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14 

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  = 110MHz / 120MHz / 140MHz  

 

 

v = acoustic velocity of interaction material 

= 5.7mm/usec (Quartz) 

 

 

 

 

 

 

 

 

= 5.96mm/usec (Fused Silica)   

 

 

d = 1/e

2

 beam diameter 

 

 

 

Figure 5.  Modulation System 

 

 

Summary of Contents for RFA2120 Series

Page 1: ...ut Options x V 0 5V analog modulation range A analog modulation only No RF gate D digital modulation only No RF gate R coolant fittings on rear face ISOMET CORP 10342 Battleview Parkway Manassas VA 20...

Page 2: ...is determined by the free running quartz crystal oscillator at 120MHz This frequency is accurate to within 25ppm and its stability is better than 25ppm the oscillator is not temperature stabilized A h...

Page 3: ...LSO RESULT IF THE RF OUTPUT CONNECTOR IS OPERATED OPEN CIRCUITED OR SHORT CIRCUITED A low impedance d c power supply is required The operating voltage is 24V or 28Vdc at a current drain of approximate...

Page 4: ...between the driver control inputs the RF waveform and AO response is shown below for analog modulation type Time Analog Modulation Input 0 10V AM Modulated RF Output Zero Order Control Range Max Lase...

Page 5: ...trol of the RF output Lower limit an input voltage of less than 0 4V will drive the RF Off Upper limit an input of 10V will result in the maximum RF output For RFA2120D type modulation control is On O...

Page 6: ...these LED s are not illuminated LEDs Off The LEDs C and D will not illuminate if a the internal driver thermal interlock switch is open Over temperature fault b the AOM thermal interlocks switch is o...

Page 7: ...r ground of the SMA The interlock connection becomes open circuit disabling the RF output if the temperature of the modulator exceeds 35 C or the internal driver temperature exceeds 70 C LED indicator...

Page 8: ...erture of the AOM Ensure the polarization is vertical 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 o...

Page 9: ...t ball of brushed short fibres removed cotton slightly moistened with clean alcohol Before the alcohol has had time to dry on the surface wipe again with dry cotton in a smooth continuous stroke Exami...

Page 10: ...modulator INT Interlock Valid monitor Output Signal pin 1 CMOS compatible Return pin 2 15V OK Minimum Connections shown below Note AOM thermal interlock connector type is model dependent PL1 3 way Min...

Page 11: ...Dimensions mm 1 25 4mm 220 Underside View CTRL ISO M ET RF DRIVER MODEL S N DC Supply Input Screw terminals Vdc GND G 1 8 Thread Water Fittings Front placement RFAXXX Rear placements RFAXXX R RF Outpu...

Page 12: ...above For the RFA2120 and similar drivers the modulation input is a combination of analog and digital control as illustrated below Peak Level set by driver PWR ADJ potentiometer RFOutput Power BNC Ana...

Page 13: ...1 Diffracted Beam Zero Order Input Laser Beam M1340 series RFA2110 RFA2120 Separation Angle Coolant circuit not shown for clarity Flow rate 0 5 liter min at less than 25deg C DC supply 24Vdc 4A 1 2 3...

Page 14: ...ace and in the plane of deflection is BRAGG fc 2 v The separation angle between the Zeroth order and the First order is SEP fc v Optical rise time for a Gaussian input beam is approximately tr 0 65 d...

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