In this paper we propose a new method

which allows us to extract the carrier recombination time

diffusion coefficient and the decay time of the grating from the experimental results.According to the theory of laser-induced dynamic gratings and the phase-matching condition

we have obtained equations (7)-(10). So the decay time of grating

the carrier recombination time and the diffusion coefficient can be derived from relative intensities of the constant background and the two peaks around τ=0 and τ=-

T

in TDFWM-IL.Using the second harmonic of a Q-Swithed NdsYAG laser with τ

e

=28 ps

seting T=230ps and θ=7.5°

we have measured

I

s

(τ) for TiO

2

ultrafine particles in the organosols as shown in Fig. 3. The intensity of the τ=-

T

peak is much weaker than that of the τ=0 peak. This phenomenon can not be attributed to carrier diffusion because the size of the ultrafine particle is much smaller than the period of the two gratings

carriers are effectively confined in the particles. We attribute

I

(-

T

)/

I

(0)

<

1 to the Brownian movement

which delocalize the excited particle makes the small period grating suffer more serious deterioration than the large period one. By Eq. (7)-(10) we have got

T

11

=1.07ns

T

12

=0.56ns

T

R

=1.08ns

and D=0.016cm

2

/s. In Fig. 3

the two peaks are symmetric about τ=0 and τ=-

T

respectively

with a constant background and separated by

T

=230 ps

just as the theory predicted.