10
ISOMET
Input the laser beam toward the centre of either aperture of the AOM. Ensure the polarization is
horizontal with respect to the base and the beam height does not exceed the active aperture height of
the AOM. Start with the laser beam normal to the input optical face of the AOM and very slowly rotate
the AOM (either direction). See Figure 4 for one possible configuration.
RF
AO crystal
Acoustic Wave
Active Aperture H
Laser Beam
Cover Aperture
Y
X
Input Beam Location
Y axis : Centre beam in active aperture height H
X axis : Not critical but avoid clipping device cover
3.12
Observe the diffracted first-order output from the acousto-optic modulator and the undeflected
zeroth order beam. Adjust the Bragg angle (rotate the modulator) to maximise first order
beam intensity with the 40MHz Frequency selected.
3.13
After Bragg angle has been optimized, slowly increase the RF power by turning PWR ADJ
clockwise until maximum first order intensity is obtained.
3.14
The modulator and driver are now ready for use.
When the 50.67MHz is selected, the 40MHz beam will be OFF. A significant proportion of the
laser beam will now be diffracted into the 50,67MHz beam location. This will be further from
the zero order beam
3.15
Remote RF Power Adjust
The RF power can be adjusted remotely using an I2C compatible interface. The control circuit
is based on the Analog Devices non-volatile 256 step digital potentiometer AD5254.
The accompanying data sheet describes the communication protocol.
