19
ISOMET
Basic AO Modulator Parameters
Driver
RF
Intensity
Modulation
Input Laser Beam
1st Order Deflected Beam
0th Order
θ
θ
BRAGG
SEP
The input Bragg angle, relative to a normal to the optical surface and in the plane of deflection is:
θ
BRAGG
=
λ.
fc
2.v
The separation angle between the Zeroth order and the First order is:
θ
SEP
=
λ.
fc
v
Optical rise time for a Gaussian input beam is approximately:
tr =
0.65.d
v
where:
λ
= wavelength
fc = centre frequency
=
40MHz / 50.67MHz
v = acoustic velocity of interaction material
= 5.5mm/usec (Ge)
d = 1/e
2
beam diameter
Figure 5. Modulation System
