Page 370 - Electrical Properties of Materials

352 Optoelectronics

Table 13.3 Properties of some materials used for acousto-optic interaction

Substance Wavelength Density Index of Sound velocity
3
–1
3
–3
(μm) (10 kg m ) refraction (10 ms )
Water 0.633 1 1.33 1.5
Fused quartz 0.633 2.2 1.46 5.95
GaAs 1.15 5.34 3.43 5.15
LiNbO 3 0.633 4.7 2.29 6.57
LiTaO 3 0.633 7.45 2.18 6.19
PbMoO 4 0.633 6.95 2.4 3.75
ZnS 0.633 4.10 2.35 5.51

an advantage to use the diffracted beam as the modulated beam because the
power in it is completely cut off when the acoustic wave is absent, whereas it
is less straightforward to extinguish the transmitted beam.
Could we use an acoustic wave for scanning the optical beam within a cer-
tain angular region? It can be done in more than one way. I shall just show the
arrangement which makes the best sense in principle.
(a) transmitted
beam

Optical input
beam
θ
θ
diffracted
beam

acoustic beam
(b)

transmitted
beam
Optical input
beam θ Δ θ
θ +

diffracted
Fig. 13.12 Δ θ/2 beam
Bragg reflection of a light beam by an
acoustic wave. (a) Deflection angle of
2θ at an acoustic wavelength of λ c ,
(b) deflection angle of 2θ + θ at an
acoustic wavelength of λ c + λ c . acoustic beam