Biophotonics_Concepts_to_Applications

The inverse of the scattering coefficient is called thescattering mean free pathLs.
Thus

Ls¼ 1 =ls ð 6 : 13 Þ

which represents the average distance that a photon travels between scattering
events. Figure6.13illustrates the photon scattering process and the concept of Ls.

Example 6.5Consider an epidermis skin tissue in which the scattering

coefficient is 1400 cm−^1 at 308 nm and 450 cm−^1 at 633 nm. What is the

scattering mean free path for each of these wavelengths at which I(x)/

I 0 = 1/e = 0.368?

Solution: (a) From (6.11) at 308 nm the intensity ratio is

IðxÞ

I 0

¼expðÞ¼lax exp½ð 1400 ÞxŠ¼ 0 : 368

Therefore

1400 cm^1



x¼ln 0: 368 ¼ 0 : 9997

which yields x = 7.14× 10 −^4 cm = 7.14μm.

(b) Similarly, at 633 nm

Input

intensity I (^0) Output
intensity
Is= I 0 exp(-μsd)
Biological tissue
Average distance
between scattering
events = Ls
Ls
Tissue thickness d
Fig. 6.13 The photon scattering process and the concept of Ls
164 6 Light-Tissue Interactions