
434 Handbook of Biomedical Optics
10 × 9 mm crystal aperture. e second advantage is that paral-
lel speckle processing is possible. e third advantage is that
this system is insensitive to speckle decorrelation because this
UOT system detects transmitted ultrasound-modulated light
through a frequency-dependent absorptive lter constructed
from an SHB crystal. erefore, it can potentially provide in
vivo imaging.
e SHB medium is a rare-earth ion–doped, inhomoge-
neously broadened optical absorber at room temperature. When
cryogenically cooled (4.2 K), it has a sub-MHz homogeneous
linewidth
H
and an inhomogeneous bandwidth