**ABSTRACT**

In this paper, three-dimensional heterogeneous medium, containing small inhomogeneous zones, subjected to a short-pulse laser has been examined by solving the transient radiative transfer equation. Both Curved-Line Advection Method (CLAM) and STEP schemes of the FTn Finite Volume Method have been applied. The CLAM predictions proved that a decrease of the false scattering and ray effects are obtained. In fact, there was a good agreement between the CLAM and the Monte Carlo method. However, the STEP results are slightly mismatching the predictions of the above mentioned reference method. Then, the effects of the absorption coefficient, the size, the number and the position of inhomogeneous zone on the transmittance and reflectance signals have been analyzed. The predictions showed that the increase of the size of the inhomogeneity reduces the intensity of radiation. For both homogenous and heterogonous medium, the change of the detector position varies both the broadening of the signal pulse-width and the time with peak reflectance and/or transmittance .That is can be explained by the effects of the distance and the medium property between the laser-incident source and the detector position. Thus, these both parameters are the main factors for determining the peak position and the pulse broadening. Finally, the effects of the absorption coefficient in the inhomogeneity zone on the Absolute Values of Logarithmic Slope (AVLS) has been discussed. The results proved that the AVLS may be a perfect indicator for detecting any abnormal absorbing zones in the medium.

**KEYWORDS**

PAPER SUBMITTED: 2018-03-02

PAPER REVISED: 2018-04-17

PAPER ACCEPTED: 2018-06-05

PUBLISHED ONLINE: 2018-09-29

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