Gigahertz photon density waves in a turbid medium: Theory and experiments

被引:105
作者
Fishkin, JB
Fantini, S
VandeVen, MJ
Gratton, E
机构
[1] UNIV ILLINOIS,DEPT PHYS,FLUORESCENCE DYNAM LAB,URBANA,IL 61801
[2] ISS INC,CHICAGO,IL 61821
来源
PHYSICAL REVIEW E | 1996年 / 53卷 / 03期
关键词
D O I
10.1103/PhysRevE.53.2307
中图分类号
O35 [流体力学]; O53 [等离子体物理学];
学科分类号
070204 ; 080103 ; 080704 ;
摘要
The predictions of the frequency-domain standard diffusion equation (SDE) model for light propagation in an infinite turbid medium diverge from the more complete P-1 approximation to the linear Boltzmann transport equation at intensity modulation frequencies greater than several hundred MHz. The P-1 approximation is based on keeping only the terms l = 0 and l = 1 in the expansion of the angular photon density in spherical harmonics, and the nomenclature P-1 approximation is used since the spherical harmonics of order l = 1 can be written in terms of the first order Legendre polynomial, which is traditionally represented by the symbol P-1. Frequency-domain data acquired in a quasi-infinite turbid medium at modulation frequencies ranging from 0.38 to 3.2 GHz using a superheterodyning microwave detection system were analyzed using expressions derived from both the P-1 approximation equation and the SDE. This analysis shows that the P-1 approximation provides a more accurate description of the data over this range of modulation frequencies. Some researchers have claimed that the P-1 approximation predicts that a light pulse should propagate with an average speed of c/root 3 in a thick turbid medium. However, an examination of the Green's function that we obtained from the frequency-domain P-1 approximation model indicates that a photon density wave phase velocity of c/root 3 is only asymptotically approached in a regime where the light intensity modulation frequency aproaches infinity. The Fourier transform of this frequency-domain result shows that in the time domain, the P-1 approximation predicts that only the leading edge of the pulse (i.e., the photons arriving at the detector at the earliest time) approaches a speed of c/root 3.
引用
收藏
页码:2307 / 2319
页数:13
相关论文
共 36 条
[31]   WHEN DOES THE DIFFUSION-APPROXIMATION FAIL TO DESCRIBE PHOTON TRANSPORT IN RANDOM-MEDIA [J].
YOO, KM ;
LIU, F ;
ALFANO, RR .
PHYSICAL REVIEW LETTERS, 1990, 64 (22) :2647-2650
[32]   TRANSMISSION OF A PULSED THIN LIGHT-BEAM THROUGH THICK TURBID MEDIA - EXPERIMENTAL RESULTS [J].
ZACCANTI, G ;
BRUSCAGLIONI, P ;
ISMAELLI, A ;
CARRARESI, L ;
GURIOLI, M ;
WEI, QN .
APPLIED OPTICS, 1992, 31 (12) :2141-2147
[33]  
Zweifel P.F., 1967, LINEAR TRANSPORT THE, V196
[34]  
1988, MODEL AR S2 PICOSECO
[35]  
1989, R2566U MCPPMT
[36]  
1988, 201A ANT OPTR INC