  The ab-plane optical spectra of two single crystals of underdoped
La_(2-x)Sr_xCuO_4 were investigated. The reflectivity of
La_(1.87)Sr_(0.13)CuO_4 has been measured in the frequency range 30- 9,000 cm-1
(0.004 -- 1 eV) both parallel and perpendicular to the CuO_2 planes, whereas
La_(1.86)Sr_(0.14)CuO_4 was studied only in the ab-plane. The extended Drude
model shows that the frequency-dependent effective scattering rate
1/tau(omega)is strongly suppressed below the high-frequency straight-line
extrapolation, a signature of the pseudogap state. This suppression can be seen
from temperatures below the superconducting transition up to 400 K. In the case
of underdoped LSCO the straight-line extrapolation is temperature independent
below 200 K, whereas above 200 K there is a strong temperature dependence of
the high-frequency 1/tau(omega,T). The out-of-plane direction is also examined
for evidence of the pseudogap state.
