed scatterers, from which the local scatterer volume density could be estimated? Many years before the cited Work of Glotov \[4, 5\], Siegert and Goldstein \[1\] suggested that pulse shaping will act in a manner equivalent to a region possessing d~nsity gradients. It logically follows from their conjecture that field gradients, either in time (pulse shaping) or in space (spatial field shaping, e.g., focusing), are equivalent to density gradients, and should thus produce backscattering. Since this idea seems to be plausible, and yet, as shown below, can be very misleading, we feel that a verbatim quotation is worthwhile: "... It is convenient, f Supported by AFOSR. :~ On leave of abscnce from the Department of Electrical and Computer Engineering, Ben Gurion University of the Negev, Beer Sheva, Israel; supported by the Louis and Bessie Stein Foundation Fellowship Program. 399

PY - 1988/5/8

Y1 - 1988/5/8

N2 - It is known that when regions of randomly distributed scatterers containing volume density gradients are illuminated by coherent radiation, backscattered radiation is produced which generally contains both spatially coherent and incoherent components. The ratio of coherent to incoherent power is a measure of the scatterer volume density. It has been conjectured that even homogeneously distributed scatterers, when illuminated by properly selected coherent radiation with suitable temporal and/or spatial dependence, should also produce a mixture of coherent and incoherent backscattering whose ratio is a measure of the local scatterer volume density. It is shown here that under circumstances when multiple scattering is insignificant, homogeneously distributed scatterers illuminated by coherent radiation do produce spatially coherent scattering, but only in the direction of the incident wave. Therefore, the information contained in coherent scattered radiation by such ensembles can be obtained only in the direction of incident wave.

AB - It is known that when regions of randomly distributed scatterers containing volume density gradients are illuminated by coherent radiation, backscattered radiation is produced which generally contains both spatially coherent and incoherent components. The ratio of coherent to incoherent power is a measure of the scatterer volume density. It has been conjectured that even homogeneously distributed scatterers, when illuminated by properly selected coherent radiation with suitable temporal and/or spatial dependence, should also produce a mixture of coherent and incoherent backscattering whose ratio is a measure of the local scatterer volume density. It is shown here that under circumstances when multiple scattering is insignificant, homogeneously distributed scatterers illuminated by coherent radiation do produce spatially coherent scattering, but only in the direction of the incident wave. Therefore, the information contained in coherent scattered radiation by such ensembles can be obtained only in the direction of incident wave.

UR - http://www.scopus.com/inward/record.url?scp=0024281498&partnerID=8YFLogxK

U2 - 10.1016/S0022-460X(88)80089-0

DO - 10.1016/S0022-460X(88)80089-0

M3 - Article

AN - SCOPUS:0024281498

SN - 0022-460X

VL - 122

SP - 399

EP - 412

JO - Journal of Sound and Vibration

JF - Journal of Sound and Vibration

IS - 3

ER -